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Project Specific Discussions => Dynamic Processors => Topic started by: abechap024 on June 11, 2011, 01:44:11 AM

Title: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on June 11, 2011, 01:44:11 AM
UPDATE(10/14/2011):

WIRING GUIDE www.acsoundstudio.com/prr_176/PRR_176_WIRING_GUIDE_j.jpg
BOM www.acsoundstudio.com/prr_176/prr_176_bom_1.pdf
Schem www.acsoundstudio.com/prr_176/PRR_SCHEM_ALL.jpg
OFF BOARD RECTIFICATION  www.acsoundstudio.com/prr_176/OFF_BOARD_POWER.png (http://www.acsoundstudio.com/prr_176/OFF_BOARD_POWER.png)  <solves all hum issues, no need to mount transformers off board>


Errata: If using INA134 input de-balancers, on left channel connect pin 1 to ground (a convenient spot is pin 8 of the same chip) and use shielded transformers for input, or move left channels input TX away from power supply for best S/N.

Hello,
This is my take on the mash up of the 176 vari-mu compressor and the PRR sidechain. It 2 channel stereo/mono switchable - Receiver chip input, or transformer balanced input. Uses a 6bc8 tube for muing action. Separate front panel Lorin switch PCB, 12 position stepped input/output, 6 attack/6 release positions. 3 on-board input and interstate transformer options: Cine-mag, Edcor. Jensen can be wired in. Driver output or transformer output. And it all fits in 1RU.

All signal-chain opamps have a dip-8 footprint and a 2520 style footprint for your discrete opamp fans.

I prototyped it on a breadboard and it sounds really great.

I'm posting the schematic (http://www.acsoundstudio.com/diyhosting/PRR_176.jpg) for any improvements/ideas.


Thanks as always,
Abe
Title: Re: PRR-176 vari-mu
Post by: dustbro on June 11, 2011, 03:07:33 PM
looks really cool
thanks!
Title: Re: PRR-176 vari-mu
Post by: strangeandbouncy on June 11, 2011, 03:13:59 PM
Blimey . . .



  I was just thinking about something similar, but never gonna get it together . . .


   Abe, you truly are a demon-fiend . . . dont you ever sleep . . .


      Very excited,


      ANdyP
Title: Re: PRR-176 vari-mu
Post by: abechap024 on June 11, 2011, 03:16:31 PM
haha well a lot of times I just sleep on the couch in my shop....so It makes getting to work that much easier.
Cheers,
Abe
Title: Re: PRR-176 vari-mu
Post by: tomcat on June 11, 2011, 07:06:25 PM
Dont burn all my money you evil  ;D
Title: Re: PRR-176 vari-mu
Post by: abechap024 on June 11, 2011, 07:08:33 PM
Hahah! Yes I see you guys are onto my evil plan....try to take over the world through VARI-MU! bWAhaHahAha!

These fill me with such evil love I don't think anyone should be deprived of one. I'm thinking in the ballpark of 35$ for a stereo set.


Cheers,
Abe
Title: Re: PRR-176 vari-mu
Post by: tomcat on June 11, 2011, 08:11:16 PM
$ 35 including PSU, Case, Tubes,.... ;D   Thats the evil thing. You tease us with pcbs and then we are lost in the mouser/digikey/... hell ;)
Title: Re: PRR-176 vari-mu
Post by: abechap024 on June 11, 2011, 08:53:40 PM
Haha!

So now you want a BOM with all the mouser parts too!?!? that takes all the fun out of it! ;)
 But I'll see what I can do......


If there is enough interest we could do a parts kit...



Its worth it....its true what they say...you gotta go through hell to get to heaven!
Title: Re: PRR-176 vari-mu
Post by: abechap024 on June 11, 2011, 08:59:13 PM
It makes sense to do a resistor kit, cause to me when I'm building a project, getting the resistors can be the most tedious part....no one selects resistors on their sound like you find with capacitors and what not(not many people at least). And its the most time consuming to sit there and add a resistor to your cart one...after one.....after one....after one at a time.

I can just get a bunch or resistors and spend a day or two putting them into baggies....

Your Master of Hell  ;),

AC
Title: Re: PRR-176 vari-mu
Post by: Neil on June 11, 2011, 10:16:53 PM
Dammit, I'm in.
Title: Re: PRR-176 vari-mu
Post by: dandeurloo on June 11, 2011, 11:10:34 PM
Haha, you know what I think!
Title: Re: PRR-176 vari-mu
Post by: abechap024 on June 12, 2011, 12:25:38 AM
Haha, you know what I think!

Good :) Your going to offer cases for this right?


Title: Re: PRR-176 vari-mu
Post by: mylesgm on June 12, 2011, 12:47:59 AM
now this is something I've been waiting for for awhile.  What about adding a hpf to the sidechain?
A kit would be cool or at least a partial kit for the main parts ie power transformer, any usual caps etc.
A case would also be cool.  What sort of meter will this require?  Edcor transformers?

Title: Re: PRR-176 vari-mu
Post by: abechap024 on June 12, 2011, 01:00:05 AM
now this is something I've been waiting for for awhile.  What about adding a hpf to the sidechain?
Yep already got the HPF on the sidechain, just forgot to mention it :)
Quote
A kit would be cool or at least a partial kit for the main parts ie power transformer, any usual caps etc.
A case would also be cool.  What sort of meter will this require?  Edcor transformers?
I'll have to look into ordering a mass of edcors to see if these is a discount. Also offering transformers (mainly power transformers) with kits the shipping really starts to add up especially with international shipments. I figure most people can probably access power transformers closer to home. For people running 110v mains its nice cause you just need a dual pri&sec 15v transformer. but for people running 220v mains you are going to need to get the 220v down to 100v and also 15v.


[/quote]
Title: Re: PRR-176 vari-mu
Post by: mylesgm on June 12, 2011, 02:26:50 AM
how about this one?

http://www.ebay.com.au/itm/120-100V-50VA-6-3V-Toroidal-Tube-Pre-Amp-Transformer-/370518162496?pt=BI_Circuit_Breakers_Transformers&hash=item56449a7c40#ht_635wt_1038
Title: Re: PRR-176 vari-mu
Post by: jackies on June 12, 2011, 03:36:38 AM
Huh, so you plan to do a PCB for this contraption?
May I humbly suggest making it a LARGE pcb, as opposed to tightly packed pcbs?
Like, so one could fit 2w resistors on it and such?
Or, desolder something from the middle of the board without other components getting in the way?
 ::)
Title: Re: PRR-176 vari-mu
Post by: tomcat on June 12, 2011, 11:19:47 AM
Im in for small pcbs (like to build small 1u stereo versions), no normal parts necessary. Dont need mouser or digikey bom as well ;)

Abe, maybe you should rethink the "include resistors" thing. Instead of counting resistors (which is not so great fun) you should follow your evil nature and create new pcb projects ;) More fun for you, more tempting projects for us :)
Title: Re: PRR-176 vari-mu
Post by: 0dbfs on June 12, 2011, 12:43:13 PM
I'll go in for a couple of these. Planning to get my pye and eat it too !  Btw, this is getting completely out of control.

Best,
jb
Title: Re: PRR-176 vari-mu
Post by: strangeandbouncy on June 12, 2011, 01:44:53 PM
Hi Abe,




  just one more question, erm . . . . .when dey come . . . .



       me in, big time . .\



    ANdyP

Title: Re: PRR-176 vari-mu
Post by: shabtek on June 12, 2011, 01:45:18 PM
I would like to see a schematic--what you've posted is more of a wiring or troubleshooting diagram.
all the IO options are not as important as the sidechain and GR elements are.
+1 for bigger board and plated through holes to allow for swapping of parts... especially since you're designing for options.
Title: Re: PRR-176 vari-mu
Post by: dandeurloo on June 13, 2011, 12:32:02 AM
Yep!

Haha, you know what I think!

Good :) Your going to offer cases for this right?



Title: Re: PRR-176 vari-mu
Post by: abechap024 on June 13, 2011, 06:18:21 AM
Great. Glad people are as excited as me about tasting the forbidden fruit!

I like uncrowded PCBs but the main board PCB is already pretty big. I've tried to leave as much room where it counts so hopefully its enough room for most. If the PCB starts getting too big, prices starts to rise pretty quickly.

The schematic is all there, I guess I could see how it looks confusing because everything is already split up onto different PCBs. But if your wondering about the parts around the tube its almost resistor for resistor just like the 176 schematic.

And the sidechain is almost just like the PRR.


If you wondering about stereo-linking I have both circuits using their attack and release controls while stereo linked. On my prototype I have it hardwired stereo, and only uses one sidechain (sums the DC after the rectification and one timing circuit) It seems to work very well.



Title: Re: "P-R-R-1-7-6" vari-mu
Post by: abechap024 on June 13, 2011, 07:46:38 AM
Also there is option for lundahl input tranny..
Title: Re: "P-R-R-1-7-6" vari-mu
Post by: mylesgm on June 13, 2011, 08:47:20 AM
Definitely in for 1 stereo possibly two.  I've got one already but I'd like the i/o, the hpf etc and I do need to build a new ps so why not start from scratch.
Title: Re: "P-R-R-1-7-6" vari-mu
Post by: abechap024 on June 13, 2011, 09:07:19 AM
Just having a bit of fun ;D  Maybe thats what the projects name should be...then everyone would really be confused....

Title: Re: PRR 176 vari-mu
Post by: abechap024 on June 14, 2011, 11:30:15 PM
So me and Dan are working out some final details on the case...we are going to have HPF option on the front of the PCB and then also stereo link on the front of the PCB. This makes wiring up a bit easier.

We want to do Bypass, but what do you guys think, a built in hardpass would be optimal but at this point its going to probably take a large redesign. What if we just bypassed the GR?
Thoughts?

Title: Re: PRR 176 vari-mu
Post by: mylesgm on June 15, 2011, 02:25:05 AM
bypass the GR then we can use the units as a colour tool.  Hard bypass can be done in the daw.

M
Title: Re: PRR 176 vari-mu
Post by: Matthew Jacobs on June 15, 2011, 04:04:32 AM
Hard bypass can be done in the daw.

And we can always add our own bypass boards...
Title: Re: PRR 176 vari-mu
Post by: jandoste on June 15, 2011, 08:26:28 AM
What if we just bypassed the GR?
Thoughts?



Great idea!
Title: Re: PRR 176 vari-mu
Post by: Davo on June 15, 2011, 09:40:17 AM
A separate relay I/O board is another option for hard bypass.... although that means extra wiring, plus the extra board... probably not the best option (although that's what I did with my
just completed PRR)

On another note, are you making separate boards for the PSU?

Cheers,
Dave
Title: Re: PRR 176 vari-mu
Post by: abechap024 on June 15, 2011, 10:29:41 AM
Ok great feedback guys.

And Yes the power supply is on a separate board. I originally had it use a tl783 to regulate the 100v until I built my prototype and found that a Zener is cheaper, simpler and works great.

All the other rails are regulated: +/-18v, +1.5v, +12.6v (heaters in series)

This is really going to be a sharp project, I think. Dan is really pulling out the stops on the case! I'm excited for this one especially.
Title: Re: PRR 176 vari-mu
Post by: 0dbfs on June 15, 2011, 11:00:41 AM
I would vote for hard-bypass. Makes the most sense for A/B'ing and closely matching levels. Bypassing GR seems much less useful because you get a level change but very nice for line-amp use with no GR.

But it is DIY and bypass relay boards can be added one way or another after the project is done or during the initial build as well as GR bypass.

So can we have both? Please?

Best,
jb

Title: Re: PRR 176 vari-mu
Post by: abechap024 on June 15, 2011, 12:35:57 PM
For conveniences sake, I would say hard bypass would be nice to have. Personally I just Hard Bypass with my patch-bay (though it doesn't wor kexactly the same i know..:)).


Because of the limited front panel space I think we need to choose between Hard bypass and GR bypass:

Gr Bypass - still lets you make judgments on what the compression is doing to your sound, and lets the unit double as a line amp and because of the transformers and tubes it does add a nice tone to things.

Hard Bypass - gives you more of a judicial standpoint to judge from, takes the unit completely out of the signal path. Separate PCBs available on the forum to add in later if one is needed.

I think it best to have the GR bypass built in, as adding hard-bypass later is much easier than trying to add GR bypass later.


Also update on stereo linking: When the stereo link is engaged, the left side controls will control both left and right, so no matching both sides. This also means that potentiometers can be used if someone doesn't want to deal with lorins...
Title: Re: PRR 176 vari-mu
Post by: 0dbfs on June 15, 2011, 12:42:27 PM
Shot down!

I'll go with the prescribed design and like it :)

I mean A/B could be sort useless because this will make everything just sound better anyway.

Best,
jb
Title: Re: PRR 176 vari-mu
Post by: Script on June 15, 2011, 04:04:17 PM
Too many knobs, too little space? Why not put "hard bypass" and "GR bypass" (I'd call it AMP) on one and the same switch?

Rotary (either):
OFF - AMP - COMP
   \       |       /

Rotary (or):
OFF - COMP - AMP
    \       |       /


Toggle:
(ON)  -- AMP
(OFF) -- BYPASS
(ON)  -- COMP

Anyway, I'd definitely separate switches for L and R. Why? Well, I might want to feed MS into the unit, using COMP on M and AMP (or BYPASS) on S, or the other way round.

What we'd get is three switches for a stereo unit:
STEREO-DUAL MONO
AMP-BYPASS-COMP (left)
AMP-BYPASS-COMP (right)

V+ on hard bypass relays should probably switch AMP & COMP in.
(If something fails inside the unit, we still have sound = radio standard).

V+ on CV relay (if relays at all) should probably disconnect the sidechain.
(I guess most people will use the unit as a compressor most of the time.)

I know, rotaries -- which need more space -- are probably better because when *toggle*-switching quickly between AMP and COMP, the hard bypass relays would be deactivated for a fragment of a second. Nothing's perfect  :-\

Anyway, option for "hard bypass" relays & "sidechain/CV/AMP" relays on board would be nice. It'd think it's easier to flywire a few connection on a slightly more costly PCB than having to add several relay boards (incl. stand-offs) later. But maybe that's just me feeling lazy today :)
Title: Re: PRR 176 vari-mu
Post by: strangeandbouncy on June 15, 2011, 04:12:49 PM
Hi,



 I would ALWAYS prefer a hard bypass myself. Something like this would definitely reside in my recording chain, and I like to be able to completely bypass anything I am NOT using.

   
    Ill be happy anyway, since I can easily add a cheep lorlin to completely bypass if necessary. ( i think . . .)



      ANdyp


   
Title: Re: PRR 176 vari-mu
Post by: abechap024 on June 15, 2011, 06:09:23 PM
Hmm good points.

because of limited front-space we are squeezing in all the switches to sit right by the lorins. Should be pretty nice when its done but it does make for a crowded switch PCB. But we do have room on the front panel for another switch.

So would a soft bypass and a hard bypass switch be too much? I think the extra cost will be maybe 5$ per channel, and probably one of those things once were out of the shop and in the control room we'll be glad we have...


OKAY you all talked me into it! ::)

Now someone point me in the right direction of good relays to use?

:)

Ps Here is the sweet front panel dan is designing
(http://WWW.acsoundstudio.com/diyhosting/1U%20PRR-176%20faceplate4.jpg)
Title: Re: PRR 176 vari-mu
Post by: tomcat on June 15, 2011, 07:26:13 PM
Alternative LED meters instead of needles?  ;D

No, honestly. On a modern 1U version i would like to see a led option too. Yes i know its not christmas. And its hot too ;)
Title: Re: PRR 176 vari-mu
Post by: abechap024 on June 15, 2011, 07:48:07 PM
Haha! A Vari-mu compressor with LEDS? That is crazy talk!  :o :o

It sounds so wrong that I honestly kind of like the idea ;D
Title: Re: PRR 176 vari-mu
Post by: shabtek on June 15, 2011, 09:45:39 PM
front panel design complete, how does she sound,

over...
Title: Re: PRR 176 vari-mu
Post by: abechap024 on June 16, 2011, 02:47:35 AM
I've built a stereo prototype, using the circuitry devised on the first post. Its a stereo unit and I used ganged pots for input/output and pots for attack/release. hardwired stereo.

I should probably post some samples. But if I was to give my (probably unforgivably biased) impressions of the unit.

The attack and release sounds like an 1176. More color than 1176 though. Its does a great job of adding the tube color we all love tubes for. Makes things just sound better. During initial testing it was noticeable for me on acoustic guitar...Hard to explain, but it just seemed to balance the frequency spectrum. Making it sound bigger and better balanced.

Where you might want to use the GSSL on your mix buss when you have a really drum heavy mix. This seems like something you would use....for everything else!

Anyway Putnam knew what he was doing when he made the 176, PRR knows this stuff up and down and made a gem when he made his vari-mu.
but his always seemed to be intended as just kind of a compressor your could make from the spare parts in your junk box, which I love about it.
This version is trying to take it a step further into a more polished design, by just adding little things (friendly with +4 operation, input/output, regulated 1.5v bias for example) and hopefully in the process I don't mess anything up, or take away from either of the designs.
And  it is sounding great!

I'm going to finalize the front panels designs with dan, and then its off to the Fab house for the PCBs. And because the majority of the design came so selflessly from this forum, I want to keep the goodwill going by offering it as inexpensive as I can.


Title: Re: PRR 176 vari-mu
Post by: strangeandbouncy on June 16, 2011, 02:50:30 AM
Hi Abe,


   I am very excited to hear of your good results. Waiting with baited breath . . .



     ANdyP
Title: Re: PRR 176 vari-mu
Post by: abechap024 on June 16, 2011, 02:55:50 AM
want to take a peek at the main PCB.... ;D

(http://www.acsoundstudio.com/diyhosting/main_pcb.jpg)
Title: Re: PRR 176 vari-mu
Post by: strangeandbouncy on June 16, 2011, 03:04:20 AM




 . . . .you teaser . . .
Title: Re: PRR 176 vari-mu
Post by: abechap024 on June 16, 2011, 03:05:23 AM
  :)
Title: Re: PRR 176 vari-mu
Post by: evilcat on June 16, 2011, 03:41:21 AM
Haha! A Vari-mu compressor with LEDS? That is crazy talk!  :o :o

It sounds so wrong that I honestly kind of like the idea ;D


The TubeTech LCA2b is a vari-mu with LEDs ! But classic Vu meter are so much cooler ;D ;D. Anyway, very interesting project Abe. In fact, all your projects are very, very cool, I'll soon have money issues !!!
Maybe it's too late but, for the bypass feeler, I would go for a "false" bypass to keep the color. If you doesn't want it, then you un-patched it !
To be continued...

Best,
Ben.
Title: Re: PRR 176 vari-mu
Post by: mylesgm on June 16, 2011, 04:36:12 AM
I hate LED vu meters. I think a universal power supply would be better than one that relies on a 110 mains voltage.  It looks like doas are possible for the opamps which I think is an excellent addition.
Title: Re: PRR 176 vari-mu
Post by: abechap024 on June 16, 2011, 04:41:47 AM
Well the power supply doesn't really rely on 117v mains. Just is convenient if you have 117v mains you don't need an extra transformer. I cant think of a way off the top of my head to make a power supply that doesn't use 2 transformers for 220v supplies?
Title: Re: PRR 176 vari-mu
Post by: EEMO1 on June 16, 2011, 04:42:06 AM
 Are you guys sure 1U is a good option?

 I would personally prefer 2U, so there would not be issues with bigger caps, heat, PSU mounting etc etc. 1U can be a pain...
Title: Re: PRR 176 vari-mu
Post by: evilcat on June 16, 2011, 08:39:06 AM
Are you guys sure 1U is a good option?

 I would personally prefer 2U, so there would not be issues with bigger caps, heat, PSU mounting etc etc. 1U can be a pain...

I agree ! My 1st built was in 1U case and tall to myself : "never again" !!! So much pain with metal work to make everything fit in such tiny place. Now it's 2U, at least.
Title: Re: PRR 176 vari-mu
Post by: 0dbfs on June 16, 2011, 10:38:52 AM
1U just means that I can get four channels into my allotted 2RU available instead of going without.

-jb
Title: Re: PRR 176 vari-mu
Post by: tomcat on June 16, 2011, 07:17:34 PM
Haha! A Vari-mu compressor with LEDS? That is crazy talk!  :o :o

It sounds so wrong that I honestly kind of like the idea ;D


Thats why i had this idea. Put old technic into new design and surprise people  ;)
Title: Re: PRR 176 vari-mu
Post by: tomcat on June 16, 2011, 07:20:40 PM
For the 2HE guys. Maybe abe adds a normal footprint for standing tubes option.

I will go 1 HE ..... with LEDs  ;D
Title: Re: PRR 176 vari-mu
Post by: living sounds on July 09, 2011, 07:56:39 AM
Any news on this?
Title: Re: PRR 176 vari-mu
Post by: abechap024 on July 09, 2011, 12:43:15 PM
Yep! PCB design is finished, just got a front panel from Collective Cases to make sure everything is glove like.  I'm hoping to have these sent to the factory very soon.
Title: Re: PRR 176 vari-mu
Post by: living sounds on July 09, 2011, 12:54:18 PM
Great!  8)
Title: Re: PRR 176 vari-mu
Post by: earl on July 10, 2011, 03:24:43 PM
This looks pretty cool...Definitely in for stereo set
Title: Re: PRR 176 vari-mu
Post by: dustbro on July 11, 2011, 05:45:57 PM
Yep! PCB design is finished, just got a front panel from Collective Cases to make sure everything is glove like.  I'm hoping to have these sent to the factory very soon.

 ;D
Title: Re: PRR 176 vari-mu
Post by: okailla on July 17, 2011, 08:47:17 PM
Count me in.
Title: Re: PRR 176 vari-mu
Post by: earl on July 23, 2011, 10:44:54 AM
Hey Abe this is certainly getting closer yes? :)
Title: Re: PRR 176 vari-mu
Post by: earl on August 03, 2011, 03:02:13 PM
Hello?
Title: Re: PRR 176 vari-mu
Post by: abechap024 on August 03, 2011, 04:22:52 PM
Haha! Sorry. Yep getting closer. Thing is these circuit boards are HUGE (well comparatively) cause they house all the transformers and everything on the board. So If I don't order a lot of boards it kind makes the whole thing cost prohibitive (well not really but I end up paying about 40$ a board!!)

So I'm saving my pennies to get the cost down to a manageable size But for the first week I get the boards I plan on letting these go super cheap, so all you guys that have been following this thread and motivating me can get yours for a good deal.

Thanks!

Abe
Title: Re: PRR 176 vari-mu
Post by: tomcat on August 03, 2011, 05:11:47 PM
Cooooool :)
Title: Re: PRR 176 vari-mu
Post by: karloff70 on August 03, 2011, 05:38:25 PM
Cool indeed!!!  :)
Title: Re: PRR 176 vari-mu
Post by: living sounds on August 03, 2011, 05:39:28 PM
Awesome!  8)
Title: Re: PRR 176 vari-mu
Post by: ilfungo on August 03, 2011, 07:06:59 PM
 :o ;) :)
Title: Re: PRR 176 vari-mu
Post by: Matthew Jacobs on August 03, 2011, 08:00:18 PM
waiting impatiently.....  ;D
Title: Re: PRR 176 vari-mu
Post by: mylesgm on August 03, 2011, 10:29:18 PM
yup, patience is a virtue that I've never understood.  Thanks for another lesson! :)
Title: Re: PRR 176 vari-mu
Post by: Neil on August 03, 2011, 10:42:01 PM
Good things come to those who wait! .......
Title: Re: PRR 176 vari-mu
Post by: adeptusmajor on August 04, 2011, 05:52:08 PM
If you have a list going, please put me on it ;D

Glad you're making progress, can't wait to get my hands on this one.


How's it sound on vox, by the way?


Title: Re: PRR 176 vari-mu
Post by: abechap024 on August 04, 2011, 06:28:16 PM
haha well there's no list, but its always nice to see support :D

The prototype I have excels at vox. Though my prototype is hardwired stereo I find myself using it on busses, i cant ever make up my mind it sounds great on many different things....Thats why I myself am waiting impatiently for some more channels, and mono switchable!!

These will definitely be fun!

Thanks Guys :)
Title: Re: PRR 176 vari-mu
Post by: earl on August 11, 2011, 01:45:03 PM
Just a weekly checkup on this one Abe also wondering if there's a bom laying around somewhere to start sourcing parts?
Title: Re: PRR 176 vari-mu
Post by: abechap024 on August 11, 2011, 02:31:55 PM
Ah Good idea! I'll get one put together. :)
Title: Re: PRR 176 vari-mu
Post by: abechap024 on August 27, 2011, 07:55:31 PM
OK! Finally getting ready to send out to Fab house on Monday.

IF you want to pre order...25$ and your in (that includes world-wide shipping).

to :

[email protected]


Thanks to everyone who participated! Pre-order is closed, Thanks!

Power supply and transformer options are built right on the board and includes the side-angle tube socket mount PCBs.

The  build isnt that expensive which is really nice, you can use edcor transformers if you are so inclined and they do sound quite nice at 10$ a pop. I'm getting a BOM together, thank you for your patience all. Im keeping the 25$ per PCB for a week or so, just a thanks to all you people on the forum! Though eventually I will up the price a bit to help compensate for other costs. So I guess what I'm saying is get them while you can!


Also a portion of the proceeds with be donated to this wonderful forum!


Thanks,

Abe

Edit: Also one PCB is 2 channels
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: mylesgm on August 27, 2011, 09:15:27 PM
Paid up...
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: Matthew Jacobs on August 27, 2011, 11:31:55 PM
Me to... Paid up!
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: Davo on August 27, 2011, 11:43:12 PM
Paid up... thanks Abe!!
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: kml23956 on August 27, 2011, 11:51:58 PM
Paid up.
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: tmuikku on August 28, 2011, 03:18:55 AM
Payment using PayPal?  :)
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: ilfungo on August 28, 2011, 03:35:29 AM
Payment sent for two board
Thanks ;)
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: living sounds on August 28, 2011, 03:38:16 AM
Payment made.  8)
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: JayDubrek on August 28, 2011, 04:55:00 AM
Payment sent!
Cheers
Jay
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: jandoste on August 28, 2011, 06:29:41 AM
Payment sent for 2 boards.
Thanks
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: pablobolche on August 28, 2011, 08:11:45 AM
Payment sent for 1 board...
Gracias
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: jackies on August 28, 2011, 08:38:19 AM
So like, 1 board is one channel? Need two for stereo?
 :o
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: earl on August 28, 2011, 09:58:16 AM
What jackies said. and ordered 1 board Abe. If 2 needed for stereo then will order another.  Thanks for this one seems like a fun good sounding project.
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: Script on August 28, 2011, 10:25:48 AM
Payment and PM.
Cheers,
s
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: Neil on August 28, 2011, 11:01:58 AM
So like, 1 board is one channel? Need two for stereo?
 :o

In for a stereo set, but I'm not sure if that's one board or two?
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: 0dbfs on August 28, 2011, 11:20:49 AM
Paid for two PCB's.

Thanks!
jonathan
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: tomcat on August 28, 2011, 12:59:34 PM
Guys, its just a 5 page thread... If you would take the immense workload of reading these pages (at least the first post) or take a glimpse on the posted layout you would see that it is stereo / dual mono.  ::)
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: tomcat on August 28, 2011, 01:03:28 PM
Paid for 4 channels  ;)
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: Soeren_DK on August 28, 2011, 01:08:33 PM
Paid for 1 board, 2 channels Vari-Mu :D ;D

Cheers
Soren
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: MrZpliff on August 28, 2011, 01:30:18 PM
Money sent for one board
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: Neil on August 28, 2011, 01:43:46 PM
Guys, its just a 5 page thread... If you would take the immense workload of reading these pages (at least the first post) or take a glimpse on the posted layout you would see that it is stereo / dual mono.  ::)

You're right, how about that! In fairness though I had read the thread, just overlooked the pertinent points.

Anyway, payment sent for 1 board!

Neil
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: fazer on August 28, 2011, 02:39:19 PM
Paid for 1 board.   Thanks Abe

Michael
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: coriolis on August 28, 2011, 05:26:53 PM
Payment sent for 2 boards!  8)
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: abechap024 on August 28, 2011, 06:09:56 PM
So like, 1 board is one channel? Need two for stereo?
 :o

Hello,
It is a stereo board.

Cheers,
Abe
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: Eje2005 on August 28, 2011, 06:49:51 PM
I´m in, payment sent for one board!
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: kquick on August 28, 2011, 07:40:32 PM
PayPal payment sent for two boards.

Thanks
Kim
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: Peps on August 28, 2011, 08:19:45 PM
Payment sent for one board.
Thanks!
Peps
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: jackies on August 29, 2011, 01:32:38 AM
Payment sent for one board.
Thanks!
 8)
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: tmuikku on August 29, 2011, 02:37:37 AM
Paid for one board
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: coriolis on August 29, 2011, 04:29:08 AM
Is it necessary to have matched tubes for this one? It's 1 tube per channel, right?
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: zmgwg on August 29, 2011, 04:40:59 AM
paypal'd
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: EEMO1 on August 29, 2011, 04:46:05 AM
two boards for me. paid!


 sweeeeeeeeeeeeet.
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: Tsane on August 29, 2011, 05:52:00 AM
Paid for one board!
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: mylesgm on August 29, 2011, 08:13:37 AM
so bom or parts list or a mouser list?
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: abechap024 on August 29, 2011, 12:25:47 PM
so bom or parts list or a mouser list?

Yep, The boards will take about 2 weeks at the Fab House, I'll get a BOM organized and hopefully a mouser list together so we can all get parts and hopefully boards at the same time!
Thanks to everyone who has already participated!

Cheers,

Abe
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: peters on August 29, 2011, 12:54:24 PM
I'm in for one board, payment sent!
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: wowi on August 29, 2011, 01:54:45 PM
Hi Abe, Payment send for 2 Boards

Best
Wolfgang
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: Hank Dussen on August 29, 2011, 07:18:40 PM
Paid for 1 board.
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: funkymonksf on August 29, 2011, 10:54:47 PM
Paypaled for one board! Yay!
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: kvintus on August 30, 2011, 02:40:19 AM
paid for 1 PCB

/Anders
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: adeptusmajor on August 30, 2011, 07:25:11 AM
payment sent for 1 board

thanks

-Sean
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: pirate on August 30, 2011, 08:43:40 AM
Paid for 1!

Cheers!
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: abechap024 on August 30, 2011, 01:14:06 PM
Great! Thanks for the overwhelming response guys! I sent out the order yesterday...! I really like this, its fun to see everyone get excited about a project!

I'll have BOM and everything within the week.

Cheers,
Abe
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: kazper on August 30, 2011, 02:09:58 PM
Couple questions

What are the transformers that you had "optioned" on the pcb?

Do you have a current layout picture like what is posted on page 3 showing the PSU? 

I'm also looking at what power transformer or transformers are needed...


KaZ
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: abechap024 on August 30, 2011, 03:51:12 PM
Hello,

Power you need 120v AC and 18v x 2 AC

If you live were 120V power is standard you can get away with getting a dual primary transformer and using one of the primaries for 100v rail. ie just one transformer.

If you live were 230v is standard you will probably have to use a transformer that has those options. Or just 2 different transformers

For input audio transformers you can use:

Edcor PCW 1:1
Edcor PC 1:1
Lundahl LL1540
Cinemag CLMI - 1515B

For output:
Edcors
and Cinemag, I forget the exact model number, but there are places to mount the transformers and solder in the leads. Jensen outputs should work too. I will get updates on exact model #s
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: tomcat on August 30, 2011, 04:22:54 PM
Maybe Volker can order a small batch of transformers for us 220V people!? Would be possibly cheaper then have them custom wound on an one by one basis.
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: abechap024 on August 30, 2011, 04:27:30 PM
Yes, great idea!
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: tomcat on August 30, 2011, 04:31:39 PM
 Btw is "classical peices" a typo?   ;D
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: abechap024 on August 30, 2011, 04:36:47 PM
Yes. facepalm.

haha saw that this morning after I sent the boards off.

I guess for those that don't know already, I rely heavily on spell check...haha and my PCB software doesn't have that!!

My apologies, :)

Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: mcfarlane_audio on August 30, 2011, 07:46:19 PM
paid for 1 board! thanks!
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: kazper on August 30, 2011, 11:06:03 PM

For input audio transformers you can use:

Edcor PCW 1:1
Edcor PC 1:1
Lundahl LL1540
Cinemag CLMI - 1515B

For output:
Edcors
and Cinemag, I forget the exact model number, but there are places to mount the transformers and solder in the leads. Jensen outputs should work too.

For input  Edcor pcw10k-10k (http://www.edcorusa.com/products/135-pcw10k-10k.aspx)

What do you have specified for T2?

4:1/10K:600R
Edcor PCW 1:4 (http://www.edcorusa.com/products/134-pcw10k-600.aspx) ?


As far as utilizing the second primary in a toroidal transformer, Does it effect the current capabilities of the secondary 18V including the heater supply? 

Is there enough coper for the option of using lower heater voltage so we could use the better 6N5P russian equivalent of the 6BC8?
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: minor_glitch on August 31, 2011, 12:03:45 AM
Payment sent for one board!
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: abechap024 on August 31, 2011, 02:12:41 AM
Yes,

Edcor 4:1 for output.
http://www.edcorusa.com/products/134-pcw10k-600.aspx

Or jensen....cinemag...etc


Yes using the second primaries will cut the current load theoretically in half. Maybe someone more mathematically inclined than me can calculate the exact size of the transformer needed, but I am using a 50va dual 18v transformer and its working fine.

Also I have the heaters for the 6bc8's wired in series at 12.6V with an lm350, the advantages of this being that 12.6v is closer to the 18v power rail than 6.3v and isn't as hard of a load on the regulator. So the 6N5P will work fine, no adjustment to the circuit necessary.

Have a good one!
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: noulou on August 31, 2011, 02:46:38 AM
money sent
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: Kingston on August 31, 2011, 06:12:29 AM
For europeans there are plenty of 230V:100V transformers out there. A very common 230V:115V would also work just fine if you drop a bit more voltage with those 2W resistors in the B+ PSU, or perhaps use a bit bigger watt zener in there (or both).

Is the first post schematic for the project a definitive one already? I have a bit of difficulty deciphering what exact balancing chip vs. DOA vs. transformer options there are.

Great flavor project by the way! Good job Abe!
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: tomcat on August 31, 2011, 08:21:17 AM
Yes there are... But you need two transformators or a custom wound one...
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: zayance on August 31, 2011, 08:33:53 AM
This link has been given a couple of times here.
But if that Volker idea fails, you can custom make them here for cheap.
Shipping will be high, but as with others i guess....
Takes 3 weeks....
Just wanted to point that out in case somebody could be interested

http://www.audiophonics.fr/transformateur-torique-sur-mesure-toutes-puissances-p-3675.html
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: Kingston on August 31, 2011, 08:43:07 AM
one more point of interest with two small transformers vs. a custom wound. The custom wound would probably end up taller than 1U rack case, it probably won't fit. Seeing as this project is designed as 1U, the two separate transformers look like the only valid solution for it.
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: zayance on August 31, 2011, 08:47:44 AM
one more point of interest with two small transformers vs. a custom wound. The custom wound would probably end up taller than 1U rack case, it probably won't fit. Seeing as this project is designed as 1U, the two separate transformers look like the only valid solution for it.

There is Low Profile Option transformer too ( Profil Bas), if this one fits of course...
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: Kingston on August 31, 2011, 09:54:41 AM
I'm looking at the schematic and was wondering why B+ is done through VR3 and R5/R6?

You could instead connect B+ directly to the T2 transformer center tap instead. No need for these resistors. I guess it will be easy to jumper it on this board if one wants it.
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: abechap024 on August 31, 2011, 10:22:34 AM
I'm looking at the schematic and was wondering why B+ is done through VR3 and R5/R6?

You could instead connect B+ directly to the T2 transformer center tap instead. No need for these resistors. I guess it will be easy to jumper it on this board if one wants it.

Yes, I'm interested to see the different mods or improvements people come up with. Thats how the power was wired up in the 176. But there are quite a few things that can be changed around for people wanting. Another example is the output transformer. 1:1 is how the PRR worked while the 4:1 is what the 176 had. I'm sure minor tweaks here in there could customize the sound.


Anyway I had to close the pre order early. Thanks again to all those who participated. Next up...BOM!

Cheers,

Abe
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: Kingston on August 31, 2011, 11:36:45 AM
1:1 is how the PRR worked while the 4:1 is what the 176 had.

I see. In your version this will only affect sidechain gain staging and output headroom. In other words, it won't make much difference whether 1:1 or 4:1 is used here. Even 1:1 (10k/10k) will easily drive all those opamps (sidechain + buffer to audio output).

This is actually an interesting topic since you also recommend 10k/10k for the input transformer. Here again, a 1:4 (600/10k) could be used (like in 176), or actually this might have been even bigger in the original 176, like 1:8. Only gain staging is affected. 600-ohm T-attenuator before the input might be a good idea when using any input transformer.
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: kazper on August 31, 2011, 12:50:06 PM

Also I have the heaters for the 6bc8's wired in series at 12.6V with an lm350, the advantages of this being that 12.6v is closer to the 18v power rail than 6.3v and isn't as hard of a load on the regulator. So the 6N5P will work fine, no adjustment to the circuit necessary.


One would not be able to see that how the heaters are connected with what is provided for this project so far....

You still have avoided the interstage transformer question regarding the PCB layout.... What transformers  are the PCB layouts for T2/T4? Your posted schematic on the first page you show 2 transformers with a optional 3rd output transformer, is this correct?

The T2/T4 space has less options from the image provided on page 6 of the thread.




Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: abechap024 on August 31, 2011, 01:05:53 PM
....600-ohm T-attenuator before the input might be a good idea when using any input transformer.

Good stuff  Kingston. Also there is an option for people that do want to go the t-pad attenuator route and hit the input transformers directly. Using the "IN_Opt" if one uses the input circuity (input debalancig chip and volume pot and then opamp buffer to the transformer) one will need to bridge the "In_Opts"  I will arrange a pdf or word document to contain all these little specifics thoug




Also I have the heaters for the 6bc8's wired in series at 12.6V with an lm350, the advantages of this being that 12.6v is closer to the 18v power rail than 6.3v and isn't as hard of a load on the regulator. So the 6N5P will work fine, no adjustment to the circuit necessary.


One would not be able to see that how the heaters are connected with what is provided for this project so far....

You still have avoided the interstage transformer question regarding the PCB layout.... What transformers  are the PCB layouts for T2/T4? Your posted schematic on the first page you show 2 transformers with a optional 3rd output transformer, is this correct?

The T2/T4 space has less options from the image provided on page 6 of the thread.

My Apologies, I  wasn't clear enough. For the output interstage transformer, the PCB layout is for Edcors. The other choices of output transformers: Cinemags and jensens are both leaded and can be mounted directly to the PCB board using the 2.38" spaced mounting holes on the PCB board. There are "+" and "-" symbols clearly marking the primary and secondary soldering points to attach your transformer of choice.

There is also an option for "TX_Out" and just in case anyone has questions about that, I would use your favorite 1:1 transformer, 2:1 for more color, 1:2 if you want more gain, and have an output opamp that can happily push it. Otherwise you can just use the output balancing chip.

Thanks for your patience all, I know there are probably a lot of questions concerning the details of the circuit. There is a schematic posted earlier in the thread and also I'm organizing a pdf/word document to help with the build. But keep the questions coming...it helps with organizing what needs to be in the info.
Title: Re: PRR 176 vari-mu (CLOSED pre-order CLOSED Thanks!)
Post by: kazper on August 31, 2011, 03:17:20 PM
No worries, I just wanted those questions all cleared up before  $$ for the board was put down and was holding out ordering some edcor Iron for a R&D of a project of my own if I was doing this project. I was going to toss the $$ this morning but you closed it if there is room for one more pcb this batch, let me know.

KaZ
Title: Re: PRR 176 vari-mu (CLOSED pre-order CLOSED Thanks!)
Post by: coriolis on August 31, 2011, 03:45:34 PM
Again - do I need matched tubes for this one (is it critical)? I haven't been able to find anyone selling matched pairs on the web for less than 100USD, which is out of the question for me right now.

I see the 6N5P is suitable also, but can only find that in singles as well.

So Abe - what did you do for tubes in your prototype? Did you have a matched pair on hand?

Christian
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: Kingston on August 31, 2011, 04:58:25 PM
Also there is an option for people that do want to go the t-pad attenuator route and hit the input transformers directly. Using the "IN_Opt" if one uses the input circuity (input debalancig chip and volume pot and then opamp buffer to the transformer) one will need to bridge the "In_Opts"  I will arrange a pdf or word document to contain all these little specifics thoug

I see. The input transformer is not optional, but actually has to be there. But then, aren't the input debalancer + DOA buffer completely unnecessary? Are they there for the DOA spice only?

Also, you gave the option for DOA's in this input buffer, and output (transformer) driver. But why not for the NE5534 right after the output transformer, since that one is also in the signal path?

I suppose this might be a prime place for your discrete-dip-8-opamp... Did you try this already? And which one would fit here, the tall or the wide one?

(I understand why DOA's in sidechain might be unnecessary and overkill).
Title: Re: PRR 176 vari-mu (CLOSED pre-order CLOSED Thanks!)
Post by: kazper on August 31, 2011, 05:12:10 PM
The 6N5P tubes are plenty on eBay and tend to be better (match) quality then the 6BC8 tube found today.
BTH the text will look like 6H5n, because of the Cyrillic alphabet letters.

I took a gamble and ended up importing 100 of them and every one I tested tested excellent!

Edit: Thanks Kingston, I know that a 6N5P is not a equal to the 6BC8. clerical error on the 6N1P
Title: Re: PRR 176 vari-mu (CLOSED pre-order CLOSED Thanks!)
Post by: Kingston on August 31, 2011, 05:16:49 PM
The 6N1P tubes are plenty on eBay and tend to be better (match) quality then the 6BC8 tube found today.
BTH the text will look like 6H5n, because of the Cyrillic alphabet letters.

careful there! 6N1P is a completely different (and wrong) tube.
Title: Re: PRR 176 vari-mu (CLOSED pre-order CLOSED Thanks!)
Post by: jeffrey_burr on August 31, 2011, 05:30:50 PM
Quote
Anyway I had to close the pre order early.

noooooooooo
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: abechap024 on August 31, 2011, 05:38:59 PM

I see. The input transformer is not optional, but actually has to be there. But then, aren't the input debalancer + DOA buffer completely unnecessary? Are they there for the DOA spice only?

I put the input circuitry in there, to buffer the transformer correctly, and a input chip, opamp and pot and a few resistors/caps is cheaper then a genuine t-pad Potentiometer. But i'm aware their are pros and cons to both designs, so people can choose whatever design suits them best.

Quote
Also, you gave the option for DOA's in this input buffer, and output (transformer) driver. But why not for the NE5534 right after the output transformer, since that one is also in the signal path?

That NE5534 is just gain for the sidechain, I decided to try and save some real estate and op just for chip opamps in those positions. Though I don't know if putting a discrete would appreciably change the sound. They might....they might not IDK. They have more current ability, maybe they would charge that timing capacitor faster? Hard to say without trying. But  seems like any audible difference will be quite subtle, if any at all.

Cheers,

Abe
Title: Re: PRR 176 vari-mu (CLOSED pre-order CLOSED Thanks!)
Post by: abechap024 on August 31, 2011, 05:44:45 PM
Again - do I need matched tubes for this one (is it critical)? I haven't been able to find anyone selling matched pairs on the web for less than 100USD, which is out of the question for me right now.

I see the 6N5P is suitable also, but can only find that in singles as well.

So Abe - what did you do for tubes in your prototype? Did you have a matched pair on hand?

Christian

It is my understanding, If you can find some that are close, The potentiometers can be adjusted for minor difference between tubes.

I used 2 tubes same manufacturer and from the same lot in my prototype and they tracked pretty nicely. Don't know if I got lucky, but I think two reasonable close tube will work, with a bit of luck
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: Kingston on September 01, 2011, 05:23:35 AM
input chip, opamp and pot and a few resistors/caps is cheaper then a genuine t-pad Potentiometer.

That's very true, didn't even think of that.

That NE5534 is just gain for the sidechain, I decided to try and save some real estate and op just for chip opamps in those positions.

I must have read the schematic wrong. It's a bit hard to see where the signal to that output DOA comes from. I thought it comes from the NE5534 between the 4:1 transformer and the DOA.

Since it's for sidechain gain only, a DOA would be overkill.

The design makes sense now.
Title: Re: PRR 176 vari-mu (CLOSED pre-order CLOSED Thanks!)
Post by: coriolis on September 01, 2011, 10:52:25 AM
Ok thanks Abe. I'll just get a few tubes and see then.

C
Title: Re: PRR 176 vari-mu (see page 4 for pre-order instructions)
Post by: Dr_J on September 03, 2011, 11:38:49 AM

Anyway I had to close the pre order early. Thanks again to all those who participated. Next up...BOM!


Ahh, what a f**** sh*t... I was thinking to myself, "I do the pre order tomorrow" and than I missed it! grrrr... >:(
Please keep us updated, I need one of these magic machines, which make you  :D
Title: Re: PRR 176 vari-mu (CLOSED pre-order CLOSED Thanks!)
Post by: baadc0de on September 05, 2011, 02:59:54 AM
Will a Lundahl LL1538 work in place of LL1540, with regards to the pinout?
Title: Re: PRR 176 vari-mu (CLOSED pre-order CLOSED Thanks!)
Post by: Kingston on September 05, 2011, 04:56:30 AM
Will a Lundahl LL1538 work in place of LL1540, with regards to the pinout?

Not perfectly. They have different pinouts, and for a good reason (very different ratio/winding configurations). It really depends on how the ground is set up in prr176. see here.

http://www.lundahl.se/pdfs/datash/1538_8xl.pdf
http://www.lundahl.se/pdfs/datash/1540.pdf

we are mostly interested in what pin "E" and pin 8 do here. if both are to ground in prr176, then it should work, otherwise you need jumpers and trace cuts.

It could do 1:5 or 2:5 ratio... probably not the best choice here, unless you really want the extra gain, and lost headroom.
Title: Re: PRR 176 vari-mu (CLOSED pre-order CLOSED Thanks!)
Post by: baadc0de on September 05, 2011, 05:45:51 AM
Thanks for the info Kingston. I'll just have to get me some *40 then. The 38 will end up in mic pres anyway :)
Title: Re: PRR 176 vari-mu (CLOSED pre-order CLOSED Thanks!)
Post by: William on September 05, 2011, 07:08:36 PM
Man, missed out on the pre-order  >:(

Let me know if there is a spare, or when you get some more done  ;D
Title: Re: PRR 176 vari-mu (CLOSED pre-order CLOSED Thanks!)
Post by: abechap024 on September 06, 2011, 02:22:11 AM
Ok, getting the information sorted out.

Here is the BOM... I should also point out the different build options so each member can decide what route they want to take and then not let the different options slow them down.

1) the 1.5V sidechain biasing power supply. As standard is an lm317 with adjustable voltage, the idea is that you can then fine tune to get "0v" after the 1n4148 diodes (compensates for the voltage drop of the diodes is my understanding). Some might feel all these extra parts are a bit over the top, so the "optional" route to the 1.5V supply is a resistor and diode.

2) optional inputs. You can either use the input chips (ina134) and input pot fader to accept the input signal and drive the transformer, or you can opt for a T-Pad input pot and drive the transformer directly...or shoot you could just set the volume externally and drive the transformer directly without any input attenuation control. I recommend using the input circuity, it leads to the most versatility and allows for more GR as depending on what gain staging you decide to use, you can make the center of the input fader "0" and have a good amount of cut or gain built in.

3) optional output circuits. You can either have the output balanced with a DRV134 chip, or an output transformer. Since there is plenty of color with the compression circuit, I feel no shame in using the DRv134 chip, it does a great job.

And of course the optional transformers.

I hope that people find what they like, tweak the circuit and post what works for them so newer people can have a place to start...

There is some flexibility especially around the gain stages. The resistors that can possibly be changed I didn't put a value on the board, this will enable the best configurations to be updated here online. I posted some initial values the work great in the BOM, but they can no doubt be improved upon.


BOM:

www.acsoundstudio.com/prr_176/prr_176_bom_1.pdf (http://www.acsoundstudio.com/prr_176/prr_176_bom_1.pdf)

Next on the List:

Wiring guide...
Calibration...


PS tip when buying headers and all that...you can get whats called "bulk headers" and you then cut to desired length, and solder in...on ebay its much cheaper then paying 0.50$ a piece...then you just get the correct housing..those don't cut very well!

Also with the 90° tube standoff boards, the idea is we shouldn't need the molex connectors, we should just be able to solder them straight onto the board.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: tmuikku on September 06, 2011, 03:53:31 AM
Hi! Bom lists attach / release pots to be "100K LIN/LOG". Does this mean they are double deck or both  Lin and Log are fine?:)
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: zayance on September 06, 2011, 04:46:23 AM
Hi! Bom lists attach / release pots to be "100K LIN/LOG". Does this mean they are double deck or both  Lin and Log are fine?:)

LIN or LOG
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: tomcat on September 06, 2011, 10:06:57 AM
Did you measure the current needed for low and 100V rails?
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: 0dbfs on September 06, 2011, 10:15:11 AM
This is looking like a sweet build. Really looking forward to four channels of these guys. :)

Thanks Abe!

Best,
jb

Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: dustbro on September 06, 2011, 10:30:54 AM
Anyone doing metal work yet?
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Neil on September 06, 2011, 10:43:07 AM
Anyone doing metal work yet?

Dan is working on it.

Neil
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on September 06, 2011, 11:44:12 AM
Did you measure the current needed for low and 100V rails?

Nope not yet....really depends on what opamps you decide to use....but the heaters will take....400ma times 2 = 800ma and then
I used a 50va transformer for my prototyped build and...its doesn't get hot...but that seems like its on the light end, probably want to get more than that to be on the safe side.

I will get down and crunch some numbers one of these days, if someone doesn't beat me to it :)

Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Kingston on September 06, 2011, 03:31:58 PM
but the heaters will take....400ma times 2 = 800ma

actually, no.

I thought you mentioned the heaters are in series to be used with a 12.6VDC line. That's still 400mA. Just that the 400mA is delivered to two 6.3VDC tube heater lines (or 600mA for the russians). Voltage doubled, not current.

It's a good choice like you already explained. Less dissipated heat (wasted voltage) on that regulator, and smaller heatsink. The +12.6VDC regulator should have a heat sink, at least a small one.

As for the calculations, something like a 40VA 2X18VAC transformer should be plenty. It gives 1.1A for each side of the 18volt rails. We are really interested in the positive side where we need at least 600mA (both heaters combined for the worst case russian scenario) and all the positive rails for chips (another worst case scenario of lets say 200mA!). The leds and 1.5V bias are negligible. Even with a fullwave bridge rectifier current drop that 1.1A is plenty, and with a good amount of headroom. In fact the negative rail side winding goes mostly unused.

No wonder that 50VA trafo is not even getting hot.

As for the B+, let's have another worst case scenario that's never gonna happen, but we need something to start the calculations. 50mA for all the tubes. So 100V 50mA translated to a 18V winding current is roughly 200mA. A safe choice would be even as small as a 5-10VA 18VAC transformer (secondary must be 115-120). If going for the Gyraf G9 dual transformer trick you'll want to insert the reversed transformer to the negative rail right before the rectifier.

To recap, you need about 40VA 2X18VAC transformer for the rails+heater, and a 10VA 115VAC/18VAC (reversed, connected to negative rail before rectifier) for the B+.

if you can't find them, round up for the next bigger model. safety first.

Furthermore, the G9 style reversed transformer trick is unnecessary if you find a trafo that supplys the 115VAC in the first place, no need to play with reversed primaries and secondaries.

If someone makes a custom trafo for the project here are very rough but safe calculations:

secondary 1: 18VAC 1.2A
secondary 2: 18VAC 0.4A
secondary 3: 120VAC 50mA

PS. I don't know how to calculate a transformer size for the original "unused primary as 100VAC supply" PRR transformer trick.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on September 06, 2011, 04:39:32 PM

I thought you mentioned the heaters are in series to be used with a 12.6VDC line. That's still 400mA. Just that the 400mA is delivered to two 6.3VDC tube heater lines (or 600mA for the russians). Voltage doubled, not current.



Ah!! Of course, I was wondering that as I typed. Thanks for such a lucid explanation of all that Kingston.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: tomcat on September 06, 2011, 06:05:03 PM
Without looking on the shematic. If the heaters are in line and you pull one tube nothing will happen/work cause the second tube will not see heater voltage!?
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on September 06, 2011, 09:44:51 PM
Without looking on the shematic. If the heaters are in line and you pull one tube nothing will happen/work cause the second tube will not see heater voltage!?

Right, how I have it setup, you pull a tube, or turn it on with only one tube in, there is not complete circuit so nothing happens.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Kingston on September 07, 2011, 04:10:44 AM
Ah of course! With just two tubes it does exactly that, like flipping a switch. I confused it with the case where there are more than one tube per channel and entire channels are in series. (I did this with one vari-mu build, not the safest configuration)
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Eje2005 on September 07, 2011, 06:17:05 AM
Abe, you are doing a great job here! Cant wait to get on this!

One question, "Separate front panel Lorin switch PCB, 12 position stepped input/output, 6 attack/6 release positions. "

I couldn't see the lorlins in the bom?
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on September 07, 2011, 11:01:22 AM
Abe, you are doing a great job here! Cant wait to get on this!

One question, "Separate front panel Lorin switch PCB, 12 position stepped input/output, 6 attack/6 release positions. "

I couldn't see the lorlins in the bom?

Ah yes thank you for bringing that up, I should find that post and change it.

The original plan was to set everything with switches, until I got to testing and pots make it much easier to fine tune the amount of compression, cause a 12 step fader resolution isn't optimal.
Also I changed the attack and release circuit to be like the original PRR, and when you put the unit in stereo link mode, it takes the right channels ATT/RELEASE controls out of the circuit so only the LEFT controls work, that solves try to "guesstimate" att/release controls for both channels,
and last reason is it is cheaper! with all those different PCBs the price started to get pretty expensive (50$ a channel) so I figure this route is best, and of course, if people still want to go the switch route they can still wire in their own rotary switches, though if you do, might I recommend you use 24 positions and don't have them go all the way to kill, maybe just within a reasonable cut/boost +/-20 db or something, that way you have more usable steps.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Kingston on September 09, 2011, 04:20:49 PM
are the PCB DOA holes big enough for mill-max sockets?

http://classicapi.com/catalog/product_info.php?cPath=71_77&products_id=122
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on September 09, 2011, 05:37:44 PM
are the PCB DOA holes big enough for mill-max sockets?

http://classicapi.com/catalog/product_info.php?cPath=71_77&products_id=122

Ah Yes. That is a yes.  The holes on the board are just under 2.4mm
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Jeremy.Starseed on September 09, 2011, 05:44:34 PM
This project seems like the best one yet, I love the 176 sound!

Every track sounds better through a 176, and they add up nicely afterwards.

I would like to get into it, but I will need a spare board from a kind soul.

Did anyone order one too many?

Thanks,

Jeremy

Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: coriolis on September 11, 2011, 10:47:49 AM
Hey Abe - what are the pcb dimensions?
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Dr_J on September 12, 2011, 06:18:33 AM
Hi,

i'm currently thinking of "my" transformer way to go.
One "mid szenario" is CINEMAG IN & OUT (CM-9589, CMLI-15-15B - right?).
Beside that LUNDAHL IN (LL1540) and/or JENSEN OUT (10k611m ??) are although
on the list.
What speaks for LUNDAHL and JENSEN?
Does anybody know what transformer are used in the RERO 176?

ROCK-ON!
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: adeptusmajor on September 12, 2011, 08:34:06 AM
I was thinking about using the Edcor transformers just to get the build done quicker.

I know the sound is dependant alot on the circuit, but does anybody have experience comparing the Edcors to more expensive options?

Just trying to figure out if I would be better off waiting and paying the extra coin for something a little nicer, how much of a difference it would make, and how the Edcors sound in general.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: MrZpliff on September 12, 2011, 09:47:20 AM
IMHO Edcors are just fine.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: earl on September 12, 2011, 12:27:28 PM
CINEMAG IN & OUT (CM-9589, CMLI-15-15B. Are these locateable in this forum somewhere? Or where can we scare these up?
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: zayance on September 12, 2011, 03:54:09 PM
CINEMAG IN & OUT (CM-9589, CMLI-15-15B. Are these locateable in this forum somewhere? Or where can we scare these up?

http://www.cinemag.biz/ (http://www.cinemag.biz/)
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Kingston on September 14, 2011, 10:02:27 AM
It isn't quite clear to me how VU's are connected here. Am I blind or has this been discussed before?

I see dan's preliminary front panel design has a meter per channel. What kind are they? Audio VU, 1mA DC or?

What are my options here with the default PCB configuration?
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: minor_glitch on September 14, 2011, 12:58:12 PM
Judging by the schematic it looks like they're 1mA meters.  There's a chart listing the pins and pin 2 says '1 ma meter positive'.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: beatnik on September 14, 2011, 01:40:55 PM
Were the pcbs available just for pre-order or am I still on time?
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on September 14, 2011, 02:01:01 PM
Hey Abe - what are the pcb dimensions?

6.9" by 11.4" inches

and the edcors....I haven't tried other transformers, but one thing the edcors have going for them is they are steel...so they tend to saturate "nicely" other than maybe nickle or other materials.

But I'm looking forward to trying out some different transformers and comparing.

Cheers!

PS Get the boards tomorrow, will start sending them out. Thanks again to all who participated. I *should* have some extra boards if I haven't contacted you already and you are interested send me a pm
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: coriolis on September 15, 2011, 04:48:36 AM
Wow - big boards! Looking forward!
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Kingston on September 15, 2011, 05:03:52 AM
ok I see it now, 1mA meters are needed. Sorry I was blind earlier, yes it's there right on the schematic.

List of the 1U meters I know. I guess they would be the same as the GSSL choices

http://fi.farnell.com/multicomp/mc34h-0-100/meter-edge-indicating-100ua/dp/143509
http://diypartssupply.com/index.php?main_page=product_info&cPath=3&products_id=29

Then there's that round Behringer BE-46 meter. Don't know who sells it anymore.

What other good 1U 1mA meters are there around these days? Does someone offer a led 1mA solution?

PS. The Jensen transformers we are interested in are any JT-11 (600:600) types for the output, JT-10K61-1M (10k/600) for interstage and any JT-11P (10k:10k) for input. Too expensive for me, and that interstage has overkill specs anyway.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: tmuikku on September 15, 2011, 05:06:50 AM
Mike sells some 1ma meters as well:
http://hairballaudio.com/shop/index.php?cPath=25&osCsid=ff2ee1f0f474623d8f39decc2d4926db
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: tomcat on September 15, 2011, 07:19:29 AM
Does someone offer a led 1mA solution?

Ahhh, another one who likes the LED idea :)
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: peters on September 15, 2011, 09:27:41 AM
Any thoughts as to how the 6386 (Fairchild) tube would work in this circuit?

I know I saw some 176 schematics that were marked up with a mod to accept the 6386. Obviously the pinout is a bit different, and I believe they disabled the pad that was across the input, so it probably needs a bit more drive.

thanks,
--Peter
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Hank Dussen on September 15, 2011, 03:50:05 PM
Since the original 175 has a VU-meter and I have 2 small ones laying around: is it possible to use a VU meter to read gain reduction?
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on September 15, 2011, 07:19:55 PM
About the meter - I'm sure a VU would work, you would just have to adjust the scale accordingly. some might prefer this (myself included) it should show more sublte gain  reduction. Also might as well open them up and take out the diodes....if they are accessible.

Got the boards today! Testing them out. They look nice....will upload some pics soon.

-Abe
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Dr_J on September 16, 2011, 10:12:07 AM
VU-Meter would be great!!
Hairball has some nice ones and as I'm going to take a 2U case there will be enough space for
2 nice big meters  :)
Even JLM has some nice ones too! Although one fitting 1U.

Have we already cleared how to conect them?
Joe offers a VU-Meter kit. Could this be an easy way?

Btw. for the "LED Guys", Joe has a LED-Meter kit too...  ;)

ROCK-ON!

Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: minor_glitch on September 18, 2011, 11:35:56 PM
Alright, I'm just about done filling up my mouser cart and I just want to confirm a few things on the BOM.

C35, 36, 38, 40 - any links/resources/tips for calculating these values?
R36, 112, 168, 169 -  I assume OPT. means optional?  In which situations are these required?

Lastly, mouser has a Triad 50VA, 115-230 primary, 15-30 secondary transformer (VPT30-1670)  Would that guy work or is there a better choice?

Can't wait to dive into this!
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: baadc0de on September 19, 2011, 06:19:50 AM
Make sure to share us the mouser cart # after you're finished :P

Alright, I'm just about done filling up my mouser cart and I just want to confirm a few things on the BOM.

C35, 36, 38, 40 - any links/resources/tips for calculating these values?
R36, 112, 168, 169 -  I assume OPT. means optional?  In which situations are these required?

Lastly, mouser has a Triad 50VA, 115-230 primary, 15-30 secondary transformer (VPT30-1670)  Would that guy work or is there a better choice?

Can't wait to dive into this!
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on September 19, 2011, 08:54:18 AM
Make sure to share us the mouser cart # after you're finished :P

Alright, I'm just about done filling up my mouser cart and I just want to confirm a few things on the BOM.

C35, 36, 38, 40 - any links/resources/tips for calculating these values?
R36, 112, 168, 169 -  I assume OPT. means optional?  In which situations are these required?

Can't wait to dive into this!

Those resistors are the terminating resistors for the inter-stage transformer. R36 and R112 are the primary termination and a good choice to start out with might be 1k. The R168 and R169 are the secondary termination and 100k might be a good place to start. Or you could try it without them. This is were experimentation can come in, as it depends on your transformers.
I hope we see some peoples optimal values come in, with the different transformers.

Also for the sidechain capacitors, if you don't want a sidechain HPF just put a 1uf in the Cap spot. If you do want HPF option, I will upload a more detailed wiring diagram, but basically the 2 capacitors are added together to equal about = 1uf and then one of the capacitors is switched out leaving just one of the capacitors inline with the sidechain circuit creating a HPF, the frequency depending on  the choice of capacitor value. you can easily calculate these values, based on the impedance of the circuit. Or you can just try two 0.47uf caps.

Thanks!
I will be uploading updated info soon
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: minor_glitch on September 19, 2011, 10:07:07 AM
Perfect, thanks!  Board looks great  :)
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: minor_glitch on September 19, 2011, 10:17:34 AM
Make sure to share us the mouser cart # after you're finished :P
Well my cart is also full of parts for an 1176, so you probably don't want that!  I can post a list of mouser part #'s for the components I chose though.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: adeptusmajor on September 19, 2011, 06:38:44 PM
"Intended for use only with classical pieces in the key of c"


I guess that means I'm screwed.

I'll probably just sell my board when it arrives, then. :'(
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: earl on September 19, 2011, 07:53:25 PM
We should at least be able to change the key around by varying some capacitors ;)
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: minor_glitch on September 22, 2011, 01:32:58 PM
Any toroid advice?  I thought I had it figured out, but after reading Kingston's post a page back I'm not so sure now.  Are two transformers required for the project or will one work just fine?

You mentioned using a 50VA dual 18V secondary.  That led me to think this guy would work: https://system.netsuite.com/core/media/media.nl?id=12599&c=ACCT126831&h=9bf90c20991f70f0e64c&_xt=.pdf
Assuming it even fits in a 1u case...
Hopefully I can avoid blowing $30 on the wrong tranny.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on September 22, 2011, 02:47:36 PM
Any toroid advice?  I thought I had it figured out, but after reading Kingston's post a page back I'm not so sure now.  Are two transformers required for the project or will one work just fine?

You mentioned using a 50VA dual 18V secondary.  That led me to think this guy would work: https://system.netsuite.com/core/media/media.nl?id=12599&c=ACCT126831&h=9bf90c20991f70f0e64c&_xt=.pdf
Assuming it even fits in a 1u case...
Hopefully I can avoid blowing $30 on the wrong tranny.

Depends on what mains you have. If you have 120v Mains you can use a dual primary, hook  one primary to the mains and the second primary to the 100V transformer in on the board.

If you have 120v mains that transformer will work fine.


Finally got them all packaged up. Starting to send them out today...get ready!! :)
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: minor_glitch on September 22, 2011, 03:11:30 PM
Awesome, thanks!  Guess I should have said I have 120V mains.

Finally got them all packaged up. Starting to send them out today...get ready!! :)
Don't know about everyone else, but I'm ready!  Just have to throw the toroid in my mouser cart and we're good to go.  Edcors have been ordered, tubes are in the mail, picking up DOAs tomorrow.  Let's do this thing!haha

Any update from Dan on the cases?
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: earl on September 22, 2011, 05:38:16 PM
Hey Abe did you by chance use the power supply from the mx2 audio mixer for prr 176 project?  You pointed to the deal on the ebay thread in the black market forum Anyway i bought one of those and was wondering if i could use it for the prr 176.
It's 15v and -15v.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: jandoste on September 22, 2011, 06:19:28 PM
Hey Guys,
I can't fine any info for D6, D7, D8, D9 ! do you have any link for 2A04?
Thanks
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: minor_glitch on September 22, 2011, 06:24:19 PM
Pretty sure this will work: http://ca.mouser.com/ProductDetail/Taiwan-Semiconductor/2A04/?qs=sGAEpiMZZMuMAfj%252bWfX4nKHoJleXsPN1
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: jandoste on September 22, 2011, 06:32:27 PM
Thanks minor_glitch  :)
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: beatnik on September 22, 2011, 07:54:40 PM
wich power transformers for europeans? what are you guys ordering? maybe we can do a group buy of custom made toroidals?
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on September 22, 2011, 11:59:33 PM
Hey Abe did you by chance use the power supply from the mx2 audio mixer for prr 176 project?  You pointed to the deal on the ebay thread in the black market forum Anyway i bought one of those and was wondering if i could use it for the prr 176.
It's 15v and -15v.

Hi Earl,
I think the transformer will work. You will just have to measure the windings to make sure.

Also, you don't "have" to have the unit run on +/-18v rails. You can choose any value you want....+/-15v should be fine, you could even run +/-24 with the correct transformer and opamps that can handle that....just saying its a very flexible project.

Also, for people ordering encore transformers, just get the 1:1 for both input and interstage positions, like Kingston was saying. all the 4:1 seems to do is lower the volume, and then you just have to boost it, increasing noise floor.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: minor_glitch on September 23, 2011, 12:09:20 AM
Also, for people ordering encore transformers, just get the 1:1 for both input and interstage positions, like Kingston was saying. all the 4:1 seems to do is lower the volume, and then you just have to boost it, increasing noise floor.

Ah damn, I'll have to order two more transformers.  I'm glad they're only $10!  So the interstage can be the same model as the input ones? PCW10K/10K in my case.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on September 23, 2011, 12:40:26 AM
Also, for people ordering encore transformers, just get the 1:1 for both input and interstage positions, like Kingston was saying. all the 4:1 seems to do is lower the volume, and then you just have to boost it, increasing noise floor.

Ah damn, I'll have to order two more transformers.  I'm glad they're only $10!  So the interstage can be the same model as the input ones? PCW10K/10K in my case.

Don't worry about it. The 4:1s work just fine too. Thats what I'm using, but just for the sake of simplicity, people can just order 4 of the 1:1
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: minor_glitch on September 23, 2011, 12:55:50 AM
Good to know.  Then again, if I order the extra 1:1's I'll have an excuse to find another project to use the 4:1's in!  (Addicted? Me? Nooo...)  :)
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: kazper on September 23, 2011, 01:24:58 AM
Can you edit the first post and have any files associated with the build linked there...
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Kingston on September 23, 2011, 02:27:09 AM
The transformers in this project seem kind of non-critical since we are actually interfaced to the outside world with DOA's. They probably could all be 1:1.

For example, I will use the 4:1 interstage. But I will use a DOA output to a 1:3 or 1:2 transformer, a la API (see classicapi EA 2503 75:600ohm configuration for example). DOA can easily drive this. A common step up output configuration.

If I still feel I need more volume, I can use a 1:2 step up input. Lundahl LL1540 certainly can be wired this way (see 1176 threads for more info). Probably needs trace cutting but that's a non issue.

Lots of gain staging and headroom variations possible when playing with these transformers.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on September 23, 2011, 10:09:38 AM
The transformers in this project seem kind of non-critical since we are actually interfaced to the outside world with DOA's. They probably could all be 1:1.

For example, I will use the 4:1 interstage. But I will use a DOA output to a 1:3 or 1:2 transformer, a la API (see classicapi EA 2503 75:600ohm configuration for example). DOA can easily drive this. A common step up output configuration.

If I still feel I need more volume, I can use a 1:2 step up input. Lundahl LL1540 certainly can be wired this way (see 1176 threads for more info). Probably needs trace cutting but that's a non issue.

Lots of gain staging and headroom variations possible when playing with these transformers.

I left all the gain staging resistors with just a part number and no value on the board in hopes that eventually we can get it sorted what values for what transformers. There are plenty of options for different gain feedback resistors at the input/output gain stages.

Also there is a lot of interesting results based on the threshold...

Eventually I want to get a calibration procedure up.

Getting more boards sent out today!

Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: dustbro on September 23, 2011, 06:48:37 PM
Getting more boards sent out today!

 :D
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: adeptusmajor on September 26, 2011, 06:10:56 PM
Board arrived today

looks nice, thank you much!
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Davo on September 26, 2011, 07:16:41 PM
Got some boards today, Thanks Abe!!

They're huge! :o ;D
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: fazer on September 26, 2011, 08:56:57 PM
got the board.   Looks Great!  Thanks Abe
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: kml23956 on September 26, 2011, 09:09:59 PM
Some very nice looking boards arrived today.  Thanks Abe.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: kquick on September 26, 2011, 10:15:52 PM
Boards came today.  Can not wait to get started.  Thanks Abe.


Kim
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: kazper on September 27, 2011, 12:05:57 AM
Boards showed up today.

One issue that popped up was the Edcor PC layout don't fit my edcor PC transformers I had in my shop. The PCW fit fine in both spots and the PCW when sitting in the PCB is slightly lower than the tube right angle pcb. I also shoved in a compatible Lundahl and it fit nicely in it's layout.

In future revisions maybe more PCB mounts around the iron may be nice. I'd also make it a option to do the 90 deg tube mount there is enough room on the pcb to provide a straight up location there.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: zayance on September 27, 2011, 05:38:57 AM
Board received. Thanks
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on September 27, 2011, 09:29:27 AM
Good input.

Some things to take into account, the polarity gets inverted in the circuit. easy fix if your using balanced connectors, just switch pin 2 & 3 of input or output.

Also I omitted DC blocking capacitors for the sake of audio fidelity, but depending on what opamps you want to put in, you might want to add a DC blocking cap to the input fader. Output section seems to be fine.


and WIRING GUIDE

www.acsoundstudio.com/prr_176/PRR_176_WIRING_GUIDE_j.jpg
Thanks,
Abe
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: living sounds on September 27, 2011, 09:55:42 AM
Something seems to be wrong with the schematics vs. BOM. For the left channel C1 is supposed to be a 1uf tantalum cap, but the corresponding position on the right channel has C40 there, according to the BOM a 1uf film cap for the HPF. Shouldn't this be C2?
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on September 27, 2011, 10:09:59 AM
Something seems to be wrong with the schematics vs. BOM. For the left channel C1 is supposed to be a 1uf tantalum cap, but the corresponding position on the right channel has C40 there, according to the BOM a 1uf film cap for the HPF. Shouldn't this be C2?

The BOM and the board jive, when I have some time I'll update the schematic.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: 0dbfs on September 27, 2011, 11:29:33 AM
Received PCB's yesterday. They look great with some cool options built in! Thanks for the wonderful project Abe!

Cheers,
jb
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: funkymonksf on September 27, 2011, 12:40:17 PM
Abe I just opened a beige package abd upon holding the board I'm way impressed. Great layout and clearly high quality. Thanks for the project.

Brice
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: earl on September 27, 2011, 03:22:20 PM
Hello Abe got the board today way cool awesomeness thank you.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: adeptusmajor on September 27, 2011, 06:30:08 PM
Hey Abe, please correct me if I'm wrong, but glancing at the wiring guide it looks like you have the attack, release, and meter wired to the opposite channel as the adjacent input and output controls.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on September 27, 2011, 07:14:51 PM
Hey Abe, please correct me if I'm wrong, but glancing at the wiring guide it looks like you have the attack, release, and meter wired to the opposite channel as the adjacent input and output controls.

Holy Smeg!
I swear sometimes I'm losing it.

Thanks for pointing that out!


Update: file is updated.

Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: ChrisPbass on September 27, 2011, 09:07:40 PM
any spare boards abe?
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: adeptusmajor on September 28, 2011, 01:26:50 PM
Hey guys, I have a beginners question, sorry if it's a little off topic. I got a matched pair of tubes for my 176, they are 6BZ8's. Everything I could tell indicated that 6BZ8's are interchangable with 6BC8's. I just wanted to make sure that they are sufficient for this circuit, and I was hoping that maybe someone could tell me the difference between the two or point me in the right direction to find out. Thanks.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: living sounds on September 28, 2011, 01:52:04 PM
Since the topic of tubes has been raised, would it be possible to use    9AQ8 = PCC85 in there (with a few changes)? It's used in the Chiswick Reach Vari-Mu Compressor.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: earl on September 28, 2011, 03:57:57 PM
Hey Abe are the Dan cases set up for the 1176 style hairball meters?  Will it use the same meter?
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: coriolis on October 01, 2011, 04:43:06 AM
YESSS! Just got the boards today - they look so good! And they're huge!
Can't wait to get started...
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: living sounds on October 01, 2011, 07:55:11 AM
Just let me ask two more idiot question: Do I understand this correctly - input and interstage trafo are mandatory, but the output trafo is optional? And are any of these transformers not in the signal path (I don't quite get it from the schematics)? Thanks!
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: jandoste on October 01, 2011, 08:04:28 AM
Just let me ask two more idiot question: Do I understand this correctly - input and interstage trafo are mandatory, but the output trafo is optional? And are any of these transformers not in the signal path (I don't quite get it from the schematics)? Thanks!

+1
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on October 01, 2011, 11:34:03 AM
Just let me ask two more idiot question: Do I understand this correctly - input and interstage trafo are mandatory, but the output trafo is optional? And are any of these transformers not in the signal path (I don't quite get it from the schematics)? Thanks!

+1


Yes, exactly. Output transformer is optional. and all transformers are in in the audio path. Sorry about weirdness in schematics. will get some better ones up when I gots some time.
Cheers!
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Jeremy.Starseed on October 03, 2011, 08:30:20 AM
Board arrived in the mail today. Thanks very much, it does look great as several people have said.

10K input impedance isn't something I really desire, since most of the gear I use is from the 60's and likes to
see 600 (or in the case of my Telefunken desk even 200) Ohms.

I'm wondering if I could simply swap the input pot and input transformer to 600 Ohm and take it from there?

What would be a suitable transformer for 600:10k, in this instance? The secondary is supposed to be 10K, no?

Looking forward to digging in, how are you guys doing so far?

Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Kingston on October 03, 2011, 09:00:53 AM
10K input impedance isn't something I really desire, since most of the gear I use is from the 60's and likes to see 600.

That's not the way these things work. Read up on bridged impedance. 10k input is perfectly fine here and all gear (low or high impedance) is able to drive it.

The only thing a 600:10k transformer would do here is limiting the options what could drive the input, and stepping up the voltage (which you would then need to attenuate even further).
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on October 03, 2011, 12:30:59 PM

I'm wondering if I could simply swap the input pot and input transformer to 600 Ohm and take it from there?

What would be a suitable transformer for 600:10k, in this instance? The secondary is supposed to be 10K, no?



I would say just use a 600 ohm attenuator input pot and feed it straight into the "opt ins" (the opt ins go straight into the first transformer.)


Also concerning the sidechain HPF, I know there are much more eloquent people out there that can tell us exactly what cut off frequency what value of capacitor will bring, I was doing some testing and found that if one uses a 0.47uf cap for the sidechain capacitor there is only a 3-4 db less GR at 20hz as compared to the sidechain running with a 1uf.

So I might recommended one use a 0.33uf or 0.22uf for HPF sidechain action. Should give a HPF cutoff at a reasonably useful frequency. As 0.47uf is a little to large a value for any useful HPF cutoff action.

Also.....had a fun Cowboy poetry/song concert I had the opportunity to run sound for, and I showed up at the gig with the PRR176 under my arm and some patch cables...
I was very happy with the sound, it glued the stereo bus together nicely, transparently making everything easier to mix and listen to, without audibly sounding "compressed".
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Kingston on October 03, 2011, 02:59:04 PM
For the sidechain high pass a 1st-order filter is formed with the C1 and R15. (and same with the other channels respective cap and resistor)

stick the values in here: http://www.sengpielaudio.com/calculator-RCpad.htm

You'll find out 1uF cap has a -3dB cut off point at 16hz. Stick in 0.47uF and it still cuts at the very low 34hz. Yeah, that's not awfully usable for choices.

Something like 0.15uF (cuts at 100hz) would be much more useful.

By the way the paralleled cap value does not have to be exactly 1uF. The other cap can always be 1uF, as long as it's cut out of the path when high pass is engaged.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Jeremy.Starseed on October 03, 2011, 05:07:48 PM
10K input impedance isn't something I really desire, since most of the gear I use is from the 60's and likes to see 600.

That's not the way these things work. Read up on bridged impedance. 10k input is perfectly fine here and all gear (low or high impedance) is able to drive it.

The only thing a 600:10k transformer would do here is limiting the options what could drive the input, and stepping up the voltage (which you would then need to attenuate even further).

I know 600 will drive 10k without an effort.

I was more concerned with the outputs of my other gear. I guess I am in the impedance matching corner of the ring. I read about correct termination, and don't want to have to switch resistors in and out on the back of my patch bay. I hope this makes sense. There is a great thread on termination over at gearslutz, with "correct termination" in the title.

It would be nice to find a suitable replacement, does anybody know if there is a model from Lundahl to fit the circuit board? Would I have to settle for 1:2 or 1:4?

http://www.kandkaudio.com/transformers.html

Thanks,

Jeremy

 
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: kazper on October 03, 2011, 08:53:24 PM
Since the topic of tubes has been raised, would it be possible to use    9AQ8 = PCC85 in there (with a few changes)? It's used in the Chiswick Reach Vari-Mu Compressor.

PCC85 (http://tubedata.tubes.se/sheets/030/p/PCC85.pdf) and 6BC8 (http://tubedata.tubes.se/sheets/137/6/6BC8.pdf)

Don't see why not, but I didn't study them to long. You could bump up the power for the heaters to 18V since the heaters are in series because the PCC85 uses 9V heaters.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Kingston on October 04, 2011, 04:50:38 AM
Forgot to mention, board came yesterday. Thank you Abe! Signal chain is so clearly laid out even the wife pointed it out and asked about it.

It would be nice to find a suitable replacement, does anybody know if there is a model from Lundahl to fit the circuit board? Would I have to settle for 1:2 or 1:4?

Yes. Check BOM. Yes, it can be wired as 1:2. You'll have to cut traces, but that should be easy if you really need to have 1:2 input. I intend to experiment with this as well.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on October 04, 2011, 12:49:49 PM
Thanks for all the kind words all! :)

Finally getting around to doing some house keeping:


   Justin Dean

you sent me payment for PRR-176 but didn't include a return email or shipping address, or your forum ID. Just want to make sure you get your board.



I'm almost 100% everything else is in order. But if anyone else hasn't received their board in a bit let me know, we'll figure out.
Thanks!!

-Abe
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: jandoste on October 04, 2011, 04:44:49 PM
My boards came today and they are AWESOME!
Thanks Abe!
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: MrZpliff on October 04, 2011, 04:45:11 PM
Board arrived yesterday. Looks great !
Thank's  :)
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Tsane on October 04, 2011, 05:13:30 PM
Board arrived a couple of days ago. Looking great. Thanks!
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: minor_glitch on October 05, 2011, 02:31:37 AM
Damn, it looks like it takes less time for a package to get overseas than north of the border!  Stupid Canada Post.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: flaheu on October 05, 2011, 04:57:52 AM
Hi,

I missed da boat here  :(

Any chance to get a set for a stereo unit ?

thanks for that great project.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: JayDubrek on October 05, 2011, 05:09:06 AM
Hi Abe- wondered why everyone else had got their boards!!! PM'd you my details... sorry about that!!!
Jay AKA Justin Dean
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Jeremy.Starseed on October 05, 2011, 06:36:39 AM

...had a fun Cowboy poetry/song concert I had the opportunity to run sound for, and I showed up at the gig with the PRR176 under my arm and some patch cables...
I was very happy with the sound, it glued the stereo bus together nicely, transparently making everything easier to mix and listen to, without audibly sounding "compressed".

I imagine the band patiently and with solemn reverence played their fiddles, in the key of C ;)
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: mylesgm on October 05, 2011, 07:03:53 AM
Got mine, thanks!
M
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: living sounds on October 05, 2011, 07:55:03 AM
Did you send the boards via registered mail? I had a note in the mail yesterday to go and pick up a registered letter at the post office - just went there and they couldn't find it...
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Neil on October 05, 2011, 07:56:52 AM
Got mine and it looks great! Thanks!!
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: jandoste on October 05, 2011, 08:06:15 AM
Hey Guys,
Can I use 100uF 25V or 470uf 35V instead of100uf 250V?
Thanks for any advice.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Kingston on October 05, 2011, 08:11:29 AM
No! Are you sure you are equipped to build this project? Seems a bit dangerous handling high voltage with questions like that.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: jandoste on October 05, 2011, 08:49:32 AM
Seems a bit dangerous handling high voltage with questions like that.

I built 12 DIY projects so I'm here.... it was just a question! thanks for the reply.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: zayance on October 05, 2011, 08:56:25 AM
Seems a bit dangerous handling high voltage with questions like that.

I built 12 DIY projects so I'm here.... it was just a question! thanks for the reply.

Kingston wasn't beeing rude there, you got to be carefull, 25V - 35V is the max Voltage of the Caps you reffered to,
S if you feed 250V then that will go BOOM and you'll spread some chimicals in your face or whatever,
Everybody is up to build stuff, but HT brings some more care to the process, I'll send you a Safety not that
i made just for info for the MK47 PSU Kingston help me out with, read it and also Gyraf's section on the G9
build about Safety dealing with HT.

NO Joke....
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: jandoste on October 05, 2011, 09:01:41 AM
Seems a bit dangerous handling high voltage with questions like that.

I built 12 DIY projects so I'm here.... it was just a question! thanks for the reply.

Kingston wasn't beeing rude there, you got to be carefull, 25V - 35V is the max Voltage of the Caps you reffered to,
S if you feed 250V then that will go BOOM and you'll spread some chimicals in your face or whatever,
Everybody is up to build stuff, but HT brings some more care to the process, I'll send you a Safety not that
i made just for info for the MK47 PSU Kingston help me out with, read it and also Gyraf's section on the G9
build about Safety dealing with HT.

NO Joke....

Thanks Zayance and Kingston... I understood what he was saying and you too! you're right!
I will be very carfull and so I'm am :) Because of that I asked this question if not I can't :) :)
Best et Merci :)
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Kingston on October 05, 2011, 09:14:28 AM
What you can do, of course, is use bigger capacitance if you can fit the caps or have a bigger case. I personally don't trust a mere CRC network for filtering tube B+. I will do CRCRC, with something like 150-220uF for each cap. But 250V rating is needed for safety. These aren't the same electrolytes as your average sports drink, should you have some exploded in your face.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: zayance on October 05, 2011, 11:19:33 AM
Quote
These aren't the same electrolytes as your average sports drink, should you have some exploded in your face.

Just sayin....
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on October 05, 2011, 06:53:48 PM
Did you send the boards via registered mail? I had a note in the mail yesterday to go and pick up a registered letter at the post office - just went there and they couldn't find it...

Hello,
Nope just sent them out regular mail. Strange they couldn't find your registered letter though...I know here they keep the registered mail in a big safe in the back. Good luck!


NO Joke....

I second that. Please everyone practice extreme caution when building this project. It does use high voltage. No reason to be scared if you are careful NOT TO TOUCH anything with your bare hands. Get a nice "poking stick", don't work with power on and get a nice big 'capacitor draining resistor'. I would much rather be too scared of something then be too injured by it.
The HV capacitors can hold their charge for days unless they are bled so keep that in mind.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: minor_glitch on October 08, 2011, 05:38:47 PM
Out of curiosity, do you think there would be any audible advantage to using...fancier caps (something like russian pio) instead of good ol' wima film caps in this unit?  Or would the difference be negligible compared the the sound of the trannies and tubes?
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Kingston on October 08, 2011, 09:54:44 PM
Out of curiosity, do you think there would be any audible advantage to using...fancier caps (something like russian pio) instead of good ol' wima film caps in this unit?  Or would the difference be negligible compared the the sound of the trannies and tubes?

Especially that 1uF time constant cap will sound much better if PIO or high quality polypropylene cap (something like wima MKP4, or Solen fast). I noticed audible differences between types of time constant caps in the poorman. The situation is exactly the same here, a cap discharging itself into the tube grids. That's as much in the signal path as can be, and highly interactive as such.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: minor_glitch on October 08, 2011, 11:22:11 PM
Thanks!  I wish ebay would find a better solution to ordering multiple items from the same seller for combined shipping.  The whole 'request quote from seller' thing kinda blows!
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: coriolis on October 10, 2011, 04:46:56 AM
Hi Abe - is the schematic updated? Or still the original?
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: ilfungo on October 10, 2011, 07:19:19 AM
Boards came today
they are AWESOME!
GREAT!!!!!!!!
Thanks Abe!!!
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: naTe on October 10, 2011, 06:34:35 PM
Got mine today, looks great Thanks
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on October 11, 2011, 12:44:29 AM
Hi Abe - is the schematic updated? Or still the original?
Still original, have plans to make an updated one tomorrow. Glad everyone is receiving their boards. :)
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: living sounds on October 11, 2011, 07:42:48 AM
The registered one has got to be something else. But I haven't received your boards yet. How long have they been on their way now?
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: minor_glitch on October 12, 2011, 11:58:45 AM
Mine arrived today.  Looks great!
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: labak on October 12, 2011, 05:03:14 PM
Hi all!

Just a question is a second order will be made or all of the last ones lost it?

Thanx
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: minor_glitch on October 13, 2011, 01:45:43 AM
Here's some naked board porn for your viewing pleasure: http://paulmantiniaudio.blogspot.com/2011/10/prr-176-it-begins.html
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on October 13, 2011, 11:35:48 AM
Hi all!

Just a question is a second order will be made or all of the last ones lost it?

Thanx

Hello,
Yes, definitely want to place a second run, but won't be for a while (hopefully not long while) but want to get feedback on the board and possible mods/etc that people might want for second run. I admit I probably should've ordered more of the first batch!
Thanks,
Abe
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: coriolis on October 13, 2011, 04:14:24 PM
Trying to figure this out: When you guys (Kingston and others) talk about using better caps for the 1uf cap - is that C38,C40 you are talking about - the hpf cap? Or C1, C2 (the tant)? Just wondering...

C
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on October 13, 2011, 05:05:34 PM
Trying to figure this out: When you guys (Kingston and others) talk about using better caps for the 1uf cap - is that C38,C40 you are talking about - the hpf cap? Or C1, C2 (the tant)? Just wondering...

C

I believe they are referring to the tant.

The HPF/sidechain cap will have an in-audible effect on how the unit sounds, but the Tant (the timing cap) will absolutely have an effect. Personally I like Tants in timing circuits. I'm not saying other caps don't sound better/different. I haven't tried every type of cap, but alot of great sounding circuits use tants and I really like how they sound.

Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: minor_glitch on October 13, 2011, 10:11:54 PM
The HPF/sidechain cap will have an in-audible effect on how the unit sounds, but the Tant (the timing cap) will absolutely have an effect. Personally I like Tants in timing circuits. I'm not saying other caps don't sound better/different. I haven't tried every type of cap, but alot of great sounding circuits use tants and I really like how they sound.
Well that's good to know.  I have tants and I just ordered a few PIO, so I might try it both ways and see which I like better. 
I'm thinking I'll try two versions of the comp.  One with 6bc8's and tants, and one with 6n5p's and pio.  I'll call that one 'the Soviet mod' (or the 'CCCPRR 176'?). haha
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: adeptusmajor on October 13, 2011, 11:42:41 PM
Do you guys think the timing cap makes enough of a difference to have a switch with different types of caps for different curves?

I have some Solen caps for it right now, I figured I would go ahead and keep the tantalums in my mouser cart and maybe experiment later.

But if there is that much of a difference, and the switch proves to be a good idea then I might go ahead and order some PIO and maybe some others.

anyone with more experience care to comment?
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: minor_glitch on October 14, 2011, 12:49:35 AM
Where is R108?  I see it on the schematic between K2 and I think the 5th pin of 'TO_A_R2' but I can't seem to find it on the board.
Oh and it's probably a rookie question, but what exactly is the purpose of the whole center tap control feed k1/k2 thingies?
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Kingston on October 14, 2011, 04:28:18 AM
Do you guys think the timing cap makes enough of a difference to have a switch with different types of caps for different curves?

I have some Solen caps for it right now, I figured I would go ahead and keep the tantalums in my mouser cart and maybe experiment later.

But if there is that much of a difference, and the switch proves to be a good idea then I might go ahead and order some PIO and maybe some others.

anyone with more experience care to comment?

It can make or break the unit. Experiment with it before drilling anything to a front panel. I also agree with abechap024 that tantalums work really well in timing circuits. For example I once changed tantalums of a 1176 unit to high end electrolytics. It's like the bite character that everyone knows 1176 for completely disappeared! WTF said I, and put the tantalums back as quickly as possible.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: labak on October 14, 2011, 05:50:43 AM
Hello,
Yes, definitely want to place a second run, but won't be for a while (hopefully not long while) but want to get feedback on the board and possible mods/etc that people might want for second run. I admit I probably should've ordered more of the first batch!
Thanks,
Abe
Here's some naked board porn for your viewing pleasure: http://paulmantiniaudio.blogspot.com/2011/10/prr-176-it-begins.html

Waow that would be really cool! So we have to stay tuned ;)

Thanks!


It looks like really huge boards, isn't it!

I drool  of :P
Hi all!

Just a question is a second order will be made or all of the last ones lost it?

Thanx
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: adeptusmajor on October 14, 2011, 08:13:34 AM
It can make or break the unit. Experiment with it before drilling anything to a front panel. I also agree with abechap024 that tantalums work really well in timing circuits. For example I once changed tantalums of a 1176 unit to high end electrolytics. It's like the bite character that everyone knows 1176 for completely disappeared! WTF said I, and put the tantalums back as quickly as possible.

Thanks, I definitely plan on experimenting. I guess I wanted to see if anyone had a good reason not to try this, like if running wires from this part of the board to a switch might induce noise, or more importantly if there was any safety concern or possibility of damaging anything by switching the cap while the unit is powered up. If not, then I will move forward and play.

Where is R108?

If you look at the wiring diagram you will see that R108, as well as R96 and the second timing cap are located off of the board, wired directly to the channel 2 attack and release pots. Took me a minute to find it , too.

Oh and it's probably a rookie question, but what exactly is the purpose of the whole center tap control feed k1/k2 thingies?

I would like to know this as well. I was persuaded to use resistors instead of the center tap for the heaters on a tube guitar amp I built a while back, it did seem to increase the touch response of the amp, but I still haven't been able to wrap my head around the concept completely. Not sure if it is the same kind of thing happening here.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on October 14, 2011, 11:09:44 AM
Where is R108?  I see it on the schematic between K2 and I think the 5th pin of 'TO_A_R2' but I can't seem to find it on the board.

Hello,
I'm getting the board and schem all sorted today, as I made some changes after I converted the schem to the board and sometimes, changing one little thing (I think I deleted some resistors) can throw off all the parts and it turns into a big mess!

Quote
Oh and it's probably a rookie question, but what exactly is the purpose of the whole center tap control feed k1/k2 thingies?

Good question, if the transformers you decide to use have a center tap, you can choose to run the control voltage to the center-tap instead of two 3k resistors. And just because a transformer is center tapped doesn't mean you have to use the center tap option. What sonic differences are there? whats the better option? Those are questions of my own! :)
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: abechap024 on October 14, 2011, 11:33:36 AM
Schem!

www.acsoundstudio.com/prr_176/PRR_SCHEM_ALL.jpg (http://www.acsoundstudio.com/prr_176/PRR_SCHEM_ALL.jpg)

updated for easier read. Checked all parts against board and everything should jive.
Title: Re: PRR 176 vari-mu (BOM page 8)
Post by: Kingston on October 14, 2011, 02:31:11 PM
What sonic differences are there? whats the better option? Those are questions of my own! :)

Doubtful there are big sonic differences. It's just takes out the input loading of the transformer out of the equation. Oscilloscope might show some differences on how the transformer is singing/ringing on sharp square wave edges, for better or worse. I usually "let them ring", but edcor line level input transformers for example are known to have phase issues on +10-20khz area. Might be a good idea to tame any high frequency crud by any means necessary with them, even by zobel networks and by having a fashionable "vintage low pass" with them. But verifying this is a matter of great oscilloscope and/or spectrum analyser. Edcor only shows their (strange) frequency responses on their datasheets, nothing about phase response, which is where the weirdness happens.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on October 14, 2011, 05:29:24 PM
Heads up for anyone still ordering parts, order an extra .1uf film cap.  C47 seems to be missing from the BOM.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on October 14, 2011, 06:33:38 PM
Heads up for anyone still ordering parts, order an extra .1uf film cap.  C47 seems to be missing from the BOM.

Great. Thank u very much sir!

Fixed and uploaded.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on October 15, 2011, 03:00:35 PM
Hi Abe,

thanks a lot!! Your board has arrived a new days ago well!!

So, now I'll start the ordering process!
Let's build this beautiful beast  :)

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: JayDubrek on October 15, 2011, 05:33:47 PM
Received my board this morning...thanks Abe!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on October 15, 2011, 10:26:11 PM
Making progress.  Remind me to double check lead spacing and voltage next time.  Turns out 250v Wima's are a snug fit.  Kinda went overkill there...  They fit if you bend in the leads though. 
Biggest concern was leaving room for the DRV134 chip, but it fits just fine.  Ok, break over.  Back to work!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on October 15, 2011, 11:42:55 PM
One more bom correction.  C50 should be 10uf and c53 should be 100uf.

*EDIT*  Make sure you check your cap sizes before ordering!  Otherwise your board may end up looking as phallic as mine! (I may replace those... or paint a smiley face on it...)
Panasonic FM 1000uf 50V and ECE Bipolar 47uf 50V are probably a wee bit too big!  The Nichicon PW 4700uf 35V is also pretty big, but there's enough space for it.

Good thing I didn't post my Mouser cart huh?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on October 16, 2011, 09:07:34 AM
The heater regulator requires a decent heat sink, or at least needs to be bolted (while insulating it) to the chassis. Installing it like that will just cause a thermal shutdown after some minutes. Probably good idea to heat sink even the rail regulators just in case.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on October 16, 2011, 11:29:18 AM
The heater regulator requires a decent heat sink, or at least needs to be bolted (while insulating it) to the chassis. Installing it like that will just cause a thermal shutdown after some minutes. Probably good idea to heat sink even the rail regulators just in case.
I was wondering about that.  Would this guy do the trick or should I go bigger? http://ca.mouser.com/ProductDetail/Aavid-Thermalloy/507002B00000G/?qs=pSohNHZZCUUy0wQfbAt4JQ%3d%3d
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: kazper on October 16, 2011, 02:59:37 PM
In general all the PSU electrolytic spacings are too small. It would have been better to have the regulators moved to the PCB edge  and space out the PSU toout to allow for proper heatsinking and allow for larger "real"sized caps.

Trying to fit this in a 1U is going to be tough without allot of stuff onboard moved offboard to get it to work. I spent a few hours looking for caps that I could get to fit in the spaces for the PSU.  I didn't find any that fit the circle, but I found a couple that will just barely fit the area but it's snug. The ones I found are going to make the 1U a hard option because there long.

I'm going to put this into a 2U case myself.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: JayDubrek on October 16, 2011, 04:31:44 PM
I'm with Kazper on this....2U case and all the regs mounted off board...
Jay
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: djn111 on October 16, 2011, 04:51:41 PM
Hi, some feedback from me on the pcb.

I was checking the bom, for parts at Farnell, Also my conclusion this far, the power supply parts for the HT en the heater supply, the 100uf 250v and the 4700uf 35v never going to fit. I also think the best solution, wire them from the pcb, and put the parts outside the pcb.

To be honest I am really thinking about cutting of the power supply part and build it on vero board. There is a header for the power so it should not be that difficult, at least I can test with the vero board supply and not populate the rest.

And a other thing, I think is not handy, the two channels are not identical/symmetrical, probably because of automated routing, not a big problem, but not very building friendly.

DJN
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on October 16, 2011, 10:13:26 PM
Abe, did you manage to fit your prototype into 1U?  If so, could you suggest some lytic caps that would fit in a 1U case and how you handled the heatsinks?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: kazper on October 16, 2011, 10:31:33 PM
I'm sure after a few revisions this will be a easy project it's just getting through the beta bugs. Just to be clear, I'm not knocking Abe one bit. He has spent allot of effort to get us this far and any lessons learned will make the next project for us all even better.

Abe any reasons why the one channel has stuff onboard and the other is offboard?

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on October 16, 2011, 10:39:34 PM
Just to be clear, I'm not knocking Abe one bit. He has spent allot of effort to get us this far and any lessons learned will make the next project for us all even better.
Oh absolutely!  Nothing but praise for Abe here.  I think it's an awesome project and I'm sure it'll sound fantastic once it's finished.  Working through the bugs and finding better solutions is kinda fun anyhow!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on October 17, 2011, 10:01:18 AM
Hi Guys,
Yea this is the first rev, I'm not taking any of this personally. I like the feedback! I know there are things that could've been better, If I was paying a professional engineer to do the layouts, etc it would've been perfect, but they price probably would've quadrupled too!
Anyway keep the feedback coming, all good ideas to eventually make an easier build.

And yes, looking at spec sheets I figured the power supply caps would fit just fine, but I also needed to squeeze some stuff around to get them to fit.

Also, I was originally going to have 2 separate PCBs with Lorin switches for the front-panel, and have the Timing cap and resistor for the right channel mounted on these, and then later in the I changed it, and though its not optimal, soldering a cap and resistor to a pot isn't optimal, but it works!

Also if your going to make and off board vero power supply, the heaters for the tubes aren't part of the rest of the power supply molex, originally they were but due to the large traces for the heaters I just have them go straight to the tubes.

I think for next rev, having the power supply separate is always a good idea, just to keep all the AC power junk away from the sensitive audio circuits.

I'm taking note and the next rev should be even better.

Cheers,

Abe

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on October 17, 2011, 10:55:58 AM
Abe, did you manage to fit your prototype into 1U?  If so, could you suggest some lytic caps that would fit in a 1U case and how you handled the heatsinks?

Bigger power supply caps are 7.5mm spacing

(Example: http://www.mouser.com/Passive-Components/Capacitors/Aluminum-Electrolytic-Capacitors/Aluminum-Electrolytic-Capacitors-Leaded/_/N-75hqwZscv7?P=1z0wrjwZ1z0scie&Keyword=1000uf&FS=True (http://www.mouser.com/Passive-Components/Capacitors/Aluminum-Electrolytic-Capacitors/Aluminum-Electrolytic-Capacitors-Leaded/_/N-75hqwZscv7?P=1z0wrjwZ1z0scie&Keyword=1000uf&FS=True))

Caps are a little big, I was able to squeeze some on, some are a little tall, but bigger caps are definitely on the list for the next rev.. Might be easier to put it in 2Ru if your going to build your own case.


Also the heater regulator is only supplying 400ma and the lm350 is rated at 3A....it should be fine without a heatsink, or just a small one if your worried.

Other regultors you really don't need heatsinks unless your using DOA in all the spots and even then small ones will be fine. Of course it wouldn't hurt to use them, but just fine without.

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on October 17, 2011, 12:40:18 PM
Also the heater regulator is only supplying 400ma and the lm350 is rated at 3A....it should be fine without a heatsink, or just a small one if your worried.

Sure it's rated at 3A. Sure, a similarly packaged LM338 is rated at 5A. But only with an adequately sized heat sink! See data sheet on dissipating the heat. They might just barely stand 400mA without one, but it's not worth the gamble. Every one will use a different transformer and even 2V more voltage drop significantly makes things worse with dissipated watts. Simply requires a good heat sink. Once it goes to thermal shutdown and heaters die, so will the tubes. And this will eventually happen in a hostile hot big rack full of other tube gear.

See poorman PSU PCB to get an idea on adequately sized heatsinks. Bolting the regulator to a case (back panel, bottom, whatever) is fine here by the way, as long as you insulate it. Even a 10cm wire will have a negligible impact on the regulator perfomance, so don't worry about wiring them even longer distances. Just pointing out that it's no big deal that the regulators are not placed on the PCB edge on this design.




Wiring caps to pots is no big deal either, many other projects do that too. But it's strange that one channel does while other doesn't. I also thought it was odd the channels were not exact copies of each other.

This will be a challenge to gracefully fit in a 1U case. But then, I already ordered the front panel.  ;)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on October 18, 2011, 10:25:52 PM
This will be a challenge to gracefully fit in a 1U case. But then, I already ordered the front panel.  ;)
Grace is overrated :P 
Shouldn't be too hard to cram big things in a tight space.  It might get a little sloppy, but it'll fit...
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on October 19, 2011, 10:10:54 AM
This will be a challenge to gracefully fit in a 1U case. But then, I already ordered the front panel.  ;)
Grace is overrated :P 
Shouldn't be too hard to cram big things in a tight space.  It might get a little sloppy, but it'll fit...

Sweet Frontpanel Kingston! PS what frontpanel service do you use?

Yes, things should squeeze into a 1ru OK. On my build there is one cap that is a little tall but It will fit. I'm still waiting on my front panels though,

Cheers,

Abe
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on October 19, 2011, 10:35:06 AM
PS what frontpanel service do you use?

Franks. I just provide him autocad format files from Corel Draw.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on October 19, 2011, 10:35:28 PM
Turns out 250v Wima's are a snug fit.  Kinda went overkill there... 

Hey guys, just going through my mouser cart and double checking cap sizes, turns out I picked the same 250v WIMAs. The only ones I could find in stock that have a 2.5mm lead spacing are rated at 63v. Is this sufficient? If not, what kind of voltage rating do I need for these guys?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on October 19, 2011, 10:48:19 PM
Well you CAN get away with those 250v's.  I ordered them because I've never done a tube project before and was paranoid about high voltage.  Thought I'd play it safe. 
If you go with those you'll just have to bend in the leads a bit.  Like this:
|_    _|
   |  |
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on October 19, 2011, 11:00:51 PM
OK sounds good. So you didn't have any problems with the casing being too large to fit around nearby components?

Still would like to know what the minimum voltage rating should be.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on October 19, 2011, 11:15:24 PM
Nah, nothing too bad.  The biggest problem is the two caps by the dip socket at the top of the attached photo.  Put the dip socket in first and you'll be fine.  The only other two that are a snug fit are c18 and 19.  they're up against two diodes in the power circuit.  Leave the diodes (or the caps) raised up above the board a bit instead of flush against it and it'll all fit in nicely.
Compared to the lytics, the film caps are a breeze to fit in the board.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on October 20, 2011, 04:13:25 AM
250V bypass caps all over the place are WAY over kill. You only need two of those for the tube B+ PSU part (C61, C14). In fact their impact is negligible and you could even leave them out. That kind of thing was necessary back in the day when electrolytics were not as good as today, but nice option to have just in case.

The rest of the 0.1uF caps are only used in low voltage bypass, ie. reducing chip noise from the 18V rails. Even 50V is dubious here, you can make due with 25V and the type you want is ceramic X7R. There are many threads on the forum why film caps have worse performance in PSU bypass compared to equal ceramic caps (keyword: inductance). Also a waste of money.

something like this:
http://search.digikey.com/fi/en/products/SA105C104KAR/478-3150-1-ND/936847

They are tiny, and will easily fit any project.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on October 20, 2011, 11:16:04 AM
Hmm, I didn't even consider ceramic.  Thanks for the tip.  Those are definitely much cheaper than the wimas!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on October 21, 2011, 02:45:42 AM
If anyone is trying to figure out which headers to order for the tube socket boards, I had some of these (Mouser prt# 571-6404539 ) lying around and they seem to work pretty well. 
There are probably much cheaper solutions since these things are 95 cents a piece.... but they work!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on October 21, 2011, 04:30:02 AM
Headers? I used fat solid core left from cutting diode leads earlier and just soldered it on the spot. 0.01 cents a piece.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on October 21, 2011, 04:40:03 AM
I actually started bending a few diode leads before I remembered I had those headers!haha  Leads are definitely the cheapest solution, but boy was I happy to have the headers.  Saved loads of time and fiddling around (not that I'm in a hurry or anything).
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on October 21, 2011, 12:42:56 PM
Headers? I used fat solid core left from cutting diode leads earlier and just soldered it on the spot. 0.01 cents a piece.

Diode leads? I just made solder bridges:)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on October 21, 2011, 12:50:00 PM
Diode leads? I just made solder bridges:)
hahaha wow just when you thought it couldn't get any cheaper!  I guess I'm Mr. Fancy-Pants with my 95 cent headers. ;D
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Hank Dussen on October 21, 2011, 12:57:15 PM
That's $17,1 for your headers only!  ;D
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on October 21, 2011, 01:03:19 PM
Huh?  Oh, no the headers weren't 95 cents per pin!  Each of the two 9 pin headers was 95 cents, so $1.90 total (or 10.6 cents per pin).  I'm Mr. Fancy-Pants, not Mr. Moneybags!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Hank Dussen on October 21, 2011, 02:05:29 PM
Hehe. My wrong. I see it now. Sometimes these small things can get expensive though.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on October 24, 2011, 12:29:25 AM
Dumb question time, once again.
Orientation of the trim pots.  Is A or B correct? 
It's A, right?! 
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on October 24, 2011, 12:52:40 AM
Oh, and here's a little more porn for your enjoyment!  There's something about tubes and trannies...

*I didn't actually solder in the edcors yet, just put them on the board for the photo.haha
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Davo on October 24, 2011, 02:48:00 AM
comin along nicely... in regards to trimmers, either way works just fine
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on October 24, 2011, 03:00:05 AM
Great, thanks!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: living sounds on October 25, 2011, 12:06:57 PM
Everyone else here from Germany who didn't receive their board yet?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: noulou on October 25, 2011, 01:24:18 PM
I'm in Greece and haven't yet received it.
 :'(
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on October 26, 2011, 07:18:43 PM
so how are you people implementing bypass on this? standard true bypass with relays? or something much more simple?

I just realised I have completely forgotten to take this into account. this will be quite the sandwich after everything is done
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on October 26, 2011, 09:30:31 PM
so how are you people implementing bypass on this? standard true bypass with relays? or something much more simple?

I was just going to go with the "pull the cables from the patchbay" method.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Davo on October 26, 2011, 09:38:48 PM
true bypass with relays
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on October 26, 2011, 09:46:06 PM
For me GR bypass. The Input/output knobs will still be functional and it will still impart a color so it can function as a line driver or color unit of sorts.

I like the patch-bay version of hard  bypass ;D

Maybe one of these days I'll catch the relay bug though..
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on October 27, 2011, 04:34:12 AM
For me GR bypass. The Input/output knobs will still be functional and it will still impart a color so it can function as a line driver or color unit of sorts.

I like these kind of bypasses best. No point wasting a perfectly good line amp when it's filled with DOA's and transformers.

How do you make the GR bypass?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Davo on October 27, 2011, 05:12:44 AM
Interesting, please do share... wouldn't mind having this option
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Paultec on October 27, 2011, 11:34:04 AM
Hi Abechap,

Are there any boards left for this project?

Thank you.

Paul
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on October 27, 2011, 12:10:04 PM
For me GR bypass. The Input/output knobs will still be functional and it will still impart a color so it can function as a line driver or color unit of sorts.
I like these kind of bypasses best. No point wasting a perfectly good line amp when it's filled with DOA's and transformers.
How do you make the GR bypass?


I think the simplest way to do it, is wire up a switch in series with the sidechain HPF capacitor. That way when the switch in open no signal goes to the sidechain - therefore no sidechain reduction.

It also makes me think...with properly calculated HPF capacitor values and a rotary switch, one could have 2 HPF frequencies (like 150hz and 300hz) and then a hpf off setting (by adding the 2 hpf filter caps together) and then a GR off setting on the same rotary switch....

Hmmm might be a good addition to rev 2  8) having all this built in

Hi Abechap,
Are there any boards left for this project?
Thank you.
Paul

Hi Paul,
I have a few that I was going to hold onto for personal use, but I've decided I might as well sell them cause they are just going to sit till I get to them. PM me, anyone that still wants one.

Cheers,
Abe
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Paultec on October 27, 2011, 12:36:50 PM
PM'd

 :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on October 27, 2011, 01:59:39 PM
PS, I'm still working on balancing the Threshold (sidechain gain), input section gain, output section gain, and getting it to a "one size fits all" type of setting. It also depends on if one is using the 4:1 or the 1:1 interstage transformer.

I'm running a 4:1 inter-stage in the unit now on both channels, but just got my box of edcor 1:1s trying some 600:600 for input and output. I've got to admit I don't know as much theory behind all the operation and TX ratios as I should, but it makes sense that there is an optimum balance between noise floor, and input and make-up gain.

The balance: if you make the input gain stage have too much gain, your going to increase the noise floor too much, and always have your input potentiometer turned down really low. But if you don't have enough make-up gain then your not going to be able to drive the unit into hard compression.

But, this also depends on where you have the threshold set. The threshold is controlled by the trimmer next to the sidechain, the more gain the sidechain has the more compression takes place per given input level. It makes sens that the lower you set the threshold, the more make-up gain one is going to need to compensate, and vice-versa.

I think with the values in the BOM (as of 10/27/2011) for the input and makeup gain stages, its about +20 db per section. Which I'm finding might be a bit much, but i still have some more hands on testing to do. It also depends on how "nicely behaved" you want the unit to be. If you know your always going to be sending the unit +4db pretty tamed peaks and all that, one my opt to not have so much built in gain on the input, set the threshold at a moderate level, and give say 10db of built in gain for the output.

But if someone really wants to smack the thing, setting the threshold really low and giving the input/output amps a lot of juice, you will have more versatility, and the expense of more touch controls and hearing some noise floor when you really crank both controls up.

Anyway I've been fiddling with it, seems to be able to handle a high amount of compression pretty well!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on October 28, 2011, 03:39:26 AM
trying some 600:600 for input and output. I've got to admit I don't know as much theory behind all the operation and TX ratios as I should, but it makes sense that there is an optimum balance between noise floor, and input and make-up gain.

Tube grid's are very high impedance, super easy to drive, takes anything as an input. 600:600 input is a terrible waste because of that. You need a strong drive to happily make that 600 ohms, when 10k (or higher!) would be more than enough. 10k:10k is then much easier to drive and make the project more flexible, doesn't limit who is connected to this compressor.

The only reason to have 600 ohm line input is if you want a step up transformer. 600:10k means 4X voltage, ie. signal was amplified greatly. In this project you might want that kind of passive gain, instead of electronic gain from opamps with more noise as a result. But not all gear can drive 600ohms so it's a trade off...

Now 600:600 is great for output. These kind of transformers are easy to wind and to get to good specs. That's the number one reason they are so commonly seen everywhere. Very basic output stages can usually drive them so it's a "slap-in". Cheap galvanic isolation. 10k:10k is harder to wind and to get to specs and hence get more expensive. Also you would lose the low impedance of output if you used it there.

In short, you can always sub a 600 ohm input with 10k, but not the other way around. For outputs we would never use 10k:10k because that won't drive anything. even 0 ohms output impedance (pure current source) turns into a weak 10k "voltage source" output if using 10k:10k.


By the way, the postman just brought my Edcors! Maybe this sunday/monday I get to fire up my build. Full field report coming up.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on October 28, 2011, 04:07:03 AM
Gotta love the smell when you open up the edcor package!

So what's the word on that front panel Dan was whipping up back on page 2?  I'm tempted to make my own, but that front panel designer software drives me insane.  I keep wanting to use photoshop keyboard shortcuts and end up swearing at the software when it doesn't obey me!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on October 28, 2011, 10:39:14 AM
Great! thanks for shedding some light on that kingston, it seems obvious now that you mention it. Maybe I'll order some 10ks for the inputs and just use the 600s for the outputs.

Gotta love the smell when you open up the edcor package!


Haha me and my wife were saying the same thing! Like they just spray painted them all :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: tfletchii on October 29, 2011, 09:15:54 AM
payment sent via paypal. looking forward to the build
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on October 29, 2011, 04:22:36 PM
So I'm about to order the rest of the parts for my build, but I have another newbie question. I'm a little confused with the power transformer wiring, hopefully someone can help.

Someone mentioned this PT earlier on in the thread (http://www.mouser.com/Search/ProductDetail.aspx?R=VPT36-1390virtualkey55310000virtualkey553-VPT36-1390 (http://www.mouser.com/Search/ProductDetail.aspx?R=VPT36-1390virtualkey55310000virtualkey553-VPT36-1390)) and I believe it was deemed adequate, so I added it to my cart.

If you run the secondary at 36V you have a center tap, but when the secondaries are paralleled for 18V operation you lose the center tap. So when hooking up, what do I do about the center tap connection to the board? Do I just leave the center tap space empty, or can I simulate it with a couple of resistors between the 18v and CT hookup points, and if that's the case, then what values or how do I calculate? I'm not really sure how to go about this, so any help would be greatly appreciated.

Also, to make sure I read another earlier post correctly, for the 100V hookup, I can just use the blue and grey primary for the mains connection, and run the violet and brown primary straight to the board for the 100V connection, right? Or do I parallel the primaries for 115V and just tap off of the mains for the 100V connection?

Sorry to be a burden, just trying to learn as I go here. Thanks guys.





Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on October 29, 2011, 10:12:14 PM
Hello.
If you run the secondary at 36V you have a center tap, but when the secondaries are paralleled for 18V operation you lose the center tap. So when hooking up, what do I do about the center tap connection to the board? Do I just leave the center tap space empty, or can I simulate it with a couple of resistors between the 18v and CT hookup points, and if that's the case, then what values or how do I calculate? I'm not really sure how to go about this, so any help would be greatly appreciated.

Here:

http://system.netsuite.com/core/media/media.nl?id=12599&c=ACCT126831&h=9bf90c20991f70f0e64c&_xt=.pdf

The bottom right of that file has a picture of the transformer. You can see, It is a transformer that has 2 coils for primary connection, and 2 coils for output.

Depending on how you wire it, you could wire the coils in series or parallel. That leaves you with quite a few options and configurations. All a "center-tapped" transformer is, is a transformer with a center tap in the coil, well if you connect the 2 secondary coils together, you have for all practical uses a center-tapped transformer. With one probe on the Center-Tap, either side of the coil will measure 18v. and that's what you want!

Transformers are just a tool, you can configure them how you please for your uses. Also they seem pretty forgiving with exact sizes and volts. A 20v transformer will work fine. You can run the opamp rails of this thing any voltage you like, as long as all your opamps and transformer can handle it. Most common will be 15v but I think with all the opamps specified you can go up to 20v. A little more headroom, probably knowing its running on higher voltage does more for the sound than in practice. Also, you can get a bigger transformer than necessary for a given project but you don't want to go smaller, that leads to excessive heat and can be dangerous.

Also heres the really cool trick that PRR mentions (Its sweet) if you live in a place that has 120v mains power, you connect one coil of the primary to the mains, and with the other coil of the primary you connect to the 100v AC input on the board and the 120v from the mains safely connects to the board through the galvanic isolation of the transformer (you would never ever, ever want to connect 120v straight from the wall into anything)

for those in 240v countries, a second transformer will be needed, or a transformer with the correct windings, a 2:1 step-down would work nicely.
Quote

Sorry to be a burden, just trying to learn as I go here. Thanks guys.

No its good to ask! Hopefully its clear as mud. ;) ;D
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on October 30, 2011, 01:15:12 AM
In a continuing string of simple questions with a potentially obvious answer...  Is there any reason why I should NOT whip up something like my diagram?
It's a simple spdt switch between two caps, one pio, one tantalum.  Thinking it might be a good way to a/b them until I settle on one. 
Any harm in quickly switching between a polarized and non-polarized cap?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: djn111 on October 30, 2011, 02:45:00 AM
Hi,

Besides hearing a click when you switch no problem, it might help to parallel a 4m7 resistor over the switch contacts (Neve style).

DJN
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on October 30, 2011, 03:16:05 AM
Hi,

Besides hearing a click when you switch no problem, it might help to parallel a 4m7 resistor over the switch contacts (Neve style).

DJN
Great, thanks!  So the resistor would hook up like this?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on October 30, 2011, 04:08:46 AM
This is the kind of wacky thing you come up with when you can't fall asleep at 4am!
I think I need a bigger PIO cap.haha
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: djn111 on October 30, 2011, 08:30:04 AM
Hi, yes that is the way, let us know if it works ?

DJN
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on October 31, 2011, 02:03:52 PM
Sweet! And becuase its in the sidechain i wouldn't worry too much about paralleling a 4m7 resistor between the contacts, it will mess with the release time, when you switch it it shouldn't be a big bother.

It  will work.
Let us know how the PIO cap sounds!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: tfletchii on October 31, 2011, 02:08:41 PM
1/4watt resistors seem like a good fit for the board anybody have any suggestions?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on October 31, 2011, 03:46:53 PM
1/4watt resistors seem like a good fit for the board anybody have any suggestions?

1/4watt are fine for everything except the 3 1k resistor 2 watt resistors in the 100v power section
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: tfletchii on October 31, 2011, 04:04:20 PM
thanks abe, and thanks for noting the 2w 1k on the board as well
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on October 31, 2011, 06:01:52 PM
1/4watt are fine for everything except the 3 1k resistor 2 watt resistors in the 100v power section

I actually thought that was a very strange arrangement. Now that I've had a chance to run this a bit (no audio yet), the four tubes are eating 13mA all together. For a 3k resistor that makes it about 0.5watts. And not for each of the 1k resistors. What you really need is just a single 3k 1-watt resistor for plenty of headroom. And this is with worst case scenario Russian tubes.

Or you could do two 6k (or close) stock standard 0.6watt small resistors in parallel.

That 3X series resistor arrangement is very strange indeed. But no worries, it just gives me room to do a more elaborate CRCRC+zener for B+ voltage.

Oh and by the way, the heater regulator is running RED HOT. Its job is to drop something like 12volts at 400-600mA, depending on the tube choice and transformer (18VAC/18VAC secondaries for most I presume). That's more than 7-watts, not including safety headroom... If you were to passively drop that you would need the resistor to be at least 10watts. Think about the size of 10watt resistors, and how big they need to be to even exist, and you quickly understand why a simple TO-220 regulator package cannot take the heat, and must be cooled with a decent sized heatsink.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on October 31, 2011, 07:10:32 PM
Interesting.
I pulled the 3 x 1k 2 watt from the original prr power supply. 2 watt resistors are harder to find than other resistors... works ok but one 3k 1 watt resistor would be preferable. I'll take a note of that for rev 2.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Paultec on October 31, 2011, 07:30:57 PM
....Rev 2.0

 ;)

Paul
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on November 01, 2011, 12:37:22 AM
Sweet! And becuase its in the sidechain i wouldn't worry too much about paralleling a 4m7 resistor between the contacts, it will mess with the release time, when you switch it it shouldn't be a big bother.

It  will work.
Let us know how the PIO cap sounds!
will do!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: baadc0de on November 01, 2011, 10:07:41 AM
Are you guys using the Edcor PCW10K/600 for the interstage? If anyone ordered more or is about to order some to europe, I'd like two as well, so if you're willing to split shipping etc please PM me.

Cheers,
B.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: tfletchii on November 01, 2011, 12:21:30 PM
pardon my laziness but if anyone has a mouser cart they'd like to share. I'd be grateful
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on November 01, 2011, 12:43:43 PM
Are you guys using the Edcor PCW10K/600 for the interstage? If anyone ordered more or is about to order some to europe, I'd like two as well, so if you're willing to split shipping etc please PM me.

Cheers,
B.
I think it was somewhat decided that 10k/10k for both input and interstage is the way to go.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on November 01, 2011, 02:13:11 PM
Are you guys using the Edcor PCW10K/600 for the interstage? If anyone ordered more or is about to order some to europe, I'd like two as well, so if you're willing to split shipping etc please PM me.

Cheers,
B.
I think it was somewhat decided that 10k/10k for both input and interstage is the way to go.

Yep!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on November 01, 2011, 04:11:33 PM
 :D

(http://www.acsoundstudio.com/prr_176/PRR%20176_1smaller.jpg)

Prototypes from Dan over at collective cases. Very nice cases! Thanks Dan for all your hard work. The meter fits a little tight (I take blame for that :-\) but these should be available very soon, I imagine!

Cheers,

:)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on November 01, 2011, 04:20:17 PM
Looks great!  I'll definitely be grabbing one of those.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on November 01, 2011, 04:23:00 PM
Looks great!  I'll definitely be grabbing one of those.

Yes seriously, I. Hate. Metal work!

too many memories of drilling and filing...aluminum dust everywhere, can't be good! And then it always ends up looking like junk and I usually never get around to labeling any of the knobs. So these pre-made cases are great.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on November 01, 2011, 04:42:03 PM
Yes seriously, I. Hate. Metal work!

too many memories of drilling and filing...aluminum dust everywhere, can't be good! And then it always ends up looking like junk and I usually never get around to labeling any of the knobs. So these pre-made cases are great.
Haha tell me about it.  Metal work is doom.  Unless cutting up your hands and inhaling metal dust is your kind of thing :-\
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: baadc0de on November 01, 2011, 04:52:48 PM
Oh. One of those then, sorry :) I'll just open a black market thread..

Are you guys using the Edcor PCW10K/600 for the interstage? If anyone ordered more or is about to order some to europe, I'd like two as well, so if you're willing to split shipping etc please PM me.

Cheers,
B.
I think it was somewhat decided that 10k/10k for both input and interstage is the way to go.

Yep!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: dandeurloo on November 01, 2011, 05:43:55 PM
Glad you guys like them!

Maybe if you can drop a name on my thread if you want one.  That way I know how many to start making. 

PS:  The PYES look pretty sweet as well!  Maybe Abe will upload a pic of those or I can.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on November 02, 2011, 05:02:25 AM
I've fired this up and played audio through it now. I have mixed thoughts about the sound. The signal path is super. I'm using DOA output with transformer, and even replaced the sidechain opamps with something better. They make a difference to very sharp attack transients. Now I'm experimenting with the input configuration and gain calibration. It's a great strong sounding signal chain. I basically have an API output, too, using the GAR DOA's and transformers from classicapi.

But compression performance is uneven. It's hard or even impossible to match the tubes for even stereo processing like you would have on maybe SSL bus comp. This is not a problem until you hit more than about 10dB of compression. Stereo image starts to flutter and sounds "nervous".

Note, that this is an issue with stereo link too. The problem is the tube curves, and having to rely on just one plate per class A/B side. I have carefully matched tubes, and still stereo compression is "wonky". Poorman compressor doesn't have this problem because after you have matched tubes, the parallel configuration irons out the last unevenness.

You don't of course notice any of this on mono sources. And note that this is just as much an issue with vintage UA176, too.

And on to the good news: as a mono compressor this thing is totally awesome and unique! It really is a hard limiter inside. It bashes the hell out of vocals and does it very cleanly with no breathing if you set time constants right. Not unlike LN1176, it really digs deep into the audio without doing much damage and attack has that really fast transient. I can imagine magic for basses, too. For drumbus bashing it works well, but maybe M/S configuration is needed (left/right unevenness is a worse problem than the same thing on mid-side).

Some additional notes:

1. attack and release should both be linear. log pots have only like 1/3 of meaningful range.
2. If you plan to use DOA's and strong modern opamps for sidechain, you can't have 100 ohm droppers in the PSU. They have to be 10-22ohm. There's is something like 60mA used per rail and 100 ohms drop way too much (6volts wasted).

There are more problems related to the build/schematic/BOM that I will get into later, now it's time to experiment and find the best gain staging configuration.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on November 02, 2011, 06:40:51 AM
I think it was somewhat decided that 10k/10k for both input and interstage is the way to go.

Where? Based on what?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on November 02, 2011, 07:39:34 AM
I think it was somewhat decided that 10k/10k for both input and interstage is the way to go.

Where? Based on what?
Page 11.  Specifically referring to using Edcors without output transformers.  You and abechap seemed to agree 1:1 is fine for both input and interstage.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on November 02, 2011, 07:42:22 AM
Sure they would work. But I still haven't decided conclusive on which it should be. 10k:10k on both input and interstage is probably not optimising the tube headroom properly, also somewhat affects compression curve as far as I know. I'm currently experimenting with this.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on November 02, 2011, 07:47:35 AM
Sure they would work. But I still haven't decided conclusive on which it should be. 10k:10k on both input and interstage is probably not optimising the tube headroom properly. I'm currently experimenting with this.
Ah, gotcha.  Let us know how your experimenting goes.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: MrZpliff on November 02, 2011, 07:55:35 AM
Great Job, Kingston  :)

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on November 02, 2011, 04:03:13 PM
Wow Kingston,

unbelievable you already put a working unit together... respect!!
I'm still busy filling my mouser cart...  :)
And mailing with cinemag... ;D

Well, for me a hell lot of work to do...

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on November 03, 2011, 07:39:46 AM
I hate metal work almost as much as I hate wiring and unreliable and flimsy molex connectors. If only there was better ways. Maybe using screw terminals everywhere? Sure it increases PCB size but the extra reliability might be worth it.

But after all the work is done the fruit is ripe for picking!  ;D  :o

(http://www.michaelkingston.fi/files/prr176front1-web.jpg)
(http://www.michaelkingston.fi/files/prr176front2-web.jpg)
(http://www.michaelkingston.fi/files/prr176inside-web.jpg)

When that panel came from Franks CNC shop I was like holy sh*t this came out nice! I've designed some good panels in the past but damn, I'm even slightly proud of this! :o Franks CNC execution was top class, too.

Thanks abe for designing the PCB. Something about this project was very inspiring and that's why I got things done so fast. I guess I was inspired with how flexible it was from the start. There's DOA's tubes' transformers and opamps and whatever you want in a perfect messy mix-up and the sound is wonderful. And still the PCB manages to be clearly laid out!

I have now also managed great stereo bus compression/limiting. Just don't use too long release times. They can be a bit uneven. Fast limiting sounds boombastic even on finished masters! But too short attacks with too short release will cause thump. But it's all about learning to use the unit, also now that the VU meters are calibrated and working fine they are actually very useful. They reflect the compression performance very well.

The high pass is the 0.15uF + 1uF and works exactly like I planned. Cuts the boomy bass and leaves the rest of the sidechain intact. A nice attack shaper. Bypass also works exactly like abe described: disconnect the hipass+hipass adder cap completely and you have a plain line amp.

I completely changed the input to something that the PCB was not designed for. The input DOA is used for de-balancing, exactly like GSSL input. That goes to 10k log stepped switch and then to the input transformer. Some wiring had to be done under the PCB but nothing major, actually just one resistor and extra wire. The reason I did this was that I still wanted another DOA but not the INA input chip so that's what I came up. Some people would argue that it's pointless to precede a high quality input trafo with an opamp. But I will argue back that DOA's sound awesome and you can't have too many. I listened to DOA input side by side with plain transformer. It was a close call. some other person might have chosen different.

B+ is changed to CRCRC (100-150uf caps and 1-2k resistors). One more filtering step just in case, only one extra wire needed under the PCB. All sidechain opamps are high voltage types so I can now run 22V rails all around. Obviously a very small difference in headroom compared to 18V rails, but the PSU transformer had the headroom so why not.

This is now officially the most interesting compressor I have, and I have lots! I've never heard anything like this strange hybrid and I can imagine awfully many uses for it.

I still haven't done stereo link. And I also still have to figure out what to do with that "opt" switch. I put that there just in case. Also thinking of doing stepped rotary switch for the output volume. Just have to figure out a good range for that. Also noticed the 1mA DC meter pre printed scale is inverted.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on November 03, 2011, 09:18:11 AM
very nice work, sir!!

what opamps did you use? I went with the gar 1731's for no particular reason, they should be arriving today.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on November 03, 2011, 09:24:18 AM
Using gar2520 here. Also for no particular reason, except curiosity because I had not heard it before. I suppose next one I will try is 1731 for some future project.

The sidechain single opamps are LME49870 (notice the red soic8 adapter I had to use) and the duals are LME49860. I picked them so I could run 22V rails, and they are one of the best high voltage chip opamps around. Could also be OPA2604 and OPA604. Changing the TL072 to something better is kind of a good idea. That one is especially crap at everything except being cheap. I once changed TL074 (quad package) of Dynaudio active speakers to modern quad alternative. The difference is so big it's like you practically have a new treble speaker element. Sure in this case the TL072 is only in the sidechain, but since attack can be really fast on this compressor, it actually makes a slight difference in sound.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on November 03, 2011, 09:49:04 AM
cool

i went with the spec chips for cheapness sake, though i did have my doubts about the TL072s (just from what I've read, no experience to back that up). I put Burr Browns in my Urei LA4 a while back and it made a huge difference for the better, maybe something for me to think about.

I'm running 18V rails, what replacement would you recommend for the TL072 for possible future upgrade?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on November 03, 2011, 10:00:13 AM
LME49860 is a very safe and great performing choice.

PS. get your modern opamps direct from the manufacturers as samples. They want to give them away for prototyping so use them to your hearts content. Good for this kind of experimentation because you don't have to always buy every new opamp just to see if it even works.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Davo on November 03, 2011, 10:46:49 AM
Very nice build... love the square tube for the power lines... and very clever use of molex to run the heater reg... never thought of that before.  Got me inspired!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: radiance on November 03, 2011, 11:49:13 AM
Very nice build Kingston!
Somehow, this project has managed to stay under my radar for 19 pages!?
Ah well...there's always something to build.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on November 03, 2011, 12:47:18 PM
Thats sweet! My hats off to you sir! Looks really nice. You've got me beat, I'm still fooling around with gain staging and everything.

Im curious, did you decide on 1:1 interstage or 4:1 interstage? Also interested in why, could it be that with the 4:1 it is easier for the tube to drive the output stage? Or...?

Got me inspired too! I want to go finish up mine! :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: fazer on November 03, 2011, 01:38:47 PM
Great build Kingston.   Are those 2503's for output Transformers?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on November 03, 2011, 05:48:57 PM
I'm still fooling around with gain staging and everything.

Im curious, did you decide on 1:1 interstage or 4:1 interstage? Also interested in why, could it be that with the 4:1 it is easier for the tube to drive the output stage? Or...?

Currently I'm using 4:1 interstage. gain staging seems fine on that one already. My gut feeling is that using 1:1 also works fine because it's only driving two opamps and their impedance is much higher. Then you don't lose any gain in the the step down either. But also it might be that the "weak" tubes are incapable of driving a 10k:10k even for opamps and step down is needed. I have 10k:10k edcors to try. I haven't done any calculations yet.

I'm still experimenting with the gain staging as well, including the input. There is some strange low pass filtering going on that I have to solve, maybe due to my alternative balancing..

Are those 2503's for output Transformers?

Yeah, wired 1:1. The output GAR opamps could probably drive it 1:3 as well, but the extra gain is probably not needed here.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on November 04, 2011, 11:45:16 PM
Here's my progress so far, I know it's not as impressive as the pictures Kingston just posted, but I wanted to test out the new gallery feature, and show off the twin towers on the 100v supply. ;D Obviously I'm planning on using a 2 unit case.

Four of my trim pots ended up being side adjust types, although I swear I quadruple checked the part number before I ordered them. I figured I'd see if I could make them work, but it's looking like I'm gonna have to swap them out.

The Edcors shipped today, as well as the rest of the terminal blocks and heatsinks, so I'll be ready to make some noise with this thing soon. I also followed Kingston's advice and arranged to get some samples to replace the TL072s, but I guess I'll test them out first since I already have them.

Abe- any chance we could see a calibration guide soon? I have a pretty good idea of what needs to happen, but I guess it doesn't hurt to be sure.

(http://www.groupdiy.com/gallery/0/38684-041111232803.jpeg)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on November 05, 2011, 02:06:49 AM
Kingston, I've gotta hand it to you, you've done some fine work.
Seeing your photo leads me to a couple questions I'm sure either you or abe could answer.  I'm not sure what to do with those in_opt pads.  The board says to either bridge or jumper them depending on the situation?  Looks like you've wired them to your input rotary switches?  Assuming I'm using DOA's and my input will just be a regular pot, what should be done with those? 
Also, it looks like you jumpered across the center tap box.  I assume if I use the two resistors above (7,8,87,95) I don't have to touch that box at all right?

Can't wait to get the case and meters so I can finish this thing up!  Just finished another DOA tonight.  Going with 2 gar2520's and 2 Whistle Rock ML918's.  Should be interesting.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: erjos on November 05, 2011, 06:59:10 AM
Nice build Kingston.
I have a question though. I see some soldering made in the top side.. Are the boards Electroplated or Not, or is this because of some excess solder passing from bottom to top?
(really funny the Chinese writings in the board,-peices- they really have problems with English)
regards, Erjos
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on November 05, 2011, 07:56:38 AM
Also, it looks like you jumpered across the center tap box.  I assume if I use the two resistors above (7,8,87,95) I don't have to touch that box at all right?

I think you have to make a jumper for either option.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on November 05, 2011, 08:17:23 AM
adeptusmajor, holy crap those are some strange looking 250V caps! Almost looks like they are photoshopped, like the long cat.

samples to replace the TL072s, but I guess I'll test them out first since I already have them.

That's what I did too. Make sure everything is running smoothly already, then it's time to experiment.

I'm not sure what to do with those in_opt pads.  The board says to either bridge or jumper them depending on the situation?  Looks like you've wired them to your input rotary switches?  Assuming I'm using DOA's and my input will just be a regular pot, what should be done with those?

Just follow abes wiring guide. Wire your input pot exactly like he did and jumper those pads. Do not look at anything I did there. I completely hacked this part of the circuit and it will only confuse.


Also, it looks like you jumpered across the center tap box.  I assume if I use the two resistors above (7,8,87,95) I don't have to touch that box at all right?

You still have to wire that box. You have to select the "or resistors" track. This is where CV (control voltage for tube grids) gets routed to the correct place.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: living sounds on November 05, 2011, 12:25:12 PM
Finally received my PCB today, looks great, thank you very much!

Already got LL1540 for the input trafo, and I have a pair of Pikatron ÜP715 lying around - would it work for the interstage (datasheet attached)?


I think I'm also going to try the PCC85 (thanks kazper!) and will report. Those are sold dirt cheap.

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on November 05, 2011, 04:48:28 PM
I'm struggling with the output stage. The output cap (to transformer) seems to be interactive with gain. Output stage max gain results to something like -5dB bass cut around 50hz. Unity gain is pretty much flat. Anyone know what this might be?

[edit]

Running the 2503 output transformers at 1:1 or 1:3 ratio seems to have no effect on this.

[edit]

I had forgotten to load the interstage (R36, R112). 1k load seems to flatten the response while 10k does not seem to do much anything. Currently experimenting and trying to find the best value. Seems to be a compromise of gain/THD/flat freq response.

[more edits]

this thing is proving to be very difficult to gain stage correctly. I now tested a 10k:10k interstage and it seems that it makes absolutely no difference whether that or 10k:600 is used, other than gain of course. with 4:1 you lose 12dB. Loading either transformer results to just about exactly the same thing. 1k loading resistors on primary result to roughly "flat" frequency response. I should say flat enough for edcors. Both transformers also result to the exact same minor bumps in the frequency response. The primary windings of edcor 10k:10k and 10k:600 are probably perfectly identical.

I'm starting to think 10k:10k interstage is the better option here. That way the output opamp make up gain can be less drastic, probably resulting in less noise. Only issue is edcor high impedance transformer quality. They tend to have phase issues and hence can sound a bit odd.

I don't know why 4:1 interstage was used in the original 176. Whatever it was does not apply here. The opamps (to sidechain and output) seem perfectly happy with high impedance 1:1 trafo.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: zayance on November 06, 2011, 07:31:56 AM
Quote
adeptusmajor, holy crap those are some strange looking 250V caps! Almost looks like they are photoshopped, like the long cat.

+1  ???
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on November 06, 2011, 01:27:16 PM
Hi,

any good hints where to buy the tube sockets and also the tubes?
How is the current state of the meter-discussion?
Can we use VUs (Hairball?) ?

Still putting my mouser cart together... :-\
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on November 06, 2011, 01:35:09 PM
any good hints where to buy the tube sockets and also the tubes?
Ebay is a good option. 
I got these: http://www.ebay.ca/itm/320718354276?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
and these: http://www.ebay.ca/itm/350451247777?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

If you're going with the 6BC8 instead of the russian 6N5P, this is one place to get them: http://www.tubedepot.com/nos-6bc8.html
I ordered 4 of them and luckily 2 of the 4 had the same manufacturer and production date.
I'll probably stick with the 6N5P though.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on November 06, 2011, 02:56:14 PM
How is the current state of the meter-discussion?
Can we use VUs (Hairball?) ?

The meters should be 1mA DC. I used these: http://hairballaudio.com/shop/product_info.php?cPath=25&products_id=61

seems to work well, although the scale is inverted.

And of course you can use VU's, but on audio inputs/outputs only. If you want to get hacking, then you could use VU meter as gain reduction, too. See the poorman thread, although the information might be a bit hard to find.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on November 07, 2011, 02:12:49 AM
Sorry if I clutter the thread, but I think some might find these experiences useful.

Initially I had a 10k:600 edcor interstage. I've used the same step down as XSM and WSM models in the past and they sound great. But then it turns out the step down is completely unnecessary here, you only lose 12dB of gain for nothing.

Enter 10k:10k interstage. I installed 1:1 edcors, but having got used to the previous sound something was very strange. Transients sounded odd and harsh. Edcor high phase issue rears its ugly head. The 4:1 does not do this at all.

I couldn't have that and went nuts and temporarily cannibalised another build so I could have a lundahl LL1540 interstage. Oh man this is the bomb! All transformer problems are simply gone, and more than 10dB of electromagnetic noise was gone too! (lundahls have good shields, while edcors have none)

Now that the signal path is perfectly clean I noticed some problems in the PSU design. There is a lot of rectifier crud leaking into the audio circuits. I don't know where yet, but I suspect B+. I have seen this before when PSU's are a bit carelessly combined with audio circuits in a single PCB (G9). Moving the B+ out of the mainboard and isolating channels with one more RC cured that one. The noise floor of this revision of prr176 looks almost exactly like G9 before the fix up. It's not a big deal - below -80dBu in most common gain scenarios - but it could be perfectly flat with a bit more work.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on November 07, 2011, 02:36:42 AM
Which Edcor 1:1 model did you try?  PCW?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on November 07, 2011, 03:08:38 AM
PCW
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: MrZpliff on November 07, 2011, 03:30:36 AM
Great work, Kingston  :)

I'm about to order transformers (and some other components) for this build
so your information is most valuable !

Kiitos !
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: peters on November 07, 2011, 09:54:28 AM
Kingston,

Are you using the LL1540 for input as well?

thanks,
--Peter
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on November 07, 2011, 09:55:18 AM
yes
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: tfletchii on November 07, 2011, 10:04:46 AM
thanks kingston keep up the good work my man
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: tfletchii on November 09, 2011, 09:24:39 AM
C50 & C53 are reversed on the BOM. They are right on the schematic and PCB so no big deal but thought I'd post it anyway
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on November 09, 2011, 05:52:51 PM
Great stuff guys all around! Rev 2 will be even better. Working on it myself, will post. Kingston: great work!!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on November 10, 2011, 01:07:44 AM
Great stuff guys all around! Rev 2 will be even better. Working on it myself, will post. Kingston: great work!!
Once you come out with rev2 do you think you could compile a list of mods that can be done to the original to match rev2?

Kingston:  Is there any way to correct the high phase in the edcor 1:1 or are we pretty much stuck with it?  More importantly, is it noticeable even with no compression going on, or only when you push the comp?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on November 10, 2011, 04:25:40 AM
Kingston:  Is there any way to correct the high phase in the edcor 1:1 or are we pretty much stuck with it?  More importantly, is it noticeable even with no compression going on, or only when you push the comp?

There is no way to correct the phase issue. You can damp it by loading the secondaries, but that means you lose some high frequencies, lets say 3-5dB at 20khz. it's not too bad, like a "vintage" response. But not really optimal either.

It's especially bad because you would have the 10k:10k on the input, and then on the interstage as well. It sounds pretty harsh.

And it's always noticeable, whether compressing or not. the signal is always going through both.

But I'm quite the princess when it comes to transformers/caps/etc. Maybe other people are not so critical about this and might even like the sound?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on November 10, 2011, 03:48:14 PM
Hi 230V-Guys,

i have asked mueller in germany (www.mueller-rondo.com) for a custom-made
power-transfomer.
Is the spec correct?

If there's some interest around here i would order some more!?
I'll have to check-out what shipping my be.

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mylesgm on November 10, 2011, 04:52:23 PM
I'd be up for 1.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on November 10, 2011, 05:08:33 PM
But I'm quite the princess when it comes to transformers/caps/etc. Maybe other people are not so critical about this and might even like the sound?
Hahaha Kingston the Transformer Princess.  Nice. 
I guess there's only one way to find out if I'll like it or not!
Knocking off a few db around 20k might not be a bad option, especially if I'm throwing it across a really sterile itb mix, or tracking with a bright mic. hmm  I suppose I could always compensate with the air band on the Night eq I'll soon be building.haha  It'll probably cheaper than replacing the edcors with lundahls!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on November 10, 2011, 05:36:30 PM
I just got my Edcors in the mail, I'm about to go solder them in and try to finish the wiring and get it fired up before band practice tonight.

Could anybody please give me some guidance on the calibration procedure? Thanks!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Hank Dussen on November 10, 2011, 05:44:56 PM
About the power transformer:
I was going to order one with an extra 7V winding for the heaters.
But then you have to make a extra PSU (with extra filtering) for this of course, and cut some traces.
But regulated 7V would be less stressful for the regulator.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: JayDubrek on November 10, 2011, 06:11:43 PM
Dr-J - I'm definitely up for a 230v Primary power transformer!
Cheers
Jay
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: EEMO1 on November 11, 2011, 04:47:49 AM

drJ,

 im in for 2 if it's what 30 euros a piece?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on November 11, 2011, 05:09:45 AM

drJ,

 im in for 2 if it's what 30 euros a piece?

drJ,
If it's 30€ one for me please....
Thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on November 11, 2011, 07:20:22 AM
Is the spec correct?

Make that B+ winding 120VAC.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on November 11, 2011, 07:23:09 AM
About the power transformer:
I was going to order one with an extra 7V winding for the heaters.
But then you have to make a extra PSU (with extra filtering) for this of course, and cut some traces.
But regulated 7V would be less stressful for the regulator.

Less stressful how? The currents in this project are relatively low. You will not see anywhere even 1/5th of the max capability of those regulator chips. And also, if you want regulated 6.3V heaters that winding must be 9V. 7VAC rectified, filtered and to regulator won't make it to 6.3V.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Hank Dussen on November 11, 2011, 08:34:43 AM
About the power transformer:
I was going to order one with an extra 7V winding for the heaters.
But then you have to make a extra PSU (with extra filtering) for this of course, and cut some traces.
But regulated 7V would be less stressful for the regulator.

Less stressful how? The currents in this project are relatively low. You will not see anywhere even 1/5th of the max capability of those regulator chips. And also, if you want regulated 6.3V heaters that winding must be 9V. 7VAC rectified, filtered and to regulator won't make it to 6.3V.

OK, fair enough. Didn't know that so much got lost after rectifying and filtering.
In that case I'll go the easy way and sign in for a Rondo power transformer as well!  ;D
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on November 11, 2011, 10:17:38 AM
so I'm having a few issues right off the bat-

Powered up, I'm reading about 130V on the 100V supply, and I'm able to adjust the -18V properly, but I am getting nothing on the +18V, 12.6V, and the 1.5V sides. (well only about 20mV on each) AC voltages coming in from the toroid look fine.

I powered up without the DOAs in place, but with the tubes installed to complete the heater circuit. I've quickly inspected and everthing looks good, components and polarities are right. I reflowed solder joints and double checked continuity between components, tested with and without all of the control wiring hooked up, still having the same issues.

I've tested all of the DOAs in a preamp and they are all functioning properly - do i need to have them in place when I set the voltages? Maybe I have some bad regulators? Bad tubes? Any ideas?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on November 11, 2011, 12:53:47 PM
so I'm having a few issues right off the bat-

Powered up, I'm reading about 130V on the 100V supply, and I'm able to adjust the -18V properly, but I am getting nothing on the +18V, 12.6V, and the 1.5V sides. (well only about 20mV on each) AC voltages coming in from the toroid look fine.

I powered up without the DOAs in place, but with the tubes installed to complete the heater circuit. I've quickly inspected and everthing looks good, components and polarities are right. I reflowed solder joints and double checked continuity between components, tested with and without all of the control wiring hooked up, still having the same issues.

I've tested all of the DOAs in a preamp and they are all functioning properly - do i need to have them in place when I set the voltages? Maybe I have some bad regulators? Bad tubes? Any ideas?

Were are you measuring? I had to take the 12.6V out of the power supply molex, because it doesn't connect to the same star ground as everything else, and runs in series to the tubes. Try measuring at a convenient spot around the voltage regulators.

For the 130V that is strange, but it has to be something. It is a pretty straight shot to the tubes....make sure there is a complete circuit.

A very quick and dirty calibration method (better info to come soon...anyone feel free to shed some light on this, I'm going off of the original PRR description)


Trimmers:
1k VR3, VR9 ....this balances the power between the 2 halves of the 6BC8 tube. Helps if you don't have a perfectly balanced tube.
100R VR1,VR4 adjust for minimum "thump"
1k VR5, VR2 Control Meters, Power on, let it warm up for a bit (10 minutes or so) turn until meters read "0" gr.




Oh and for rev 2, no big changes. Just little things to make it easier and better to build.

thanks!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on November 12, 2011, 12:23:42 AM
Finally getting some more time to mess with it and found this minor fix-up:

if using INA134 inputs, on left channel, connect pin 1 to ground, otherwise you'll be getting some pretty big voltage readings on the output of the chip. You can connect pin 1 to pin8 of the same chip, as that is tied to ground.

Much Thanks, and sorry for any inconveniences this no doubt has caused.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on November 12, 2011, 09:13:40 AM
hi 230V guys  :)

currently i count 6, someone else?

I think 30 euros will be a good straight price...

Rock-On!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on November 12, 2011, 11:56:07 AM
Were are you measuring? I had to take the 12.6V out of the power supply molex, because it doesn't connect to the same star ground as everything else, and runs in series to the tubes. Try measuring at a convenient spot around the voltage regulators.

For the 130V that is strange, but it has to be something. It is a pretty straight shot to the tubes....make sure there is a complete circuit.


I was measuring at the power supply molex, but i still have nothing at the pins of the tube socket.


Right now I am measuring about -25V at the junction of D6 and D7. At the other side of the rectifier, junction of D8 and D9 measures about 1.5V with both tubes installed, it goes up to about 5V when i remove one or both tubes.

???


edit: I pulled the regulators from the +18V and 12.6V sections and now I am reading 25V where their inputs should be, but only
-1.5V at the LM337. Maybe I should replace both if not all regulators?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Tsane on November 12, 2011, 03:29:51 PM
Dr_J, I'm in for a 230v trafo also :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: beatnik on November 13, 2011, 07:09:48 PM
one for me too! thanks

120vac winding as kingston suggests?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: EEMO1 on November 14, 2011, 03:56:09 AM
hi 230V guys  :)

currently i count 6, someone else?

I think 30 euros will be a good straight price...

Rock-On!


 please take account some additional rc filtering!!!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: baadc0de on November 14, 2011, 07:59:18 AM
Dr_J, I'm in for a 230v trafo also :)

+1 here
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on November 15, 2011, 02:53:19 PM

Make that B+ winding 120VAC.

Hi Kingston,

why would you suggest to change to 120VAC instead of 100VAC as Abe recommends?

ROCK-On!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on November 15, 2011, 09:58:10 PM
Thats my mistake. You want to end up with 100v rectified, and that means starting out with 120v coming out of your transformer to rectify and smooth down to 100v.

Cheers!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on November 16, 2011, 02:50:19 AM
100VAC rectified to a filter cap practically means only about 120-130VDC voltage. That's not enough for good filtering and a zener shunt to make clean 100VDC. You need some headroom for it.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on November 16, 2011, 03:09:43 PM
Hi Abe,
hi Kingston,

that makes in principal sense to me.

Kingston, i have a little understanding problem.  :-\ 
How can I get 120VDC out of 100VAC only by rectifying? ( => SQRT(2) !!!  :o Idiot, me!!!!)
If I get it right, we need 120VAC to get ~110VDC smoothing leads to ~100VDC!?

ROCK ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on November 16, 2011, 07:24:11 PM
Actually the full-wave bridge rectifier used here results to about 1.4 times the AC voltage. In theory. Practically you get about 1.2-1.3 times the AC voltage on the first filter cap. For 120VAC that results to about 150-160VDC (for 100VAC it would be 120-130VDC). It's not even close to clean DC at that point so we filter it with more RC networks. And then use the zener shunt as a poormans regulator to make it stable at 100VDC.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on November 19, 2011, 08:16:00 AM
Are you guys using the Edcor PCW10K/600 for the interstage? If anyone ordered more or is about to order some to europe, I'd like two as well, so if you're willing to split shipping etc please PM me.

Cheers,
B.
I think it was somewhat decided that 10k/10k for both input and interstage is the way to go.

Yep!

Hi Abe,
My bad  :-\ I just received my edcore tranx 10K/600 :(  Can I use 600 or I need to get 10K?
Thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on November 19, 2011, 10:41:47 AM
I'm using 10k/600 stepdown in my first build. It works fine. But on the left channel there is hum if you crank the gain all the way. Since its the one closest to the power supply I'm guessing maybe the unshielded edcor interstage is where the hum is getting in. I'm planning on taking the interstage out and mounting it further away from the power supply to see if that helps. I'll post what I find.

PS for Rev 2 definitely making the power supply board separate! :)

EDIT
Isolated the hum to the L channel input TX. Preferably want to use a shielded TX, or mount your input transformer away from the power supply. I'm going to test some more on exactly why it hums when mounted.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: zayance on November 19, 2011, 11:50:36 AM
Another question concerning the Transformer, isn't it better to have a separate Heather Supply than one taken from a Positive feed, here beeing the 18V.
Just curious.
If you go external on the Rev2 will it be the same?

Thanks


EDIT: Sorry if this has already been spoken of....
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on November 19, 2011, 12:02:34 PM
That is something to be considered. I think that with a properly designed circuit taking the heaters off of the same transformer tap as the positive rail shouldn't be a problem. It should work fine. But I've had someone trying to convince me to use a constant current source for the heaters using an lm317....sounds interesting, might be worth looking into...

The only big drawback of having a separate heater feed is then we has to start using custom/more expensive transformers (or more than one for us 120v folks) with a separate tap just for the heaters.

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: zayance on November 19, 2011, 12:06:26 PM
Yes i understand the drawback, and the price point, But if you go custom anyway than will it be that much? US or EU.....

3 or 5 Euros more on the transformer for another supply (TAP) maybe? hmmm, depends on the supplier also....
 
Anyway just curious.


Thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on November 19, 2011, 01:56:11 PM
I'm using 10k/600 stepdown in my first build. It works fine. But on the left channel there is hum if you crank the gain all the way. Since its the one closest to the power supply I'm guessing maybe the unshielded edcor interstage is where the hum is getting in. I'm planning on taking the interstage out and mounting it further away from the power supply to see if that helps. I'll post what I find.


Thanks Abe
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on November 19, 2011, 05:13:43 PM
Another question concerning the Transformer, isn't it better to have a separate Heather Supply than one taken from a Positive feed, here beeing the 18V.

There are some advantages for consumer/production units. You can optimise the transformer size to perfection with a custom heater winding. This way you can also make sure no watts are wasted in dropping the heaters top correct voltage. Lots are wasted (as heat) going from 18VAC to 12.6VDC.

But actually none of that matters for DIY builds. You just don't have to care. Sound does not enter this equation in any way.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: tfletchii on November 19, 2011, 07:07:33 PM
Anybody using the optional output transformer? if so what is working out well?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on November 19, 2011, 07:19:22 PM
Anybody using the optional output transformer? if so what is working out well?
Can't go wrong with your favorite 1:1 transformer. Any output type will do. Cinemag, Jensen....edcor


Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on November 22, 2011, 04:09:42 PM
Hi Abe,
hi Kingston,

would you although recommend a factor of ~1.3 for the 18VAC secondary output?
This would lead to approximately to 24VAC smooth to 18VDC or do I miss something, do I?

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on November 22, 2011, 05:18:14 PM
Kingston might want to chime in, but I can tell you my experience with it, I'm using a transformer rated at 18v secondaries and I can get the positive rail up to about 17.5 volts that is well regulated. Usually a 50VA 18v secondary is fine for a couple channels of +/-18v regulated solid state stuff, but because of the 2 taps feeding off one of the transformer windings (the + rail and heaters) there is a slight sag that limits the + rail. So I would recommend (and its good design practice) about a 20v dual secondary transformer if you wanted to regulate to +/-18v. Also 24v should work fine, but I imagine you might want to make sure your regulators don't heat up too much.

Also like kingston was doing, depending on what opamps you choose you could beef up the power supply rails to +/- 24V. on the flip side, you could also run the unit on +/-15v without problems.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: myker on November 23, 2011, 11:15:09 PM
scored a board! super excited about that...
thankful for guys like abe and kingston...experts
-mike
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: tfletchii on November 28, 2011, 12:01:28 PM
how are the edcor transformers shaping up sonically for everyone? I know kingston had some sonic/phase issues. Is it bothering anyone else? I'm about to purchase transformers and I'm debating...
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on November 28, 2011, 06:50:18 PM
The Edcors are working fine for me. I've been tweeking around over the last couple of weeks, still have a tiny noise issue that the unsheilded edcors may be contributing to, was hoping Abe had a report from mounting the transformers off board soon. I was thinking about rebuilding the supply off board and putting a panel for sheilding in the case, maybe that will alleviate the problem. I was getting more noise at first, but moving the toroid around fixed 99% of it. At this point the noise is only really noticable when there is no signal running through it and I have the output cranked.

As far as the sound- I am digging it, very colorful, very controllable. Hitting the input hard gets a nice saturation, not sure if the edcors are solely responsible. I'm not going for a "pristine" sound, so my aims may be a little different than Kingston's. There is definitely some coloration on the top end, be it from the edcors or the 1731's or whatever else, but so far I am really enjoying what this thing does. This thing has so much balls that I'm gonna have to leave a couple of empty spaces below it in the rack. ;D

I've also been playing with the timing cap, I have tried the tantalums and Solen fast caps. The tantalum seems to have more midrange push or growl, where the solens lose the midrange character but seem to extend the response on the very top and bottom giving a more "hifi" sound. I didn't really like the solens at first, but after playing around a bit i decided to keep them. I ordered some PIO caps and some four way switches for a "response" control which will include the three types of caps and leave a space open for GR bypass. Good stuff.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on November 29, 2011, 02:31:13 PM
Good! Glad to hear everyone is taking this project and making it their own. That is what DIY is all about. I have some comments on the Edcors, and what I've found.

If using unshielded input TX, you will want to mount the L (top) channels' input transformer off the board. Or at least if you are going the edcor route, get an edcor that isn't PCB mount, just for that spot. I tried cutting the B+ voltage regulation off the board, but that didn't help the noise, so the noise is either coming from the heaters or elsewhere. I tried a whole lot of different things with the power supply, but the noise is only coming in via the windings of the Left channel input TX.

I am using 4:1 interstate, and seems to work quite well. I am going to get around to putting a 1:1 in there to decrease possible noise floor, but so far, noise isn't really a big issue especially after mounting the TX off board and using proper gain staging.

I think a lot of it is also there is a lot of gain built into the output section, so you can really listen to the noise floor if you want. But under "normal" (Not driving the equipment down stream into smoke and fire) the noise floor is respectable.

Sound wise: Edcors sound great, I haven't build one with the cinemags that are on my desk, so I don't have anything to compare it to, but as-is I definitely am confident that it offers a nice color and vibe that is very useful, not transparent, but useful none the less.

And when you consider prices 60$ plus compared to 10$ its a no brainer. Maybe have one with edcors for your guitars, or drums 8) and then one with luhndalls or cinemags for you masterbuss ;)

PS Cases should be available soon through Collective Cases (Dan). I told dan that people will probably be ready for them. Also we are going to mount the meters inside, because we agreed it looks a little cooler and will let us have "Limiting Amplifier" on the front. Which seems like those two words together on the front of a piece of equipment are too nice to pass up! But that means one is going to have to cut the bottoms of their hairball meters to get them to sit correctly. An easy thing to do, and we agree is well worth it. Dremel tools ready!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on November 30, 2011, 10:44:09 AM
As far as the sound- I am digging it, very colorful, very controllable. Hitting the input hard gets a nice saturation, not sure if the edcors are solely responsible. I'm not going for a "pristine" sound, so my aims may be a little different than Kingston's. There is definitely some coloration on the top end, be it from the edcors or the 1731's or whatever else, but so far I am really enjoying what this thing does. This thing has so much balls that I'm gonna have to leave a couple of empty spaces below it in the rack. ;D

You're not going to hear any saturation from any of the transformers in this project. The tube stage has probably more than 10dB lower saturation point. Everything will turn into tube-fart-mush before you even tickle a transformers saturation point on this signal chain.

By the way, I was not really looking for pristine sound from this project either, but the edcor 10k:10k forced my hand. It was pretty harsh in my opinion. Besides the lundahls I have no other options. I wouldn't mind trying some other 10k:10k input or especially interstage, but I don't know how to get anything cheap at the moment. (lundahls aren't cheap either, I just happened to have some around)

I think I will have to incorporate a PIO/tantalum time constant network switch in my build somehow. That sounds like a pretty useful option.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on November 30, 2011, 07:45:20 PM
You're not going to hear any saturation from any of the transformers in this project. The tube stage has probably more than 10dB lower saturation point. Everything will turn into tube-fart-mush before you even tickle a transformers saturation point on this signal chain.

By the way, I was not really looking for pristine sound from this project either, but the edcor 10k:10k forced my hand. It was pretty harsh in my opinion. Besides the lundahls I have no other options. I wouldn't mind trying some other 10k:10k input or especially interstage, but I don't know how to get anything cheap at the moment. (lundahls aren't cheap either, I just happened to have some around)

I think I will have to incorporate a PIO/tantalum time constant network switch in my build somehow. That sounds like a pretty useful option.

Bad wording on my part, sorry if I seemed like I was trying to put words in your mouth. I just meant that I haven't been as bothered by the Edcors as you seemed to be, specifically addressing tflechii's question. Not to say that I won't try some other transformer options eventually, though.

Interesting point about the transformer saturation. Must be the 1731's, I am definitely hearing some kind of colorful drive from something before it turns to "tube mush".
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: tfletchii on December 01, 2011, 10:45:17 AM
thanks for the responses everyone. I think I'm going to take the route adeptusmajor is thinking. I'll get the edcors and get it running see what I think and either build another down the road or switch out the transformers down the road and use the edcors for another build.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: beatnik on December 01, 2011, 12:44:27 PM
How is the current state of the meter-discussion?
Can we use VUs (Hairball?) ?

The meters should be 1mA DC. I used these: http://hairballaudio.com/shop/product_info.php?cPath=25&products_id=61

seems to work well, although the scale is inverted.

And of course you can use VU's, but on audio inputs/outputs only. If you want to get hacking, then you could use VU meter as gain reduction, too. See the poorman thread, although the information might be a bit hard to find.

For this project I really would like to use standard vu meters instead of the required 1mA meter to display gain reduction, as I have many of them available.

Especially I have some big tape machine meters that would fit great in my panel layout.

Is there any way to adapt them? I tried to look in the poormans thread as suggested, but found nothing useful.

Please any input is higly appreciated.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on December 01, 2011, 01:31:10 PM
How is the current state of the meter-discussion?
Can we use VUs (Hairball?) ?

The meters should be 1mA DC. I used these: http://hairballaudio.com/shop/product_info.php?cPath=25&products_id=61

seems to work well, although the scale is inverted.

And of course you can use VU's, but on audio inputs/outputs only. If you want to get hacking, then you could use VU meter as gain reduction, too. See the poorman thread, although the information might be a bit hard to find.

For this project I really would like to use standard vu meters instead of the required 1mA meter to display gain reduction, as I have many of them available.

Especially I have some big tape machine meters that would fit great in my panel layout.

Is there any way to adapt them? I tried to look in the poormans thread as suggested, but found nothing useful.

Please any input is higly appreciated.

I would say stick them in. In my prototype I used a VU meter. Works fine. If you really wanted to get technical though there is a way to adjust the trimmers, and resistors around the meter circuit...But the VU will work, and will be fine. It will just be a bit more sensitive and slow.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: beatnik on December 01, 2011, 01:35:32 PM
Thanks Abe, I'll try them.

btw, have you managed to find tracking code for my shipment? I tried to send an email but got no answer. Please let me know when you can.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on December 01, 2011, 01:37:32 PM
no not yet, sorry. :( Hopefully they arrive soon. Keep your fingers crossed. It sometimes takes a long time for those parcels to arrive.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: beatnik on December 01, 2011, 01:47:30 PM
don't worry, actually i'm not so hurrying up because i already have many project to finish before. but i hope they arrive safe and fine at some point
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on December 01, 2011, 04:08:43 PM
Hi 230V Guys,

so I'll like to place my order at mueller next week.
I'll change secondary to 120VAC, 20vAC, 20VAC.

Currently there is interest for a little group order from:
- mylesgm 1x
- JayDubrek 1x
- EEMO1 2x
- jandoste 1x
- Tsane 1x
- beatnik 1x
- baadc0de 1x

Please P-Mail me your address and your PayPal-Mail.

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Hank Dussen on December 01, 2011, 04:44:07 PM
Hi 230V Guys,

so I'll like to place my order at mueller next week.
I'll change secondary to 120VAC, 20vAC, 20VAC.

Currently there is interest for a little group order from:
- mylesgm 1x
- JayDubrek 1x
- EEMO1 2x
- jandoste 1x
- Tsane 1x
- beatnik 1x
- baadc0de 1x

Please P-Mail me your address and your PayPal-Mail.

ROCK-ON!

I want one as well!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on December 01, 2011, 04:46:38 PM
Hi 230V Guys,

so I'll like to place my order at mueller next week.
I'll change secondary to 120VAC, 20vAC, 20VAC.

Currently there is interest for a little group order from:
- mylesgm 1x
- JayDubrek 1x
- EEMO1 2x
- jandoste 1x
- Tsane 1x
- beatnik 1x
- baadc0de 1x

Please P-Mail me your address and your PayPal-Mail.

ROCK-ON!

PM'ed :)
Thanks again! youppi :) :)
cheers,
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on December 01, 2011, 11:45:01 PM
don't worry, actually i'm not so hurrying up because i already have many project to finish before. but i hope they arrive safe and fine at some point
You are a gentleman and a scholar! Thank you for your patience.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Peps on December 02, 2011, 10:21:32 PM
Hi 230V Guys,

so I'll like to place my order at mueller next week.

Hi Dr_J,
Sent a PM. Count me in!
Thanks
Peps
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Tsane on December 03, 2011, 08:12:26 AM
Hi 230V Guys,

so I'll like to place my order at mueller next week.
I'll change secondary to 120VAC, 20vAC, 20VAC.

Currently there is interest for a little group order from:
- mylesgm 1x
- JayDubrek 1x
- EEMO1 2x
- jandoste 1x
- Tsane 1x
- beatnik 1x
- baadc0de 1x

Please P-Mail me your address and your PayPal-Mail.

ROCK-ON!

PM'ed. Thanks!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: JayDubrek on December 03, 2011, 01:54:57 PM
PM'd yer DR-J...
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Matthew Jacobs on December 03, 2011, 04:15:20 PM
Hi 230V Guys,

so I'll like to place my order at mueller next week.
I'll change secondary to 120VAC, 20vAC, 20VAC.

Currently there is interest for a little group order from:
- mylesgm 1x
- JayDubrek 1x
- EEMO1 2x
- jandoste 1x
- Tsane 1x
- beatnik 1x
- baadc0de 1x

Please P-Mail me your address and your PayPal-Mail.

ROCK-ON!

I would like 1 as well...

Thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: beatnik on December 06, 2011, 09:53:56 AM
Dr_J PM to you
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Script on December 06, 2011, 12:07:56 PM
Hi 230V Guys,

I know it's a little late to ask, but would the price change substantially if it was a dual primary (115/115)? Step-up/down converters weigh a lot...
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: tomcat on December 06, 2011, 06:02:51 PM
pmd as well :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on December 09, 2011, 04:15:53 PM
Hi 230V guys!

Good and bad news...

The good one, i received a new offer from mueller after we changed the spec
to primary 230VAC, secondary 20VAC 0.1A, 20VAC 0.5A, 120VAC 0.1A.

The bad is that the price has raised to 34 Euro plus shipping.

I'll place my order the next days.

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on December 09, 2011, 04:43:31 PM
Hi 230V guys!

Good and bad news...

The good one, i received a new offer from mueller after we changed the spec
to primary 230VAC, secondary 20VAC 0.1A, 20VAC 0.5A, 120VAC 0.1A.

The bad is that the price has raised to 34 Euro plus shipping.

I'll place my order the next days.

ROCK-ON!

it's ok for me!:)
Thanks again...
cheers,
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: tomcat on December 09, 2011, 07:04:22 PM
No prob, still 2 for me pls
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: JayDubrek on December 09, 2011, 09:28:13 PM
Still good for me.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Hank Dussen on December 10, 2011, 06:50:05 AM
Good here as well...
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: baadc0de on December 11, 2011, 01:23:57 AM
No probs with new trafo price
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on December 11, 2011, 02:01:43 AM
Wait stop the presses! Where did you get those numbers? :o They are way too low! You simply have no safety overhead at all in that spec!

Also, were you guys thinking of running DOA's with that transformer? One DOA alone could peak a rail some 20-50mA (worst case scenario). What about the four needed in this project?

That 20VAC 0.5A winding right now barely covers the tube heaters. Actually it doesn't even cover the russian tubes.

You have to realise that the AC amps do not directly translate to DC amps when rectified to a filter cap. You get maybe 60-70% of the AC amps.

So let's say we need like 20VDC 0.2A (opamps), 20VDC 0.6A (opamps + heater), 120VDC 20mA (B+).

That means your AC amps should be scaled with that 60% AND a safety overhead.

Now we have a decent spec of 20VAC 0.5A (opamps), 20VAC 1A (opamps + heater), 120VDC 50mA (B+).

GroupDiy has a bad history of ordering or commissioning underspecified transformers. Don't make that mistake again.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: tomcat on December 12, 2011, 08:00:02 AM
Good point.

For me its fine and i would prefer to get reasonably or oversized transformers, as long as they fit 1RU.

Price difference doesnt matter, a few euro more would be much better then to run into possible problems. Remembering the PM670 story ;)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on December 12, 2011, 08:18:58 AM
I would (and did) go for off the shelf transformers, and would recommend to you all as well. No need to complicate things with any special order transformers. Price difference is negligible.

You need two transformers, widely available all over the place: one roughly 50VA 2X24VAC (or perhaps 18-24VAC) and another with maybe 5-10VA 2X15 (or maybe 12VAC).

And then do the gyraf G9 trick, with the exception that the small transformers primaries are in series (actually secondaries, since the transformer is reversed). Someone really oughta do a drawing so that the people who don't understand ohms law won't be scared of it.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: tomcat on December 12, 2011, 11:43:17 AM
Price difference: yes

But you will run into space problems using a 1ru case. It would be more packed which makes it more difficult to move the transformers away from audio and possibly it would be also a thermal issue, especially with the russian tubes.

Still like to go the custom wound route, had good results with that in the past.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on December 12, 2011, 12:03:22 PM
It would be more packed which makes it more difficult to move the transformers away from audio and possibly it would be also a thermal issue, especially with the russian tubes.

I already built it 1U and the transformers sit nice and tight in the corner out of the way. If both are toroids there won't be any hum unless the signal chain transformers suck (read: edcors with no shielding). And if that's the case theres no transformer you can move far enough inside a 1U case to make any difference. I already tested this extensively, and I'm using extra toroidal transformer shielding sheets as well.

No there isn't a thermal issue either. If there was, it would be where the tubes are, perhaps the heater regulator too, but not in the transformer. Also, 5-15VA transformers are tiny!

Also, I don't know where you get your PSU toroids but it looks to me two standard toroids from lets say rapid electronics will actually be cheaper than an adequately sized custom wound.

Just trying to save you guys a lot of time and bother.

[edit]

just look

http://www.rapidonline.com/Electrical-Power/115-230V-Toroidal-Transformers-Dual-Primary-82719
http://www.rapidonline.com/Electrical-Power/Miniature-open-style-toroidal-transformers-72687

Mini Open Toroid 7.0va 12v+12v £8.77 + Toroidal Transformer 50va 0-25v 0-25v £7.79
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on December 12, 2011, 12:12:31 PM
I could understand wanting one transformer to power everything, nice, clean, and easy (well once its all ordered and sorted). I'm not discouraging anyone from buying a custom TX, but Kingston does bring up a lot of good points. I've used the G9 transformer trick several times and it works great. If it were me I would just settle on the 2 easy to source transformers.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: dandeurloo on December 18, 2011, 07:38:20 PM
You guys have been doing amazing work with this project! 
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on December 19, 2011, 07:56:50 AM
Hi Kingston,

THANKS a lot for your info! It was just in time (hope so), because I just did the order... :-\
And stopped it!

For the values, that's why I posted them several times... thanks for pointing out!!!!! :D :D
15 transformers for the bin would be a disaster...

I'll have to see what the price will be with your new spec.
If the price is around of 2 of-the-shelf transformers, I would like to go for a custom made one...maybe... ::)

THANKS A LOT MAN!!!

ROCK-ON!

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on December 20, 2011, 08:10:16 AM
Hi Kingston,

THANKS a lot for your info! It was just in time (hope so), because I just did the order... :-\
And stopped it!

For the values, that's why I posted them several times... thanks for pointing out!!!!! :D :D
15 transformers for the bin would be a disaster...

I'll have to see what the price will be with your new spec.
If the price is around of 2 of-the-shelf transformers, I would like to go for a custom made one...maybe... ::)

THANKS A LOT MAN!!!

ROCK-ON!

Hey Dr_J link,
So, what we do now?:)
cheers
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on December 20, 2011, 02:03:54 PM
Hi,

I have asked for a new offer regarding the new spec that Kingston recommended.
I have to see what price it now will be. Maybe 2 of-the-shelf transformers may cheaper...!?
I'll let you know.


ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on January 05, 2012, 08:53:16 PM
sorry
can I use
http://www.canford.co.uk/Products/23-056_OEP-Z3003E-TRANSFORMER-Analogue-audio-PCB-line-bridging-or-output

Instead of Edcor, for T1-T2-T3-T4?
thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on January 06, 2012, 12:57:26 AM
sorry
can I use
http://www.canford.co.uk/Products/23-056_OEP-Z3003E-TRANSFORMER-Analogue-audio-PCB-line-bridging-or-output

Instead of Edcor, for T1-T2-T3-T4?
thanks


There is no dedicated pcb footprint for those transformers. But wouldn't be too hard to rig something up if you really wanted to use them.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on January 06, 2012, 06:53:46 AM
thanks
it is only because for me in Italy are more easy to find .....
I also have a pair of Jensen JT-11P-1, I can use as input
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: earl on January 07, 2012, 05:50:56 PM
Hey Abe powered up the project tubes glowed fine unplugged plugged back in and poof the 1n4007 (115v) blow. Any ideas?  Check the 100uf 250 volt caps? replace?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on January 09, 2012, 11:33:38 PM
Hey Abe powered up the project tubes glowed fine unplugged plugged back in and poof the 1n4007 (115v) blow. Any ideas?  Check the 100uf 250 volt caps? replace?


hmmm....so the diodes blew?? they are rated at 1000v? something isnt right....check around...carefully of course. the caps should be fine unless you saw smoke and explosions. Maybe try powering it up again?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: gemini86 on January 09, 2012, 11:36:35 PM
Is it possible the inrush current is a bit higher than 1a?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on January 10, 2012, 12:01:51 AM
Is it possible the inrush current is a bit higher than 1a?

The B+ lines eat some 10mA. Inrush would not be 100X that. Sounds to me like a simple build error, like a reversed diode etc.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: earl on January 10, 2012, 11:48:33 AM
Things to meditate on... Think I'll put it up for a while and come back to it. Often times that helps.  Thanks for the input.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: myker on January 13, 2012, 09:50:24 PM
hey guys, ordering parts, but have a few questions...

1. what voltage rating do you guys recommend for the ceramic and film capacitors and the 47uf bipolar?
2. what trimpots and potentiometers are recommended for this project?


Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on January 14, 2012, 04:58:00 PM
Hello,
Ceramic capacitors, pretty sure any kind will work, they are pretty resilient. Plus most all the caps are only seeing low voltage rails. But the ones around the high voltage rails, make sure they are 200V...but pretty sure most all ceramics are rated pretty high. The 47uf Bipolars should be 50v, just in-case the unit somehow gets 48v up the wrong end...But 25v will work absolutely fine. Probably get away with 6.3v if you wanted to live on the edge! i don't think those caps will ever see very much voltage.
Cheers.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on January 14, 2012, 05:34:27 PM
HI 230v guys,

Christmas holiday is over, time get this project running..
I received a new offer from mueller for the transformers.
Good news, the price hasn't changed.
I already check the spec with Kingston.
So, if still some interest is around, let me know.

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Tsane on January 14, 2012, 05:52:47 PM
Yup Dr_J, still very much interested! :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: baadc0de on January 14, 2012, 06:30:15 PM
Still interested indeed
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on January 14, 2012, 06:49:46 PM
HI 230v guys,

Christmas holiday is over, time get this project running..
I received a new offer from mueller for the transformers.
Good news, the price hasn't changed.
I already check the spec with Kingston.
So, if still some interest is around, let me know.

ROCK-ON!

Yep:) it will be for my second unit...
cheers
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: myker on January 14, 2012, 08:22:44 PM
thanks Abe!
Hearing you guys describe your finished compressors is driving me to hurry and finish mine. I have no tube gear in my rig now and wanting something with some color...

what is a good mouser number for the trimpots?
and potentiometers? regular alpha pots w/ .25" shaft? I plan to use the Dan case...

thanks for all the help and all of the great advice..
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: JayDubrek on January 15, 2012, 03:38:32 AM
DR_J - I'll still take a power transformer...
Cheers
Jay
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: MrZpliff on January 15, 2012, 03:49:28 AM
HI 230v guys,

Christmas holiday is over, time get this project running..
I received a new offer from mueller for the transformers.
Good news, the price hasn't changed.
I already check the spec with Kingston.
So, if still some interest is around, let me know.

ROCK-ON!

Interrested !
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Hank Dussen on January 15, 2012, 10:07:15 AM
HI 230v guys,

Christmas holiday is over, time get this project running..
I received a new offer from mueller for the transformers.
Good news, the price hasn't changed.
I already check the spec with Kingston.
So, if still some interest is around, let me know.

ROCK-ON!


One here please!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: EEMO1 on January 16, 2012, 06:06:58 AM
 yes please! one for me!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on January 17, 2012, 04:08:38 PM
One for me!!!!
Thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: tomcat on January 20, 2012, 06:41:08 PM
In case you didnt get my pm: Still two for me :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: okailla on January 21, 2012, 11:18:01 AM
One for me, too.
Danke.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on January 22, 2012, 08:20:14 AM
sorry
I'm buying the components

Lundahl LL1539 is fine as Output?

R36, R112, R168, R169 (interstage TX terminator) OPT. ???
Thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on January 23, 2012, 07:57:21 PM

R36, R112, R168, R169 (interstage TX terminator) OPT. ???
Thanks

Those are for the resistors that tame certain transformers. for the interstage primary try 1k to 10k (or depending on tx leave out) and for the secondary try 100k.

Have a good one!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: 0dbfs on January 24, 2012, 02:49:33 PM
Hey Guys, I just wanted to see what people have been using for transformers and what they think about the results.

I am starting to source parts for these babies now and am going with gar1731's for the DOA goodness...
I see 10k:10k as input and don't mind using the edcors but would like these units to have a little more of a "story" associated with them...
Are we still looking at 4:1's as the interstage or did some have varying results and end up with 1:1's in that position?
Also since I am using the gar1731's would an API style OT make most sense or perhaps something else. Maybe a Carnhill or something NOS?

Cheers,
jonathan
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: dandeurloo on January 24, 2012, 03:09:43 PM
Hey guys, I have these cases in stock now.  So if you need one hit me up.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on January 24, 2012, 06:36:48 PM
hey abe, was this a one time thing, or do you have more boards left?

thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: grantlack on January 24, 2012, 11:11:30 PM
missed this one too...  been too busy playing in mic land. >:(
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on January 25, 2012, 12:14:43 AM
hey abe, was this a one time thing, or do you have more boards left?

thanks

Heya, Yes I'm definitively plan on doing a rev 2. I might have a few Rev 1 boards left...let me check, as I probably won't get ot rev 2 for a bit...


But one thing I'm going to implement in rev 2 is an off board power supply. There is too much current voltage crazy-ness going on to be put on the same PCB as the main board. So I might be sending off for the power supply PCB soon. That way people can use them with their Rev 1s

The Rev 1s  S/N ratio is -85 to -95 depending on gain etc...I've chopped traces, ran heaters off the board,,,did all sorts of tricks that I could think of, but I know the S/N can be better and the only solution I can think of is to move the power supply of board. I don't want people with Rev 1s that have already hooked everything up to feel like this in "necessary" as the Rev 1s as is I find to be quite useful as it, but of course your mileage may vary. I think the off board power supply will enable the un-shielded edcor TX inputs to be used, and my goal of the S/N ratio to be greater than 100 db. We shall see...

Stay tuned, I'll try to offer these boards cheap, keeping in line with this being a project of goodwill.

Hey Guys, I just wanted to see what people have been using for transformers and what they think about the results.

Hello,
I've tried edcor 10k:10k for input, edcor 4:1, and 1:1 interstage. I've also tried the cinemag 15K:15K for input and pm-1000 output transformer as interstage (1:1) (yep!)

My thoughts are this: Cinemags are of course a great choice, 50$ per TX. They are shielded so that is of course a plus especially for the inputs. Their sound is more transparent than the edcors (only thing I have to compare to) the edcors being more colored, but I do prefer the edocrs actually....in the low end, but then the cinemag/pm-1000 transformer combo was overall cleaner, and the high end wasn't soo...phase -ish. Still, for the price of edcors, they really are worth it and nice, a usable color, but I would use the 4:1 for interstage if your going the edcor route, like kingston was saying the 1:1 in the interstage using edcors can get hairy, but when you load it with the terminating resistors its not as bad.

The gain difference of the 4:1 vs 1:1 wasn't as big of a deal as I thought it might be, could be because I used the terminating resistors with the 1:1 output stage and none with the 4:1...i don't really remember! Anyway i would encourage you to experiment, might be surprised what works!

Also Im getting a calibration procedure down, after i build my next one I'll try to get it all compiled into a pdf. really you just set the threshold, zero the meter, and reduce thump and thats it.

Cheers!

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on January 25, 2012, 12:47:01 AM
Excellent!  Nice to see some progress.  I've had mine sitting on the bench for the last few months.  Work always seems to get in the way!
Any updates on a case?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on January 25, 2012, 02:15:20 PM
Hi Abe,

interesting news about the transformer options!
I'm still not sure which way to go? Cinemag or edcor!?
A sound sample would be great  ;D

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on January 25, 2012, 02:18:15 PM
Hi 230V-Guys,

order is placed @mueller.
Delivering time will be approximately 4 weeks from now.
I'll let know know.

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: 0dbfs on January 25, 2012, 02:46:51 PM
Abe, Thanks for the trafo info. I'll go back and re-read everything here before I order trafo's but heck...
I'm making  two of these...
If I am counting correctly that comes to 12 transformers... Ugh... Forgot about that!

Anyway, 10k:10k for input (shielded preferred), 1:1 as interstage, and 1:1 as output.. Sounds like a plan! There's got to be some cool/unique transformers out there that meet these requirements...

Can also do complete transformerless right? Hmm... I like to finish, button up, and leave em that way... so... We'll see...

Cheers,
jb

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on January 25, 2012, 04:19:53 PM
Abe, Thanks for the trafo info. I'll go back and re-read everything here before I order trafo's but heck...
I'm making  two of these...
If I am counting correctly that comes to 12 transformers... Ugh... Forgot about that!

Anyway, 10k:10k for input (shielded preferred), 1:1 as interstage, and 1:1 as output.. Sounds like a plan! There's got to be some cool/unique transformers out there that meet these requirements...

Can also do complete transformerless right? Hmm... I like to finish, button up, and leave em that way... so... We'll see...

Cheers,
jb


No matter what you are going to need the input and interstage transformer. The output transformer is up to you...

If your going to be doing 2, I would recommend a version with the edcors...because since this is kind of a "colored" piece anyway (no one pulls out a vari-mu when your looking for transparent right?) the Steel core edcors add that "transformer" color we all know and love...also if doing edcors I would order a 4:1 for the interstage, sounds better...


Cinemags are nickle core, and much cleaner...and nice...

Yea, go for it! I know in the original PRR, people were using basically crap transformers and still getting good results.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on January 26, 2012, 09:06:05 AM
Heya, Yes I'm definitively plan on doing a rev 2. I might have a few Rev 1 boards left...let me check, as I probably won't get ot rev 2 for a bit...
cool, let me know if you find anything stashed away.  Would be interested in the PSU pcb eventually as well, but I'll confirm that when they're around, maybe I can P2P it.

thanks for looking into it.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: MrZpliff on January 27, 2012, 08:47:47 AM
Hi 230V-Guys,

order is placed @mueller.
Delivering time will be approximately 4 weeks from now.
I'll let know know.

ROCK-ON!

Sounds great ! Please let me know where/when to pay.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on January 28, 2012, 01:02:29 AM
Hi Gents,
Was thinking, Instead of a whole power supply of board, probably would be just as good to put the rectifiers and caps off the board. and then feed the smoothed AC to the board, caps and regulators. I'm going to wire it up when I got a minute and post my results.

Also, I am surprised at my stupidity sometimes...I am now learning that I have been wiring up pin 1 wrong all this time. I'm glad that I now am learning more on the subject but so stupid for how many problems its caused! I haven't tried wiring up the PRR-176 correctly....could've been the cause of some of the hum, we'll see.

Pin 1 goes to chassis! Connect audio ground at one point to the chassis! Connect earth to chassis!

Duh! :o :o

So don't necessarily feel obligated to follow the input and output molex's (1,2,3).

Please someone correct me if I'm wrong, but I would:

1) Solder all pin "1"s on the I/O XLRs to Chassis connection, on the XLRs, ensuring each one has a solid connection.

2) Wire input "L" as stated on molex, 1 => pin 1, 2=>pin 2 etc

3) for all other connections, leave "1" on the molex disconnected.

Sometimes the most simple stuff can ironically be the most confusing!

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: tmuikku on January 28, 2012, 03:23:42 AM
As in general an IO cable shield carries poop from the outside world so you should dump it to ground (earth) as soon as it hits to the equipment. No reason to bring it to the PCB to mess with audio circuit ground potential. So, daisy chain pin1 from the IO connectors and dump the poop to the mains ground / stargroundpoint of your chassis  ;)

Experiment of course, you could leave the pin1 unconnected if the equipment at the other end of the cable does the dumping (console). Have earthlift switch at the back panel that disconnects IO connectors' pin1 from the chassis to break a huge ground loop if necessary (no plan for your studio grounding?). Never lift the mains power safety ground!!!!

Disclaimer: In this post I was too clever so it propably contains errors :D

I bet Kingston will give a tip or two about how to arrange grounding on this project at some point, he has got the "black as black mans cape" thing going on recarging to noise :D
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on January 28, 2012, 12:48:38 PM
Yes that makes sense. Live and learn! Now to go rewire some equipment :o
Thanks! :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on February 03, 2012, 08:40:03 AM
Hi all,

i'm still at the planning stage.
Currently i'm thinking about a switching HPF.
Looking at the schematic i think it could work like this, could it?
Bridging C1 and C35 and adding a switch with new Cx.

Would it better to put the capacitor before or after the switch?

ROCK-ON.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Script on February 03, 2012, 09:17:41 AM
Why bridge? Replace. Capacitors in parallel add up.

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: coriolis on February 07, 2012, 05:04:05 PM
Sorry for being dim, but the Gyraf G9 transformer trick as regards to these transformers mentioned by Kingston:
Quote
Mini Open Toroid 7.0va 12v+12v £8.77 + Toroidal Transformer 50va 0-25v 0-25v £7.79
Am I right that the mini toroid is hooked up like this:
Mains >> 12V sec >> 12V sec >> 100 V out? I'm waaay confused here!

C
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on February 07, 2012, 05:46:56 PM
That's exactly how you do it.

to be more exact:

Mains >> 25VAC sec (the winding from the big trafo that also creates the negative rail) >> 12-15VAC sec (both windings of the small trafo in series) >> 100-150 VAC out

That's what I did, but something like 18VAC (big trafo) to 12-15VAC (small trafo) windings would also work.

Also note that this trick is not a good idea for tube projects where there are big currents on the high voltage rail. For these very small currents like 10-20mA it's still safe.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: soundsactive on February 07, 2012, 07:36:00 PM
won't lie, I'm already patiently waiting for the rev 2 boards! depending on when these happen, it might cut ahead of my p2p la2a!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: coriolis on February 08, 2012, 04:24:48 PM
@Kingston:
Thanks for trying to explain it, but I'm still struggling with the concept here.
A transformer has a voltage conversion ratio, right? I mean, divide the input on the primary with the output of the secondary, and you get the number by which you must multiply the sec to get the primary voltage!

So, when I look at the mini toroid you linked to, I get a ratio of around 1:19 if I calculate it like above. If I want 100V from the "secondary", I need to put around 5V on the "primary", right?

This is my (probably flawed) thinking, so you see why I am confused! And why the secondaries in series? What does that do?
I understand if this is too much to get into, but I am having a tough time deciding on the right transformers because of it.

C
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on February 14, 2012, 09:49:11 AM
@coriolis

Don't convert to ratios, just compute using the voltages themselves.

With the secondaries (which become primaries) of the second transformer  in series, you now have a 30VAC->220VAC transformer.

If you feed it with 24VAC from the first trafo, you will get less than 220VAC on the other side.  Like when mains voltage sags.  With those numbers you will get something like this:  [(24/30) * 220] =  176VAC.  If you want 150VAC you could use a 2x18VAC transformer for the second one, in which case you'd get [(24/36)*220]=  146 ... hmmm, maybe a little low.
 
btw, I'm shooting from the hip here, as I haven't started mine yet.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: coriolis on February 15, 2012, 04:02:08 PM
Hmm - I actually went ahead and ordered those transformers Kingston mentioned, but with 18VAC on the primary of the first transformer. Dual secondaries on the second transformer are 12VAC. Following your math: (18/24)*220 = 165VAC. Sounds like a lot to rectify and regulate down to 100VDC, doesn't it?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on February 16, 2012, 04:58:01 AM
Hmm - I actually went ahead and ordered those transformers Kingston mentioned, but with 18VAC on the primary of the first transformer. Dual secondaries on the second transformer are 12VAC. Following your math: (18/24)*220 = 165VAC. Sounds like a lot to rectify and regulate down to 100VDC, doesn't it?

Not really. 165VAC realistically only gives about 180VDC. Dropping 80V is no big deal and you'll have an opportunity for much better passive filtering.

Better have a bit too much than too little, is why I suggested those transformers. The tubes eat only some 14mA of that B+ line. Dropping a lot is not a problem even with standard 0.6W resistors.

[edit]

just got through experimenting with tantalum caps on the timing network. Like on the SSL bus comps they work excellent here as well. Compared to PIO they are "rounder" and the attack transient is less sharp. PIO is obviously more transparent, but when they are listened side by side PIO also comes off as boring.

First I was somewhat confused about the way abe had done the stereo link here. Then when I got how it works I didn't entirely agree with it, with strange choice of connecting some resistors on PCB, some directly on the pots, and different for each channel.

What I did was build two perfectly equal channels, and tied the CV's of both networks together. The switch is much simpler (SPST) with less wiring. Time constant shifts a bit since the two network caps are now in parallel, but it actually "relaxes" the stereo tracking, making things sound better.

I would suggest this simplification for V2 boards.

Which brings me to another tweak: using 1uF for the time constant might make a single channel a bit "nervous", with abrupt limiting and the two channels are more difficult to match this way. Use a 2-3uF cap and things will be much smoother.

I certainly don't recommend using a 0.47uF for the network (as has been suggested by some). It only turns into a bad sounding distortion this way. If you want butter smooth vari-mu action, go the other way.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on February 17, 2012, 09:28:24 PM
good stuff kingston. thanks.  I hope to have mine done next month some time. we'll see how soon the extra parts arrive and if they make it through customs unscathed.

Keeping with PRR's idea for his original varimu, I'd like to not have to purchase a lot of new parts for this.  Ordering pots for it now and a few other little bits.

I plan on using some beautiful vintage VUs I got from a member here and am hoping they'll work...  will I be able to make this thing read "0 VU" while not compressing?


In my prototype I used a VU meter. Works fine. If you really wanted to get technical though there is a way to adjust the trimmers, and resistors around the meter circuit... But the VU will work, and will be fine. It will just be a bit more sensitive and slow.
Abe can you elaborate on these changes? Did yours act "sensitive and slow" before/after changes or both? Hoping I won't regret my decision...

question on input section and trafos.. I don't have or plan on getting any INA chips, and when I read about the DOA input, I thought that sounds easy enough, so I might do the same, setting it up like figure 4 from the attached API 2520 paper.  I think this can be done simply by moving one side of R28 from ground to the - input. and obviously R25 to + input.  R23 and C37 I'll make 10K (for unity gain, higher for more gain) and 100pF respectively.    I'll actually probably make R23 a trimmer so I can adjust gain to where it works/sounds best.  but I don't have my PCB yet, so won't know for sure for a little while.

If the above works, then I should be able to use a 600:600 input trafo? (bifilar nickel output trafo, or steel API wired 2:2) that's another reason for the desire for an opamp input).   The interstage I may have to purchase, but I'll first see if an API 2503 wired 3:1 doesn't work. Impedance is pretty low (900:300) but I may have one in nickel, that should give me a bit more inductance and might work better. Or not, guess we'll see.

that's as far as I am right now in planning. 

appreciate any comments. thanks!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on February 18, 2012, 04:16:03 AM
That API 2503 won't work as an interstage at all. The tube plates need to see 10k (or even more) load.

I don't quite get how you are about to wire the input.

The DOA input skipping the INA, this is how I wired it. No need to cut traces. Balanced high impedance input +70dB CMR. Wire a 100k log pot between this and the input trafo to the tubes.

This is from GSSL, with some reductions. Input caps are optional also.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on February 18, 2012, 06:20:38 AM
haha, I attached the wrong file!   I changed it..  the 100K log is wired like a volume/output pot?  2520 to top, wiper to trafo?  Is that what your switch is doing?

thanks for the trafo tip, it was a long shot.  Time to go shopping or winding.

a nice weekednd and happy carnaval to all!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on February 18, 2012, 09:07:38 AM
the 100K log is wired like a volume/output pot?  2520 to top, wiper to trafo?  Is that what your switch is doing?

yes, exactly. Could probably use a 10k log as well, a DOA will easily drive it. mine's 100k log (rotary switch). You're not going to need 20dB gain on the DOA input stage by the way. I suggest setting it to unity gain. The vari-mu stage doesn't like to be overdriven at all - it's a fartland - you only need attenuation here. Set the compression threshold/operation point with the sidechain trimmer and you only need to do it once.

All make up gain that one will ever need will come from the output stage.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on February 18, 2012, 06:45:40 PM
Cool, thanks for the tip, I was wondering how to get a "modern" attenuator on the front of this thing. The PM660 I have half-built here has a 600 Ohm Tpad on the front which seems to work nicely, but I wasn't too sure of that here.  BTW, I planned to use the 2520 in unity gain by lowering the feedback R and maybe upping the feedback cap.

I haven't looked much at the rest of the circuit, I'm deciding stuff in blocks. I'm very glad it's customizable.  Makes it easy to use what's at hand or "upgrade" if one wishes.

btw, besides using higher (or same) power rails all around, what benefit have you seen with the higher performance side chain amps?  Is it a subtle listening difference here? Would a DOA be more effective here, or maybe even an opamp with discrete output transistors?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on February 18, 2012, 08:14:37 PM
Of course you can use a 600-ohm t-pad in front of the input transformer. Abe provided a specific option for it. Then you can skip all the active stuff on the input. It's technically the most light weight option, and also the cleanest, but you lose high impedance input. No big deal. The only reason I personally did the DOA input was for more color.

As for sidechain, the modern opamps I'm using makes compression attack transients "tighter", and overall sound more transparent and controlled. It's hard to explain, but it's a similar thing that happens to GSSL when using high performance opamps in the rectifier and VCA drivers.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on February 18, 2012, 08:57:39 PM
Of course you can use a 600-ohm t-pad in front of the input transformer. Abe provided a specific option for it.
  :-[  guess I should be more attentive. I'm not looking for more or less color, I was looking for a higher impedance, more universal input option, hence the electronic input, and DOA, well, because we can!  8)

Quote
As for sidechain, the modern opamps I'm using makes compression attack transients "tighter", and overall sound more transparent and controlled. It's hard to explain, but it's a similar thing that happens to GSSL when using high performance opamps in the rectifier and VCA drivers.
I haven't done any opamp swapping in the GSSL, just stuck some OPAs in the I/O of one, but built a couple of SB4000's with 5534, but never directly compared, and haven't touched the other opamps, but I do remember you talking about that some time. I think I "see" how that would work, I'll get the thing going and then experiment. thanks!
 
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: king-rb on February 19, 2012, 09:53:30 AM
is there one of this stereo pcbs left or when are the rev2 finished?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: JayDubrek on February 20, 2012, 08:06:34 PM
Any word on the 230v trafos yet DrJ? Looking forward to finishing this fella!
Cheers
Jay
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: myker on February 21, 2012, 03:57:10 PM
Hey guys, anyone want to share a Copy/Paste Mouser BOM or share what pot's and other components they are using?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on February 21, 2012, 04:18:44 PM
Hey guys, anyone want to share a Copy/Paste Mouser BOM or share what pot's and other components they are using?

I'm not sure about the audio trafos yet (I know I'll be using API type outputs, just not sure about the input+inter). The rest I've got lying around (2520 DOAs, russian tubes, antek toroid power trafos) and I just ordered pots (along with a few other ones) from small bear for 95 cents each.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: myker on February 21, 2012, 04:46:44 PM
So every day carbon pots are ok?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on February 21, 2012, 06:55:58 PM
Well, I don't see why not, but I'm not 100% sure.  If not, it's a cheap (and reusable) mistake!  I'm trying to keep this as low cost as possible for now, and later buy some decent transformers. But the pots, unless they don't work, are not getting changed.  :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on February 21, 2012, 07:24:21 PM
Heyo,
Carbon pots are fine, especially for attack and release. For input/output they pass audio so you probably want conductive plastic, especially since they aren't that much more expensive and are better for sound.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on February 22, 2012, 04:14:25 PM
well, I'm cheaping out on pots.  ;D Speaking of cheap, those Edcors are like $10, wow.

I don't want to wait for them to ship so I think I'll wind my own.  I don't have anything here anywhere near 10K:10K or 10K:600 but I have some steel lams here and I'm thinking of winding my own just cuz it'll be faster, not that I have my boards yet! :)

Abe, I just read you used yamaha 1:1 outputs as interstage...and they work OK? I have some (PM2K I think...) they are quite large though, and for sure nickel looking lams.  definitely not a board mounting option. I also have some PM2K inputs I could try backwards, they are 1:3 IIRC.. hmm, maybe I'll only need to wind the inputs after all. nice!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on February 22, 2012, 08:49:01 PM
In my prototype I used a VU meter. Works fine. If you really wanted to get technical though there is a way to adjust the trimmers, and resistors around the meter circuit... But the VU will work, and will be fine. It will just be a bit more sensitive and slow.
Abe can you elaborate on these changes? Did yours act "sensitive and slow" before/after changes or both? Hoping I won't regret my decision...


Hi, you can pretty easily just pt a VU in there, no problem. The meter circuit is pretty forgiving and you just adjust vr5 and vr2 to zero out your meter.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on February 23, 2012, 05:50:04 PM
Hey Kingston,

which caps do you recommend to change to Tantalums? C9, C10, C11, C12 and C2 increasing to 2-3uF?

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on February 23, 2012, 05:54:41 PM
Hi 230V guys,

the power transformers have been arrived  ;D

Now i'll check postage and let you - as soon as possible-  know about the price and PayPal.

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: baadc0de on February 24, 2012, 04:57:17 AM
Sounds great, keep us posted!

Hi 230V guys,

the power transformers have been arrived  ;D

Now i'll check postage and let you as soon as possible now about the price and PayPal.

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on February 24, 2012, 11:30:11 AM
Hi guys,
Some updates on my end, I took the rectifiers off board with some perfboard and it helped get the hum down to around -100db (it was at -86ish). The HV (100v) helped the most. I just wired up some rectifiers and some smoothing caps (100uf for HV and 1000uf for +/-15) and then ran that into the main power board. I just left the original rectifying diodes in there, the respective +/- finds its way to were it is supposed to go just nicely, but If you don't want the extra voltage drop you can bypass the diodes (use a DMM to find out which ones)

All in all pretty easy to do, and if hum is something that really bugs you, its worth it.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on February 24, 2012, 02:14:38 PM
Hey Kingston,

which caps do you recommend to change to Tantalums? C9, C10, C11, C12 and C2 increasing to 2-3uF?

ROCK-ON!
I'm guessing it's C1 and C2, the timing caps.  Maybe the HPF caps as well, not sure about that.

C9-C12 are PSU filtering, keep those as electrolytic and film bypass.

Thanks for the update Abe!  Easy enough to do this on perfboard, and -100dB is good enough for me!
Did you do a whole CRC offboard or just one cap per rail then connect to the onboard PSU?

I'm going to try to wind some input trafos tomorrow, won't know how good/bad they are until I build this thing, but I'll do my best!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on February 24, 2012, 09:43:22 PM
Hi guys,
Some updates on my end, I took the rectifiers off board with some perfboard and it helped get the hum down to around -100db (it was at -86ish). The HV (100v) helped the most. I just wired up some rectifiers and some smoothing caps (100uf for HV and 1000uf for +/-15) and then ran that into the main power board. I just left the original rectifying diodes in there, the respective +/- finds its way to were it is supposed to go just nicely, but If you don't want the extra voltage drop you can bypass the diodes (use a DMM to find out which ones)

All in all pretty easy to do, and if hum is something that really bugs you, its worth it.

Great tweak! Where do you have the common star ground attached with this set up?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on February 24, 2012, 11:35:40 PM

Great tweak! Where do you have the common star ground attached with this set up?

Thanks Kingston, I got the idea from what you were talking about earlier with this project and another tube project thread. As far as the star ground, I left the board intact (didn't cut any traces). I didn't connect any grounds together on the extra rectifier board either. On the +/-15v side I ran the transformer centertap to the smoothing caps on the extra rectifier board and then that to the center tap transformer input  on the PCB(along with all the other voltage wires  15+ and 15-, 100v and its 0v).

Then as far as grounding the I/O jacks, I made sure that all the I/O pin 1/sleeve was connected directly to the chassis and then connected the chassis to the PCB ground at one point. (i believe I used the L input XLR pin one for this) Then I connected the safety ground to the chassis right by the IEC.

And maybe -100 was and over statement, probably -96ish with everything cranked, but still much better than before (and I tried everything before, cutting traces, routing grounds - the works!! my other PCB is all hacked up haha) Figured that hum has to come from the AC being on the board, so once the AC was off the board noise was much better.

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on February 25, 2012, 12:22:57 AM
I'm glad to hear about your success with this Abe, I had planned to move the power section completely off-board but haven't had the time to get around to it yet. I have hum on the first channel, not so much (audible) on the second. The first channel's proximity to the power section seemed to be the obvious answer to the problem. I moved the input transformer off board with minimal results. I was thinking the heater circuit might be one of the main culprits, along with the high voltage, but if you had good results with just moving the AC and 100V sections I might just try that first. Then I might try putting the input tranny back on the board, just to make things prettier.

Regarding the timing caps - I believe they are already spec'ed to be tantalum. What I did, as I mentioned earlier in this thread, was to put a four way switch as a "response" control. The top position gives me GR bypass/ line amp mode, the next three change the timing cap: tantalum- Solen fast cap- PIO. The different caps make a noticable and very usable difference in the way the unit reacts and "pronounces" different parts of the frequency spectrum. I guess some people might call the difference subtle, but it's a very worthwhile mod in my opinion.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on February 25, 2012, 01:38:22 PM
Hi Abe,

are you sure that the hum reduction is due to taking the rectifier diodes off the board
or is it a result of doubling rectifying with additional smoothing?
Just thinking about that... :-\

Btw. you wrote that VU meter will work fine too, so I'll order some Hairball VUs and take you by word  ;D

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on February 25, 2012, 05:36:47 PM
Hi Abe,

are you sure that the hum reduction is due to taking the rectifier diodes off the board
or is it a result of doubling rectifying with additional smoothing?
Just thinking about that... :-\


Well its no doubt a little bit of both, having more smoothing caps doesn't hurt, but I think here in this situation moving the AC (converting it to DC) off the board really helps. I tried to increase smoothing caps with rectification happening on board and I couldn't tell that it helped at all. You could probably replace the +/-15 rail on board smoothing caps with a smaller value 100uf? And still get great results. For the HV rail though I think having the extra smoothing cap does help quite a bit.
Quote
Btw. you wrote that VU meter will work fine too, so I'll order some Hairball VUs and take you by word  ;D

ROCK-ON!

If your going to get a meter from harball why not get the 1ma one? It will work better :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on February 26, 2012, 04:10:19 PM
Hi Abe,

If your going to get a meter from harball why not get the 1ma one? It will work better :)

The VUs are bigger...  ;D ;D
But i'm fighting currently with the front-panel package... the VUs are to big.... ;D ;D

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on February 26, 2012, 05:25:13 PM
Hi aBe,  can you tell me the PCB dimensions please? thanks!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on February 27, 2012, 09:21:27 AM
Hi aBe,  can you tell me the PCB dimensions please? thanks!

Hello,
Approx:
173mm x 290mm
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on February 27, 2012, 11:18:01 AM
Thanks! planning the fit..   Haven't been this excited about a project since the PM660..  (I'm confident this one will get finished quicker though!)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: MrZpliff on March 02, 2012, 02:33:27 AM
Hi 230V guys,

the power transformers have been arrived  ;D

Now i'll check postage and let you - as soon as possible-  know about the price and PayPal.

ROCK-ON!

Great  :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: roy on March 07, 2012, 05:21:41 AM
Hi 230V guys,

the power transformers have been arrived  ;D

Now i'll check postage and let you - as soon as possible-  know about the price and PayPal.

ROCK-ON!

Am I too late to put my name down for one of these?

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: JayDubrek on March 07, 2012, 09:48:10 AM
Hi 230V guys,

the power transformers have been arrived  ;D

Now i'll check postage and let you - as soon as possible-  know about the price and PayPal.

ROCK-ON!

Any news?
Ta! Jay
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on March 07, 2012, 03:18:36 PM
Hi roy,

PM me your PayPal address and I'll see what we can do...  ;)

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on March 07, 2012, 03:24:56 PM
Hi Jay,

transformers are ready for the post.
I'll do PayPal to you tonight!

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on March 07, 2012, 04:45:37 PM
Hi 230V guys,

the power transformers have been arrived  ;D

Now i'll check postage and let you - as soon as possible-  know about the price and PayPal.

ROCK-ON!

Any news?
Ta! Jay

+2 :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on March 07, 2012, 08:15:03 PM
Some Inspiration :)

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on March 07, 2012, 10:39:31 PM
nice! I see those yamahas you mentioned earlier! Is that a custom toroid?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on March 07, 2012, 11:32:52 PM
nice! I see those yamahas you mentioned earlier! Is that a custom toroid?

Thanks! The torriod is just a normal dual primary dual secondary 15V. But I live were power is 120v so I take a feed off the primary to power the HV rail.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: volker on March 08, 2012, 05:33:09 AM
nice! I see those yamahas you mentioned earlier! Is that a custom toroid?

Thanks! The torriod is just a normal dual primary dual secondary 15V. But I live were power is 120v so I take a feed off the primary to power the HV rail.

Not sure I understand you right, but are you saying you power the HV directly from the wall without any transformer in between? :o

If so, that is not only illegal but also really dangerous. If I understood you wrong just ignore, I just wanted to be sure.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on March 08, 2012, 12:24:58 PM
nice! I see those yamahas you mentioned earlier! Is that a custom toroid?

Thanks! The torriod is just a normal dual primary dual secondary 15V. But I live were power is 120v so I take a feed off the primary to power the HV rail.

Not sure I understand you right, but are you saying you power the HV directly from the wall without any transformer in between? :o

If so, that is not only illegal but also really dangerous. If I understood you wrong just ignore, I just wanted to be sure.

Thanks for catching that, don't want to give people the wrong impression, I could've explained better. We DON'T want anyone thinking that they can connect the HV directly to Wall power. I have one side of the primary connected to 120v and then with the second side of the primary connected to HV so there is galvanic isolation.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on March 08, 2012, 01:23:13 PM
Never thought to do that, I assume this halves the safe current capacity of the torroid (half the mains-connected copper)? 
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on March 08, 2012, 07:15:03 PM
Never thought to do that, I assume this halves the safe current capacity of the torroid (half the mains-connected copper)?

Yep! Exactly. But running the tubes in series also halves their current consumption. So It works out.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on March 08, 2012, 10:03:07 PM
seems you thought of everything for me! This project just keeps getting better! :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Hank Dussen on March 19, 2012, 04:36:31 AM
Custom toroidal has just arrived here!  :)
But it seems it's too hight to fit in a 1U case  :-\
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on March 19, 2012, 07:09:28 PM
Hi Hank,

well #1 i've posted the height.
#2 i'm sorry, i didn't know either that the cables are on top. >:(
#3 i tested a 1HU and had came to the conclusion that it may would be possible to fit it
in 1HU, maybe some add on handcraft is needed.. :o or/and maybe a buckle is on the top  ;D

But i'll think they look very good, especially with that additional shield (-wire)!

If you would like to fit it in 1HU and you'll managed it, let us know! (pix)

ROCK-ON!

P.S.: I'll post some pictures soon!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: brianvino on March 20, 2012, 05:24:03 AM
only two questions :
1) do we have a schematic file better defined (to make a readable print)

2)are all audio transf optional ?

thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on March 20, 2012, 05:27:55 AM
Hi Hank,

well #1 i've posted the height.
#2 i'm sorry, i didn't know either that the cables are on top. >:(
#3 i tested a 1HU and had came to the conclusion that it may would be possible to fit it
in 1HU, maybe some add on handcraft is needed.. :o or/and maybe a buckle is on the top  ;D

But i'll think they look very good, especially with that additional shield (-wire)!

If you would like to fit it in 1HU and you'll managed it, let us know! (pix)

ROCK-ON!

P.S.: I'll post some pictures soon!

I got it :) Awesome!
Thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on March 20, 2012, 11:34:44 AM
only two questions :
1) do we have a schematic file better defined (to make a readable print)

2)are all audio transf optional ?

thanks

Hi,
1)Yea the schematic file is probably too big to print on one page, maybe on four?

2) You need the 2 interstage transformers around the tube GR stage, because that cancels the DC thump. Without them it would not work. But input/output transformers are optional.

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: brianvino on March 22, 2012, 01:47:28 PM
thank you Abe.
trasf on schema are T1, T2 and T3, T4
are T2, T4 interstage ?
because on BOM are named "Cinemag, Jensen output"
about graphic resolution schema, i don't be able to make four page; anyone know how do it ?
thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on March 22, 2012, 08:25:09 PM
thank you Abe.
trasf on schema are T1, T2 and T3, T4
are T2, T4 interstage ?
because on BOM are named "Cinemag, Jensen output"
about graphic resolution schema, i don't be able to make four page; anyone know how do it ?
thanks

Hi,
Sorry i meant 2 transformers per channel, so you need all 4 transformers. also i wish the resolution of the schem was better but thats the best my program outputs.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: brianvino on April 04, 2012, 12:23:16 PM
for better understanding.
could anyone check it ?
thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on April 04, 2012, 01:23:05 PM
for better understanding.
could anyone check it ?
thanks

Looks good to me, giving it a quick once over.  :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: earl on April 06, 2012, 10:05:34 PM
Hey Abe are round 2 boards on their way? I'm ready for another whack at this. ;D
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: sedit1 on April 08, 2012, 01:18:38 AM
Hey Abe are round 2 boards on their way? I'm ready for another whack at this. ;D
+1  ;D
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on April 09, 2012, 11:43:27 AM
Hey Abe,
I just got some questions  :D
- Can I use 10uF 100V instead of all 10uF 25V?
- what is the values : R36- R168- R169- R112 [ I use edcors tranx for in and out with 990C or 2520]
- Center-Tap or Reisitors? what does mean? :)
- and last one is about 4m7 resistor! %1 and 1/4w is ok?

Thanks
best regards
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on April 10, 2012, 03:07:23 PM
Some Inspiration :)

Did you use the 8027-WF-1mA meters from hairball?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on April 11, 2012, 10:36:59 AM
Hey Abe,
I just got some questions  :D
- Can I use 10uF 100V instead of all 10uF 25V?
- what is the values : R36- R168- R169- R112 [ I use edcors tranx for in and out with 990C or 2520]
- Center-Tap or Reisitors? what does mean? :)
- and last one is about 4m7 resistor! %1 and 1/4w is ok?

Thanks
best regards

Hi,
1) 100v will be fine, you can most always go up in voltage value with capacitors, you never want to go down
2)Those "opt" (optional) resistors depends of what transformers you use and more importantly what ratio they are. You can pull up an original PRR schematic and see that he uses 1K on the primary side of the interstage. And then 100k on the secondary. Really it depends. I think with the edcore 4:1 I didn't use any, but with a 1:1 it was necessary. Load it down too much and S/N is compromised and also bass response, don't load it enough and it distorts. Just do what sounds good.
3)Center-tap is if you have a transformer that has a center tap and you want to drive the transformer directly without the use of the 3k3 resistors. resistors is driving the transformer with the resistors. One or the other must be selected for the compression to work.
4) I'm not sure I know what 4M7 resistor you are talking about...you mean 4k7?


@ Minor Glitch: Yep thats the one!

Best,
Abe
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: tmuikku on April 11, 2012, 11:00:20 AM
100v caps must be physically larger than the 25v one with same capacitance. Confirm they fit on the PCB before ordering.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on April 11, 2012, 01:00:11 PM
Hi,
1) 100v will be fine, you can most always go up in voltage value with capacitors, you never want to go down
2)Those "opt" (optional) resistors depends of what transformers you use and more importantly what ratio they are. You can pull up an original PRR schematic and see that he uses 1K on the primary side of the interstage. And then 100k on the secondary. Really it depends. I think with the edcore 4:1 I didn't use any, but with a 1:1 it was necessary. Load it down too much and S/N is compromised and also bass response, don't load it enough and it distorts. Just do what sounds good.
3)Center-tap is if you have a transformer that has a center tap and you want to drive the transformer directly without the use of the 3k3 resistors. resistors is driving the transformer with the resistors. One or the other must be selected for the compression to work.
4) I'm not sure I know what 4M7 resistor you are talking about...you mean 4k7?

Abe

Hey Abe,
Thanks for the details! Awesome!
I meant this resistor...
(http://i1236.photobucket.com/albums/ff442/jandoste/indexswtch.jpg)
Best regards
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on April 11, 2012, 01:01:59 PM
hahahaha that's a giant russian pio capacitor I was experimenting with. that would be for c2 and whatever the other tant cap is.  you definitely don't need to wire up that crazy contraption in my photo.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: 0dbfs on April 11, 2012, 01:35:11 PM
But it looks cool! Can we wire it up based mostly on cool-factor? Russian PIO's pretty much always add the ghost-of-mojo. So, liberally peppering the innards with these buttery-morsel-nuggets is quite. Beneficial..

Just out of curiosity, what were you testing and what did you find?

Thanks!

Cheers,
jb
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: minor_glitch on April 11, 2012, 01:45:13 PM
Haven't tested yet, but it's to compare the pio and tant caps (c2 and c....38? the one between the attack/release pots.) to see which sound better.  Once I decide I'll get rid of that contraption and go with whichever I like best.  Totally unnecessary and I suspect tant will win, but hey, why not!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on April 11, 2012, 02:28:36 PM
Just out of curiosity, what were you testing and what did you find?

I did this already. And now I've a tant/PIO time constant cap switch on the front panel. Tantalums have a sloppier "fatter sounding" attack, and PIO's sound a bit boring and controlled ie. transparent. But wait, there's more! If you want even more of that sloppy fat attack, use a 1uF electrolytic. Also, PIO are very similar to film caps in time constant networks, but the difference between a tantalum and PIO is not big. I would therefore recommend either a film cap or an electrolytic. It's much easier to hear the difference, and choose what best fits your music.

Also, a 2uF time constant cap might sound better to some of you. I liked it more than 1uF on mine, slower, but better "contour" time constant.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on April 12, 2012, 11:42:24 AM
SorryI need some advice
I only have 2 DOA (Whistle rock audio) ML918.
In your opinion, is best used for input or output?
Someone has compared DOA vs IC in this machine?
Thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: living sounds on April 13, 2012, 06:21:12 AM

I did this already. And now I've a tant/PIO time constant cap switch on the front panel. Tantalums have a sloppier "fatter sounding" attack, and PIO's sound a bit boring and controlled ie. transparent. But wait, there's more! If you want even more of that sloppy fat attack, use a 1uF electrolytic. Also, PIO are very similar to film caps in time constant networks, but the difference between a tantalum and PIO is not big. I would therefore recommend either a film cap or an electrolytic. It's much easier to hear the difference, and choose what best fits your music.

Also, a 2uF time constant cap might sound better to some of you. I liked it more than 1uF on mine, slower, but better "contour" time constant.

Interesting! Have you tried bypassing the tant/electrolytic with a small high quality film/PIO cap? Does it make a difference for this application?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on April 13, 2012, 06:56:51 AM
Interesting! Have you tried bypassing the tant/electrolytic with a small high quality film/PIO cap? Does it make a difference for this application?

why would I do that? I already have a plain PIO time constant which is the most transparent one. There's barely any difference between that and the tantalum.

What I was really trying to say that if you're going to do a switch, use a PIO/film (awfully similar) and an electrolytic if you actually want to change the response in a meaningful way. Skip the tantalum.

Or if you have no switch, use the tantalum since it's the midway solution.

And don't forget to try 2uF time contant. I think many would prefer it especially for bus/general duties.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on April 14, 2012, 02:24:31 PM
Interesting info Kingston 8)

I want to try the 2uf!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on April 14, 2012, 02:29:38 PM
SorryI need some advice
I only have 2 DOA (Whistle rock audio) ML918.
In your opinion, is best used for input or output?
Someone has compared DOA vs IC in this machine?
Thanks

I actually have the same question, as I'm knee deep in my console innards and rechipping it with some discrete opamps. But I don't know if  for some reason they sound better on the input or output....

Common sense might sway that whatever stage has more "makeup" then the discrete should go there, as you will get more "flavor" but who knows, unless you actually try it. My common sense is sometimes backwards.

BUT....in this particular application, I have my discrete opamps on the output. It does have a nice amount of gain while the input stage actually has negative gain. (pad)

For me, the discrete on the output added a bit more weight and seemed to smooth things in a pleasing way. Want to try it on the input though.

Anyone else chime in?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on April 15, 2012, 03:15:33 PM
Sorry

16 x 100n polyester..... how many volts?

Thanks....
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: brianvino on April 16, 2012, 07:13:48 AM
100 V
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on April 16, 2012, 07:39:56 AM
Thanks Brianvino!
I can not find 400uf NP ...
Can i use 470uF polarized (+ to IC)?
If I use the T-PAD can omit all the components before the input transformer?
thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on April 16, 2012, 08:33:27 AM
Thanks Brianvino!
I can not find 400uf NP ...
Can i use 470uF polarized (+ to IC)?
If I use the T-PAD can omit all the components before the input transformer?
thanks

Yes and yes.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on April 18, 2012, 08:04:46 AM
sorry for the stupid question
I want to use Lundahl 1540 as  interstage transformer.
I can mount it reversed for a better pinout  match?
Thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: roy on April 18, 2012, 09:42:11 PM
Hey Abe are round 2 boards on their way? I'm ready for another whack at this. ;D
+1  ;D

+1 ;D !
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on April 18, 2012, 11:28:00 PM
Hey Abe are round 2 boards on their way? I'm ready for another whack at this. ;D
+1  ;D

+1 ;D !

Thanks for the patience guys :) rev 2 should be good!

@ilfungo check the datasheets, I'm pretty sure you can just flip them around.

Cheers,
Abe
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on April 19, 2012, 02:06:06 PM
Thanks abechap024!!!
sorry
what changes do I need to use a standard VU Meter?
thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on April 20, 2012, 01:02:36 AM
Thanks abechap024!!!
sorry
what changes do I need to use a standard VU Meter?
thanks

it will work just fine. You might want to put a resistor (1k - 10kish?) in series with it if it is too sensitive, but there is the 1k meter trim so you could zero it out easy enough.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Jeremy.Starseed on April 23, 2012, 08:16:43 PM
Any of those 230V trafo's available?

I am using a 2U rack, so have room for one of those that didn't fit the smaller case.

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on April 25, 2012, 05:01:12 PM
Hey Abe,
I almost finished my build  but I have any idea :o that how can I connect the  bypass switches? ::) ::)
Thanks

PS: Frank has done a wonderful FP! :) Thanks Frank!
 :)
(http://i1236.photobucket.com/albums/ff442/jandoste/5b5336bb.jpg)
(http://i1236.photobucket.com/albums/ff442/jandoste/b93292ea.jpg)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on April 25, 2012, 06:02:55 PM
Yo,

great to see some pics (working pics :) )!!
Well, i see you have the same plan to move the trannies off the board, my plan is
put them all off the board...

Ohh, 990C OP Amps for in and out... would be great to hear the result...  ;D

Good soldering!!  ;D ;D
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on April 25, 2012, 06:06:06 PM
Hi all,

i have nearly populated my board, but the tantalum caps (timing) are still confusing me a bit...
To me it looks like this:
C2 (1uF) left channel and C40 (schematic) (1uF) right channel (both may changed to 2uF /2.7uF) and C40 isn't on the board, it's the one shown near the link switch in the wiring guide.
C1, C35 are HPF caps left channel and C38 and C36 are the corresponding ones on the right channel.
Am I right?

By the way, has somebody already tested different values for R36 (R112) and R168 (R169) on EDCOR 10k:10k? Any comments on that?

All IN_OPT_2(4), IN_OPT_3(5) have to bridged when using the "straight design", have they?

ROCK-ON!

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on April 25, 2012, 11:36:43 PM
Hey Abe,
I almost finished my build  but I have any idea :o that how can I connect the  bypass switches? ::) ::)
Thanks

PS: Frank has done a wonderful FP! :) Thanks Frank!
 :)


Looks Great!

for bypass, I just have a switch to connect and disconnect the side chain via one side of the side-chain capacitor.

Also, you probably are going to want to move your Rectifying diodes off board with some smoothing caps for a very hum free experience. I think without off board rectification hum was around -85db but once I took the rectifiers off board the hum dropped to like -95 or so. Well worth it.

I'll draw a pic so everyone knows what I mean...
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on April 26, 2012, 05:07:30 PM
Hi,

I just trapped in an other question/problem concerning the HPF option.
Well i have a problem to figure out how to put C1 (C38) and C35 (C36) in, as there are
so many holes in the pcb... and they seem to be all connected, except those marked with "1" ...!?  ???  ???

Any hint would be great...  :o

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on April 26, 2012, 06:33:09 PM
Hi all,

i have nearly populated my board, but the tantalum caps (timing) are still confusing me a bit...
To me it looks like this:
C2 (1uF) left channel and C40 (schematic) (1uF) right channel (both may changed to 2uF /2.7uF) and C40 isn't on the board, it's the one shown near the link switch in the wiring guide.
C1, C35 are HPF caps left channel and C38 and C36 are the corresponding ones on the right channel.
Am I right?

Sounds good, have you seen the picture of all the wiring on the 1st page?

Quote

By the way, has somebody already tested different values for R36 (R112) and R168 (R169) on EDCOR 10k:10k? Any comments on that?

A little bird told me that you *do* need the 1K resistor strapped to the primary of the interstage transformer (thanks!), no matter what the ratio, it helps the transformer behave. What you have strapped to the secondary (if anything) is up to you, (10k to 100k...ish? Really don't know but you'll test and hear what you like)

Quote
All IN_OPT_2(4), IN_OPT_3(5) have to bridged when using the "straight design", have they?


Yes sir!

Quote
ROCK-ON!

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on April 26, 2012, 07:35:47 PM
OFF BOARD RECTIFICATION www.acsoundstudio.com/prr_176/OFF_BOARD_POWER.png (http://www.acsoundstudio.com/prr_176/OFF_BOARD_POWER.png)  <solves all hum issues, no need to mount transformers off board>


I found mounting the rectifiers off the board really helps. Sorry for people that have already take their transformers and stuff off board but taking the rectifiers off really solves the issue and then no need to take the transformers off board.
How I did it is put the caps as in the above picture on the perfboard with the diodes (bridge rectifiers) and then wire from the perfboard into the main board. I opted to take out the diodes on the +/-18v side because the heaters tend to eat a lot of current and we need all the headroom we can get cause the voltage from the transformer will sag (because of the current draw from the heaters).

You can leave the diodes on the HV sid. Then those diodes direct the +/- were they need to go.

I also left the smoothing caps on the main board, you could probably get away with smaller cap values if you want.

Anyway good luck! be safe!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on April 26, 2012, 07:40:13 PM
Hi,

I just trapped in an other question/problem concerning the HPF option.
Well i have a problem to figure out how to put C1 (C38) and C35 (C36) in, as there are
some many holes in the pcb... and they seem to be all connected, except those marked with "1" ...!?  ???  ???

Any hint would be great...  :o

ROCK-ON!

I just did that so there will be a lot of different options with cap sizes. Just make sure one leg is in pin "1" and the other in one of the other holes, and you mentioned, they are all connected so it doens't matter which one :)

Best!

Abe
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: JayDubrek on April 27, 2012, 10:57:18 AM
Hi Abe- just like to clarify a few points on your diagram. Are just two of the 2A04's being jumpered or all of them? You say to stuff some of the 100v diodes so which ones need to be excluded from the board? Caps C2-4 in your diagram- which are they replacing on the board? Maybe for those following your diagram it may be worth listing which components to exclude from the PCB?
Sorry if this seems dumbass!!
Cheers
Jay
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on April 27, 2012, 12:14:06 PM
Hi Abe- just like to clarify a few points on your diagram. Are just two of the 2A04's being jumpered or all of them? You say to stuff some of the 100v diodes so which ones need to be excluded from the board? Caps C2-4 in your diagram- which are they replacing on the board? Maybe for those following your diagram it may be worth listing which components to exclude from the PCB?
Sorry if this seems dumbass!!
Cheers
Jay

Clarification is always good :)  You don't want to stuff any of the 2A04s. Then jumper just the ones shown, because basically you are bypassing the whole bridge rectifier, and taking the +/- voltage that you rectified/smoothed with the external board and feeding it directly in (via the jumpers) to the Lm337, and LM317.
Could you leave the 2A04 diodes in? Of course, but they are going to drop the voltage about 1.5V on your power rails, generally not to be desired, but wouldn't blow anything up.

Then for the "100v" diodes, I probably should have really said "the 1n4007 diodes that rectify the 100V voltage rail" you might as well leave those in, because 1.5v (or less because not that much current is being drawn) is not really a huge deal when your dealing with higher voltage. If you wanted to remove those you could, just make sure to jumper the correct ones, and note the polarity of of your wires and make sure you don't feed the +100v to ground. You can figure this out with a DMM set on measuring resistance and see what goes were, as double layer boards are harder to "see" where the traces lead.

Preferably if you don't know what caps the caps in my diagram are replacing, then you should leave all the caps as is on the board. In mine I've left them as is, and it helps with power regulation. BUT if someone was strapped for cash, or parts, or whatever you could get away with replacing the power smoothing caps (the 1000uf ones on the board) with something of significantly smaller value, as you already have the 1000uf smoothing caps on the off board rectifier board.

Hopefully I haven't confused anyone more by all this...really all we are doing is converting the AC voltages to smoothed DC off board, so the grounds on the PCB are essentially clean of all rectification *crud* (the 60hz and 120hz that we all love ;) ;D)

Granted this is basically like a simplified CrC board keith was doing with the GSSL to get hum even lower.

Its a handy trick that can be done to any PCB with on board power.
 one thing I've learned from this is separate power supply PCBs seem to always be preferable, unless someone is Really savy with Layout (and even then, especially with High current tubes, I imagine its hard to get totally hum free operation)

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: JayDubrek on April 27, 2012, 02:17:43 PM
Thanks Abe that's a big help!
Jay
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on April 28, 2012, 03:37:56 PM
Hi abe,

well that was exactly what i guessed at the first glance, but... what confuses me is that i can measure a link between hole "1" in the "1uF or HPF"box and all of the other holes (includes those in the "HPF ADD"box), except to hole "1" of the "HPF ADD"box ... ??? ??? ???
Maybe it due to the fact, that the board is already populated...??

Btw. I"ll leave the rectifiers diodes on board at the first step (i have a second set laying in the box) and will try some 0.1uF in parallel to the diodes to kill EMC... a common technique as far as i know...

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on April 28, 2012, 08:22:40 PM
.. what confuses me is that i can measure a link between hole "1" in the "1uF or HPF"box and all of the other holes (includes those in the "HPF ADD"box), except to hole "1" of the "HPF ADD"box ... ??? ??? ???

When the switch is connected for the side-chain hpf then it connects the pin 1's together.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on April 29, 2012, 11:29:32 AM
.. what confuses me is that i can measure a link between hole "1" in the "1uF or HPF"box and all of the other holes (includes those in the "HPF ADD"box), except to hole "1" of the "HPF ADD"box ... ??? ??? ???

When the switch is connected for the side-chain hpf then it connects the pin 1's together.

Hey Abe,
I am not sure if I am right or not can you please tell me[ us :] if it's not :)
thanks!

EDIT: the pictures were wrong!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Script on April 29, 2012, 03:24:33 PM
Caps in parallel add up: 1uF + 1uF = 2uF

You want the HPF to filter out the low end in the sidechain so that the comp reacts less to the low end, right?

If so, for the HPF to work in this filter configuration you want to decrease the value of one capacitor and switch in a second one so that the two together add up to 1uF or slightly higher.

I do have the "PRR176" boards, but haven't started populating them yet. However, the entire sidechain and TX configuration is more or less copied straight from the ingenious :) "PRR vari-mu" and decreasing the value of the corresponding capacitor there (i.e., C8 in the PRR vari-mu schematic) was the way to go for a functional HPF.

I think a tube-savvy DIY colleague on this board used "0.15uF + 1uF" in the "PRR176" sidechain. That's the HPF frequency he was looking for (not the values you have to use!), but they are good values, cos 0.15uF + 1uF = 1.15 uF; that is, together they are close enough to the minimum value of 1uF for a "flat" response.  But any two cap values should work as long as they add up to 1uF when paralleled. Even 0.01uF + 1uF would work -- not sure it's useful though (a lot of filtering).

However, if you put in 1uF (fixed) + 1uF (on a switch) you get 2uF (when switch is activated and caps are in parallel) -- meaning: the transfer function of this specific filter gets pushed down lower, even below 20Hz. See? The opposite effect of what I think you want to achieve.

Not sure the "wiring guide" puts it correctly (maybe C1 and C35 should be the other way round!?) actually it's difficult to see on this "guide", and I can't look at the board traces right now. Maybe someone can chime in, but I think it's this:

U1-out
|
|______
|            |
|            |
A           B
|            \ <--Switch
|______|
|
R15
|

A + B = 1uf. Close switch to get flat response (A + B = 1uF). Open switch to activate HPF (cap A only).

For starters you could solder cables into the "1uf or HPF" slot (C1 it says in the "wiring guide", not sure this is correct though -- well, the one between U1-out and R15 -- and use aligator clips to test various values until you get a HPF value (comp SC less reactive to low frequencies) that you think works for you. You can do this even while the unit is on (pretend it's a SC on/off switch). Just make sure that your cables and clips can never accidentally touch any high-voltage components (ouch, ouch, ouch!!). Then calculate which other cap value you need to add up to 1uF or slightly higher (=switch is activated to put caps in parallel for a "flat" SC freq response).

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on April 29, 2012, 05:15:46 PM
I used either a .1 or .15uF + a 1 uF for the HPF, don't remember the exact value right now, but it works perfectly. I haven't measured or calculated where the exact cutoff freq ends up with this combo, but I'm very happy with it.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on April 29, 2012, 05:25:52 PM
I used either a .1 or .15uF + a 1 uF for the HPF, don't remember the exact value right now, but it works perfectly. I haven't measured or calculated where the exact cutoff freq ends up with this combo, but I'm very happy with it.

Hey Adeptusmajor,
Can you put any picture for us? I think it will be very useful for us:) [ newbies as like me:]
thanks for any advice.
Cheers
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on April 29, 2012, 06:58:44 PM
I'll try to post some pics - my camera broke the other day, I'll see if my buddy could bring his with him to band practice tomorrow night.

It's a bit of a kludge inside from recent tweaks that need to be cleaned up. I just finished customizing the meters yesterday, so at least I can show off a little with the front panel.

to amend my previous post - the cap combo I used for the HPF was .1uF +1uF


oh, and when it comes to understanding this stuff I'm a newbie myself at best (getting better all the time though), so I'll just throw it out there that I continue to be extremely grateful to all of the more knowledgeable individuals here who have been generous enough to share information and offer projects like this.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on April 30, 2012, 07:58:29 AM
Just wanted to chime in, and say 3 things concerning the HPF, one is that I think I use .1 uf and that give a filter around 150-200hz if I remember correctly. ( i kind of like a more drastic HPF) But you can of course use whatever you like, You could even think about using something crazy like 0.01uf to turn it into a "de-esser" of sorts. Good for cymbals or vox possibly.

Anyway, and then I don't think I showed this on the wiring guide, but on the 7 pin connectors on the board (the same ones were you wire up the volume controls) there are 2 pads that say "HPF" if you wire up a switch that shorts these 2 pads, that connects the 2 caps together.

And lastly the cap that is always in the side-chain is "1uf or HPF" and the one that gets switched in/out of parallel is "HPF ADD"

Hope this helps,

Abe
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on April 30, 2012, 03:43:14 PM
...I think I use .1 uf and that give a filter around 150-200hz if I remember correctly. ( i kind of like a more drastic HPF) ...

Yeah I kind of figured it was right around there. I'm happy with that value - super effective on bass or drums.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on April 30, 2012, 07:00:03 PM
Yo,

i think the HPF values aren't the issue, they can be calculated easily and have been discussed some threats ago...
to me the problem lies in the interpretation of the PCB, the schematic is clear so far...

As Abe wrote the caps have to be placed between Pin #1   and one of the other holes in the printed boxes...
the HPF switch adds in series parallel the second HPF cap.
What me still confuses is the fact that I can measure a link between those pins, which means that the cap would be parallel to
something ( some link trace) which i can't find in the schematic.... ???  ???  ???

I'll give it a try as Abe wrote.. he must know best, hasn't he??

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on April 30, 2012, 11:52:24 PM
I believe there is no continuity between pin 1 of each cap until they are linked via a switch. The switch connects to the HPF pins (6 & 7) at the 7 pin connector, left side of the board. The "ADD" cap should be your 1uF, the other one is your lower value. Leaving them connected in parallel (continuity between pin 1 of both caps) will give you flat response, switching out the "ADD" cap (no continuity) will give you your HPF.


EDIT: just noticed you said "adds in series" which is incorrect, they add in parallel. So one side of each cap is always connected and the other side is switched.


NEW EDIT: I guess I just repeated everything Abe just said. Sorry, I'll try to pay attention next time.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on May 01, 2012, 01:44:46 AM
Here's the pics I promised. I have to apologize for the mess inside, I will clean it all up when I am done tweaking, I swear! Luckily the (B-word) donor chassis hides most of the mess behind the front panel 8). I moved part of the power supply off-board, still need to try Abe's mod with the extra smoothing caps and diodes. Most of the noise issue was resolved by just moving everything, but I still feel it could be better. Also, it's not easy to see the proper orientation of the HPF caps because I have one side wired to the GR bypass switch. And I think I made the meter scale wrong, it only goes 0-10 but I'm thinking it should go to 20, maybe someone can confirm this for me in case I need to fix it.

(http://www.groupdiy.com/gallery/0/38684-010512010000.jpeg)

(http://www.groupdiy.com/gallery/0/38684-010512010153.jpeg)

(http://www.groupdiy.com/gallery/0/38684-010512010245.jpeg)

(http://www.groupdiy.com/gallery/0/38684-010512010326.jpeg)

(http://www.groupdiy.com/gallery/0/38684-010512010058.jpeg)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: flaheu on May 01, 2012, 04:26:03 AM
cool !!!!

me likes  :P :P
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: JayDubrek on May 01, 2012, 07:35:01 AM
I see you've stuffed both DOAs and chips on the inputs and outputs... What were were your opinions between the two options? Nice panel!
Jay
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on May 01, 2012, 08:35:42 AM
I see you've stuffed both DOAs and chips on the inputs and outputs... What were were your opinions between the two options? Nice panel!
Jay

On the input there is a space for an NE5534 chip opamp underneath the DOA, which I have not tried. I was under the impression that the de-balancing chip was still necessary on the input unless you are using a t-pad attenuator. Somebody please correct me if I am wrong.

On the output I am using the balancing chip because there is no output transformer. I don't think it has anything to do with the DOA, again somebody please correct me if I am wrong. Maybe I will try transformer coupled outs one day, but I don't really think it needs it if the intention is to get more color.

.
Some other notes:

I am still using the Edcor 1:1 for both the input and interstage transformers. I like the way it sounds right now, but I know Abe said that the 4:1 sounds better. I definitely plan on ordering a couple, for just $20 more it seems worth a try.

For the timing caps options I have tant, Solen fast, and PIO (GR bypass at top position of switch). I agree with Kingston that the tantalum and the PIO sound pretty similar, although there have been several occasions where they sound different enough to make me choose one over the other, sometimes the tant wins, sometimes the PIO. PIO does sound better for the most part, so I intend to try his idea of changing the value of the tant to 2uF just to get a little more variation.

I'm kind of at a loss with the "thump" adjustment, not sure how to trim it properly. I have tried monitoring the signal with a scope and an analyzer, also tried adjusting by ear but I can't tell much difference in what I am doing. If someone could clue me in to the proper way to make this adjustment, I would be grateful.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: JayDubrek on May 01, 2012, 09:09:10 AM
Haha I'm such a dumbass...yeah of course the chip input sits under where the DOA is. I'm so used to staring at my partially stuffed board! Has anyone tried the chip input/output? Still undecided on this...
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on May 01, 2012, 09:12:02 AM
Here's the pics I promised. I have to apologize for the mess inside, I will clean it all up when I am done tweaking, I swear! Luckily the (B-word) donor chassis hides most of the mess behind the front panel 8). I moved part of the power supply off-board, still need to try Abe's mod with the extra smoothing caps and diodes. Most of the noise issue was resolved by just moving everything, but I still feel it could be better. Also, it's not easy to see the proper orientation of the HPF caps because I have one side wired to the GR bypass switch. And I think I made the meter scale wrong, it only goes 0-10 but I'm thinking it should go to 20, maybe someone can confirm this for me in case I need to fix it.

Thanks adeptusmajor for the pictures!
Awesome FP!
cheers,
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 01, 2012, 11:52:44 AM

I am still using the Edcor 1:1 for both the input and interstage transformers. I like the way it sounds right now, but I know Abe said that the 4:1 sounds better. I definitely plan on ordering a couple, for just $20 more it seems worth a try.

That was my initial impression, but after installing the "1k" on the primary of the interstage and 100K (or 10k) I forget on the secondary, the 1:1 behaved much better, and now I can't say that there is one real advantage over the other. Like always, try it out and see what you like, but if your liking it as-is I say keep the 1:1s in there.

Quote
I'm kind of at a loss with the "thump" adjustment, not sure how to trim it properly. I have tried monitoring the signal with a scope and an analyzer, also tried adjusting by ear but I can't tell much difference in what I am doing. If someone could clue me in to the proper way to make this adjustment, I would be grateful.

VR3, VR1 for the left channel and VR9, VR4 for the right channel. VR3 and VR9 balance the high voltage power going to the 2 different sides of the 6bc8 tube, and VR1 and VR4 adjust the "thump"

Basically they both adjust the "thump"

How I've done it (someone please chime in if they have a better way) is basically leave VR3 and VR9 alone, unless you max out VR1 or VR4 to one side or the other without getting rid of the thump, then adjusting VR3 or VR9 (respectively) will work. But really in practice, I just play with both trimmers till the thump is minimal.



1)So you put something with a lot of High frequency signal through the compressor, preferably High pass it, say at 1k. (like a high hat) Then slam the compressor with fastest attack and release.

2) Listen for the "thump" you'll know it when you hear it. adjust VR3 and VR1 for minimum thump for the left channel. Then VR9 and VR4 for the right channel. If you don't hear any thump, the turn one of the trimmers anyway, stop at the point were the sound sounds the thinnest.

Hope that helps,

Abe

adeptusmajor - sweet looking build! digging the front panel. great job!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on May 01, 2012, 06:56:42 PM
Thanks for the compliments everyone.


I am still using the Edcor 1:1 for both the input and interstage transformers. I like the way it sounds right now, but I know Abe said that the 4:1 sounds better. I definitely plan on ordering a couple, for just $20 more it seems worth a try.

That was my initial impression, but after installing the "1k" on the primary of the interstage and 100K (or 10k) I forget on the secondary, the 1:1 behaved much better, and now I can't say that there is one real advantage over the other. Like always, try it out and see what you like, but if your liking it as-is I say keep the 1:1s in there.


Ok, good advice. I put the resistors on both sides initially, so I guess that's why I didn't notice some of the weirdness that other people might have. I was thinking of ordering the 4:1's and then using the 1:1's for inputs on ruffrecords' PM-PEQ1 project, but I think I have decided to hold off on that one for a little while anyway so I can finish some other projects that I have been sitting on. So I guess that means I'm keeping the 1:1's in the 176. Like I said, they really don't bother me, I like how the unit sounds.


1)So you put something with a lot of High frequency signal through the compressor, preferably High pass it, say at 1k. (like a high hat) Then slam the compressor with fastest attack and release.

2) Listen for the "thump" you'll know it when you hear it. adjust VR3 and VR1 for minimum thump for the left channel. Then VR9 and VR4 for the right channel. If you don't hear any thump, the turn one of the trimmers anyway, stop at the point were the sound sounds the thinnest.


I will try this. I adjusted VR3 and VR9 to get identical voltage readings at both sides of the trimmer before trying the thump adjustment on VR1 and VR4. I was unable to hear any kind of "thump" when adjusting, even with the trimmer maxed out in either direction, but I wasn't too sure what exactly I was listening for either. Nothing jumped out at me, could have been my mind playing tricks on me but I thought I heard a VERY minimal distortion coming in and out as I adjusted so I just left it at a spot where that seemed to go away. But I believe I was using a bass heavy track when adjusting, so I will try it again the way you described. Thanks for the suggestions.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on May 04, 2012, 09:54:39 AM
Hey Abe,
I fear that the high voltage  :o and because of this reason maybe I am asking some silly questions :) sorry!
I almost finished  to my build and I calibrated +/- 18V and 100v so everything is right now! except;
- R13 and R 18  smoke!
- Left channel is not clear sounding  :o it's too low! I hear some saturation, attack and release are not working :( I checked wire connexion but everything is look good...
[ Right Ch is perfecto :) except HPF?? I used a 1uf for the moment because I have any 0.1uf and I will change it! but I am not sure[ again:] is it right? there is too much info about HPF and I can't understand which one is that I can understand easily]

EDIT; The picture was wrong....

- and I 'm not sure if I can do the new Diode rectification modification myself... I'm not sure... plus I don't have any more space in the case for this operation :( :( Yes, I got to much HUM and I didn't like it but what I hear from right ch is great! smooth and transparent

Thanks for any advice!
cheers
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 04, 2012, 10:52:58 AM

- R13 and R 18  smoke!
[ Right Ch is perfecto :) except HPF?? I used a 1uf for the moment because I have any 0.1uf and I will change it! but I am not sure[ again:] is it right? there is too much info about HPF and I can't understand which one is that I can understand easily]
(http://i1236.photobucket.com/albums/ff442/jandoste/PRRSWCHT.png)

Hi Jandoste! Glad it got it mostly working ,we can get it all the way working.  Sounds like something simple. Firstly that picture you posted is wrong. You don't wire a switch there at all. The HPF switch connects at the connectors with the volume controls and the capacitors connect inside the boxes, you do not want to connect a capacitor and a switch across the two separate HPF capacitors if you only have one capacitor stick in in the "HPF ADD" capcitor box with one leg in the "1" spot and the other in one of the other spots within that same box. Then wire the switch to the "HPF" thats on the in/out volume connector. and keep is switched, then when you get the 0.1uf you can just solder them into the "1uf or HPF" box.  Sorry I know it probably seems a littl confusing at first, but look at the schematic for a bit and it should make sense.

How you have it wired up in the picture could be the cause of your resistors smoking

Also Please take down that picture as it is wrong and we don't want someone that is just skimming through the thread to see that and think that is the way its done (because that sounds like something I would've done when I was learning :) )

Quote
- and I 'm not sure if I can do the new Diode rectification modification myself... I'm not sure... plus I don't have any more space in the case for this operation :( :( Yes, I got to much HUM and I didn't like it but what I hear from right ch is great! smooth and transparent


Well its definitely worth it, hum drives me crazy :) The board really doesn't take up much room, you just need a 2" x 3" empty square of space. Definitely worth it if you can wrap your head around it. If your worried about the High Voltage (which IS a GOOD thing) just work slowly and carefully.  Stand clear when you power up, and discharge the HV caps when you power down to continue working. You can do this with a 1K resistor 5W (or something close to it) across the terminals.

Best,
Abe

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on May 04, 2012, 11:24:20 AM
Thanks Abe!
cheers
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Jeremy.Starseed on May 04, 2012, 08:16:10 PM
Hey guys. I'm not familiar with these products, so I'm wondering if anyone here has tried and can tell anything about the sound and value of their goods. http://www.soundskulptor.com/uk/products.php?cat=2 (http://www.soundskulptor.com/uk/products.php?cat=2)

Which model of this OP-amp might be suitable for this project?

Been getting excited to finally start assembly, but there are a lot of parts to find and purchase first.

Looking really nice, you guys. Thanks for all the info that's been added since the builds began.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on May 04, 2012, 08:34:12 PM
Hey guys. I'm not familiar with these products, so I'm wondering if anyone here has tried and can tell anything about the sound and value of their goods. http://www.soundskulptor.com/uk/products.php?cat=2 (http://www.soundskulptor.com/uk/products.php?cat=2)

Which model of this OP-amp might be suitable for this project?

Been getting excited to finally start assembly, but there are a lot of parts to find and purchase first.

Looking really nice, you guys. Thanks for all the info that's been added since the builds began.

Hey  Jeremy,
you can get some of them from Jeff also,
http://classicapi.com/catalog/product_info.php?cPath=71_72&products_id=136
http://classicapi.com/catalog/product_info.php?cPath=71_72&products_id=169
I used 990 Discrete Op-Amp! you can get it from here http://www.johnhardyco.com/990OpAmpDetails.html but he is not a fast guy :)
cheers,
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on May 04, 2012, 08:48:34 PM
Hey Guys,
I am trying to finish this amazing project but got some more problem :-* :D
I don't have the same values with the DRV 134 chips and TL042 chips too... I guess that my left Ch has not enough volume than right Ch! Maybe I need to change these chips but I am not sure why they don't have the same values? also R13 | R81 if I am not wrong they must be 1W or more? because they smoke :o ;D
Thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 04, 2012, 11:28:05 PM
Hey Guys,
I am trying to finish this amazing project but got some more problem :-* :D
I don't have the same values with the DRV 134 chips and TL042 chips too... I guess that my left Ch has not enough volume than right Ch! Maybe I need to change these chips but I am not sure why they don't have the same values? also R13 | R81 if I am not wrong they must be 1W or more? because they smoke :o ;D
Thanks


If your using a lot of discrete opamps that take more than 50ma a piece you probably want to decrease the value of those 2 resistors to 10 ohms or so. If your just using IC's the 100ohm 1/4 watt will be fine. If those resistors are smoking check for a short, or mis wiring.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on May 05, 2012, 06:59:57 PM
Hi,

it seems that all of you are using "special" OP-amps... are they an option on top of the NE5534 or are they a must have... ?? :o
I'm confused.... ;D
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 05, 2012, 07:12:38 PM
Hi,

it seems that all of you are using "special" OP-amps... are they an option on top of the NE5534 or are they a must have... ?? :o
I'm confused.... ;D

NE5534 or "Special" discrete opamps not both at the same time....I don't *think* that would work, anyway It would be scary to try ;)

One or the other.

I built one with all Ne5534s and then switched out the outputs and there was  a noticeable difference. Preferred the discrete opamps of course! :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on May 05, 2012, 08:52:52 PM
Thanks Abe,

that was what i had in mind, but i was confused by seeing that everybody uses discrete OP-amps...
I think I'll have to order my self some...  ;D
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Jeremy.Starseed on May 06, 2012, 12:03:06 PM
On the subject of OP-amps and discrete ones: Would the NTP M100 work in this circuit?

http://www.groupdiy.com/index.php?topic=11943.0

I have a few original ones. I'm not sure if they operate at 15 or 24 V.

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on May 07, 2012, 10:10:22 AM
Hey Abe,
I am trying to build a new "psu" that with your new wiring guide but I need your help :) please can you tell me which diodes I will move from the old Psu to the "new one" also I just move 100uF 250V / 2x 1000 uF 50V that's all? maybe you can mark on this picture[attached] that which components we need to move? 
Thanks
(http://i1236.photobucket.com/albums/ff442/jandoste/PRR.png)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: erictj on May 07, 2012, 12:34:38 PM
Hi there-

Been lurking for a while, first post though.

Super excited about starting this project.  However, I'm unable to find any PCBs or kits for sale?  Are the PCBs that were originally manufactured for this project gone already?  If so, are there Eagle files available so that I can get my own created?

Thanks!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: dandeurloo on May 07, 2012, 01:29:30 PM
Thanks Abe!

(http://dandeurloo.com//collectivecases/images/Front%20Panel%20Photos/PRR-side1web.jpg)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on May 08, 2012, 05:13:53 AM
great job!
Samples?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on May 08, 2012, 12:04:30 PM
Good to see that now one after another finished build comes up!  :D
Some inside pictures?

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 08, 2012, 12:50:24 PM
please can you tell me which diodes I will move from the old Psu to the "new one"
the 2A04's (edit: you can use regular 1n4007's if you want) those rectifiers feed the heaters and +/- 18v rails.

Quote
also I just move 100uF 250V / 2x 1000 uF 50V that's all? maybe you can mark on this picture[attached] that which components we need to move? 
preferably just get another set of 1000uf 50v and 100uf 250v and then leave the original ones in.

good luck!

http://www.acsoundstudio.com/prr_176/OFF_BOARD_POWER.png
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on May 08, 2012, 02:04:46 PM
Thanks Abe,
as I  said before that I'm afraid  :o :D so I am asking some more silly questions  :) sorry again!
we got two 100uF 250V and on the new rectification guide I am seeing just one 100uF 250V? so it's mean that I  need to use just one of them? D10/D11/D12/D13 I already moved them and I think I will move the other diodes too! D16/D17/D21/D22
I hope my postes can help for newbies as like me :) :)
Thanks

(http://i1236.photobucket.com/albums/ff442/jandoste/ec2c7dd9.jpg)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on May 08, 2012, 02:05:28 PM
the 2A04's (you can use regular 1n4007's if you want) those rectifiers feed the heaters and +/- 18v rails.

whoops not quite safe for 1n4007.

Heaters + the rest eat way more than 1A in a worst case scenarie. 1n4007 might work for a while, but then what happens? No point gambling, use any standard +2A diode.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on May 08, 2012, 02:44:05 PM
hi Abe,

what VA rating is your toroid?  And what, may I ask are you using in your build, DOAs, IC in/out, etc? Tubes are 6bc8?

just asking cuz I'm planning on using those russian tubes which IIRC consume a bit more, as well as 4-6 DOAs in mine, and want to make sure the single primary scheme you're using will work for me. I think a 25VA, 2x15V trafo will fit in a 1U case...

cheers,
d
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 08, 2012, 03:30:41 PM
the 2A04's (you can use regular 1n4007's if you want) those rectifiers feed the heaters and +/- 18v rails.

whoops not quite safe for 1n4007.

Heaters + the rest eat way more than 1A in a worst case scenarie. 1n4007 might work for a while, but then what happens? No point gambling, use any standard +2A diode.

I agree, better safe than sorry, but how do you figure the circuitry takes more than 1 amp? My (very) rough calculations:

2 tubes (run in series, double voltage) = 400ma
INA134 = 2.9ma x 2 = 5.8ma
Ne5534 = 6ma x 6 = 36ma
Tlo72 = 4ma x 2 = 8ma
drv134 = 5.2ma x 2 = 10.4ma

Total = 460ma

Thanks leaves 540ma for the 1.5v bias etc... (and if your using all discrete opamps add another 200ma)

Am I missing something?

I do agree though, sticking with 2a04 since we are talking about pennies here,  but 1n4007 would work in a pinch. They do have 30A surge capability for turn on transients.




Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 08, 2012, 03:40:24 PM
Hi there-

Been lurking for a while, first post though.

Super excited about starting this project.  However, I'm unable to find any PCBs or kits for sale?  Are the PCBs that were originally manufactured for this project gone already?  If so, are there Eagle files available so that I can get my own created?

Thanks!

Hi!, Welome! :) I'll planning on having a new group buy type thing here soon. In the next couple weeks or so.

Thanks!
Abe
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 08, 2012, 03:49:18 PM
Thanks Abe,
as I  said before that I'm afraid  :o :D so I am asking some more silly questions  :) sorry again!
we got two 100uF 250V and on the new rectification guide I am seeing just one 100uF 250V? so it's mean that I  need to use just one
of them?

Correct, You need just one extra. So one on your extra power board and the 2 on the PCB board.

Quote
D10/D11/D12/D13 I already moved them and I think I will move the other diodes too! D16/D17/D21/D22
I hope my postes can help for newbies as like me :) :)
Thanks

I would put d10 through d13 back on the PCB board. And moving d16 - d22 offer no practical advantage at all, as those are diodes that protect the regulators from over voltage and power up / power down.

Look at the attached pic. The only things you want to "remove" from the board are the 4 2a04 diodes: D6 through D9. then jumper the ones shown (place a bare piece of wire through the holes) and note the polarity of the wires you feed from the off board power rectification power board to the PCB board.

Good Luck!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on May 08, 2012, 04:56:19 PM

I agree, better safe than sorry, but how do you figure the circuitry takes more than 1 amp? My (very) rough calculations:

2 tubes (run in series, double voltage) = 400ma
INA134 = 2.9ma x 2 = 5.8ma
Ne5534 = 6ma x 6 = 36ma
Tlo72 = 4ma x 2 = 8ma
drv134 = 5.2ma x 2 = 10.4ma

Total = 460ma

Thanks leaves 540ma for the 1.5v bias etc... (and if your using all discrete opamps add another 200ma)

Am I missing something?

Abe, those IC currents look a little low.  Are they from the datasheet? They are probably quiescent current, not counting any kind of load.  Actual numbers should be higher.

Instead of calculating, the best way to check this is to measure the current on those rails with a DMM.  If you have the time, Abe, that would be very helpful as a base number, since from what it looks like your build is stock (6bc8, no DOAs, etc).  Then every change can be assumed to add to whatever your numbers are.

cheers!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on May 08, 2012, 05:01:14 PM
Am I missing something?

Well I did say worst case scenario:

2X 6N5P in series: 650mA
4X some heavy duty opamp running stupid redhot: 300mA
misc leds and sidechain opamps taking 10mA each: 100mA

It just went over 1A.

No point gambling when +2A diodes are basically the same price as 1A.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on May 08, 2012, 06:08:48 PM
Kingston,

have you measured the current consumption on yours? 

-d
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on May 08, 2012, 06:13:37 PM
Yes,

but I forget the exact values. It was about 0.2A lower than the above worst case scenario.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on May 08, 2012, 07:16:38 PM
cool, and that's with russian tubes, 4x DOAs, and IIRC a different sidechain opamp? 
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 08, 2012, 07:47:46 PM
 Yea those were the Q current, under load they would draw more, that makes sense. Thanks for the explanation! So stick with the 2A04s :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on May 09, 2012, 07:02:53 AM
cool, and that's with russian tubes, 4x DOAs, and IIRC a different sidechain opamp?

LME49870 as the single package and LME49860 as the double for sidechain. I used these so I could do 22V rails. For no other reason than "because I can". I didn't do any lower vs. higher rail comparisons either. I did the same with Igor's Sontec boards some years back. LME49870 is SMD only so I used a makeshift adapter.

Another option would be OPA604 and OPA2604 and then you could do even 24V rails.

By the way, the headroom difference between 15V rails vs. 24V rails is ~4dBu. Probably not worth the fuss.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: brianvino on May 09, 2012, 11:28:20 AM
sorry for request ....
Abe, have you prepared short tarature note ?
thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on May 09, 2012, 11:48:46 AM
Actually I'm wondering if the difference in opamps might cause different attack characteristics.  As in, higher slew rate, more precise opamp might give more control over attack, and a slower, less precise, would be more sloppy.  Or maybe just higher current output opamp.  Sort of the same as adding more caps in parallel, but looking at it other way around. 

btw, I'm going 15V-18V rails max, using 2520s so I don't want to get over 20. 18 is good enough for me.

cheers!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 09, 2012, 12:11:31 PM
sorry for request ....
Abe, have you prepared short tarature note ?
thanks

Hello,

Reply 631 about 3/4's the way down this page should get you started http://www.groupdiy.com/index.php?topic=44586.631

I do need to put together a nice pdf one of these days.

Thanks!
Abe
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on May 09, 2012, 12:45:08 PM
Actually I'm wondering if the difference in opamps might cause different attack characteristics.  As in, higher slew rate, more precise opamp might give more control over attack, and a slower, less precise, would be more sloppy.  Or maybe just higher current output opamp.  Sort of the same as adding more caps in parallel, but looking at it other way around.

Forgot to mention, these high quality opamps definitely change timing characteristics of the compressor, and it behaves exactly like you are guessing. The same happens with SSL variants when the rectifier opamps are changed. But high current ability has no advantage here since load doesn't change (timing network/tube grids), just the same as SSL variants.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on May 09, 2012, 01:11:32 PM
thanks for confirming.  As for high current, I was thinking back to the PM660 with its huge timing cap (should hopefully get mine done next couple months  ::) ) , and thinking more current would fill the caps faster, so larger caps could be tested and then release times played with.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on May 09, 2012, 02:55:28 PM
thanks for confirming.  As for high current, I was thinking back to the PM660 with its huge timing cap (should hopefully get mine done next couple months  ::) ) , and thinking more current would fill the caps faster, so larger caps could be tested and then release times played with.

You would still need to change the load, a modification I am slightly too lazy to check right now. Fatter current capability doesn't automagically pump current anywhere.

And yes, that's a great avenue of research, a big-ass high-watt solid state amp charging time constant caps. Who said they have to be tubes, even in poorman? How about a gainbloak?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on May 09, 2012, 03:55:29 PM
I think some people had talked once about using the gainclone power amp chips for sidechains.. 50-68W or something per channel!  So I udnerstand about chaging the load... but what exactly defines the load on these guys?  Is it a "simple matter" of recalculating the resistor network between the cathodes, or do the trafo ratios come into play as well? 
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on May 09, 2012, 04:59:06 PM
The two opamps being rectified by the 1n4148 diodes are the only amp dealing with the load here - TL074 in the original PRR vari mu. Change it to a gain bloak, and time constants would still stay the same because the amp load didn't change.

None of the transformers have anything to do with any of this by the way. They are there just doing the class A/B transforms. (this is different in poorman, don't compare)

And no, it's not a simple matter of changing the cathode loads. I'm a bit of a n00b on this topic, but I remember it was explained really well by lolo-m somewhere on the forum. Load is - as far as I understood it - the interaction of the whole time constant network with the tube grids. Something there needs to pull way more current to change compression timing behaviour, not sure how to do it.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on May 12, 2012, 03:35:07 PM

Hey Abe,
Bad news  :o I tried the new PSU with the DJ's tranx but I don't have right values on +/-  :( I checked the new PSU and looks like everything is ok but maybe your diode rectification wiring guide is for US guys :) I am in France and so we got 230V :) :)
especially when I connect 110V[sec] the tranx is angry and hot... but very hot :)
so I used all diodes and caps that you used for this Psu and I don't have any idea what's happen?... please see the picture for the details... Thanks

(http://i1236.photobucket.com/albums/ff442/jandoste/PSU2PRRDIODE.jpg)

Thanks Abe,
as I  said before that I'm afraid  :o :D so I am asking some more silly questions  :) sorry again!
we got two 100uF 250V and on the new rectification guide I am seeing just one 100uF 250V? so it's mean that I  need to use just one
of them?

Correct, You need just one extra. So one on your extra power board and the 2 on the PCB board.

Quote
D10/D11/D12/D13 I already moved them and I think I will move the other diodes too! D16/D17/D21/D22
I hope my postes can help for newbies as like me :) :)
Thanks

I would put d10 through d13 back on the PCB board. And moving d16 - d22 offer no practical advantage at all, as those are diodes that protect the regulators from over voltage and power up / power down.

Look at the attached pic. The only things you want to "remove" from the board are the 4 2a04 diodes: D6 through D9. then jumper the ones shown (place a bare piece of wire through the holes) and note the polarity of the wires you feed from the off board power rectification power board to the PCB board.

Good Luck!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 14, 2012, 12:24:48 PM
Jandoste,
Try disconnecting the wiring from the PCB board and measure voltages. Should be normal. If not there is a short/miswiring going on somewhere on the off board rectification. As always be careful.

If when you disconnect the power wires from the PCB you get normal voltage readings (20 - 25v) then the problem is somewhere on the main board. Look for shorts.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on May 14, 2012, 01:03:52 PM
Jandoste,
Try disconnecting the wiring from the PCB board and measure voltages. Should be normal. If not there is a short/miswiring going on somewhere on the off board rectification. As always be careful.

Thanks Abe,
I didn't connect new PSU to the PCB board. I think that I am wrong on the off board rectification! as I said before that I'm not strong but I think my board is totally wrong :o ;D ;D it was my first try and will be last :)  :)
(http://i1236.photobucket.com/albums/ff442/jandoste/photo-8.jpg)  (http://i1236.photobucket.com/albums/ff442/jandoste/1photo.jpg)

But I won't stop to finish this amazing baby!  ::)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 14, 2012, 04:14:37 PM
Hmm...Hard for me to tell, also I've ran into this before, but are you sure your transformer Center-Tap is correct? If your shorting a secondary and then putting the other secondary to the cirucit, +/- 13 volts seems about what it would put out and your transformer would be getting very hot...
So maybe double check the +/- 18v secondaries.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on May 15, 2012, 10:57:25 AM
jandoste,

start from scratch. First measure the transformer alone with nothing but the 230VAC connected to it. Then one by one, rail by rail, start connecting the windings to your offboard-thingymabob.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on May 15, 2012, 01:42:30 PM
Thanks Abe and Kingston,
I think I found my bad bug but now I need to ask quick question! I am using a Tranx that it has 1x20v - 1x20V- 120V!
So I now the tranx is cool and no noise etc etc.... just I am reading out of PSU +/-35V[DC] So is it right value?
I hope it is right  :)
Thanks

Hmm...Hard for me to tell, also I've ran into this before, but are you sure your transformer Center-Tap is correct? If your shorting a secondary and then putting the other secondary to the cirucit, +/- 13 volts seems about what it would put out and your transformer would be getting very hot...
So maybe double check the +/- 18v secondaries.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on May 15, 2012, 02:08:09 PM
Oh for...

The voltage out of a transformer is VAC!! Set your multimeter to VAC position.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on May 15, 2012, 03:13:34 PM

I just see out of PSU +/-35V and 120V... I get the tranx from DJ and wires are;
Blue/blue=20V
green/green=20V
I connected one blue 20 and second green is other 20V port? the second blue and green are go to GT?
and
red/red for 120V
maybe something worng with my new PSU board but I checked it again and agin :o :o



Oh for...

The voltage out of a transformer is VAC!! Set your multimeter to VAC position.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on May 15, 2012, 03:35:28 PM
Listen, you need to learn the difference between VAC and VDC right now before you seriously hurt yourself!

Everything you write is basically gibberish before you carefully start stating EXACTLY what you are measuring. PSU, transformer, just what the heck are you even probing in there?? I have no idea, you seem to think the two are interchangeable.

Although clearly this is a paint by the numbers project for you, these are not Legos. 230VAC is lethal and I'm worried with you probing around with absolutely no idea what you should be doing.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on May 15, 2012, 04:06:58 PM

has been very useful.... >:(

Listen, you need to learn the difference between VAC and VDC right now before you seriously hurt yourself!

Everything you write is basically gibberish before you carefully start stating EXACTLY what you are measuring. PSU, transformer, just what the heck are you even probing in there?? I have no idea, you seem to think the two are interchangeable.

Although clearly this is a paint by the numbers project for you, these are not Legos. 230VAC is lethal and I'm worried with you probing around with absolutely no idea what you should be doing.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 15, 2012, 04:52:19 PM
Thanks Abe and Kingston,
I think I found my bad bug but now I need to ask quick question! I am using a Tranx that it has 1x20v - 1x20V- 120V!
So I now the tranx is cool and no noise etc etc.... just I am reading out of PSU +/-35V[DC] So is it right value?
I hope it is right  :)
Thanks


Those sound like the correct values. I assume your talking about the power coming off the off board rectifier board. Or the power rails on the PCB?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on May 15, 2012, 05:49:24 PM
Hey Abe,
Thanks man!
yes, I'm talking about the power coming off the off board rectifier board.

Thanks Abe ,
I think I found my bad bug but now I need to ask quick question! I am using a Tranx that it has 1x20v - 1x20V- 120V!
So I now the tranx is cool and no noise etc etc.... just I am reading out of PSU +/-35V[DC] So is it right value?
I hope it is right  :)
Thanks


Those sound like the correct values. I assume your talking about the power coming off the off board rectifier board. Or the power rails on the PCB?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 15, 2012, 06:22:29 PM
Good! Glad you got it figured out! What was it that was wrong? Maybe to help others avoid common pitfalls.
Best,
Abe
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on May 15, 2012, 06:47:47 PM
So, time to go :D
my problem was the diodes legs were touching everywhere :o :o and I didn't see that :o :o ::)
I'm a musician so sometimes I need to do more attention more than engineers  ::) ::) I love to build some amazing gear -as like this project-for my music !
Thanks again Abe! Awesome support! and great sound!
regards,

Good! Glad you got it figured out! What was it that was wrong? Maybe to help others avoid common pitfalls.
Best,
Abe
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on May 15, 2012, 09:24:06 PM
jandoste just mailed me some extremely worrying private emails. I feel this is too important to handle privately because it concerns all you beginners out there.

1. Do you know the difference between VAC and VDC right now?

2. Did you measure these both correctly with your multimeter?

Answer no to either of them, you should not be handling 230VAC wall power at this point in your life.

230VAC directly from the wall might kill you!

Learn the difference between VAC and VDC right now and measure them with your multimeter correctly.

Your life is literally in your hands.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on May 17, 2012, 03:25:01 PM
Sorry
I want to use Lundahl 1539 as Output,ù
How I must connect it?
Thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on May 17, 2012, 03:48:01 PM
Sorry
I want to use Lundahl 1539 as Output,ù
How I must connect it?
Thanks

secondary and primary should both be in series. In the datasheet application example connect secondary just like it's shown, and figure out the same arrangement for the primary.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on May 17, 2012, 05:36:59 PM
Hey Abe,
The new PSU is alive :)
- put d10 through d13 back on the PCB board
- moved d16 - d22
- removed from the board are the 4 2a04 than then jumpered  D6-D9
- wired from the off board power rectification power board to the PCB board! +/- are right!

result
- I still got the hum :o
- Left ch in is working but the Out is not...
- maybe that I already asked to you [but I don't remember sorry:] I am using the bypass switches and I guess that you also used this switches and  I would like learn that how did you connect  them?

maybe this picture can say something but I can't realize[see] in my mind  :) :)
Thanks
(http://i1236.photobucket.com/albums/ff442/jandoste/38684-010512010326.jpg)



Good! Glad you got it figured out! What was it that was wrong? Maybe to help others avoid common pitfalls.
Best,
Abe
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 17, 2012, 11:01:34 PM

result
- I still got the hum :o


Measure the +/- voltages coming into the PCB and then you will know how high you can set your regulators. For example: I had a +/-18v transformer, but due to the extra current draw from the heaters the power rails sagged to about 18v before the regulators so I adjusted the +/- accordingly I think 16v or so. You want to leave a couple volt headroom (more if you can help it).

That might be the reason for your hum.

Also how are you grounding you input and output jacks??
Its something easily taken for granted and not really talked about because everyone should already be born knowing it ;)

Basically, Solder ALL the pin 1's of the XLRs (both in and out) to the chassis tab. Then on only ONE of the inputs, connect the pin one (that is also connected to chassis mind you) to the ground of the circuit board. on ALL the other pin 1's they should only be connected to the chassis. Then of course you remembered to earth your case to the ground wire of the IEC cable right? :)

That SHOULD fix your hum. if not its something else.
Quote



- Left ch in is working but the Out is not...


What exactly do you mean? The output volume isn't working? Or there is not sound coming from the output? Check your wiring. Check your pots. Sometimes they do go bad.

Quote
- maybe that I already asked to you [but I don't remember sorry:] I am using the bypass switches and I guess that you also used this switches and  I would like learn that how did you connect  them?

well its up to you. You could hook up some relays if you wanted "hard" bypass, but I think the easiest way and the most versatile (you can use the comp as a colorful line driver in bypass) you need to make sure that the Sidechain of the compressor "thinks" that there is no audio, therefore no compression. How we trick the Sidechain into thinking there is no audio, is disconnect it from the main audio. You do that by disconnecting c1 and c38 (the sidechain caps) from the circuit. Wiring the switch in between one of the legs and the pcb board.

Quote

maybe this picture can say something but I can't realize[see] in my mind  :) :)
Thanks


The picture is pretty fuzzy, and hard to really make out specific parts, but it does help.
goodluck!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on May 17, 2012, 11:52:37 PM
The wires in the picture are the leads to the bypass switch implemented exactly as Abe described above. I just lifted one leg of each cap (the legs that are connected to each other on the pcb) and twisted them around to connect to one of the wires going to the switch. The other switch wire connects back to that point on the pcb. I used a 2 pole 4 position switch, so one side of the switch activates the bypass in the top position, the other side toggles timing caps with the bottom three positions. Sorry about the fuzzy pictures.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 18, 2012, 10:16:28 AM
... Sorry about the fuzzy pictures.
Hello,
I thought those were provided by jandoste of his build, and he wanted someone to glean why he was getting hum etc from them. My mistake, i see he was just explaining what those wires are doing. Cool idea about the multi position rotary switch btw

Abe
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on May 18, 2012, 12:25:51 PM
excuse me i need some help
I figured out how to connect the secondary of 1539
can anyone help me with the primary?
in the datasheet pin (2.5) (1.6)??
Thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on May 18, 2012, 01:51:10 PM
excuse me i need some help
I figured out how to connect the secondary of 1539
can anyone help me with the primary?
in the datasheet pin (2.5) (1.6)??
Thanks

*sigh*

 :(

Could you please and least try for christs sake! My last post had a very clear instruction.

It's literally painting by the numbers in the datasheet.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on May 18, 2012, 05:49:43 PM

 Cool idea about the multi position rotary switch btw

Abe

Thanks, I actually used a small slide toggle switch. I wanted to keep it unobtrusive since it's pretty much a set it once and leave it alone kind of control.

(http://www.groupdiy.com/gallery/0/thumb_38684-180512173649.jpeg) (http://www.groupdiy.com/index.php?action=gallery;sa=view;id=106)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on May 18, 2012, 07:19:20 PM
.. yo
great switching. solution .. really cool! How do you fix the switches to the front panel?? (Pix?)
Thanks for the pix, you made my decision to go for Hong Kong meter and an custom made scale!!

@kingstone: thanks for your great support and patience: i feel with you, some times bang your head against the wall... reading it.. :)

rock-On!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on May 18, 2012, 08:10:36 PM
How do you fix the switches to the front panel?? (Pix?)


Very carefully, with this :http://www.gorillatough.com/index.php?page=gorilla-glue (http://www.gorillatough.com/index.php?page=gorilla-glue)  ;D

Couldn't find a switch with mounting holes, but the glue works great.


A note on the Hong Kong meters - after having them installed and working great for a few months, they began to gradually drift upward until they were off the top end of the scale and couldn't be calibrated back. I ended up putting a 100 ohm resistor in line with them and that solved the problem, they've been working perfectly since.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on May 20, 2012, 07:21:59 PM
Hey Abe,
Thanks for long explanation!
but I can't move the hum and the left Ch out is strange... I tried with a signal[1K/0dB] than the Vu meter can see this signal but I hear anything from the left ch! but when it is on stereo mode left Ch's release and Attack work... right Ch's release[/i] and Attack can't control signal when it's on the stereo mode! I guess that is not normal?
Thanks...
- Everything seems like right :-\  ; all wire connexion is right!
- The voltage values are correct=  -/+18 / 110V [ the end I got them :]
(http://i1236.photobucket.com/albums/ff442/jandoste/5c1cc48a.jpg)
(http://i1236.photobucket.com/albums/ff442/jandoste/1dace7e6.jpg)
(http://i1236.photobucket.com/albums/ff442/jandoste/2b3dfe08.jpg)
(http://i1236.photobucket.com/albums/ff442/jandoste/75f50b99.jpg)
(http://i1236.photobucket.com/albums/ff442/jandoste/4d19d599.jpg)

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: adeptusmajor on May 21, 2012, 07:39:19 AM
... right Ch's release[/i] and Attack can't control signal when it's on the stereo mode! I guess that is not normal?


That is normal. When in stereo mode, both channels are controlled by the left attack and release. Input and output levels remain independent.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 21, 2012, 10:38:15 AM
Hmm Check your wiring and grounding. Looks like you have an extra wire connecting the grounds on the XLRs together, they should all be grounded through the case via the ground pin on the xlr. Check the soldering on the tube standoffs, it has to be something.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on May 22, 2012, 11:34:44 AM
hello i am doing a version with T-pad input ....
I have to connect as in 1176?
thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 22, 2012, 12:22:56 PM
hello i am doing a version with T-pad input ....
I have to connect as in 1176?
thanks

Yes Sir!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: brianvino on May 23, 2012, 06:41:42 AM
sorry for request ....
Abe, have you prepared short tarature note ?
thanks

Hello,

Reply 631 about 3/4's the way down this page should get you started http://www.groupdiy.com/index.php?topic=44586.631

I do need to put together a nice pdf one of these days.

Thanks!
Abe
some news  :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Hank Dussen on May 23, 2012, 03:44:48 PM
Somebody has a Mouser partnumber for the 3,69mm header?
I can't seem to find any headers with this spacing...
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Holger on May 23, 2012, 04:25:30 PM
Should be 3.96mm header.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Hank Dussen on May 24, 2012, 03:27:01 AM
Thanks Holger!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on May 24, 2012, 08:42:30 AM
hello
I finished the compressor
sound wonderful but I have a lot of noise hum
Diode off board
XLR pin 1 to Chassy
only one XLR (pin 1) to main PCB
what could be the problem?
I used the toroidal bought from this forum...
thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 24, 2012, 11:17:35 AM
hello
I finished the compressor
sound wonderful but I have a lot of noise hum
Diode off board
XLR pin 1 to Chassy
only one XLR (pin 1) to main PCB
what could be the problem?
I used the toroidal bought from this forum...
thanks


do you have smoothing caps off and on board?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on May 24, 2012, 11:32:47 AM
hello
I finished the compressor
sound wonderful but I have a lot of noise hum
Diode off board
XLR pin 1 to Chassy
only one XLR (pin 1) to main PCB
what could be the problem?
I used the toroidal bought from this forum...
thanks


do you have smoothing caps off and on board?

no all on board...
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on May 24, 2012, 11:53:51 AM
Hey ilfungo,
Maybe you can upload some pictures and maybe this can help to find your problem and us too..
cheers


hello
I finished the compressor
sound wonderful but I have a lot of noise hum
Diode off board
XLR pin 1 to Chassy
only one XLR (pin 1) to main PCB
what could be the problem?
I used the toroidal bought from this forum...
thanks


do you have smoothing caps off and on board?

no all on board...
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on May 24, 2012, 12:45:41 PM
Thanks!!!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on May 24, 2012, 12:46:50 PM
And This....
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 24, 2012, 01:22:37 PM
Add a few caps next to those diodes (try 1000uf for the +18 and 1000uf for the -18 and one 100uf for the 100v rail) mounted on that same protoboard as the diodes and that should solve it!

Best,
Abe
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on May 24, 2012, 02:15:37 PM
I've tried but nothing change :-\
I tried everything, I do not know what to do....
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on May 24, 2012, 02:58:29 PM
I've uploaded a sample of noise
input pot in the middle
 output pot at max

Input pot don't add noise....
http://soundcloud.com/ilfungo/176-noise-01/s-9DzT0
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on May 24, 2012, 05:59:48 PM
How many ground wires do you have connected to your PCB?  You said you have pin1s going to chassis but have one going to the PCB. why? I haven't wired mine up but that seems wrong.   Normally, XLRs should all go directly to chassis only, and the PCB should go to PSU ground close to the main filter caps (if using separate PSU), and then PSU would get connected to chassis ground. 
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: jandoste on May 24, 2012, 06:57:19 PM
Hey  ilfungo,
Did you check that?
Finally getting some more time to mess with it and found this minor fix-up:

if using INA134 inputs, on left channel, connect pin 1 to ground, otherwise you'll be getting some pretty big voltage readings on the output of the chip. You can connect pin 1 to pin8 of the same chip, as that is tied to ground.

Much Thanks, and sorry for any inconveniences this no doubt has caused.


and here...
Hi Gents,
Was thinking, Instead of a whole power supply of board, probably would be just as good to put the rectifiers and caps off the board. and then feed the smoothed AC to the board, caps and regulators. I'm going to wire it up when I got a minute and post my results.

Also, I am surprised at my stupidity sometimes...I am now learning that I have been wiring up pin 1 wrong all this time. I'm glad that I now am learning more on the subject but so stupid for how many problems its caused! I haven't tried wiring up the PRR-176 correctly....could've been the cause of some of the hum, we'll see.

Pin 1 goes to chassis! Connect audio ground at one point to the chassis! Connect earth to chassis!

Duh! :o :o

So don't necessarily feel obligated to follow the input and output molex's (1,2,3).

Please someone correct me if I'm wrong, but I would:

1) Solder all pin "1"s on the I/O XLRs to Chassis connection, on the XLRs, ensuring each one has a solid connection.

2) Wire input "L" as stated on molex, 1 => pin 1, 2=>pin 2 etc

3) for all other connections, leave "1" on the molex disconnected.

Sometimes the most simple stuff can ironically be the most confusing!

I got the same problem and my left ch is not working  ::) :o
maybe you need to Connect audio ground at one point to the chassis! Connect earth to chassis!

I've tried but nothing change :-\
I tried everything, I do not know what to do....
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 24, 2012, 07:14:03 PM
You can connect audio ground and chassis ground together at any point you deem worthy as long as they are connected and only in one spot. I've found 1 pin 1 is a good spot, but I'm sure there are others. I've gotten hum down to -90dB (volume maxed out) using the tricks outlined in these posts, so the problem has to be somewhere. I which I could help more, but its hard without being there. Osciiliscopes sure help if you got one...
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on May 24, 2012, 08:05:51 PM
You really should not use pin one as circuit/chassis connection.   What is the pad marked *G on the PCB? Seems the best place to connect to earth?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 24, 2012, 08:20:17 PM
You really should not use pin one as circuit/chassis connection.   What is the pad marked *G on the PCB? Seems the best place to connect to earth?

Why not? Just curious.
 
Yes you can connect it there. Its basically a star ground.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mitsos on May 24, 2012, 11:51:42 PM
Far be it for me to try to teach anyone how to ground things, and in this circuit it may or may not make a difference, as the PSU is on board. In the case of an offboarded PSU as you recommend, you should take the circuit's ground reference from the PSU ground, near the main filter caps. 

If using the onboard PSU, it seems point *G should be connected (via a FAT wire) to Earth, no other ground point at all. But, like I said, I have only half-stuffed my PCB so far, and I reserve the right to change my mind!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on May 25, 2012, 10:10:48 AM
Thanks to everyone for the help!!!
I tried everything, but the hum remains ...
I discovered that the area noisier, is between tubes and  interstage transformer ( edcor PCW 10k:10K)
using a 1k resistor on the primary, 2.2k on secondary  the noise decreases  (possibly because it decreases the volume?)
I'm sure the problem is not on the input sage , but in the second part of the circuit.
Could be the valves?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 25, 2012, 10:21:11 AM
You could try to add another 100v smoothing cap in between some of the 1K resistors for the HV rail. Also yes to using the 1k on primary, possibly 100k on secondary.

Trying to think what else....after you are 100% sure the power rails are smooth then where would the hum be coming from? It has to be from the diodes, maybe double check that you have the smoothing caps/grounds hooked up correctly.

PS on the off board power you want to take your ground feed and power rail feeds from were power supply caps are, not further back of that makes sense. Example: you wouldn't want to take the ground wire that goes to the PCB from where you connect the CT of the transformer, you want to take if from as close to the ripple smoothing caps as possible, as this ground "reference" will be much much smother (ie no hum). Same idea for the +/- rails. Connect your wire that goes to the PCB right from where you connect the smoothing cap on the protoboard.

Also the 100V rail is "high tension" so you want to make sure that is as smooth as possible before coming onto the board. And then adding that other capacitor on board should help too...I've been learning a lot from this build!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on May 25, 2012, 10:30:38 AM
Thanks abechap024!!!
Can you post some photos of your compressor (Perhaps I understand better :()
Thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on May 26, 2012, 03:45:18 PM
I did several tests ...
I excluded several areas of the circuit and I noticed that the problem is in the area of doa ...
I am sure that the two DOA work well ...
may be the two 400uf capacitors that are polarized?
thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on May 28, 2012, 12:26:11 PM
And here's my PRR 176!!!
Thanks to all for your support and thanks for this wonderful project!!!
The sound is shocking, perhaps, the best compressor I have built ....
My noise measured in pro tools with  pot at maximum is -70db, I could not do better.
Thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on May 28, 2012, 12:27:14 PM
 :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on May 29, 2012, 08:28:08 AM
... cool build!
Really great big, big VU Meters  ;D
How do they work? I frist thought of VU meters too, but finally changed to mA-Meters.
Did you use yellow LEDs for the illumination?

Looking forward to finish mine!

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on May 29, 2012, 08:46:39 AM
Thanks  Dr_J

The meters work well the only problem is the tracing that is little off
I do not know how to correct the tracking ...
putting a trimmer in series or in parallel on the meter, can it work?
Thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on May 29, 2012, 08:47:48 AM
sorry
Yes ,yellow led!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 29, 2012, 09:04:19 AM
Thanks  Dr_J

The meters work well the only problem is the tracing that is little off
I do not know how to correct the tracking ...
putting a trimmer in series or in parallel on the meter, can it work?
Thanks

Yes a trimmer in series should do it. Glad you like the sound!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on May 29, 2012, 09:19:05 AM
YES abechap024 I love this compressor!!! ;D
I've tried the trimmers in serie but don't work...

I move only the 0
and when I put it in place I'm at the starting point


I noticed a funny thing
what viewing is perfectly half of the true

4 db of compression = 2 db on the meter

there is a way to redefine the scale (a resistance to change)
thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on May 29, 2012, 06:06:57 PM
Hi ILFUNGO,

great to see "my" transformer working :)

And thanks for the yellow LED advise; I'll think i'm trying some yellow ones too.
Which takes me to an other point; in just finished a racking of a telefunken U 373, and i've done a new scale; it was more work than i exacted at the first glance.
I'm currently preparing a threat of what i've done...
But in short, i did a measuring row, supported by calculation and fitted a polynomial curve (5th degree) to calculate the new scale.

ROCK-ON!

P.S.:
What I'm still wondering about is, that nobody uses caps in parallel to the bridge diodes?!?  Which is more or less a state of the art (damping the switching)
If moving the bridge diodes away from the main PCB, it must be an issue of EMC!! Not of smoothing (no effect on distance, in my little theoretical brain :) )
I'll try that...  ;)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on May 30, 2012, 11:59:25 AM
Ilfungo:

Are you using VU's? If so you can go inside and take out the Bridge diodes inside and then you should be OK.


Dr_J:

Yes! That is correct thinking. The hum isn't "magically" coming from somewhere, it has a source. And like I was telling Ilfungo, mounting the diodes off-board without any caps, doesn't make any difference, you have to mount some caps off-board too, to smooth the 60hz and harmonic noise, so it doesn't reach the board. Otherwise electrically it looks like the diodes just have very long leads.

Best,
Abe
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on June 01, 2012, 08:46:52 AM
hi  abechap024
 
I removed the diodes from the VU meters but they are always in the same situation, I read half of the truth
I think it's a problem of VU meters scale.
For noise, Now I try to add the capacitors after the diodes.
Thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Kingston on June 10, 2012, 05:31:45 PM
I did some DOA comparisons with PRR 176 input stage. I modified my unit earlier so the input stage right before input transformer is like igor sontec debalancing stage but with a decoupling cap instead of a servo (then input level pot). Not using the chip input at all.

I have several different types of DOA opamps so I thought other builders might be interested what effect they have.

http://www.groupdiy.com/index.php?topic=27972.msg618444#msg618444
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on June 15, 2012, 08:31:03 AM
HI
I encountered a strange problem.
I have problems with unbalanced connections and 176.
My Amek M2000 has unbalanced inserts (pin 1+3 connected to ground)
When increasing the input, the compressor goes into oscillation
and begins to pulse compression ...
I do not have this problem with balanced connection
you know what can be?
thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on June 15, 2012, 08:53:54 AM
hmm strange. are you using the ina and drv chips? maybe try disconnecting the ground pin on the cables you use to interface with you console. sounds strange. are you using a patchbay?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on June 15, 2012, 09:20:56 AM
I'm using only Ina134 on input and transformer on output.
Yes i'm using patchbay ( butt all my compressor are connected to the patchbay)
Thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on June 15, 2012, 01:00:56 PM
Maybe check and make sure their isn't a short in your patchbay making the input feed into the output? thats the only thing i could think of.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on June 15, 2012, 08:15:24 PM

I'm sure there are no shorts, I plugged in the same position, with no problems other compressors....
I will experiment
thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on June 21, 2012, 01:19:11 PM
hello
I tried everything but still have a very high background noise.
I would try to exclude one of two tubes, because I noticed that if approached the hand, make much noise.
What resistance should I use to simulate a tube (for heater)?
thanks
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: nokama on June 23, 2012, 02:03:29 PM
Hi All,

I have a rev 1 board that needs stuffed..

I'm new to this diy thing, and was wondering if anyone in the UK has compiled a parts list from the BOM?? Headers in particular I'm having trouble with..

Also, if you've done a multi buy to get parts, and have spares at a reasonable price, let me know, I'd be happy to take some off your hands for what I need..

Here's hoping:D
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on June 23, 2012, 09:04:22 PM
Hi All,

I have a rev 1 board that needs stuffed..

I'm new to this diy thing, and was wondering if anyone in the UK has compiled a parts list from the BOM?? Headers in particular I'm having trouble with..

Also, if you've done a multi buy to get parts, and have spares at a reasonable price, let me know, I'd be happy to take some off your hands for what I need..

Here's hoping:D


The secret to the headers is something that I've think I have solved...I always though headers were the most confusing part of DIY with all the different kinds and essentially doing NOTHING for sound quality, but very important for build/ease of build purposes.
SO  2 major things I've found regarding headers.

Bulk buying 2.54mm headers in 40 pin strips and breaking them off in sections to fit you needs.
Using DuPont connectors so connect the headers.

Save you tons of $$$$$


Examples:

http://www.ebay.com/sch/i.html?_trksid=p5039.m570.l1313&_nkw=40+pin+headers&_sacat=0


http://www.ebay.com/sch/i.html?_nkw=dupont+connectors&_sacat=0&_odkw=40+pin+headers&_osacat=0

thats my 2cents hope it helps someone!

Abe
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: astroschnautzer on June 26, 2012, 11:50:48 AM
Tayda has pretty cheap headers, and many other basic components: http://www.taydaelectronics.com/connectors-sockets/pin-headers.html
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on July 08, 2012, 01:04:58 PM
Hi guys,

i finished my build some days ago. After first powering up it was dead quiet, actually it was dead..  ;)
After tracing the audio signal I lost it at both tubes, checking the tube voltages showed that the plate voltage was very much to low (1.5V). Tracing the plate voltage leads me to VR1. I found out that the outer-line point for the trim pot was not connected to the middle one in-line on the pcb.  After fixing that the plate voltage was ok and audio was passing the unit, but no compression...  >:(
So, i bridged all trim pot outer-line points  to the middle in-line ones, after that it seems that the unit is now working so far. I have to do some finishing and calibration work...

One point makes me currently wondering, my meters are working counter clockwise...  :o
I use "standard" 1mA meters. Switching on they go to 1mA and then show reduction....

Any hints on that!?


ROCK-ON!


P.S. Noise floor @59.5db on both channels. Still rectifying on-board.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on July 09, 2012, 08:23:59 AM

One point makes me currently wondering, my meters are working counter clockwise...  :o
I use "standard" 1mA meters. Switching on they go to 1mA and then show reduction....


Thats how they work, the "old school" way of showing compression, 1176 style. You probably want to do the off board rectification dealio...kinda a pain but really worth it.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on July 09, 2012, 01:07:01 PM
Hi Abe,

thanks for the infomation about the meter. I was uncertain about them, because the pic of the finished units showed
db-Meters with a scale clockwise e.g. the hairball meter. But good to know that i'm fine...  ;D

For the noise level, i will go step by step, there's still a lot of work to do ... and maybe I'll end up with the off board rectification (parts are laying in the box :) ).

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on August 13, 2012, 09:28:31 PM
Hi guys,

so tonight i finished the off-board rectification, but it doesn't seemed to have a big effect on my build ??? ???
Noise level in ProTools is around -64.5db in- and output full engaged.

Another thing concerning the tubes makes me wonder, the tube on the left channel show at heater pin 4 13.8V and at pin 5 7.0V and at the right channel i only get 7.0V at pin 4 and 0.0 V at pin 5  ???
Is that normal?

Plate voltage left 91.6/91.7V, right 93.0/92.8V.

Any new hints on calibration??

Testing will go on...

ROCK-ON
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on August 14, 2012, 06:46:10 AM
Do you have a scope? The noise has to be coming from somewhere... Also you heaters should be clocked at 12.6V.

The off-board rectification should really clean up the hum.

Let me ask you, your still using all the caps on board right?
 
Also try putting another 100uF 250V cap in between one of the 1K resistors on the HV line.

I have mine will hum down around -90dB.

Also your power TX is far away right?

Also (last but not least) how is your grounding? Every pin 1 of the XLRs should be connected to chassis and then take the pin1/chassis connection of the 1st input and connect that to the ground of the PCB.

Anyway, sorry for the trouble & hope this helps!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on August 14, 2012, 08:13:58 AM
Hi Abe,

Thanks a lot for the reply!
Well, yes i have a scope, but until now i didn't trace the (noise) signal.
I did the off board rectification as you discribed it, so all caps are still on board plus the additional ones off board.
The power TX is as far away as possible, moving around seems to have no effect.

I'll check my grounding!

For the heaters, both at each tube have to have 12.5V, rigth!?
So here I really have a problem  :(

Thanks and ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on August 14, 2012, 08:32:45 AM
Hi Abe,

Thanks a lot for the reply!
Well, yes i have a scope, but until now i didn't trace the (noise) signal.
I did the off board rectification as you discribed it, so all caps are still on board plus the additional ones off board.
The power TX is as far away as possible, moving around seems to have no effect.

I'll check my grounding!

For the heaters, both at each tube have to have 12.5V, rigth!?
So here I really have a problem  :(

Thanks and ROCK-ON!


Good! Ok each tube needs 6.3V but the tubes are wired in series, so the "top" tube should be 12.6V and then the "top" of the second tube should be 6.3V (or close)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on August 14, 2012, 02:20:40 PM
hello
this is my experience:
for me all the noise problems came from interstage transformer (from EDCOR).
I changed the transformers with Lundhal and the noise is gone....
I hope it can help
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on August 14, 2012, 05:07:16 PM
Hi ilfungo,

great you share your experience!
I currently use although Lundhal for the interstage and I did them off-board (for noise and
easy  changing option, btw. i did all the transformers off-board).


@Abe:
I just checked my grounding: I have pin 1 on both input connected to the case, the output pin 1 are open.
I run one wire from one input to input 1 left at the pcb.
Connecting the output pin 1 to the ground doesn't change anything.
I don"t think it's a grounding problem.... :o
Well, yes, 6.3V for the heaters! I have reduced the heater voltage pin 4 left channel tube to 13.0V,
less makes some strange meter movements... :o
But I guess 13.0V is fine...leads to 6.5V/6.5V.

Well, for the noise level I'm getting closer... one problem lies around the NE5534 output (left). Pin 8 COMP is reading -2.1V (right -0.8V). What could cause this??
Noise at the NE5534 input is nearly the same on both.
V_in = 15.9V, Balance Pin 1 = 13.5V.


ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on August 15, 2012, 11:09:47 AM
Are you using shielded wire for input output pot wiring? I wouldn't worry too much about the comp pins...The hum has to be getting into the board from somewhere....

is it 60hz hum or 120hz?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on August 16, 2012, 04:45:12 AM
Hi Abe,

thanks a lot for your reply.
Well, good point. I use shieded wires for the input but currently use the shield as third wire; I'll check that.

So far I traced by scope the noise through the board, i couldn't find any big level changing coming for
the XLR input until the NE5534. After the NE5534 I could see a massive noise level increase, so I am of the assumption that the problem must be laying around the NE5534 at the output stage!?
And the left NE5534 is even worth than the right one. (Swapping doesn't change anything!)

I'll have to check the frequency, but as it looks to me the hum is masked in the white noise level anyway.

In your prinzipal diagramm it's not 100% clear to me how the NE5534 is feed.


ROCK-ON!

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on August 16, 2012, 10:27:11 AM
...so I am of the assumption that the problem must be laying around the NE5534 at the output stage!?

Well the output stage is were the makeup gain is, so the output ne5534 has a lot of built in make up gain, so the signal (and the noise floor) are being amplified quite a bit, so are you sure its not coming in before that? my guess is its comming in at the tube section, have you tried switching tubes?

Also if you have a PC, rightmark audio analyzer is a great program to check noisefloors
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on August 17, 2012, 03:09:08 AM
Hi Abe,

again, thanks for your help.

Unfortunately I'm not able to do some new tests before next friday.

I'll let you know!

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on August 26, 2012, 01:52:21 PM
Hi,

back again to the noise floor, it is approximately -67.5 db for both channels.
Level and form don't change along the signal chain until it meets the output NE5534.

The dominant frequency seems to be 95kHz.

When the unit is powered off i measure a noise floor in PT around -88db, unconnected it's -93db.

I think i'll leave it now as it is.

Next point is calibration.
After trying the "thump method" without any satisfying result (well maybe i'm deaf, but i didn't hear any
thump) all trimer were messed up...
To get them back aligned I did this...
For VR3 and VR9 i measured the voltage at R5 and R6 and equaled them, matching both channels. (92V)

For VR1 i measured the resistance between R1 and R3 and matched it between both channels (30 Ohm)

Any tips on that?

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: herrmann on August 26, 2012, 04:53:14 PM
Check this post http://www.groupdiy.com/index.php?topic=22291.0 (http://www.groupdiy.com/index.php?topic=22291.0)
You will hear the thump with this method.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on August 27, 2012, 12:19:52 PM
Hi,

back again to the noise floor, it is approximately -67.5 db for both channels.
Level and form don't change along the signal chain until it meets the output NE5534.

The dominant frequency seems to be 95kHz.

When the unit is powered off i measure a noise floor in PT around -88db, unconnected it's -93db.

I think i'll leave it now as it is.

Next point is calibration.
After trying the "thump method" without any satisfying result (well maybe i'm deaf, but i didn't hear any
thump) all trimer were messed up...
To get them back aligned I did this...
For VR3 and VR9 i measured the voltage at R5 and R6 and equaled them, matching both channels. (92V)

For VR1 i measured the resistance between R1 and R3 and matched it between both channels (30 Ohm)

Any tips on that?

ROCK-ON!

Hello!

The hum is getting in somewhere, could be a lot of different things going on. Somehow I don't think the power is getting correctly rectified and smoothed from the off board rectification. Because if it was there would be no  100hz to dirty up the signal.

Anyway, also on doing the sidechain, make sure you HPF the audio signal you are feeding the compressor to trigger it. You will hear the thump :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on August 27, 2012, 06:33:09 PM
Hi Abe,

thanks a lot for your help!!
I just want to push this project to next level, so please for give me...

I'm not sure if i got it right, but i guess the rectification is right!! (noise is @95kHz)
There's no indication that the noise floor has some power hum relation!? It has to come from somewhere else...!??
You're right, it could be a lot of sources... maybe my test environment (just putting the unit on my desk (crapy behringer)) has some impacts on the results...  or who knows...

I'll post some pix, when i've cleaned up some things :)

Calibration and new meter scale are the next steps!

Great project...!!!
 
ROCK-ON!


P.S.:
unbelievable that is project started a year ago!!! 



Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on August 27, 2012, 06:44:10 PM
Wow the noise is in the 95 Khz region? Sorry I just assumed you meant to type 95Hz which if your using 50hz power mains, 100hz would be right about were the rectification hash would be. Anyway, if its above in the 95khz region how are you measuring that? With a scope I expect?

Wow that is krazy its been a year!! Time flies!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on August 29, 2012, 12:29:18 PM
Hey,

thanks for the link Hermann!
Do I get it right, the sinus has be switched ON and OFF once per second? How long has the OFF-Phase to be?
I'll try that later.

@Abe: Yes, i'm using a scope for that! It's a fine sinus that can be detected.

Next Friday night I'll do some test again.

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on August 29, 2012, 12:43:09 PM
Hey,

thanks for the link Hermann!
Do I get it right, the sinus has be switched ON and OFF once per second? How long has the OFF-Phase to be?
I'll try that later.

@Abe: Yes, i'm using a scope for that! It's a fine sinus that can be detected.

Next Friday night I'll do some test again.

ROCK-ON!

You want the silence  long enough for the compressor to recover from compression. What op-amps are you using?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: dogma on October 28, 2012, 08:58:22 PM
Hey - first up, great project. I;m about to purchase a PCB and was wondering if anyone had a mouser/digikey parts list for a DIY noob like myself. Also, what was the parts cost roughly minus case and transformers. Thanks very much, Matt
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on October 29, 2012, 03:15:15 PM
Hey - first up, great project. I;m about to purchase a PCB and was wondering if anyone had a mouser/digikey parts list for a DIY noob like myself. Also, what was the parts cost roughly minus case and transformers. Thanks very much, Matt

Hi Matt,
You want to go to the Rev 2 thread, and look at the 1st post for all info.
Thanks,
Abe
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on November 26, 2012, 04:47:46 PM
Hi Abe,

it has been a long run, finally here are some pictures of my build.
But i'm not sure if i'm finished yet... thinking about DOA for Input/Output, Timing Caps experimental ....
And still I'm measuring around to check all sort of things... looks all good so far.
One tube (old Ampex) shows a different compression behavior  than the other (more color and tube style maybe!? :) ) and one timing cap
shows a different meter response!?

To me, a rotating switch for different timing caps is something that I would think about for a next build or a setup up to change these easily.

After a long run (over one year I guess) it has been a great project to me, learned a lot, had a lot of fun and had always had a target for my spare time :) THANKS!

Next some sound shout-outs have to be done :) Looking forward to that!!

ROCK-ON!



P.S.: Front panel from [email protected]
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on November 26, 2012, 04:51:07 PM
... and the inside as well...  8)

I'll have to work on my wiring...
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on November 26, 2012, 04:58:36 PM
... and here some measurements i did to make my own meter scale...

I adjusted the threshold to a minimum, as much as I could (-25db), as you see :) :) :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Script on November 26, 2012, 10:17:03 PM
Hi Dr J,

what meters did you use?

s
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on November 26, 2012, 11:46:51 PM
Dr_J Veryy cool build! Glad to see it off the ground :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: sedit1 on November 27, 2012, 01:37:36 AM
Hi,

just starting this project and I need some opinions?
I'm building this mainly to use in master buss, first I tought that I would use Lundahls but after reading the thread I got intrested about Edcors adding some nice character. So do you guys think that using Edcors will add too much characted If used mainly in master buss?

Thanks!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Dr_J on December 01, 2012, 11:30:57 AM
... meters are 1mA,  cheap Hong Kong ones (e.g. evilbay).

ROCK-ON!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Esoterimix on December 09, 2013, 04:55:25 PM
Anyone have opinions on whether it's really worth the couple extra dollars to get the 1/2 watt TX's from edcor instead of the 1/4 watt PC Tx's?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ding on December 09, 2013, 11:01:04 PM
I vote for a Rev 4 thread to be started by Abe. I think the boards are different enough to warrant it. Just a thought. ;)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Spencerleehorton on December 10, 2013, 03:50:15 AM
Hi Guys,

anyone got a rough estimate in price for the overall build please?

regards

Spence.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ding on December 10, 2013, 07:52:51 AM
This build is so customizable that it can be pretty cheap but then again it can get pretty expensive depending on many factors. Mine is looking like around $700 with cinemag/edcore iron, vintage meters, a milled front panel/collective 2U case and sato knobs. Since I am in the US I can save a bit on a power tranny. You can definitly go lower with all edcore trannies, no output transformer and a DIY case. Or you can go all out with it using pio caps, Lundall iron, 6 Hairball 990-DOA's, etc...

Alain
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: berkleystudios on December 10, 2013, 04:23:12 PM
I vote for a Rev 4 thread to be started by Abe. I think the boards are different enough to warrant it. Just a thought. ;)


I agree I think a rev 4 thread should be started.


Im definitely going all out on this one, stepped switches instead of pots, 6 discrete op amps; have gar1731 ready to build but will be trying Abe's 2520s and Gustav's Nuemman OA10, (possibly even using Abe's dip 8 discrete op amps to make my build 100 discrete), 100% dale resistors, pio caps. custom 2 U face plate, think im going with lundahl input, edcor out, inter-stage is still up in the air....

I have 4 6bc8 tubes but they are unmatched... so I just ordered http://www.ebay.com/itm/200983195574?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649  hope they are compatible. I read the heater was slightly different but that E180CC would work


its going to be costly but sooo worth it I think. cant wait to get the boards in! already have a lot of the pieces in....
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ding on December 11, 2013, 11:33:02 AM
Jesse at http://www.audiotubes.com (http://www.audiotubes.com) matched me a pair for a very reasonable price. For interstage I would go with Cinemag. They sound great and David is just one great dude to deal with. I'm going to build the DOAs that came with it if I can only figure out the parts list.  :) I'm doing Edcore interstage for now but might throw some Lundalls down the line. I read that the Edcore's have that vibe and the Lundall's are better for mastering. Wish there was a switch you could flip to switch between the two. ;D
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: berkleystudios on December 11, 2013, 01:07:48 PM
Wish there was a switch you could flip to switch between the two. ;D

now theres an idea....


this build just keeps getting better and better haha
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Spencerleehorton on December 27, 2013, 03:40:55 PM
HI,

any news on when the pcbs are being sent?

regards

Spence.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: berkleystudios on December 27, 2013, 03:51:25 PM
HI,

any news on when the pcbs are being sent?

regards

Spence.


should be on the way, people have started getting them
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Spencerleehorton on December 27, 2013, 05:24:30 PM
Ah, thats what i thought as was told about a couple of weeks ago they would be coming but not received anything yet? :(

regards

Spence.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: shot on December 28, 2013, 06:41:14 PM
Same here...

I've ordered and paid for three boards back in july... still haven't received those boards...

 :(
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: rmaier on December 29, 2013, 02:23:55 AM
They seem to be coming in slowly but surely. Just got mine today (Calgary).
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: prh on December 30, 2013, 05:50:14 PM
They seem to be coming in slowly but surely. Just got mine today (Calgary).

Mine arrived yesterday in Australia.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: druu on January 01, 2014, 10:32:21 PM
They seem to be coming in slowly but surely. Just got mine today (Calgary).

Mine arrived yesterday in Australia.

Here's hoping mine arrives soon then!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: shot on January 02, 2014, 08:57:48 AM
I'm checking my mail box every day...
Fingers crossed...
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: e.oelberg on January 10, 2014, 05:31:36 AM
did you get your's I'm still waiting in Berlin
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: shot on January 10, 2014, 06:55:18 AM
Nope... still waiting...
 ???
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Spencerleehorton on January 12, 2014, 05:58:24 AM
HI, Im still wait in UK.

regards

Spence.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: tazwolf on January 12, 2014, 09:29:31 AM
Got Mine here in Sweden on Friday, although the packaging had split so the opamp PCBS seem to have got lost but the
Main pcb and PSU pcb are intact.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mrdarwin on January 13, 2014, 03:22:05 AM
Got Mine here in Sweden on Friday, although the packaging had split so the opamp PCBS seem to have got lost but the
Main pcb and PSU pcb are intact.

Hi!
Received my boards on thursday 9th... The packaging had split too and one opamp pcb lost!!!
Did someone noticed that the opamp footprints don't match with original 2520footprints? Do we have to use only Abe's opamp?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: tazwolf on January 13, 2014, 07:49:00 AM
You can use any discrete opamp i believe, but the bigger problem is the pcb for the tube, which
is harder to replace.

/Taz


Got Mine here in Sweden on Friday, although the packaging had split so the opamp PCBS seem to have got lost but the
Main pcb and PSU pcb are intact.

Hi!
Received my boards on thursday 9th... The packaging had split too and one opamp pcb lost!!!
Did someone noticed that the opamp footprints don't match with original 2520footprints? Do we have to use only Abe's opamp?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: e.oelberg on January 13, 2014, 11:26:23 AM
boards arrive, look fantastic great job abe !
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: shot on January 13, 2014, 04:14:29 PM
Boards arrived!
Yesss! Finally!

Now we wait for the official BOM since DOAs don't have values silkscreened...

:) :)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: leitmo on January 13, 2014, 04:19:36 PM
Boards arrived!

i'm very excited!

Thanks for your work and patience Abe!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: prh on January 14, 2014, 03:33:09 AM

Hi!
Received my boards on thursday 9th... The packaging had split too and one opamp pcb lost!!!
Did someone noticed that the opamp footprints don't match with original 2520footprints? Do we have to use only Abe's opamp?

I had a look at this just now.

The footprints on Abe's opamp boards and on the main board match each other.  However, these footprints do NOT match the 2520/990 footprint.  It is almost like Abe's opamp footprint is upside down.

It would be really helpful if Abe would confirm is this is intentional or an error.  I am a little disconcerted by the lack of a v4 schematic and official BOM and wiring diagram.  The opamp boards don't have values on the silk-screen, so without a schematic these are useless. 
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: abechap024 on January 17, 2014, 01:30:40 AM
It was a mistake. DUH! I feel pretty dumb. But the DIP8 are correct and you can always install a 3rd party 2520 upside down from the bottom....  ;) Let me know if you didn't get any 2520 pcbs with the same weird footprint and I'll send you some.

All boards sent out! Sorry for the longer wait to some more than others.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: mus1k_freak on January 28, 2014, 08:35:38 PM
Is anyone making a case for this project? I'm gonna have to build one now!   ;D
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ding on January 28, 2014, 09:40:48 PM
I know plenty of people have been posting in this thread for the Rev4 boards it has it's own thread. You might get better responds there in the future. Dan is still making a case for this project AFAIK.
http://collectivecases.com/prr176.html (http://collectivecases.com/prr176.html)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Spencerleehorton on February 11, 2014, 12:16:43 PM
Hi all,

just got my boards, looks great btw, thank you very much.

regards

Spence.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: coriolis on February 19, 2014, 04:37:47 PM
Ahem...so back to Rev 1 boards  :)
Just finished mine today (only took me like 2 years  ::), but ack, no sound - only hum! Sounds a lot like the problem ilfungo had (his file on soundcloud sounds exactly like what I'm hearing).

My build:
- Offboard rects and filtering (I stuffed all the caps onboard as well.
- Grounded everything as per the instructions in this thread, but currently to the CT input on the main PCB - not the *G point.
- Chip inputs and outputs.
- 5534 for opamps
- Edcor pcb mount iron
- Right now, my I/O wiring is unshielded (just twisted wires) so I was expecting some hum - but NO SOUND?

Observations:
- I adjusted the heaters to around 12.5V on the first tube and the second is half that. Okidoki. But then after about a minute after I switch the comp on, the heater voltage drops to about 3.5V on the first tube (and half that on the second), with most of the hum fizzing out. Still no sound though.
- The tubes seem to be somewhat microphonic. They seem to be picking up the sound if I tap them or their surroundings.
I tried swapping them around to see if that helps with anything, but no. Not the heater prob either. I do have more tubes I can try though.

Why the heck does the heater voltage do that? A bad cap? Rifts in the space-time continuum?

A question:
- The sidechain bias ckt. I stuffed the regulator and all that. Do I leave out all the stuff in the optional box then? No resistor, jumper and LED? Or what? A bit confused about that part.

Hope anyone still reads this thread!

Update: Seems the 350 reg got too hot and shut down after a minute or so. Put a bigger heatsink on, and now the heaters stay on. It still gets rather hot to the touch. Not blistering, but still.

It seems there is a mod I need to do around the INA134, but other than that, I am leaning towards heavy grounding issues causing my problems. Had the grounding set up to Abe's instructions in this thread, but tried this http://groupdiy.com/index.php?topic=14147.0 (http://groupdiy.com/index.php?topic=14147.0) as well. That is to say, Donnysparks last drawing combined with squibs following comment. No dice.

In this thread http://groupdiy.com/index.php?topic=46776.20 everyone seems to agree that the common regulator 0V node is what should be connected to chassis. Would this be the *G...errr...spot? :D

Thanks...
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: G-Sun on March 12, 2014, 04:08:04 AM
What do you use the PRR 176 on?
Is it an affordable and easy build?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: DIY-solder on March 17, 2014, 07:19:51 PM
Hi,

looking forward to build this one. I just tested friend's version and I like it ;)

I have one question (for now) exactly what power transformer do I need?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: weiss on September 13, 2014, 10:29:08 AM
I have one question (for now) exactly what power transformer do I need?
Just read the manual..

Quote
The power supply for the PRR-176 has 5 power supply rails. A
bipolar +/-16V power supply drawn from one 18VAC tap. A 1.5V biasing
voltage taken from the +16V rail. A 12.6V rail for the tube heaters
taken from one 18VAC tap via a voltage dropping 10R resistor. And
finally a 100V rail for the tube plate voltage

btw this seems like a nice project, i think i am going to build this in the near future :)
how much did you guys totally spend on tubes, tx's etc?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: gt_jumper on January 03, 2015, 11:14:52 PM
I have one question (for now) exactly what power transformer do I need?
Just read the manual..

Quote
The power supply for the PRR-176 has 5 power supply rails. A
bipolar +/-16V power supply drawn from one 18VAC tap. A 1.5V biasing
voltage taken from the +16V rail. A 12.6V rail for the tube heaters
taken from one 18VAC tap via a voltage dropping 10R resistor. And
finally a 100V rail for the tube plate voltage

btw this seems like a nice project, i think i am going to build this in the near future :)
how much did you guys totally spend on tubes, tx's etc?

I cant find a power transformer with those in and outs, at least for 240v australian power.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ForthMonkey on January 04, 2015, 02:32:34 PM
Now i'm building V1.Can i use this version's transformer for V1?

Input 10K:10K
Interstage 10K:600
Output 600:600
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ForthMonkey on January 09, 2015, 06:46:37 PM
 :o
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: bluesbaz on March 10, 2015, 05:28:40 AM
Its late and I could use some help and encouragement. Signal flows on both sides but I can only get one side to compress.
I realize my main problem is I have no idea how this thing works and that would be the first place to start really. I have swapped the tubes for no difference. I have a rev 2 board and I can get compression which does not show up on the meter when jumping   r58/56 I am at a loss here and really just need to understand the circuit to know what I am missing here.  Thanks again!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Baltimore on June 19, 2017, 09:10:55 PM
Does anyone have the original documents for this? i have a PCB i'd like to finally build.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: vitopower on June 22, 2017, 12:34:21 AM
Just emailed rev 4 manual & BOM with docs (wiring guide, schematics, jumper info, layout) to admin, should be available soon.   8)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: saint gillis on December 20, 2017, 10:12:20 AM
Is the triodes' matching as critical as in the UA 175/176 ?
Or as another way of asking the question, how much does the 1k vr3 plate current trimmer help for the triodes' matching?
Did you guys had to buy a full truck of tubes to get a suitable one or was it quite easy?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: saint gillis on April 25, 2018, 03:12:13 PM
  Hello dear friends, here's my PRR 176, it has 2 ratio modes, "compress" and "limit" :

http://sub-continental.com/partage/d%26d%20schematic.jpg (http://sub-continental.com/partage/d%26d%20schematic.jpg)

  We could use a that1246 instead of the 2:1 transformer, if you use a 1:1 transformer just change the gain of IC1 but use the unity gain compensation capacitor.
  I used a 600:600Ohm transformer before the grids, because it is driven by a low impedance source and the grids have a high impedance so a lot of transformers would work here.
  The anodes drive a LL1521, because they have a high impedance we need a good input transformer like LL1540 or any good quality line input transformer.
  If you use other transformers' ratios just change the gain of the according stages (IC1 IC2 IC3).

  The trimmer before IC2 is to ajust tube gain differences between left and right channel, you can trim to 1dB, if you need more just use a 20K trimmer with a  68K for instance.

  The deeser is not very usefull (to me), so I will modify it to get a 2nd HPF mode like 100Hz or I don't know yet..

  Well, it's an awesome compressor and thank you PRR and Abechap and everybody who provided great brain juice on the forum!

  Here are some pics of the finished unit :
(https://scontent.fbru2-1.fna.fbcdn.net/v/t1.0-9/31349737_2177496438934683_1928594566638211510_n.jpg?_nc_cat=0&oh=dc3ed198bc02b7764849585276896b81&oe=5B64D7C2)

(https://scontent.fbru2-1.fna.fbcdn.net/v/t1.0-9/31277566_2177496448934682_2431074859532348706_n.jpg?_nc_cat=0&oh=eea2d0d965be78d0f16c41f74c7c49d6&oe=5B64DB34)

(https://scontent.fbru2-1.fna.fbcdn.net/v/t1.0-9/31120725_2177496612267999_3796082055512420558_n.jpg?_nc_cat=0&oh=96c41360311111ce3202fb8d03cabaef&oe=5B5153BD)

(https://scontent.fbru2-1.fna.fbcdn.net/v/t1.0-9/31265372_2177496462268014_1848492216129979402_n.jpg?_nc_cat=0&oh=2523657c0e6029856931e5702cef433e&oe=5B65F83D)

(https://scontent.fbru2-1.fna.fbcdn.net/v/t1.0-9/31301932_2177496622267998_4023380853964713038_n.jpg?_nc_cat=0&oh=6dc37cb733dd203509581f854dfcb24e&oe=5B9AF672)
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: scott2000 on April 25, 2018, 04:20:17 PM
Marvelous! Thanks for sharing!!!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: saint gillis on May 03, 2018, 05:37:52 AM
Also the cathode balance trimmer may not necessarily be a multiturn, maybe because I used well balanced tubes but I found difficult to really adjust the low-frequency distortion.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: saint gillis on July 15, 2018, 08:08:13 PM
Also the cathode balance trimmer may not necessarily be a multiturn, maybe because I used well balanced tubes but I found difficult to really adjust the low-frequency distortion.

Yes you are right, I didn't get any significant difference in low frequency distortion moving the trimmer...
I ordered a transformer from Audiophonics 6,3VAC  14VA - 130VAC  14VA - 34VAC-CT  35VA, the heaters are AC
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: saint gillis on July 16, 2018, 05:52:39 AM
Yes, it's slightly oversised but the price was for a 63VA transformer. For the low voltage it depends which op amps you use, see the datasheets make the math and use the double power..
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: saint gillis on July 16, 2018, 05:56:45 AM
If you use leds etc you need to add their current also
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: scott2000 on July 16, 2018, 05:59:23 AM
Thanks!

Did you do your own pcbs ?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: saint gillis on July 16, 2018, 07:19:06 AM
Yes eagle cadsoft, iron perchloride, and go. Also I had thoose esoteric lundahls hanging around
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: scott2000 on July 16, 2018, 07:30:47 AM
Yes eagle cadsoft, iron perchloride, and go. Also I had thoose esoteric lundahls hanging around

Yeah... I like how you did  it. You used every inch of that chassis....How would you say you feel about it? Are you really happy with the way it operates and sounds? 
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: saint gillis on July 16, 2018, 07:37:05 AM
Yes definitely! It's awesome. Thanks to PRR for the sidechain circuit.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: scott2000 on July 16, 2018, 08:22:27 AM
Definitely! Thanks so much for sharing your project! It's really inspiring!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: shabtek on July 20, 2018, 05:57:32 AM
Another beautiful diy project!congrats
Definitely! Thanks so much for sharing your project! It's really inspiring!
indeed
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ravachol on January 10, 2019, 12:10:35 AM
Is the AC Sound website still up and running? The last time I looked, it seemed kinda sketchy.
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: weiss on March 20, 2019, 06:24:37 PM
Is the AC Sound website still up and running? The last time I looked, it seemed kinda sketchy.

seems offline. just wanted to order some pcb's...  :(
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: scott2000 on March 21, 2019, 12:39:27 AM
Didn't someone take the remaining boards from Abe? Was it collective cases???? I'm not sure if that's right or even relevant in timing but, I remember seeing some boards not too terribly long ago......



edit//////maybe it was the clx160....now that I just looked.... :-[

http://collectivecases.com/?product_cat=pcb


guess you could always reach out to Dan and ask if he knows anything about some being around??
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: weiss on March 21, 2019, 03:02:09 AM
Thank you!
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Jeremy.Starseed on May 02, 2019, 03:29:48 PM
Does anyone have the original documents for this? i have a PCB i'd like to finally build.

I also have a PCB slowly filling up (OK, so really slowly). A 2011 "Rev 176", and well, I'm wondering if anyone here has the documents still?

None of the documents are online, I notice (and I never received the other PCB's I paid for, nor heard anything back). Probably a good reason for that...I remember there was even a "build butler" online at one point, such a bummer things went off track.

Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: scott2000 on May 03, 2019, 07:21:36 AM
Some rev4 docs/links here... not sure how relevant to you  though??.... guess should be useful...

There's a build butler link in there somewhere that works as well afaik....

https://groupdiy.com/index.php?topic=54563.580
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Jeremy.Starseed on May 05, 2019, 01:36:08 PM
Unfortunately it all got taken down before I got to the project. I got a Rev 2 board which I don't have access to now, and decided to finish the rev 1, or "rev 176" as is printed on the PCB. That's this thread, I believe.

Looking around for parts for it now. Does this ( https://www.don-audio.com/Edcor-PCW10K-7K-300-32 ) look like the right output transformer?

In the Rev4 BOM it says "Edcor PWC"  in a couple of places. This one has the  code Edcor PCW10K-7K/300-32 and is the closest, linguistically speaking.  As for function, it looks about right to me, but hey...wiser to ask.

Another question is:  where the funkiest-sounding OP amps are to be found these days?

Clean, OK...but not sterile, or I will regret the whole build. The behavior of the PRR-176 is a little on the "spitty" side, from what I can tell, so something with a smooth and sweet response would make sense.

Thank you

JB I I
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: Jeremy.Starseed on May 05, 2019, 02:57:51 PM
Thanks for chiming in, I just found the correct reference, and you're right, 1:1...but, it says 4:1 on this early version, and there are two footprints, marked Edcor and 4:1. I am guessing they fit the PC and PCW versions, having found references to those types in the original thread. 

The thing is, I want to interface old 600 Ohm gear, and this unit is said to have a ton of gain inherent, no? My sound card and one other piece of gear are my only typical 10K devices.  Perhaps that one I asked about is a good fit?
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ruffrecords on August 10, 2019, 02:01:27 PM
Looks like acsound.com is no more. Anyone have another link the the docs?

Cheers

IAn
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: vitopower on August 10, 2019, 02:07:09 PM
just sent you two emails w/attachments
Title: Re: PRR 176 vari-mu (check first post for docs)
Post by: ilfungo on August 10, 2019, 02:09:47 PM
If needed I have some rev 2 docs.
Send me your email.