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General Discussions => The Lab => Topic started by: [silent:arts] on August 17, 2008, 05:13:22 PM

Title: the pimp / mod the Poor Man 660 thread
Post by: [silent:arts] on August 17, 2008, 05:13:22 PM
started this to keep the original support threat a little bit easier.
you are welcome to post your suggestions here.
Title: the pimp / mod the Poor Man 660 thread
Post by: radiance on August 17, 2008, 05:43:08 PM
Ok, here goes....

Would it not be nice to have a MS facility build in just like the original Fairchild 670? Maybe done passively with two 1+1:1+1 transformers. I've some 1517 Lundahls laying around that would be nice for such a thing but I'm sure Edcor has a nice (& cheaper) transformer for the job as well.....
Title: the pimp / mod the Poor Man 660 thread
Post by: flintan on August 17, 2008, 06:04:16 PM
Volker, great idea!  :thumb:  I have a feeling the PM support thread will be veery long..

Radiance, i was thinking about that as well. I'm planning to try and build up the original 670 lat./vert. switching with some relais around the in+out transformers of the amp section. I'm planning to use Edcors and try to desolder the center tap to have dual windings for that job. Don't know if/how it will work...

I'm also thinking of having the option of either in/out/in+out encoding.

Any thoughts on this? Any other related mods that would add to this, metering, time constants, stereo linking etc?
Title: the pimp / mod the Poor Man 660 thread
Post by: EmRR on August 17, 2008, 06:09:33 PM
The original switches the 600 ohm input AND output transformer windings to both encode and decode.  So you'd need 4 external transformers for a PM670.  Or, as I said in the other thread, hack the appropriate Edcor center taps apart to get separate windings and do it there.  Both CT wires come out to the CT lugs.    Study the original schematic if in doubt.  I have had the Edcors apart in this manner (for repair of mis-wiring from Edcor), but have not tried them in a M/S configuration.  

NONE OF THIS HAS BEEN ATTEMPTED IN THE FIELD WITH A PM660!
Title: the pimp / mod the Poor Man 660 thread
Post by: EmRR on August 17, 2008, 06:09:56 PM
Matched 1M resistors from attenuator sweepers to center of the two 15K arms would give safety against attenuator failure and open grid condition.

NONE OF THIS HAS BEEN ATTEMPTED IN THE FIELD WITH A PM660!
Title: the pimp / mod the Poor Man 660 thread
Post by: EmRR on August 17, 2008, 06:49:39 PM
I'm not going to recommend any of these in particular, only point them out.  Feel free to respond with any negatives that alarm you greatly.  Note Analag considers the stock stepped attenuators with well matched resistors important.

NONE OF THIS HAS BEEN ATTEMPTED IN THE FIELD WITH A PM660!


Slightly stock attenuator variations

The existing method on the secondary keeps the level in the input iron consistent regardless of setting, and reflects a higher 1800 ohm Z back to the source(s).

If you use a 12 position at 2 dB/step you have a range of 0 to -22 dB, etc etc. Is it enough?   Analag says 12 position is fine, more steps is a matter of finer control.  Do you want or need finer steps? 24 position at 1 dB/step seems reasonable to me.  We are supposed to see 18 dB of gain available, so 22 dB range would get you down to both unity and -4, and there would be 18 dB of make-up gain available.  

One possibility is to use fewer steps plus a switchable input pad (to make up for lack of more steps) on the primaries, say 10, 15, or 20 db. Could be a 'U' pad on both audio and side chain amps.  Amount dependent on your overall attenuator plan.

Stick with dual stepped atten on the GR amp input secondary as prescribed, but use dual pot on the SC amp. That would do away with the 'ultra-precision balance' factor in the side chain, but not in the audio amp path. Considering the number of limiters that use dual pots in the audio path position, I'm not sure how much difference the average punk rock engineer would notice with them only in the SC amp.  The Fairchild uses dual linear pots with taps and paralleled resistances for the threshold; basically impossible to source.  

You could use dual pots in the audio amp, like the Gates Sta-level and several other pieces. Not as accurate, but clearly works 'good enough'. Not that you will find a 15K dual audio pot; there's one rub.  You could slug 50K dual pots down to 15K with paralled resistances, but the effect on the taper may be too strange.  


Transformer primary side attenuator variations

The Fairchild uses 1 dB/step input attenuators on the primary side.  Looks like T attenuators, but might be ladders.  

If you went with a primary side arrangement you'd probably want to stick with 600 ohm input attenuators, meaning lower 600 ohm load on input source(s), and the level in the input iron would vary with setting. You'd have to work out optimal secondary load resistances; maybe dual 15K resistors, maybe not. Only real benefit is you could use existing Daven 600 ohm ladders, which (at this junction) aren't terribly expensive. BUT, ladders will automatically kill 6 dB of input level, unless you add ANOTHER switch to bypass them at the top of the throw. Unless you already have some magically expensive Daven 600 ohm Ts. Or wire up the NYDave dual knob H pads.


NONE OF THIS HAS BEEN ATTEMPTED IN THE FIELD WITH A PM660!
Title: the pimp / mod the Poor Man 660 thread
Post by: EmRR on August 17, 2008, 08:16:13 PM
There's been no mention of stereo linking method to date, and it's not on the PM schematic. The Fairchild simply ties the two control voltages together.  Here's some food for thought.

Many limiters use diode isolation to ensure dual mono and stereo operation match in timing. The Fairchild fails to correct for this, for better or worse. As is, in the original design, if you toggle between linked and unlinked the time constants will change because of the nature of paralleling networks. We do not have the complexity of time constant switching found in the Fairchild, so it's not as if I'm suggesting we alter something that already mimics exact original operation. As far as I can tell, the only thing possibly changed by addition of diodes is the relatively minor need to overcome the diode voltage drop through additional drive on the threshold control.  

NONE OF THIS HAS BEEN ATTEMPTED IN THE FIELD WITH A PM660!

Here's a comparison of the mono Collins 26U-1 with the stereo 26U-2 for example.  This is not to be taken as a cookie-cutter drop-in, given the differences in design.  The Collins being the more common type of side chain driven from a high impedance source with fairly high bias voltages present, and the PM660 being a side chain driven from a low impedance source with fairly low bias voltages present.   The Collins manual describes the 1N459's as preventing feedback into the 1 mfd caps, to avoid increase in attack time from effective lowering of 1 mfd value.  


(http://farm4.static.flickr.com/3007/2771971717_e76b746cff_o.jpg)

The unattached connection from the 0.01 cap below runs to the link switch, then to the other identical side chain and audio channel.  
 (http://farm4.static.flickr.com/3108/2772818784_97a4faf058_o.jpg)
Title: the pimp / mod the Poor Man 660 thread
Post by: EmRR on August 17, 2008, 09:06:56 PM
Note it's very easy to separate the input of the side chain amp and implement totally separate external side chaining.
Title: the pimp / mod the Poor Man 660 thread
Post by: [silent:arts] on August 18, 2008, 04:58:41 AM
Doug,

thanks for all this great suggestions :thumb:
I hope I find the time to build a second unit, which will be the "emrr edition".
got a mail today from analag that he is busy at the moment, but observes this thread (+ the support thread) with interest. I'm sure he will comment when he finds the time.
Title: the pimp / mod the Poor Man 660 thread
Post by: [silent:arts] on August 18, 2008, 05:02:43 AM
Quote from: "emrr"
Note it's very easy to separate the input of the side chain amp and implement totally separate external side chaining.

never thought of this before, but yes, this is easy to do.
this is also a way to switch between "feed backward" and "feed forward" compression. have to try this.
Title: the pimp / mod the Poor Man 660 thread
Post by: RedNoise on August 18, 2008, 02:38:39 PM
:cool:
Title: the pimp / mod the Poor Man 660 thread
Post by: flintan on August 18, 2008, 05:49:25 PM
Lots of ideas and thougts here!  :grin:

Quote from: "emrr"
Quote from: "[silent:arts
"]this is also a way to switch between "feed backward" and "feed forward" compression. have to try this.


Hadn't thought of that!


To make a feed-forward option how would you connect the SC transformers? Paralell (would give too low input impedance i guess?), series or series with only "half" winding..or do we need some type of buffer from the input?

This is maybe not the first thing i will try but i find it very interesting and educative.
Title: the pimp / mod the Poor Man 660 thread
Post by: [silent:arts] on August 18, 2008, 06:12:22 PM
feeding the sidechain transformer in parallel to the input transformer should work fine.

I like this:
NONE OF THIS HAS BEEN ATTEMPTED IN THE FIELD WITH A PM660!
 :wink:  :green:  :green:  :green:
could be a cool new signature ...
Title: the pimp / mod the Poor Man 660 thread
Post by: flintan on August 18, 2008, 06:17:20 PM
Ok. Thanks!
Title: the pimp / mod the Poor Man 660 thread
Post by: Gachet on August 20, 2008, 10:56:29 AM
Hi,

Is that ok to feed the sidechain input with the input signal taken before the transfo ?

I wondered about a switch connected to a relay to make the job.
Is that the feedback/ feed forward mod?

Thanks
Title: the pimp / mod the Poor Man 660 thread
Post by: Gachet on August 20, 2008, 01:01:12 PM
?
Title: the pimp / mod the Poor Man 660 thread
Post by: EmRR on August 20, 2008, 01:56:38 PM
Quote from: "Gachet"
?


[silent:arts] covered it in the previous posts.   There are a lot of ways to make the connection, depending on whether you want back/forward and/or side chain input.

NONE OF THIS HAS BEEN ATTEMPTED IN THE FIELD WITH A PM660!
Title: the pimp / mod the Poor Man 660 thread
Post by: Moby on August 29, 2008, 08:53:05 AM
Quote
There's been no mention of stereo linking method to date, and it's not on the PM schematic. The Fairchild simply ties the two control voltages together. Here's some food for thought.

Sorry, can you describe solution for PM? Do you say that in stereo mode PL1 (sec center tap of input tx) have to be short connected from L and R channel? Also, can you draw that part with diode isolation?
Title: the pimp / mod the Poor Man 660 thread
Post by: [silent:arts] on August 29, 2008, 09:01:04 AM
Quote from: "Moby"
Do you say that in stereo mode PL1 (sec center tap of input tx) have to be short connected from L and R channel

Yes (the "original" way without diodes)
http://www.groupdiy.com/index.php?topic=28274&start=356
Title: the pimp / mod the Poor Man 660 thread
Post by: [silent:arts] on October 20, 2008, 10:49:54 AM
bridge rectifier diode experiments with moby:
http://www.groupdiy.com/index.php?topic=28274&start=666
(note: starts with post nr 666) :green:
Title: dual ganged pots
Post by: lewilson on October 29, 2008, 08:47:17 PM
I think Im going to try dual ganged 25k pots in my poorman 670. It looks like the taper will be o.k when each pot is in parallel with a 40k resistor. Ill let you know how it goes
Title: the pimp / mod the Poor Man 660 thread
Post by: Moby on October 29, 2008, 09:29:35 PM
Why? You want to raise input resistance? Or something else?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: bluebird on November 18, 2008, 02:52:49 AM
First off thanks to Volker and Analag for getting together such a great project !

Its been a while in the making but I finally finished my unit.

The first problem I had was a funky looking waveform even without any compression. I found out I had a meter with a high internal resistance so I ended up replacing R6 (22K) with 100 ohms. If your not using the recommended meter I suggest you check your output on a scope to make sure your not starving your 6BC8 plates.

The Main mod I wanted to suggest has to do with the time constants.

I just wasn't getting the flexibility out of the attack and release I wanted.

So I started off by adding a switch to change C4 (10uF) I used these values.
10uF, 6.8uF, 4.7uF, 1uF

I still felt like the attack knob wasn't changing the time constant enough.
I glanced over the original 670 schematic and realized it has a resistor in parallel with the time constant caps not in series that changes.

EDIT I'm sorry there are also resistors in series with the capacitors in addition to parallel. these would have an effect on attack time. EDIT

So basically I PUT (RV7) IN PARALLEL WITH (C4).

I put RV7 on a 5 position switch and used these values:


25K, 65K, 150K, 470K, and an open position (you could use 2 megs)

The higher the resistance the longer it takes the cap to discharge through it. longer release.
the smaller the cap the shorter time it takes to fill up. shorter attack.

switching up the combination of the two makes for a lot of flexibility.


I can't tell you cool this thing sounds....

If you already have a panel with only one hole for a time constant switch you can use a double pole six position switch. Play around with different caps and resistors in parallel. Heck just use the fairchild values!

Anyhow I hope someone is brave enough to try this. It really turns this thing into a magic squasher.

Peace,
Bluebird
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: CJ on November 18, 2008, 03:25:25 AM
Good Lord I though you were gone for good, how wonderful to see you!

Rock on.

What happened to the rest of the band?
I still play that CD,  love it.
Thanks again, cj.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on November 18, 2008, 07:36:15 AM
Quote
I found out I had a meter with a high internal resistance so I ended up replacing R6 (22K) with 100 ohms. If your not using the recommended meter I suggest you check your output on a scope to make sure your not starving your 6BC8 plates.
Thanks god that somebody experienced that problem. I still don't have my unit finished but it was obvious that "VU" must be some low internal meter (ma meter or ua meter). BTW, I don't think that scoping the waveform is necessarily for checking unit. Just proper supply voltage after meter. I presume that you had a huge voltage drop with few kohm meter so tubes were working with low voltage  ;). Bluebird, can U tell us about your voltage after meter? It will be great to know is somebody experienced same problem as you.
Quote
I still felt like the attack knob wasn't changing the time constant enough.
I glanced over the original 670 schematic and realized it has a resistor in PARALLEL with the time constant caps not in series that changes.
Hey, that's great pimp! Do you have a time to draw a final combination (values) of your time constants?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: EmRR on November 18, 2008, 07:51:13 AM
yes!  submit drawings if possible!  That way you won't have to explain it 38 times!   ;D
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: bluebird on November 18, 2008, 05:53:12 PM
Still Alive C.J. !! ;D

Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Kid Squid on November 18, 2008, 06:05:32 PM
Nice !

Steve
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on November 18, 2008, 09:54:52 PM
Quote
Heck just use the fairchild values!
Thanks for drawing  :) BTW, did you tried fairchild values?
Also, did you tried without capacitor in some position?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: bluebird on November 19, 2008, 11:59:10 AM
No, I didn't try the exact fairchild values. Remember I'm using TWO seprate switches. The fairchild had a double pole switch.

The best way to find the values you like (if using a single switch) is to use a decade capacitor box and a decade resistor box in parallel and just mess around with the values until you find the combinations you like.

A setting without a capacitor would mean you are left with (C3) 0.22uF. I'd imagine you would get a distorted signal when turning the threshhold up at all. I'm not sure 0.22uF is enough to filter the DC control voltage. Hey it might sound cool...
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on November 21, 2008, 09:11:21 AM
Ok, I compiled this picture so we can see what's going on with the original 670 time constant. Fastest attack is 0.2msec and position 6 seems interesting since is automatic, depending from program material. I don't want to criticize the PM just to make it closer to fairchild.  :D I have a feeling that it has "too poor time constant" so it will be great if we can hear the author comment about. I know that 10uf with variable 10k in series works, but I'm afraid that it has much larger attack time than 0.2ms , not sure about release  ???. Bluebird's version is something good for a start, but I'm afraid that without two separate switches it will be too limited. Hmm, why Analag went with 10k and 10uF? I wonder ???
(http://i52.photobucket.com/albums/g8/mobidik/660-time-constant.jpg)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: khstudio on November 21, 2008, 10:58:40 AM
Quote
Hmm, why Analag went with 10k and 10uF? I wonder

Interesting... Maybe because it works. How good though I've yet to hear for myself.
BUT if we're trying to copy a Fairchild... why not go all the way & use the original time constants & values?

The question is... will it work correctly on the PM version?

I don't know enough about it to dive into it without asking. :-[


Also,
That's great info about the METER's!!!
I got some "old school" meters that are pretty heavy duty & cool looking but I think they MAY be too beefy for the PM670. :(
They were originally labeled - one for 100 VDC & the other 100 mA.
I tried removing the resistor inside & put the diodes on them JUST to see how they'd respond as "AC" VU's & the needle hardly moved at all... compared to ALL my other AC VU's like Modutec, etc...

What "resistance" should I be getting for the PM670 to work correctly???

May be time to look for other meters... but I'd like to get these to work.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on November 21, 2008, 11:11:41 AM
Quote
I tried removing the resistor inside & put the diodes on them JUST to see how they'd respond as "AC" VU's & the needle hardly moved at all
If I understand correctly PM meter works like a DC ma meter since it's connected in series with DC supply. There is no AC voltage. Just DC voltage drop around meter resistance. I think that resistance have to be few Kohms but less can work even better since current is not static because of constant gain change of Valves. I asked few times for DC currents through meter but nobody gave me an answer  :(.
i would try 10ma meter and try to tweak with some resistance across and in series to make max movement for max GR.
Quote
BUT if we're trying to copy a Fairchild... why not go all the way & use the original time constants & values?

The question is... will it work correctly on the PM version?
I think that it should work, I don't see any reason for not... just, c3 have to be changed to 2uF....R18 is not important , I think..  ::)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: khstudio on November 21, 2008, 11:22:48 AM
Quote
PM meter works like a DC ma meter since it's connected in series with DC supply. There is no AC voltage.

Sorry, I though I was clear when I said:
Quote
"JUST to see how they'd respond as "AC" VU's"

The resistance on the meters I have measures:
DC 100 Volts meter = 100k
DC 100 mA Meter = 1 ohm

They look like the same meter & most likely just have different resistors (or not ) in them.

Do you think these will work???
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: khstudio on November 21, 2008, 11:28:25 AM
What TYPE of capacitors "Should" be used for the Fairchild time constants???

Or should I ask..

What TYPE of capacitors did the REAL Fairchinld use?
or does it even mater?

I'd think it would... tants or electro's?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: [silent:arts] on November 21, 2008, 11:39:50 AM
olives in oil are known to be the best ;D

tantals are unethical these days (and I haven't seen one in a Fairchaild yet)
electros are not the best for "time cocnstant"

mhm, I wonder why there is a film cap in analags design.
must be just for the look and the costs I think ;D

never mind
Volker
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: khstudio on November 21, 2008, 12:00:32 PM
mhm.. I wonder why people can't give a straight answer without being sarcastic? :-*
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: [silent:arts] on November 21, 2008, 12:15:35 PM
sorry mate, nothing personal, will try to avoid it :-*

back on topic:
what capacitors did fairchild use ?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on November 21, 2008, 12:31:20 PM
Well I'm not sure about original Fairchild capacitors but since they were stated as 180V polarised (20 uf) I'm pretty sure they were ELCOS. Tant's at 150V will be better but it will cost  ;) Some block bypassing with Elco can be nice. Other, smaller values can be anything "block" MKT, MKS, Or MKP....
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: [silent:arts] on November 21, 2008, 12:35:20 PM
there is no high voltage in this stage.
in my opinion you are fine with - let's say 63V.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on November 21, 2008, 12:51:40 PM
REAL FAIRCHILD... REAL FAIRCHILD... REAL FAIRCHILD...
First, the real fairchild uses 6386. PoorMan's uses 6BC8... IT WON'T SOUND THE SAME .

You are building a varimu compressor with the Fairchild topology... The smart Fairchild topology is the only thing shared between the two... And this is really great !!! I'm finishing mine and I'm quite sure it is a GREAT COMP... But NOT A FAIRCHILD...

If you want a Fairchild you'll have to spend about 3000€ for a close clone...

Thanks again to Analag for this clever work... I like new designs... Thanks again...
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: EmRR on November 21, 2008, 01:18:51 PM
What TYPE of capacitors "Should" be used for the Fairchild time constants???

Or should I ask..

What TYPE of capacitors did the REAL Fairchinld use?
or does it even mater?

I'd think it would... tants or electro's?

Films make the most sense as the absolute value is usually a tighter spec than an electrolytic would yield.  Beyond that, I see no reason to have an opinion beyond voltage requirement and footprint.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on November 21, 2008, 01:26:05 PM
Quote
You are building a varimu compressor with the Fairchild topology... The smart Fairchild topology is the only thing shared between the two... And this is really great !!! I'm finishing mine and I'm quite sure it is a GREAT COMP... But NOT A FAIRCHILD...
Of course that sound is not the same, but we are talking about time constants. That's part of topology...
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on November 21, 2008, 03:15:57 PM
I do agree, but thinking about the time constants, what about the input transformer inductance ???. The PM670 has got on the tube side a 10K impedance transformer paralled with a resistor (the pot), the Fairchild has got a 50k transformer only... Different transformer means different inductance means different time constants... IMO the input transformer is a part of the Fairchild's time constants (RLC)... Bad news isn't it ? :(

Don't think I don't understand you, I would like to have those time constants too (plus a few others...). But I think this is impossible. I'm maybe wrong (I hope to). I think that trying different caps is a cool idea... There's certainly a lot to find on this way.
Anyway, I read everything you post, and there's always something to learn... ;)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on November 21, 2008, 03:22:49 PM
Quote
The PM670 has got on the tube side a 10K impedance transformer paralled with a resistor (the pot), the Fairchild has got a 50k transformer only... Different transformer means different inductance means different time constants... IMO the input transformer is a part of the Fairchild's time constants (RLC)... Bad news isn't it ? Sad
Yes, that's true  :( But I still believe that it's possible to recalculate the constants... Hmmm it's just R/C constant but I was always poor in math... Let's wake up our math experts  ;) If I'm right "thing" will be faster...5 times... am I'm wrong
Quote
Anyway, I read everything you post, and there's always something to learn... Wink
Thanks, I'm just trying to think loud and to stay sharp as possible. Hope I don't hurt someone feelings  ;D
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on November 21, 2008, 03:45:20 PM
Hope I don't hurt someone feelings  ;D
Not mine, anyway ! :)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on November 21, 2008, 04:08:54 PM
Thinking again... we are talking about DC time constant. Right? DC resistance of the EDCOR's sec is around 300 ohm not sure about Fairchilds. Termination doesn't change the DC resistance  10k or 50k doesn't matter. ???
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: khstudio on November 21, 2008, 05:04:36 PM
Quote
You are building a varimu compressor with the Fairchild topology... The smart Fairchild topology is the only thing shared between the two... And this is really great !!! I'm finishing mine and I'm quite sure it is a GREAT COMP... But NOT A FAIRCHILD...
Of course that sound is not the same, but we are talking about time constants. That's part of topology...

EXACTLY.


Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on November 21, 2008, 05:27:59 PM
What I'm trying to point is the complexity of the Fairchild's time constants.
But copy the time constants schematic of the fairchild. I think you'll get close to them. I don't know if the PM670 can handle it...
Wolker ? Analag ? anyone else ?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Kingston on November 21, 2008, 06:22:44 PM
What I'm trying to point is the complexity of the Fairchild's time constants.
But copy the time constants schematic of the fairchild. I think you'll get close to them. I don't know if the PM670 can handle it...
Wolker ? Analag ? anyone else ?

What do you mean complex? The schematic only shows parallel caps and their charging time resistors for generating the time constant curves.

Yes the PM670 can handle them, and yes you can use the exact replica of the fairchild 670 time constant knob in your poorman, and yes it will probably even sound somewhat similar.

I personally don't see the point when you have the option to test what values work for your specific compressor usage. Those fairchild time constants were not really designed for the same tasks we see in the average mastering or mixdown session today. Use those fairchild constants as starting points if you insist. I've a feeling those longer time values from fairchild are quite useless in this day and age.

The attack/release method that guy bluebird suggested is a very handy mod. Heck, you could go crazy and add *dual* attack and release knobs if you do it the fairchild way. Two attack knobs per channel! Not the worst idea for the control freaks out there.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Kingston on November 21, 2008, 06:40:49 PM
About that mid-side transformer winding trick thing.

Who was it that said it was even possible with Edcors with some digging of the windings? How would I go about doing this?

What other options are there? I mean, are there some quality transformers with correct taps off the shelf? cinemag/sowter etc?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: bluebird on November 21, 2008, 07:33:29 PM
I used 150v to 250v film caps...I'm sure 63v would work.

Moby I would give you some voltage readings and current readings but I can't get my self to pull the thing out of my rack now.

I think a good rule of thumb is to just try and have the smallest resistance you can on the meter resistor. On the scope the sign wave looked great with no resistor (a short) at all.

On a side note: I think before anyone starts having strong opinions on what to do or not to do to the original design they should actually build the unit stock and start from there.

It wasn't hard to lift the board out of my unit and take the 10uF cap out. Same deal with the meter resistor.

don't be afraid to get your hands dirty... :)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on November 21, 2008, 09:39:32 PM
Quote
Those fairchild time constants were not really designed for the same tasks we see in the average mastering or mixdown session today. Use those fairchild constants as starting points if you insist. I've a feeling those longer time values from fairchild are quite useless in this day and age.
I agree  ;D I never used 5sec release time. But I have an impression that PM has too slow attack time. I'm just thinking because I miss few parts to finish the unit and can't do any measuring or experiment....  :-\
Quote
Moby I would give you some voltage readings and current readings but I can't get my self to pull the thing out of my rack now.
No prob, if you find some time it will be useful  :)
Quote
I think a good rule of thumb is to just try and have the smallest resistance you can on the meter resistor. On the scope the sign wave looked great with no resistor (a short) at all.
Yes, that's the point  8) Otherwise voltage will swing together with gain reduction and it's possible that it will drop too much for proper tubes supply  ;)
Quote
Heck, you could go crazy and add *dual* attack and release knobs if you do it the fairchild way. Two attack knobs per channel! Not the worst idea for the control freaks out there.
Oh, what an overkill ! But who knows maybe it's fancy to have a lot of knobs  8)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: khstudio on November 22, 2008, 12:29:27 AM
Good info everybody, thanks for all the diverse input :)

Quote
Those fairchild time constants were not really designed for the same tasks we see in the average mastering or mixdown session today. Use those fairchild constants as starting points if you insist. I've a feeling those longer time values from fairchild are quite useless in this day and age.
I would have to agree... they're quit long release times.

For all the time & money involved in this project, I just felt the sidechain (time constant section) was a little limited & possibly under designed.
I know it's not fair for me to say this without finishing my own build & hearing for myself FIRST...but I do understand HOW it works & there doesn't "appear" to be enough control in the original PM670 design... this seems to be confirmed (to some degree) by Bluebird.

Bluebird,
Thanks for sharing!!!
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on November 22, 2008, 05:00:24 AM
What do you mean complex? The schematic only shows parallel caps and their charging time resistors for generating the time constant curves.
I mean there's a RC network followed by the inductance of the input transformer. Don't you think this inductance will change something in the time constants ? I'm maybe completely wrong ... ;D

Quote
The attack/release method that guy bluebird suggested is a very handy mod. Heck, you could go crazy and add *dual* attack and release knobs if you do it the fairchild way. Two attack knobs per channel! Not the worst idea for the control freaks out there.
I think that this is a really more interresting mod... But this is just my opinion...
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on November 22, 2008, 09:57:55 AM
Quote
I mean there's a RC network followed by the inductance of the input transformer. Don't you think this inductance will change something in the time constants ? I'm maybe completely wrong ... Grin
I think that transformer resistance and inductance doesn't react with time constant. C4 is pretty close to the ground through RV6 and that's the resistance he is "looking at". So, that's something like 660 ohm.   ::)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Kingston on November 22, 2008, 11:14:40 AM
What do you mean complex? The schematic only shows parallel caps and their charging time resistors for generating the time constant curves.
I mean there's a RC network followed by the inductance of the input transformer. Don't you think this inductance will change something in the time constants ? I'm maybe completely wrong ... ;D

The effect of inductance on the time constants would only come to play here if the design would use some advanced transformer tricks that would skew the frequency response (say, pre- and de-emphasis tricks) with each i/o stage (much like an EQ in the sidechain would).

But that's not a fairdhild/poorman thing, and the frequency response (in conjunction with the inductance and loading) should be flat everywhere in the unit.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: EmRR on November 22, 2008, 11:41:52 AM
I said something about M/S hacking of the Edcors in several places, none of which I can point out in a quick manner.  I have not tried it, but it should work fine.   I've had to repair a number of Edcors straight from the factory; windings connected to wrong tabs. 
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Kingston on November 22, 2008, 11:52:34 AM
I said something about M/S hacking of the Edcors in several places, none of which I can point out in a quick manner.  I have not tried it, but it should work fine.   I've had to repair a number of Edcors straight from the factory; windings connected to wrong tabs. 

they're cheap so I'll just hack away. What exactly am I looking for in there, and any suggestions for a tool for the task?

Damn this cheap mobile phone camera. I can't get accurate enough pictures to post in here.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on November 22, 2008, 12:11:04 PM
Quote
I've had to repair a number of Edcors straight from the factory; windings connected to wrong tabs. 
How do you determine wrong windings connection? By measuring DC resistance or inductance.. or something else. It will be great if you can give info about proper connection and how to measure that  :)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: mikeyB on November 22, 2008, 01:01:14 PM
I said something about M/S hacking of the Edcors in several places, none of which I can point out in a quick manner.  I have not tried it, but it should work fine.   I've had to repair a number of Edcors straight from the factory; windings connected to wrong tabs. 

Is it about time that we all added our signatures to a wish list and send it to Brian at Edcor - I can't see it being too much effort to keep the windings seperate instead of centre tapped - look at the bobbin formers on the wsm/xsm txs. They have capacity for 8 solder tags - must add 2 cents for the tags ;D

New thread/poll ???
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: EmRR on November 22, 2008, 03:13:02 PM
I said something about M/S hacking of the Edcors in several places, none of which I can point out in a quick manner.  I have not tried it, but it should work fine.   I've had to repair a number of Edcors straight from the factory; windings connected to wrong tabs. 

they're cheap so I'll just hack away. What exactly am I looking for in there, and any suggestions for a tool for the task?

two wires on the CT that you can move and wire elsewhere in M/S matrix mode. 


How do you determine wrong windings connection? By measuring DC resistance or inductance.. or something else. It will be great if you can give info about proper connection and how to measure that  :)

like 1/2 the sec and primary tied together on both sides instead of both pri and sec tied to each other.   so CT is clearly misbalanced.    Or one half of a winding wired out of polarity so it sounds terrible.    obvious easy stuff.

Remember, at that price there is no quality control.  No free lunch. 
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: bluebird on December 03, 2008, 01:59:21 AM
Alright so I went a little overboard on the pimping... :D

i was doing some sign wave tests on this thing and I kept getting just a hair of crossover distotion in the wave about halfway through the gain reduction range. I had strong matched 6BC8's and everything was calibrated right.

So I started to mess with the two bias pots and I couldn't seem to get the wave to look nice all the way through the GR range with out having the output pretty low. Useful compression was happening about 10 to 15 db down from where the input signal was.

To make a long story short I shoved in two 6BA6's wired as triodes and set both bias pots to -11 volts and my crossover distortion disappeared. I tried four to mimic the four 6BC8 triodes but I got oscillation at certain gains.

the two 6BA6's sound great!! Sound is tighter and doesn't break up as much in deeper reduction...I guess what I have now is a Sta Level front end and a Fairchild side chain...kinda ???

I'm REALLY happy with this now. I think I can put the cover on it for good.

Picture below is the 6BA6's tagged on to a 9 pin socket pigtail and stuck into the rear 9 pin socket.

Title: Re: the pimp / mod the Poor Man 660 thread
Post by: EmRR on December 03, 2008, 02:08:59 AM
Cool; a real hacker.  No other parts changes?   Only trimmer adjustments? 

Any personal theories as to why?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: [silent:arts] on December 03, 2008, 05:08:03 AM
this is really creative looking ;D ;D ;D
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on December 03, 2008, 07:59:54 AM
Quote
i was doing some sign wave tests on this thing and I kept getting just a hair of crossover distotion in the wave about halfway through the gain reduction range. I had strong matched 6BC8's and everything was calibrated right.
Huh, that sounds like a real problem. Wiring two different tubes instead of 4 is a big difference.  Is the author of this project around? What about other working units? All have a same crossover issue? Volker, did you tried to measure your PM?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Kingston on December 03, 2008, 08:31:42 AM
What is the cross-over distortion here exactly? I'm only familiar with cross-over phase distortions in filters.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on December 03, 2008, 08:41:21 AM
What is the cross-over distortion here exactly? I'm only familiar with cross-over phase distortions in filters.
http://en.wikipedia.org/wiki/Crossover_distortion
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: nielsk on December 03, 2008, 08:49:04 AM
Bluebird, any chance you would post a drawing of this mod, I would like to try it & compare, but I'm not good enough to get it from your verbal description....
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: [silent:arts] on December 03, 2008, 08:54:44 AM
Quote from: Moby
Huh, that sounds like a real problem
Quote from:  bluebird
a hair of crossover distortion
I don't think this sounds like a real problem
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on December 03, 2008, 09:04:46 AM
I'm still waiting for my metalwork to be finished so I still didn't connected my unit... So , I must wait to hear the sound :-(
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Kingston on December 03, 2008, 10:02:13 AM
What is the cross-over distortion here exactly? I'm only familiar with cross-over phase distortions in filters.
http://en.wikipedia.org/wiki/Crossover_distortion

Doh! I'm just used to hearing the term "class A/B switching distortion" (probably not so common). Heck, I've even modelled a DSP plugin based solely on several types of these AB switching distortions! http://www.michaelkingston.fi/retroband/ (a result of my University dissertation)

Quote from: Moby
Huh, that sounds like a real problem
Quote from:  bluebird
a hair of crossover distortion
I don't think this sounds like a real problem

Doesn't sound like a problem. In fact, this parasitic can be highly usable in many sound sources. While I haven't built this unit, based on my measurements with this effect, it will be a big part of the "mojo" of poorman. I would not remove it.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on December 03, 2008, 10:17:08 AM
Sorry I missed the word "hair" That can be a nice character if it's just a 'hair"  ;)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: bluebird on December 03, 2008, 11:59:56 AM
Sorry I don't want to freak everybody out. There is nothing WRONG with the sound of this compressor stock. I just felt I could make it suit my needs better.

I was getting the crossover distortion only at VERY HIGH INPUT LEVELS. My input transformers ARE NOT STOCK they have a bit more step up gain.

This all said, I felt the gain and compression range where everything looked right was a little lower than I would like considering there is not a lot of makeup gain inherent in this unit.

Other compressors using the 6BC8 like the UA175 have a separate makeup amp so they can get away with smaller signal levels on the input.

But remember, things are going to get weird if you push anything to the limit. I just like pushing things and I felt the 6BA6's could handle a little more.

Once again this is the PIMP thread NOT the "THERE'S SOMETHING WRONG AND I"M FIXING IT" thread.

So go and build your units stock..don't worry be happy.. :D

Here is a quick hand drawn picture of the waves I was getting. I exaggerated the crossover distortion a little bit. I know its not to scientific. :-\

Title: Re: the pimp / mod the Poor Man 660 thread
Post by: smallbutfine on December 03, 2008, 12:30:19 PM
So, if I understand it right, your higher step-up input transformers push things too far for the stock tube gain structure, creating too much IMD on higher levels, which you now compensate for with the 6BA6 replacement.
Correct?  ???
Kind regards,
Martin
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: EmRR on December 03, 2008, 01:24:59 PM
Reading between the lines, I'm guessing we're talking about 1 kHz tone at 0 dB plus stock non-compression amp gain of about 18 dB plus additional few-ish dB of whatever input transformers you are using.    Seems things look normal at both light and maximum compression.   

On my 'to do' list is a more comprehensive set of measurements regarding distortion point of signal amp with no compression, etc etc.  Maybe you can beat me to it and save me the trouble.   Wonder if you are pushing that line with your input level. 

I have to wonder if your changes in the time constants have any effect on the distortion you were seeing, or if they affect the distortion when fiddling about in the highest distortion range of compression.   


So far you win the 'Mod the PM660' competition!   ;D
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: bluebird on December 03, 2008, 02:38:17 PM
So, if I understand it right, your higher step-up input transformers push things too far for the stock tube gain structure, creating too much IMD on higher levels, which you now compensate for with the 6BA6 replacement.
Correct?  ??

Yes and no...
I'm using this transformer http://www.jensen-transformers.com/datashts/6110kb.pdf So its not that much different. The 6BA6 is doing a bit more than just compensating for the high input level.

And I'm not pushing it so much as to skew the wave form with no compression...if that makes sense.

I have to wonder if your changes in the time constants have any effect on the distortion you were seeing, or if they affect the distortion when fiddling about in the highest distortion range of compression.  

I fiddled with the time constants and it didn't seem to have an effect over the wave form...

 
On my 'to do' list is a more comprehensive set of measurements regarding distortion point of signal amp with no compression, etc etc.  Maybe you can beat me to it and save me the trouble.

I really don't have the equipment (or brains :P) to do a proper analysis. So I'll just leave it up to you. ;)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on December 03, 2008, 06:18:56 PM
Quote
I'm using this transformer http://www.jensen-transformers.com/datashts/6110kb.pdf
Sorry, what did you replaced with 6110k-b? 600/10k or 10k/600  transformer?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: EmRR on December 03, 2008, 06:34:32 PM
The input, using that Jensen backwards I must assume. 
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on December 03, 2008, 07:41:03 PM
Cool, and you are happy with the response?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: bluebird on December 03, 2008, 09:30:08 PM
Yes I'm using the Jensen backwards for the input transformer. This is really not a significant mod. the edcors are great transformers.

And yes, I am now VERY excited about how this sounds now.  ;D

I wanted to mention an easy way to get a good range of time constants without big changes is to just use the resistor values I mentioned earlier in parallel with the 10uf cap. You don't really have to change the cap value to get a good variation of release times. It has a lot more effect than the stock 10K pot in series with the 10uf cap.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Gachet on December 04, 2008, 07:07:25 AM

I wanted to mention an easy way to get a good range of time constants without big changes is to just use the resistor values I mentioned earlier in parallel with the 10uf cap.

What value?
I couldn't find it....
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: flintan on December 27, 2008, 11:24:41 AM
Anyone know what the U-pad in front of the SC amp transformer is for? Talking about the original here.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: EmRR on December 27, 2008, 12:32:00 PM
Anyone know what the U-pad in front of the SC amp transformer is for? Talking about the original here.

isolation
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: khstudio on December 28, 2008, 02:43:24 AM
Yes I'm using the Jensen backwards for the input transformer. This is really not a significant mod. the edcors are great transformers.

And yes, I am now VERY excited about how this sounds now.  ;D

I wanted to mention an easy way to get a good range of time constants without big changes is to just use the resistor values I mentioned earlier in parallel with the 10uf cap. You don't really have to change the cap value to get a good variation of release times. It has a lot more effect than the stock 10K pot in series with the 10uf cap.

Is the 10k pot in Series (Original setup) still needed or usable along with your parallel values?

Also, how does the original "Series" pot setup even affect the "Release"???
I'd think it would mostly control the "Attack"... no?

Sorry, I'm designing my face-plate & I'm trying to get a grip on the "Time-Constant" debate/choices before I Drill holes & move forward.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on December 28, 2008, 08:06:17 AM
Quote
Also, how does the original "Series" pot setup even affect the "Release"Huh
I'd think it would mostly control the "Attack"... no
Yes, series resistance determines the attack time (cap charging) . If you want to add proper names under the switches, my advice will be that you  call switch with capacitors as time constant and parallel resistance as release. Not 100% true but close to be true  ;). Yes, series resistance with C's can be useful (see the Fairchild) but is gonna take some to determine value and position. (I still don't know my values  :-\)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: flintan on December 28, 2008, 04:33:45 PM
Anyone know what the U-pad in front of the SC amp transformer is for? Talking about the original here.
isolation

Hmm.. Isolation from what? The channels interacting with each other in lat/vert mode or something else?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: EmRR on December 29, 2008, 03:33:20 AM
Isolation between the side chain amp and the audio output/following input.  Many vintage broadcast and recording amps use resistive build out as part of isolation networks.  In many cases to help fix the load Z range while providing a degree of isolation with situations such as phone line connection during remote broadcast work. 

Also sets audio amp load Z range; can't comment since don't know sec Z of side chain input.    Situation is similar in regards to the PM660 as to isolation, different in regards to load Z range.  One would ideally assume the values of input load shunt were tweaked for best response in each. 
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: bluebird on December 29, 2008, 04:48:31 AM
Hey, just a little update on the bluebird mod...

I've scaled back to three caps. 10uf, 6uf, and 2uf.
Also using just three resistors in parallel with the caps. 68K, 470K, and 3m (or no resistor).
With those caps and resistors you can simulate the first three or four time constants of the real 670.

I ended up cranking the power supply up to about 210 volts and using four 6BA6's per side. I matched the 6BA6's up with a tube tester. I wired two 6BA6's  to a 9 pin tube socket with buss wire kind of like the Manley T bar to eliminate some oscillation I was getting earlier when using  4 inches of wire from the 7 pin tube sockets to the 9 pin tube socket. Both adjustment points are at 7 volts.

The power supply seems to be handling 8 6BA6's fine. I just changed one resistor (R9 to 470K...) in the power supply to up the voltage. I do have 2 fans in my box. I feel like I'm over clocking a PC or something.. :o

New mod....

I changed the input a bit
I took the jensens out and put the edcors in for the input transformers.

I removed the input attenuator and hooked the input transformer secondary right up to the grids of the 6BA6's. I attached the CV voltage to the center tap of the input transformer like on the original 660.
I used a 600 ohm T attenuator in front of the input transformer.

It sounds better to me now... ;D
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on December 29, 2008, 12:41:17 PM
Quote
Hey, just a little update on the bluebird mod...
hehe a little  ;D
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: bluebird on December 29, 2008, 01:42:03 PM
Just wanted to comment on the tube change.

The whole reason I did all this is because I wanted more gain reduction than the original circuit could provide. The 6BC8's are cool tubes for compressors. The UA175 is possibly the best sounding varimu out there. A company makes a reissue of the UA175 that people go nuts over.

BUT for this compressor they dont seem to like being pulled down to far.

I think the reason the 6386 tube is so special is because the grid wire is wrapped around the support posts non linearly. The wraps get wider towards the middle of the support posts. kind of like a ladder with a couple of steps missing from the middle. I had a chance to talk to a tech here in LA who has worked on over 100 Fairchilds and he told me about the 6386. So I busted open (CJ style) a 6BA6 an sure enough the grid was wound non linearly. So now I know why the curves are similar between the two tubes.

Picture of a 6BA6 grid



Title: Re: the pimp / mod the Poor Man 660 thread
Post by: EmRR on December 29, 2008, 03:35:03 PM
The UA175 is possibly the best sounding varimu out there.

 I busted open (CJ style) a 6BA6 an sure enough the grid was wound non linearly. So now I know why the curves are similar between the two tubes.

Good man!  Cracking open a tube.  Thanks for the pic.

To register another opinion (remember, like assholes  ;)), I never found any use whatsoever for the several UA 17x series limiters I had access to.  Always unplugged them and went with something else.  Among the vari-mu types here I count Collins 26U, Gates SA-39, Gates 28-CO, RCA 96, RCA PA-136, and have had GE Unilevels, Gates Stalevels, RCA BA-25's and Langevin Levelines.    I tend to think people flip out over the units with the most control range (attack/release/threshold/output), and I find that there are simple range expansions that can be done to all of the relatively 'control-less' types listed above.  I know the UA has more control range than the others right out of the box, and have to think that is why so many people like them so much.   
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: joe-electro on December 29, 2008, 09:48:15 PM
Among the vari-mu types here I count Collins 26U, Gates SA-39, Gates 28-CO, RCA 96, RCA PA-136, and have had GE Unilevels, Gates Stalevels, RCA BA-25's and Langevin Levelines. 

Enough bragging! We want gear porn!!!! Especially the RCA 96 and Gates 28-CO! Got any pics of the Levelines?

Sorry for the off-topic post.

---Joe


Title: Re: the pimp / mod the Poor Man 660 thread
Post by: analag on December 31, 2008, 01:06:03 PM
I think it's time I posted on this here thread....there is another pimp, but it involves way more than just turning up the regulator and changing tubes. Then it's no longer the Poor Man 660 is it.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: bluebird on December 31, 2008, 03:29:00 PM
Hey Analag bust it out... It can be called the Pimp Poor Man 660 Or the "PPM 660

I was thinking I might try throwing in a couple of the new 6386's with some socket converters but other than that I can't think of much else to do to this thing. I'm really digging what this is doing to vocals and drums on the 2uF and 68K setting. Its starting to be my go to compressor.

What might make it better is to get a little more out of the sidechain amp. I might try using the center tap and one side of the secondary of the sidechain output transformer into the bridge for more current drive. More of a step down. BUT that would mean less threshold voltage.


To register another opinion (remember, like assholes  ;)), I never found any use whatsoever for the several UA 17x series limiters I had access to.  Always unplugged them and went with something else.  Among the vari-mu types here I count Collins 26U, Gates SA-39, Gates 28-CO, RCA 96, RCA PA-136, and have had GE Unilevels, Gates Stalevels, RCA BA-25's and Langevin Levelines.    I tend to think people flip out over the units with the most control range (attack/release/threshold/output), and I find that there are simple range expansions that can be done to all of the relatively 'control-less' types listed above.  I know the UA has more control range than the others right out of the box, and have to think that is why so many people like them so much.  

Understood. Do you like the Altec 436C ? that also uses a 6BC8, my point is the 6BC8 is not a bad tube for varimu work, But in this circuit it doesn't seem to like being hooked up to the load...or something. Everywhere else I see it the next stage is a tube grid.

Sound is so subjective anyways. I try to refrain from being to creative explaining the way something sounds.

I don't want someone to go through all the trouble of doing what I did to a piece of gear and then go "damn this sounds like sh*t".
But on the other hand this whole forum is about experimentation and learning from our (and others) mistakes.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on December 31, 2008, 03:46:59 PM
Analag, do I smell a JJ6386 around  :P
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: joe-electro on December 31, 2008, 06:38:46 PM
I think it's time I posted on this here thread....there is another pimp, but it involves way more than just turning up the regulator and changing tubes. Then it's no longer the Poor Man 660 is it.

Okay, enough teasing, out with it!!!

---Joe
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: EmRR on December 31, 2008, 07:03:24 PM
Do you like the Altec 436C ? that also uses a 6BC8, my point is the 6BC8 is not a bad tube for varimu work, But in this circuit it doesn't seem to like being hooked up to the load...or something. Everywhere else I see it the next stage is a tube grid.

Been a long time on the 436; don't remember being wowed, and never considered getting one after they shot up so high. 

Title: Re: the pimp / mod the Poor Man 660 thread
Post by: joe-electro on December 31, 2008, 07:35:57 PM
Enough bragging! We want gear porn!!!! Especially the RCA 96 and Gates 28-CO! Got any pics of the Levelines?

Not trying to brag, just establish a baseline for my experience.    Not many good pics.  Here's some OT bandwidth hogs:

Collins 26U-2 stereo limiter with added control panel (http://farm4.static.flickr.com/3284/3154740250_f8fe7a9af4_b.jpg)
Collins 26U-2 (http://farm4.static.flickr.com/3258/3154741826_f883442b21_b.jpg)
Collins 26U-2 with back open (http://farm4.static.flickr.com/3256/3153901877_629d8b9fbc_b.jpg)
Collins 26U-2 stereo limiter with top open. (http://farm4.static.flickr.com/3087/3154738952_3319af8e18_b.jpg)
Collins 26U-2, close-up of PSU recap using perfboard and radial caps (http://farm4.static.flickr.com/3200/3153899723_b4f5b92e40_b.jpg)
Collins 26U-2, bottom view showing wiring to added control and connector brackets (http://farm4.static.flickr.com/3215/3153900337_8f6e92df6a_b.jpg)
Collins 26U-2, with added bottom panels and significant control set modifications. (http://farm4.static.flickr.com/3057/2628692642_d4bcb39dac_o.jpg)
Collins Radio 26U-2, shown in limiting and below threshold, with stock slowest attack and fastest release. (http://farm4.static.flickr.com/3097/2695706505_4a248576ee_o.png)

RCA BA-25A rack-up; front (http://farm4.static.flickr.com/3224/3154743410_451d3f7c6d_b.jpg)
RCA BA-25A rack-up; top (http://farm4.static.flickr.com/3284/3154745338_cdedcc56b9_b.jpg)
RCA BA-25A rack-up; rear (http://farm4.static.flickr.com/3292/3153911365_e5a83febe6_b.jpg)   
RCA BA-25A tubes (http://farm4.static.flickr.com/3119/3153911517_066cf22525_o.jpg)   
RCA BA-25A guts (http://farm4.static.flickr.com/3244/3154752016_f00554479d_b.jpg)
RCA BA-25A rack-up. Someone else started this one; I changed a bunch of stuff and got the cosmetics happening. (http://farm4.static.flickr.com/3176/3153915657_2188b9f9d4_b.jpg)    
RCA BA-25A rack-up; controls (http://farm4.static.flickr.com/3085/3153917647_eb6910cf13_b.jpg)
RCA BA-25A rack-up rear (http://farm4.static.flickr.com/3102/3153919637_7136493a5c_b.jpg)
RCA BA-25A rack-up guts (http://farm4.static.flickr.com/3223/3154759746_669b6e500b_b.jpg)   
RCA BA-25A rack-up; bottom showing PSU changes including DC filaments (http://farm4.static.flickr.com/3223/3153924367_2b1c03734c_b.jpg)

RCA PA-136 front (http://farm4.static.flickr.com/3096/3154773426_10ba153cfc_b.jpg)    
RCA PA-136 top (http://farm4.static.flickr.com/3241/3154775356_0ca76b9578_b.jpg) 
RCA PA-136 side (http://farm4.static.flickr.com/3089/3154777200_8a85c2f29b_b.jpg) 
RCA PA-136 guts (http://farm4.static.flickr.com/3110/3153941629_d574502418_b.jpg)   
RCA PA-136 showing amp disassembly from rack and wiring harness. The amp rotates from a pivot point while in the rack of access to top and bottom without full removal.  Can be powered with AC or DC with change of jumpers. (http://farm4.static.flickr.com/3090/3153943723_9577f3d544_b.jpg)

Gates 28-CO limiter front before restoration.  Note totally incorrect knobs. (http://farm4.static.flickr.com/3212/3154736264_363f04a6e0_o.jpg)
Gates 28-CO limiter rear before restoration (http://farm4.static.flickr.com/3110/3154736294_11a9c8e3b5_o.jpg)   
Gates 28-CO limiter bottom before restoration (http://farm4.static.flickr.com/3259/3153898583_9031ea908c_o.jpg)   

Gates SA-38A with modified attack and release controls (http://farm4.static.flickr.com/3094/3153926063_e84d43bbee_b.jpg)    
Gates SA-38A, open (http://farm4.static.flickr.com/3113/3154765732_922380a555_b.jpg)    
Gates SA-39 with modified attack and release controls (http://farm4.static.flickr.com/3199/3153934001_c0441c8298_b.jpg)   
Gates SA-39 rear (http://farm4.static.flickr.com/3084/3154770058_17fa429d87_b.jpg)    
Gates SA-38 with attack and release control modification (http://farm4.static.flickr.com/3223/3153947381_1a4a609482_o.jpg)   
Gates SA-38, door open (http://farm4.static.flickr.com/3250/3153947261_7bea1c3847_o.jpg)   
Gates SA-38 rear (http://farm4.static.flickr.com/3202/3153947135_598dcb3ab2_o.jpg)   
Gates SA-39 (http://farm4.static.flickr.com/3130/3154785214_a30cbf2f74_o.jpg)    
Gates SA-39 rear.  Note replacement power and input transformers (http://farm4.static.flickr.com/3285/3154785352_84a4ff0640_o.jpg)   


Now that's what I'm talkin' about! Thanks Doug!!!

---Joe
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: analag on January 01, 2009, 02:14:28 AM
(http://i8.photobucket.com/albums/a22/analag/Back2-1.jpg)

A lot of money, time and effort. I have enough tubes to re-tube it three times. As much as I love it, I wouldn't build another one...too much work.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: veermaster on January 01, 2009, 03:12:32 AM
Is that a pinball ?  ;)
Amazing box!
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on January 06, 2009, 03:28:58 PM
Quote
I wired two 6BA6's  to a 9 pin tube socket with buss wire kind of like the Manley T bar to eliminate some oscillation I was getting earlier when using  4 inches of wire from the 7 pin tube sockets to the 9 pin tube socket. Both adjustment points are at 7 volts.
Bluebird, did you connected 6BA6's dirrectly in the triode mode or U used some resitors?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: inputoutput on January 07, 2009, 09:40:27 AM
Has anyone ever implemented a temperature sensor in their builds?.. how about doing it in this one?

To have a fan spinning all the time in the studio is a no-no here. But if the PM670 gets hot like an own, then it could be ok to have an automatic switchable fan.  Sound like a fun thing to build. Hope that the switching of the relay won´t affect the sound in any way....I am afraid that it might produce clicks or level-changes due to power consumption.

I was thinking to maybe build a thermistor sensor -based switchboard (with a LM339 comparator), which switches a relay controlling one or more small fans, say reacting around 60-70 Celsius. The set point for the temperature could be adjusted by a pot on the back of the unit, for later fine-tuning.


Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on January 09, 2009, 03:36:35 PM
Guys, what's the difference between 6BA6 and 5749. Or is it 5749 good replacement for 6BA6 Vari mu ? Also there is 6660.... similar but how good?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on January 11, 2009, 05:52:19 AM
Bump for Bluebird  ;) are you around? How did you connected 6BA6's in triode mode? Directly or U used some resistors? Also , do I see well on pic? U used 5749's versions of 6BA6?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on January 11, 2009, 06:19:56 AM
Guys, what's the difference between 6BA6 and 5749. Or is it 5749 good replacement for 6BA6 Vari mu ? Also there is 6660.... similar but how good?
5749 is more shock resistant... A kind of military specs 6BA6... But I can't say more for the sound... I bet it will sound the same. ::)
If you or someone else don't know this url, it's the best tube data sheets site I found :
http://frank.pocnet.net/ (http://frank.pocnet.net/)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on January 11, 2009, 06:37:59 AM
Quote
5749 is more shock resistant... A kind of military specs 6BA6... But I can't say more for the sound... I bet it will sound the same.
Yes, I compared the sheets, looks similar (but not exact the same). I just wonder about sound.  ??? Must be that it's less microphonics since it's industrial-mil tube .
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on January 11, 2009, 11:06:22 AM
Hi to everybody trying to mod the PM670 with the Fairchild's time constants... I was kind of suspicious about the fact that cloning the network will give the same results. It was impossible to check this at that time for me because my PM670 wasn't finished... Now it is. :)

The fairchild's time constants network is working in the PM670 with better results IMO than the stock  ;D
but it doesn't give the same results  :'( :'( :'(.
The first position give about 300ms of attack and release times... The answer why is there :
http://www.groupdiy.com/index.php?topic=31345.0 (http://www.groupdiy.com/index.php?topic=31345.0)
The PM670 has got a SC-amp of 5 Watts or so, the Fairchild has got about 25W... The current out of the transformer that fills the RC network cannot fill the same caps at the same speed... That's certainly one of the reasons Analag didn't copy it ...

I'm trying to find the good cap to reach the 0,2ms of the position 1,2 and 6... But there's another problem I suspect to occur : thump will maybe show its ugly face !  >:(
I'll keep you informed  ;)

PS: The Analag's time constants network is based on the position 5 and 6, a kind of automatic function program compression with quicker release (I didn't check really if it's quicker but it seams to...).
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on January 11, 2009, 12:17:08 PM
Wow, thats great pimp. Just keep on with that  :)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on January 11, 2009, 12:54:01 PM
At the moment I've got on channel modified and the other stock for a quick possibility to compare.
I wil certainly stop my research now for today (I've got children to pimp ... sorry, to wash  ;D)
So, about 8ms attack time and 300ms release time : remove R17, shunt (or not it's not important here) R18, shunt C4 and change the pot (RV7) for a fixed 1M resistor.  :D

Listen, compare, it's really different !!! A lot quicker than stock, and maybe clearer, but I'm not sure I must perfect my settings between the two... I want to be sure they sound close without compression but I won't have time enought today to do this...

See ya later  ;)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on January 17, 2009, 10:18:53 AM
Hi, i'm back with some new results...
The real difficulty is to know how fast attack we can get with a PM670...

I found two solutions to have about 0,1ms attack time and 300ms release time.  ;D

One is a change in Analag's network but have the same compression signature, with a more program dependant maximum compression...
R17 : 221K
C3 : 100nF
R18 + RV7 : Fixed 10K
C4 : 1uF

The other is certainly more different, more "a la Fairchild position 1 compression", but I would like to have the advice of some "tube eagles". It seam to be stable in my PM670 but my knowledge in tube technology don't allow me to say do it ! I don't know if this second mod is secure, so wait some time before trying this !!!
I simply did :
C3 :100nF
R17 : 3M. Just unplug everything else...
Reading the 6bc8 data sheet, I seen that grids should be grounded though a 500K maximum resistor... Even if in a varimu grids are not grounded, I wonder if it shouldn't be the same in the PM670...
If someone knows the answer, I would be glad to read it  !!!!  ;D ;D ;D

Edit : The second mod is highly unrecommended !!! Read these PRR explainations :
http://www.groupdiy.com/index.php?topic=31088.0 (http://www.groupdiy.com/index.php?topic=31088.0)


Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Kingston on January 17, 2009, 12:25:41 PM
One is a change in Analag's network but have the same compression signature, with a more program dependant maximum compression...

[snip]

The other is certainly more different, more "a la Fairchild position 1 compression".

You just gave me an idea. When I get to where you are with building the PM670 and tweaking the time constants, I'm going to teach myself "basic PCB making" by creating a tweakable time constant network expansion, with relay selectable networks.

I was already going to do a "lat/vert" board to hide the large amount of let/vert related wires behind relay switch and in a small PCB. There's an opportunity to put feedback/feedforward switch on that same PCB as well.

Guess I have work to do now.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on January 17, 2009, 12:37:00 PM
At the moment, I do all those tests really easily...
I made a few wires shunts on the Volker's board, and putted out a few components...
Shunt C4 and R18, put out R17 and C3 and connect the new networks to the attack connector (only 2 wires are used there) !!!  ;)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on January 17, 2009, 01:28:45 PM
Here are some snapshots of the mod :
12K "sine wave" sent into the PM670...
The upper wave is the unrecommended mod.
The lower wave is the sure to work properly mod.
ATTACK snapshots :
(http://pagesperso-orange.fr/NBNS-Studio/PM670/ATTACK-N1a.jpg)
(http://pagesperso-orange.fr/NBNS-Studio/PM670/ATTACK-N1Ba.jpg)

RELEASE snapshot :
(http://pagesperso-orange.fr/NBNS-Studio/PM670/RELEASE-N1a.jpg)

Not that bad isn't it?  ;D

Edit : The second mod is highly unrecommended !!! Read these PRR explainations :
http://www.groupdiy.com/index.php?topic=31088.0 (http://www.groupdiy.com/index.php?topic=31088.0)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on January 18, 2009, 06:34:52 AM
Quote
Not that bad isn't it?
Not at all  :). But , how it sounds? Are you happy with overall results? Are you tweaking 660 for tracking , mix bus or mastering purpose, or you want to have "all in one"  ;) Also, it will be great if you can do some sound samples. I will try your time constants but it will be great to hear results ;D
Quote
One is a change in Analag's network but have the same compression signature, with a more program dependant maximum compression...
R17 : 221K
C3 : 100nF
R18 + RV7 : Fixed 10K
C4 : 1uF
Is that recommended mod?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on January 18, 2009, 12:36:50 PM
how it sounds? Are you happy with overall results?
It sounds really good if you like ultra fast comps. I do. There's a magic thing with the varimu comps : the compression is always very natural, quite impossible to hear...

Are you tweaking 660 for tracking , mix bus or mastering purpose, or you want to have "all in one"  ;) Also, it will be great if you can do some sound samples. I will try your time constants but it will be great to hear results ;D
I'm trying to have a quick comp... I love quick comps... I will work on differents attack and realease times to have a really versatile compressor... I don't do a lot of mastering but because I'm always disapointed with others results, I would like to have a mix and mastering comp...
I will put a few samples online in a few days if you want...

Quote
One is a change in Analag's network but have the same compression signature, with a more program dependant maximum compression...
R17 : 221K
C3 : 100nF
R18 + RV7 : Fixed 10K
C4 : 1uF
Is that recommended mod?
Yes, it is that one !
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on January 18, 2009, 01:42:32 PM
Quote
I will put a few samples online in a few days if you want...
Of course  :)
From the very beginning I was bit suspicious about time constants , now I see that it's possible to tweak this beast  ;D
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: SaMpLeGoD on January 18, 2009, 07:21:13 PM
Hey Lolo... nice you're working on the PM670 time constants... I almost finished mine, and I'm looking forward to apply this mod!

Cheers,

Eddie  ;D
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: SaMpLeGoD on January 21, 2009, 08:35:43 PM
Hello, is anybody have some better solution for the PM670's Time Constant? to get them near to the original Fairchild? I think the 10k pot wired with 2k step resistors is not that good as I expected...  Any conclusions Laurent?
Cheers,

Eddie  ;D
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on January 22, 2009, 01:40:16 AM
Eddie, try my recommended mod and tell us what you think about it  ;) !!! You surely have the components at home...
I will post some audio samples this week end (I'm not at home now)...
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: SaMpLeGoD on January 22, 2009, 10:35:16 PM
All Right Laurent! Yeah I'm plenty of resistors down there  ;)
I'll do your mod!

Cheers

Eddie  ;D
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on January 25, 2009, 08:28:37 AM
Here are the samples ( just a part of a live track of a band I'm working with, choosen for its nice dynamic ). They are 24bits 48KHtz wav files. Same channel used , same settings, hardcomp means hard compressing, and soft comp soft compressing:
http://pagesperso-orange.fr/NBNS-Studio/PM670/ORIGINAL_01.wav (http://pagesperso-orange.fr/NBNS-Studio/PM670/ORIGINAL_01.wav)
http://pagesperso-orange.fr/NBNS-Studio/PM670/ANALAGS-HARDCOMP_01.wav (http://pagesperso-orange.fr/NBNS-Studio/PM670/ANALAGS-HARDCOMP_01.wav)
http://pagesperso-orange.fr/NBNS-Studio/PM670/LOLO-HARDCOMP_01.wav (http://pagesperso-orange.fr/NBNS-Studio/PM670/LOLO-HARDCOMP_01.wav)
http://pagesperso-orange.fr/NBNS-Studio/PM670/ANALAGS-SOFTCOMP_01.wav (http://pagesperso-orange.fr/NBNS-Studio/PM670/ANALAGS-SOFTCOMP_01.wav)
http://pagesperso-orange.fr/NBNS-Studio/PM670/LOLO-SOFTCOMP_01.wav (http://pagesperso-orange.fr/NBNS-Studio/PM670/LOLO-SOFTCOMP_01.wav)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on January 25, 2009, 08:58:49 AM
I really like what I hear  :) :) Definitely sounds musical and well glued  ;D
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on January 25, 2009, 11:07:47 AM
I do think the same but the other mod give really interresting results... Because there is a +17/-17 rail, I wonder if I should use this to get more close to the Fairchild compression style. The only question is how much negative goes the CV in the peaks of compression. If it's less than -17V an other mod is possible, but it won't be a all tube comp... But who really cares ? The idea is to keep all the sidechain amp as is, and to buffer with an opamp the CV after the Time Constant network... It will be possible to use resistors with a more than 1M value...

Note to everybody: in Analag's design, the faster attack is with the 10K pot set at 10K... The lower it's value, the longer is the attack or to be precise the softer is the attack... The release time is fonction of the program which charged the network. More clearly, if the comp compress during a short time, the 10uF will be charged during a short time and the release will be quite fast. If the comp compress during a long time, the 10uF will be charged more and its discharge (release) will be longer... It is an adaptation with really interresting attack/release of the position 5 and 6 of the Fairchild.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on January 25, 2009, 11:37:06 AM
Quote
I wonder if I should use this to get more close to the Fairchild compression style
Hmm, with 6BC8 i doubt it's possible. Of course if you are talking just about T.constants maybe it's possible... I think that 6BA6 is better  because of varimu curve, but that will be pseudo triode sound signature. I'm still waiting for my 6BA6's . Also I'm not sure about wiring in triode mode. Direct?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on January 25, 2009, 11:54:51 AM
My idea is this :
To have a 0,2ms attack time the SC-amplifier needs a 100nF cap. If we want a release of 300ms we need a 3M resistor in parallel. This 3M resistor isn't good for the 6BC8 (or 6BA6) grids.
If the voltage out of this network is not going lower than -17V, we can had a buffer to adapt the impedance of the network to the grids needs with an op-amp  ;D

I think that 6BA6 is better  because of varimu curve
You can't go out of the varimu curve of the 6BC8 in the PM670. The PM670 is a varimu comp.
To change the 6BC8 will change the way it compress but won't give you really more compression... 6BA6 is one of the possibilities... But the main "problem" if we can call this a problem, is the Side Chain amp IMO.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on January 25, 2009, 04:34:43 PM
Quote
But the main "problem" if we can call this a problem, is the Side Chain amp IMO.
Yes I understand what you are talking about. I just wanted to say that 6BC6 has real varimu knee  ;) Regarding time constants, yes, some buffering will probably improve thing. I'm not sure about maximum DC SC swing needed  :-\ Did you tried to measure voltage at max Gain reduction? I;m away from my unit  :(
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: bluebird on January 25, 2009, 05:04:05 PM
Hey, moby I've been away for a while...

Yes I wired the 6ba6 in triode. Pins 6,5,2 all together for the plate. and remember I boosted the voltage up to about 210 volts.

Like I said earlier the 6ba6's really made this thing rock. they can go into deep compression without the wierd crossover distortion the 6bc8 was getting.

I do think the time constant thing is more important than the tube change though.

I've been using the 2uf and 68K in parallel setting the most. this is closest to the fastest fairchild setting. its great on bass drums vocals, just about anything. I'm sure its not the exact same because of the weaker sidechain but I'm loving it.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on January 25, 2009, 06:53:22 PM
Quote
Yes I wired the 6ba6 in triode. Pins 6,5,2 all together for the plate. and remember I boosted the voltage up to about 210 volts.
Great, I thought that it's dirrect triode connection  ;D About voltage boost I can see in the first post. Thanks  :)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on February 02, 2009, 12:44:47 PM
I've got another working mod to make the PM670 be able to handle the Fairchild's time constant networks... and so many more... Cheap and easy to build !!!
Interrested ?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: veermaster on February 02, 2009, 02:38:48 PM
No, absolutely not. Of course damn it! ;D
I´m still waiting for my tube sockets to arrive so I can play with attack and release times myself. I want to control them separately for better flexibility. I´m really thankful for any information and advice, so please share your experience!
Thanks, Emre
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on February 02, 2009, 02:42:46 PM
Yees, keep them  coming  :)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: radiance on February 02, 2009, 03:04:01 PM
I've got another working mod to make the PM670 be able to handle the Fairchild's time constant networks... and so many more... Cheap and easy to build !!!
Interrested ?

Yessire!!
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on February 02, 2009, 05:05:10 PM
Here it is !!!
The main problem in the PM670 is the output power of the SC-amp. The idea is really simple :
- Not enough power = let's add a power amp !

OK it is not a all tube comp, but the mod isn't in the signal path, so I don't care  ::) .

My main problem was to know were I could get something easy to deal with. I thought about having the time constants network buffered by an op-amp but the high impedance of the resistors ( up to 3M ) was a real problem. So I decided to make a big balled follower of the rectified signal after the Sc-amp.
More simple than what I was trying to deal with at the begining !!! The simpler the better !!!

It is working as is but there's a few thing I'm still working on. The extra diode makes the control voltage a little bit lower than original. There's two solutions to solve this, to had another polarisation pot for this mod, if you want both stock and modded mode, or to use a low forward voltage diode which can handle high repetitive currents during short periodes...

 ;D ;D ;D Any idea is welcome  ;D ;D ;D!

(http://pagesperso-orange.fr/NBNS-Studio/PM670/boost-analags-sc-amp.gif)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on February 02, 2009, 06:57:30 PM
Great Lolo  :) Did you tested the "thing" or it's just idea?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: SaMpLeGoD on February 02, 2009, 10:59:52 PM
Nice Lolo... so, boosting the Sc will can use the Time Constant's network from the original PM670 design? isn't it? is that the idea?

Cheers,

Eddie :)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: khstudio on February 03, 2009, 02:53:56 AM
I can't help to wonder where the "Designer" of this project is & his input on the "Side-chain" subject or even an explanation of WHY he chose to build it this way.  ???

If nothing else... it could help those of us who wish to have more options with the sidechain understand a little better what direction to go.... or not to go. ;)

Rowland... you out there bro? :-X
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Kingston on February 03, 2009, 03:10:15 AM
nice hacking lolo-m!

I guess the original PSU has plenty of power for all this.

so now you grab the "extra" +17V to your opamp, but also lose it for 12V gadgets (meters, relays)? Do you branch (regulate) the +17V down to 12V somewhere there as well, or did you just strap some resistors to your meters/relays get 12V?

Also, where do you grab the "additional V+" and how much did you intend this to be?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on February 03, 2009, 04:02:49 AM
Did you tested the "thing" or it's just idea?
Yes, it is tested ! And it is working !  ;D

Nice Lolo... so, boosting the Sc will can use the Time Constant's network from the original PM670 design? isn't it? is that the idea?
Yes, the idea is to have the possibility to plug the real Fairchild's model 670 time constants network... And many more !!!
Faster attack is possible with a 1uF but you'll have a faster release too...

Attack time is about 0,2ms with a 2uF, about 0,1ms with a 1uF...
The release time is simple to calculate in the 1 to 4 positions : R* x C* !!!
A lot of things to experiment !!!  ;D
 
nice hacking lolo-m!

I guess the original PSU has plenty of power for all this.

so now you grab the "extra" +17V to your opamp, but also lose it for 12V gadgets (meters, relays)? Do you branch (regulate) the +17V down to 12V somewhere there as well, or did you just strap some resistors to your meters/relays get 12V?

Also, where do you grab the "additional V+" and how much did you intend this to be?
You've got it, I use the +17V/-17V of the PSU board. Because my relays ( and later leds... ) are not supplied with 17V, I had a regulator to feed them ( 78XX where XX is the voltage you need !): this is the additional V+.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: khstudio on February 03, 2009, 04:26:47 AM
Hey guys... sorry if I missed it but what is the Fastest Attack Time with the "Stock" circuit?

Actually, what are the ranges of the Attack & Release with the stock circuit?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on February 03, 2009, 05:50:38 AM
Hey guys... sorry if I missed it but what is the Fastest Attack Time with the "Stock" circuit?

Actually, what are the ranges of the Attack & Release with the stock circuit?
I can check more precisely later if you want, but faster attack time is around 1 or 2 ms stock... But the attack look like the second wave curve there, Fairchild's position 1,2,3 and 4 look like the first...
(http://pagesperso-orange.fr/NBNS-Studio/PM670/ATTACK-N1a.jpg)

Release time is program dependant from 48ms up to 2,3s but again program dependant. Don't think I don't like the Analag's design. It does work perfectly as is . I will leave Analag's time constant circuit in mine... But I want more !!!
I'm just playing with a marvellous toy ! I would be proud to say Rowan made an error there or there but he didn't make any error... Analag's gave us a really finished compressor that poeple would buy 2500€ in the shops as is...
There are some limitations that I want to overpass... And most of all, I learned more in 2 months than before in 2 or 3 years !!!
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on February 03, 2009, 06:25:22 AM
Great Lolo, I think that Volker will have one more PCB design to do  ;) Volker, are you around?  ;D
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: EmRR on February 03, 2009, 08:35:07 AM
Lolo, your second attack response appears to show tube imbalance, since the shape is not symmetrical.  That looks like the example given in the Collins 26U manual.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: analag on February 03, 2009, 08:54:55 AM
I can't help to wonder where the "Designer" of this project is & his input on the "Side-chain" subject or even an explanation of WHY he chose to build it this way.  ???

If nothing else... it could help those of us who wish to have more options with the sidechain understand a little better what direction to go.... or not to go. ;)

Rowland... you out there bro? :-X

I do follow this thread. I try not to influence the direction the DIYers want to take.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on February 03, 2009, 09:00:33 AM
Yes, there's maybe some unbalanced tubes. But what I want to point is:
The same channel was used for the two waves. The only difference is that I changed the network. The attack isn't linear because the first peak charges the 220nF (100nF in my example) and then the 10uF (1uF in my example) gets charged through the 10K resistor... This is why the volume changes after the peak reduction down to stabilisation. You've got the same attack shape in the position 5 and 6 in a real Fairchild (more symetrical with well balanced tubes). Analag's time constant network is a usable position 5 and 6.

Analag, am I right ?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: [silent:arts] on February 03, 2009, 09:01:48 AM
Volker, are you around?  ;D
I'm lurking :-X

so many options ;D

and I'm still happy with my unmodified prototype ;D ;D
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on February 03, 2009, 09:09:42 AM
As I said sooner, I will keep a non modified mode in mine... Plus a modified one for different purposes.

Stock mode does work really well... Better than what I was thinking when I received the boards  ;D !!!
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: analag on February 03, 2009, 09:22:45 AM
Many things can be done with the TC network...the observations I made with this was modified and coupled with a 50Watt CV amp to achieve some extensive settings. The PM660/670 was designed to work well at reasonable cost as the name implies, but if you guys want to take it up a notch, then I got just the thing fer ya. Will require some point to point wiring though.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on February 03, 2009, 09:28:52 AM
yes ! yes ! yes ! I want to know  ;D
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on February 03, 2009, 09:50:53 AM
Quote
The PM660/670 was designed to work well at reasonable cost as the name implies, but if you guys want to take it up a notch, then I got just the thing fer ya. Will require some point to point wiring though
:) :) :)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: SaMpLeGoD on February 04, 2009, 10:07:20 AM
Quote
The PM660/670 was designed to work well at reasonable cost as the name implies, but if you guys want to take it up a notch, then I got just the thing fer ya. Will require some point to point wiring though

I just can't wait for your mods analag! althrought Lolo's mods are nice too!!! great job people!!! It's a very nice comp... I'll put some my gear's photos in a near future!

Cheers,

Eddie  ;D
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: smallbutfine on February 22, 2009, 11:17:23 PM
Oh WOW!
I'm already very impressed now after I listened to the samples and read this thread today.
Great work, Lolo!
I don't even dare to imagine what Rowan might come up with now ...
...but I am pretty sure it can be a brilliant way to pump up the circuit even more ...
tube or silicon
who knows? (haha sure we know....)
Exciting!!!

Thanks for the excellent read so far!  8)
I had to extend some kudos while lurking here and waiting for my tubes.

Kind regards
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: analag on February 23, 2009, 12:17:19 AM
My mod would be to redesign the boards. Replace the 6BZ6 with 6BJ6's, replace the 5687's with EL84's and have Edcor bring up the secondary of the transformer to 600 ohms
http://www.edcorusa.com/products/transformers/gxpp/GXPP10-8-8k.html. Call it GXPP10-600-8k. Move up the B+ to 280V to the SC amp and down to 240V for the GR tubes. Add a driver tube to the SC amp, a 12AT7 would do. That's sounds more like a rebuild I think.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: jackies on February 23, 2009, 01:25:27 AM
Wow, thats cool! So do we have to organise another edcor group buy for this transformer?
 ;D
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on February 23, 2009, 03:12:49 AM
My mod would be to redesign the boards. Replace the 6BZ6 with 6BJ6's, replace the 5687's with EL84's and have Edcor bring up the secondary of the transformer to 600 ohms
http://www.edcorusa.com/products/transformers/gxpp/GXPP10-8-8k.html. Call it GXPP10-600-8k. Move up the B+ to 280V to the SC amp and down to 240V for the GR tubes. Add a driver tube to the SC amp, a 12AT7 would do. That's sounds more like a rebuild I think.
:) :) :)
That's sound more like a rebuild indeed !!!
But having a varimu comp in the studio bring you to own another !  ;)
Looking at the Fairchild schematics, I was planing to make a sc -amp with EL84... And to go for 6BA6 as remote cutoff tubes... These should work too, aren't they ?
Out topic question: I bought a C-core kit to make an output transformer... Must I wind the primary on one bobin, and the secondary on the other, or is it better to wind both on both bobins ? Analag, I know you've got the answer... I'm quite sure it's better to wind on both and if it is, primaries closer to iron or secondaries ?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on February 23, 2009, 07:04:45 AM
Quote
Out topic question: I bought a C-core kit to make an output transformer... Must I wind the primary on one bobin, and the secondary on the other, or is it better to wind both on both bobins ? Analag, I know you've got the answer... I'm quite sure it's better to wind on both and if it is, primaries closer to iron or secondaries ?
I think that it will be better to start completely new thread about it. Here is a lot knowledgeable TX guys who can really help, but they are not involved in the PM660. (CJ, Max...) So start the thread and ask exact question about TX you are trying to wind and viola  ;D . And yes, post the link here so we caln lurk  ;)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on February 23, 2009, 05:32:10 PM
post the link here so we caln lurk  ;)
Here it is :
http://www.groupdiy.com/index.php?topic=32204.0 (http://www.groupdiy.com/index.php?topic=32204.0)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: smallbutfine on February 24, 2009, 07:23:33 AM
Ha, looks like some of us will build another varimu additionally...
I guess p2p....
Now following 2 threads.
More than a mod, it's more like a new design, Rowan. Great!
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: SaMpLeGoD on February 24, 2009, 09:15:42 AM
Well, nice to start an almost new project, but I just finished my PM670, didn't tested in the studio yet, and did'nt do any mod for the TC network so far... Is better leave this this way and dig into the new one? That will be so much different than this? what i understand so far is the new mods will get this unit's behaviour near to the original Fairchild, am i right?
Well I really don't care about if it is a Fairchild or not... just want a versatile unit :) can I get that with my stock unit? any experiences?

Looking forward to see the mods

Cheers!  ;D

Eddie
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on February 24, 2009, 09:40:04 AM
Well, nice to start an almost new project, but I just finished my PM670, didn't tested in the studio yet, and did'nt do any mod for the TC network so far... Is better leave this this way and dig into the new one? That will be so much different than this?
Test your PM670 stock if you finished it. Listen... listen again... Then you'll know if it is what you were looking for... There's a lot of chances that it'll be what you were searching... The PM670 is a really great comp, musical and sweet...
To leave this one and to dig in a new one is a solution... but at a cost  :P

what i understand so far is the new mods will get this unit's behaviour near to the original Fairchild, am i right?
Well I really don't care about if it is a Fairchild or not... just want a versatile unit :)
I don't care too to have a Fairchild or not... I won't have one... I'm certainly too poor !!!
The Fairchild is the holy grall of the tube comps because is was the faster and certainly the cleanest one... To reach its performances is having the most opened possibilities... You can slow down a Ferrari, but you won't go 350km/s with a cheap car ;D. I don't own a Ferrari but I would like an ultra fast comp ;D

can I get that with my stock unit? any experiences?
Listen to your comp !  ;D ;D ;D
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: SaMpLeGoD on February 24, 2009, 11:49:59 AM
Quote
Listen to your comp ! ;D ;D ;D


I will Lolo, I will :)
It's my 5th DIY comp ;) and I like a lot the 1176 REV D and the GSSL! so I' looking for a fast and clean comp...
I'll use the PM670 on a mix next week, so I'll post the results  ;)

Thanksssss!

Eddie ;D
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on March 06, 2009, 08:57:42 AM
I made a board layout for my second mod. I will share it. It is single-sided so I would like to know if it's worth to make some professional boards. The thread is here :
http://www.groupdiy.com/index.php?topic=32406.0 (http://www.groupdiy.com/index.php?topic=32406.0)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: mikeyB on March 11, 2009, 07:54:15 PM
It's getting late and I can't find what I thought I had seen - maybe another thread -but didn't someone mention using a hybrid poweramp chip to replace the valve sidechain? Will this affect the sound drastically?
nite nite - need sleep!!
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on March 11, 2009, 08:35:35 PM
It's getting late and I can't find what I thought I had seen - maybe another thread -but didn't someone mention using a hybrid poweramp chip to replace the valve sidechain? Will this affect the sound drastically?
nite nite - need sleep!!
It's maybe here :
http://www.groupdiy.com/index.php?topic=31088.0 (http://www.groupdiy.com/index.php?topic=31088.0)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on March 23, 2009, 11:07:11 AM
A few days ago, looking the amazing results Rotheu had on his PM660, I realized that there was maybe an "all tube" pimp that can be done on the Analag's PM660...
The first stage of the real Fairchild SCamp is a 12AX7 in class B mode. On Analag's design, this stage isn't present. I didn't scope (yes, I know, I should have  ;D) the SCamp, but I'm quite sure the PM670 SCamp is a classic push-pull amp. So I added this missing ( ??? ) stage... And the result is: it seams to work !!!
I will have a lot of shows in the next 15 days so I won't be able to check this idea correctly untill next month. If someone wants to test it, it is quite simple. Look the Fairchild schemo and copy the first stage, then connect the output to the "threshold connector". Use the Threshold pot output to feed the 12AX7 grids.

Analag, am I right to think the 5687 are in pure AB mode ? I don't have anything to simulate the 5687 so...
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on April 11, 2009, 03:17:35 AM
My last investigations on this mod aren't really revelant  :-\... I only managed to add a DC threshold with this mod so I give up...
Anyway, for poeple who want to implement the "missing" DC threshold (not sure it is really a missing point but more Analag design wish), there's a way to do it with the SCAB (SCAmp Booster)... I will fix this Tuesday or Wednesday and post results here :
http://www.groupdiy.com/index.php?topic=32965.0 (http://www.groupdiy.com/index.php?topic=32965.0)

Thank you again Analag and Silent Arts for this wonderfull comp !
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lewilson on April 16, 2009, 12:27:31 PM
Hello all,
   I have found the Russian 6n5p tube to be a nice sub for the 6bc8 tube, Much smoother fuller compresion and overall a better quality tube than the american tubes. Its the same pinout as the 6bc8  but uses more filiment current. 
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Moby on April 16, 2009, 08:22:30 PM
Hello all,
   I have found the Russian 6n5p tube to be a nice sub for the 6bc8 tube, Much smoother fuller compresion and overall a better quality tube than the american tubes. Its the same pinout as the 6bc8  but uses more filiment current. 
It will be nice if you can post some sound samples, 6N5P against 6BC8  :)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on April 17, 2009, 02:46:18 AM
Hello all,
   I have found the Russian 6n5p tube to be a nice sub for the 6bc8 tube, Much smoother fuller compresion and overall a better quality tube than the american tubes. Its the same pinout as the 6bc8  but uses more filiment current. 
Is it a direct substitute ? I mean did you just plug them with the same settings or did you change the 2 bias settings ? I bought some to have different compression flavours on my 2 PM670...
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: khstudio on June 08, 2009, 09:04:03 AM
I'm gettin close. I'm also lucky that my brother can make me Vinyl stickers.

Pos 1 thru 5 will be some of Blue Bird's & Pos 6 will be stock... should be cool & give enough options.

(http://www.khstudio.us/DIY/PM670-K6-YEL-2sm.jpg)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: khstudio on July 06, 2009, 06:01:47 AM
See Below
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: khstudio on July 09, 2009, 10:30:11 PM
I posted a Blank - VOLTAGE CHART for everyone to download & hopefully fill out & post.
these measurements will help others troubleshoot none working units & narrow down problem areas.
Also confirm if your unit is working properly.

I made a voltage chart in EXCEL & a TEXT doc.

EXCEL VERSION = http://www.khstudio.us/DIY/PM670/PM670-VOLTAGE-CHART.xls (http://www.khstudio.us/DIY/PM670/PM670-VOLTAGE-CHART.xls)

PL1 - Control Voltage (Threshold Off, Then 1st ON Position, Med & Full on) This one is tricky but important!
...Must have audio going thru unit, say 1.2v Test tone @ Input (Please measure AFTER connecting to input! due to loading)
& then set gain to have 1.2v at the output (with Threshold fully off)
Obviously everyone's measurements will be slightly off due the differences of Threshold controls, Taper & values chosen...
but if you KNOW your switch & values, posting the value along with the Voltage reading will be more accurate!

((((Sorry... This Test should have been added to the Test Sheet.))))

PLEASE DOWNLOAD & POST YOUR VOLTAGES... Thank You!

Below is the TEXT version & Attachment Version Below that.
------------------------------------------------------------------  
PM670 Voltage Chart   USER NAME =
"Inital setup"   input gain & threshold control at 0

Measure voltages referenced to ground - Set RV3 wiper to -2.4VDC - Set RV6 wiper to -4.5VDC   
      
Power Transformer & High Voltage output =          
HR* = Heater resistor Value =          
Volts - Before & After HR* =          
VU METER "Type" =
         
POWER SUPPLY         NOTES
KL1   AC-IN      HIGH VOLTAGE AC IN TO DIODES
R1   Before      47r - 2w
R1   After      47r - 2w
R2   Before      47r - 2w
R2   After      47r - 2w

CHANNEL - 6BC8 - Section         
PL1   PIN 2      CONTROL VOLTAGE - THRESHOLD OFF
Q1   Emitter      "Common node voltage of R1, 2, 3, 4 = 330r"
R2   330r      Cathode = V1a
R1   330r      Cathode = V1b
R4   330r      Cathode = V2a
R3   330r      Cathode = V2b
PL2   Pin 2      Center Tap  of T2 - 10k:600 - 136v from R6 / VU Meter
PL2   Pin 1      Outer Tap 1 of T2 - 10k:600 - Voltage to Plates - One side of R6
PL2   Pin 3      Outer Tap 4 of T2 - 10k:600 - Voltage to Plates - One side of R6
PL3   Pin 2      Should be same as PL2-Pin 2 voltage
PL3   Pin 1      136v INPUT - to R6 & VU Meter

CHANNEL - 5687 - Section         
R10   330r      "Common node voltage of R11, 12, 13, 14"
R11   47r      Cathode = V3a
R12   47r      Cathode = V3b
R13   47r      Cathode = V4a
R14   47r      Cathode = V4b
PL8   Pin 2      Center Tap  of T4 - 10k:600 - 245v INPUT
PL8   Pin 3      Outer Tap 1 of T4 - 10k:600 - Voltage to Plates - One side of R15
PL8   Pin 1      Outer Tap 4 of T4 - 10k:600 - Voltage to Plates - One side of R15
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: buschfsu on August 04, 2009, 01:47:27 PM
kev,
i have a 2 deck 6 position switch for my TC that works with my purusha case.  Can you share how you wired yours?  looks like you jumpered the 10uf on the board? is that right?


Also my purusha case has a hpf knob silk screened on the back.  did i miss a thread on this?  anyone have one built this way?

thanks
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: khstudio on August 04, 2009, 03:57:54 PM
I will try to make a drawing as soon as I have time... it's not too hard.
I think if you read back I mentioned what values i used & I like them a lot!
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: khstudio on August 08, 2009, 04:21:21 AM
This is part of an email I sent to Rowan concerning using only ONE 5687 in the sidechain:

Quote
I ran some tests, using 1x 5687 in the left ch & 2x 5687's for the right.
All of the voltages into & out of the sidechain section & the control voltages matched at various settings!
So then I did some "Burst" tests to check & see the "Attack Time" in the computer... they also were no different & appeared to be pretty fast (aprox 2-5ms)
Then I listened & could not tell a difference between the 2 channels...

I'd like to run the 670 with just One 5678 instead of 2 but I need to ask, what is the downside of this if any
& does the cathode resistor need to be adjusted & to what?
The Voltage at the 330r & 47r node is:
2 tubes = 12-13v
1 tube =  10-11v
The main reason for me wanting to run it like this is the HEAT is drastically reduced everywhere except the heater resistor.
I know the sidechain amp has a lot to do with the "Attack Time" but how is it that the One tube does the same job as having 2?
*** The Philips & newer Tung-Sol both reacted the same when doing the "single tube" test. ***


Rowan's TC network doesn't need a lot of power to work... It charges a really small cap on attack...

Thanks for the info...
Do you see any downside to the one tube side chain at all?
What about charging the 10uF Cap?

This comp really pulls a lot of current & if it reacts the same with 1 or 2 tubes I wonder why it even has 2 to begin with.

My next question should be about the possible need to adjust the cathode resistor for the single tube operation.

I must say I'm really surprised that no one else is having issues with a HOT Edcor Power transformer.

Here are the readings:
Total Heater Current draw = 5.27 amps

15 min = 98 deg F
30 min = 110 deg F
45 min = 115 deg F
60 min = 120 deg F
90 min = 128 deg F
120 min = 135 deg F

At this point the PT is too hot to keep your hand on for more than 5 seconds... if that!  :o

Here are the readings with "Just ONE Tube in the Side Chains" - Both Ch:
Total Heater Current draw drops from 5.27 amps to 3.58 amps

15 min = 95 deg F
30 min = 98 deg F
45 min = 103 deg F
60 min = 106 deg F
90 min = 107 deg F
120 min = 107 deg F

MUCH Better, no?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: noulou on August 12, 2009, 11:47:15 AM
Right! Pimping time!!  ;D

First of all, many thanks to lewilson for the Russian valves tip. I tried them and they work great as a 6bc8 sub. I have to say I also prefer the sound to the american valves. East-West 1-0.

I am thinking of upping the supply voltage to them, like bluebird did with his 6ba6s.

I think 200v should be cool with them, what do you all think?

http://www.mif.pg.gda.pl/homepages/frank/sheets/049/6/6BC8.pdf (http://www.mif.pg.gda.pl/homepages/frank/sheets/049/6/6BC8.pdf)
http://www.mif.pg.gda.pl/homepages/frank/sheets/113/6/6N5P.pdf (http://www.mif.pg.gda.pl/homepages/frank/sheets/113/6/6N5P.pdf)

Now, with the all important time constants...

In my opinion, this is where it's at!

The original design has far too long release times for my taste. I tried to measure the release time, got bored, went for lunch and when I came back the meter returned to 0vu. About 25 minutes i think.  ;D ;D
(joking)

So, I took out c4, jumpered it and substituted it with different capacitors and resistors in parallel.

At the moment I have
1u2 // 50k
3u3 // 100k
4u7 // 150k
5u6 // 1meg
6u8 // nothing
10u // nothing

Mind you, these are just values I had in hand. I installed them in order to start aurally tweaking the beast.

BOOM!!!

I haven't taken it to the studio yet, but listening at home I can easily see the poorman becoming my favourite compressor.

Beautiful compression action, especially with those short release times.

Who cares about 50 watt sidechains and sub-microsecond attack times?

If I wanted to completely trap the transients I'd turn to a digital limiter, which can also look into the future.  :P

I don't think I have a need for lolos boards after all. I say let some of those sneaky transients through!

I'll report back once I tweak those time constants even more. (hopefully with sound examples).

Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on August 13, 2009, 03:30:24 AM
This is part of an email I sent to Rowan concerning using only ONE 5687 in the sidechain:

Quote
I ran some tests, using 1x 5687 in the left ch & 2x 5687's for the right.
All of the voltages into & out of the sidechain section & the control voltages matched at various settings!
So then I did some "Burst" tests to check & see the "Attack Time" in the computer... they also were no different & appeared to be pretty fast (aprox 2-5ms)
Then I listened & could not tell a difference between the 2 channels...

I'd like to run the 670 with just One 5678 instead of 2 but I need to ask, what is the downside of this if any
& does the cathode resistor need to be adjusted & to what?
The Voltage at the 330r & 47r node is:
2 tubes = 12-13v
1 tube =  10-11v
The main reason for me wanting to run it like this is the HEAT is drastically reduced everywhere except the heater resistor.
I know the sidechain amp has a lot to do with the "Attack Time" but how is it that the One tube does the same job as having 2?
*** The Philips & newer Tung-Sol both reacted the same when doing the "single tube" test. ***


Rowan's TC network doesn't need a lot of power to work... It charges a really small cap on attack...

Thanks for the info...
Do you see any downside to the one tube side chain at all?
What about charging the 10uF Cap?

In stock TC network (as in Fairchild's pos 5 &6) the SCAmp charges the cap paralleled to the grid resistor first. This gives you the attack time ( in Analag's it is a 220nF). Then it charges the rest of the circuit... Less power will certainly mean in Analags' TC network only less release (or a weird release action)...
Paralleled tubes in push pull  technology gives you more power and more linearity....
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: khstudio on August 13, 2009, 05:04:11 AM
Do you have any tips you could share about how best to test the release times?
I'd like to do a comparison once I get my unit back up & running.

Thanks for you help.  :)

Quote
less release (or a weird release action)

Do you mean slower, faster or what?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on August 13, 2009, 05:09:32 AM
Certainly a faster release as the cap won't be charged enough but certainly too with a fast peaky reduction and a release time starting at a different gain reduction... I don't know how it can sound...
All this is what I suppose, I can't say this is what happens...
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: khstudio on August 13, 2009, 05:31:56 AM
Cool... The reason I'm asking is, before my unit went down I had tried it both ways but settled on the Single side-chain tube because of the heat (or until I got it situated) I had recorded a few different tracks with each setup + I still remember how it felt... especially on this one Bass track I'm working on.
I do think it was a little better sounding with both tubes... something is a little strange with the release I think but can't put my finger on it.

I will say that it still does work very well... just maybe not optimal.

Thanks.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: buschfsu on February 03, 2010, 10:41:59 AM
buying caps for my PM670 and purusha case (6 selections for TC)

trying to understand this and so far i have...

Slow attack                                     Fast attack

10uf   6.8uf   4.7uf   2uf   1uf   0.5uf
None   2M   470k   150k   65k   25k

Slow release                   Fast release
EDIT: had release descriptions backwards based on this bluebird quote...
The higher the resistance the longer it takes the cap to discharge through it. longer release.
the smaller the cap the shorter time it takes to fill up. shorter attack.

as i understand it putting these in parallel on a switch means that these six combinations are possible?  do these combos match what i have for descriptions above?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on February 03, 2010, 11:06:09 AM
buying caps for my PM670 and purusha case (6 selections for TC)
trying to understand this and so far i have...

Slow attack                                     Fast attack

10uf   6.8uf   4.7uf   2uf   1uf   0.5uf
None   2M   470k   150k   65k   25k

Fast release            Slow release

as i understand it putting these in parallel on a switch means that these six combinations are possible?  do these combos match what i have for descriptions above?
Will you use my mod ?
If you do, you'll get approx 0,2ms attack with a 2uF; 0,4ms with a 4uF. Release is the R*C...  If you want longer attack times, I've got tips but it doesn't belong to this thread....
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: buschfsu on February 03, 2010, 11:13:42 AM
trying to understand it first.  so are you saying the attack time is not related to the paralleled 'RV7' resistor subs and the 'C4' cap subs?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on February 03, 2010, 11:31:15 AM
trying to understand it first.  so are you saying the attack time is not related to the paralleled 'RV7' resistor subs and the 'C4' cap subs?
In analag's network it is more or less. I mean the attack is given by C3 charge more than by the C4's. Electricity is like water, it fills quicker a small glass (C3) than a big one (C4) especially if you reduce the throat of the bottle (RV7+R18) to fill the bigger one (C4)...
Of course the caps are charged in parallel so changing C4 for a smaller value will change a bit the attack time but C3 is 45 time smaller than C4 stock so...
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: buschfsu on February 03, 2010, 03:17:06 PM
so based on what you explained (thanks by the way)
my table....

Slow attack                                     Fast attack

       10uf   6.8uf   4.7uf   2uf   1uf   0.5uf
        None   2M   470k   150k   65k   25k

Slow release                                   Fast release

is accurate?  obviously there are other factors at work as well.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Kingston on February 28, 2010, 06:03:36 PM
I've been experimenting with 6K4P's all weekend.

I didn't want to end up with oscillation with some quick slap-on-wire-only tests, so I built a very sturdy adapter from each 9-pin socket to two 7-pin sockets using turretboard/bus-wire/sockets combo for each 6bc8 position.

I looks quite impressive actually, I should take some pictures.

Anyway, I was able to match these even better, quite perfectly actually, since I wasn't stuck with dual triode halves. I bumped B+ up to 165V and set the trimmers to 5,5V each (just a quick test, I'll optimise later). It allows about 22dB maximum gain reduction, and more headroom. Of course I had to experiment with more B+ for more headroom, but less maximum gain reduction. 190VB+ would allow around 15dB max gain reduction, for example (tested quickly)

I don't know why some people said earlier 6K4P is not a good fit for poorman, and why it was suggested only about 6dB gain reduction would be possible. 6K4P is a brilliant fit actually. It cuts the unusable distorted ranges available with the 6BC8, basically fixes gain staging. 6BC8 is simply not capable of 40dB gain reduction in this circuit, so why even have that much range available? It just sounds bad.

6K4P makes a much more balanced set up with it's wider grid curve and it's no longer easy to make poorman a distortion generator. VU meters now display much more usable information, instead of sitting "buried" whenever something compresses.

And the sound, obviously the the 6K4P at higher B+ compress a bit different than 6BC8. To me, this sounds more like the big brother and its variants, more controlled somehow.

I did say that 6BA6 (and so 6K4P) is not suitable in the PoorMan. The grid voltage swing needed to have -10dB of effective gain reduction is far more than 12Volts.
How did you check the gain reduction ? With the Vumeter or with a real Gain meter ? Did you use the SCAB or stock Sidechain ?

But I agree on one point, the 6BA6 sounds cleaner than the 6BC8  ;).


I don't know why you keep saying that. Did you test yourself, or just read some datasheets? I'm using the VU meter to read the gain reduction obviously. It acts the same in compression, or when used with the tube matching rig. 14V = about 17-20dB gain reduction at 160V.

I wonder what's a good way to beef up the sidechain for more voltage swing? Would be interesting to run the tubes closer to the edge.
OK, it's time to end some unopened project. I'm working with another member on a prototype based on 6BA6... The voltage swing needs to be a lot more important with this kind of tube than with 6BC8 or ECC189. For example in our prototype, the -20db gain reduction need a CV of -40V and -10db is around -20V, both referenced to the grid voltage for 0db gain reduction.
That would mean in the PM670 a CV swing from -5,5V to -45,5V to get -20db of GR...
The vu resistor have to be choosen well to track correctly the gain reduction. The movement is showing you some compression but maybe not the real amount of compression.
As my prototype use different resistors values and different transfos, I will try tomorrow in the PM setting but I'm quite sure you can't get -22dB without a huge voltage swing... But if it is, that's a really great news  ;D !

It is definitely possible. I do realise the VU meter is not a perfect measurement, but I know I'm in the ballpark with it. I can hear it. If it was compressing less than 10dB it would be near invisible and hard to tell because of the extremely soft knee of the grid curves. Remember, I have no Scamp yet.

I can hear it compressing like mad at max settings. It sounds gorgeous. Just like with the 6BC8 and variants, but no distortion.

Remember I only chose tubes that would go to about 18-20dB reduction at -14V grid. About one quarter of my sets could do this. Another quarter would not even hit 10dB at -14V.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on February 28, 2010, 06:28:31 PM
It is definitely possible. I do realise the VU meter is not a perfect measurement, but I know I'm in the ballpark with it. I can hear it. If it was compressing less than 10dB it would be near invisible and hard to tell because of the extremely soft knee of the grid curves. Remember, I have no Scamp yet.

I can hear it compressing like mad at max settings. It sounds gorgeous. Just like with the 6BC8 and variants, but no distortion.

Remember I only chose tubes that would go to about 18-20dB reduction at -14V grid. About one quarter of my sets could do this. Another quarter would not even hit 10dB at -14V.
Now I understand better how your setting can work that way ! 6K4P seam to have more diferences between curves than the 5749 (6BA6W) I tested.
And I agree it is a lot more easy to match single triodes than dual triodes. Well matched triodes are a huge improvement in terms of distortion and attack times.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Kingston on February 28, 2010, 06:35:06 PM
6K4P seam to have more diferences between curves than the 5749 (6BA6W) I tested.

Yes. I have 5 6BA6 meant for another project but I quickly checked (with your matching rig) just how "equivalent" they are to 6K4P. They all fell in the "higher quadrant" of the 6K4P sets, with only one barely going under 10dB with -14dB grid. None could be matched with the "steep curve" 6K4P's I'm using.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on February 28, 2010, 07:09:48 PM
6K4P seam to have more diferences between curves than the 5749 (6BA6W) I tested.

Yes. I have 5 6BA6 meant for another project but I quickly checked (with your matching rig) just how "equivalent" they are to 6K4P. They all fell in the "higher quadrant" of the 6K4P sets, with only one barely going under 10dB with -14dB grid. None could be matched with the "steep curve" 6K4P's I'm using.
That's what I always thinked for 6BA6 use ! But I was sure (and I was wrong) the 6k4p was a close equivalent of the 6BA6. But obviously, it isn't !

Just because I'm curious, how did you wired the 6K4P ?

PS: If you plan to use the SCAB, you'd better change the 5532 for OPA604 and power it with +/-24V rails. It'll give you more compression headroom in SCAB mode especialy for the peaks.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Kingston on February 28, 2010, 07:20:41 PM
That's what I always thinked for 6BA6 use ! But I was sure (and I was wrong) the 6k4p was a close equivalent of the 6BA6. But obviously, it isn't !

Just because I'm curious, how did you wired the 6K4P ?

Well it is "an equivalent", but 6k4p has more ranges it seems. Or maybe they are equal but we just haven't tested enough 6BA6 batches.

From some other thread: Safe triode mode for 6BA6 is : pin2 tied to pin7 and pin5 tied to pin6 (lewilson:Yes, this is exactly how mine is. )

I wired it like that. Actually 6K4P cathode is hardwired to grid 3 (and screen) so it's even easier (pins 2 and 7 internally connected).


PS: If you plan to use the SCAB, you'd better change the 5532 for OPA604 and power it with +/-24V rails. It'll give you more compression headroom in SCAB mode especialy for the peaks.


I had not thought about Scab headroom. hmm. This might be a bit difficult since my power supply might not be able to provide +/-24V rails. I will experiment.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: lolo-m on March 01, 2010, 04:30:33 AM
I had not thought about Scab headroom. hmm. This might be a bit difficult since my power supply might not be able to provide +/-24V rails. I will experiment.
Don't bother... Try to set the +/- voltage as high as possible with stock PSU with some margin for regulation and you'll be fine.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: inputoutput on June 24, 2010, 01:58:01 PM
New trafos Mounted! a pair of vintage Chicago trafos (BIH 1) on the input T1. 600/50K (Thought they were 1:1 ratio, but now I'm not sure anymore. Anyone?)  On T2 theres a pair of LL1676


Before and after :


Edcor :
(http://kaada.no/DIY/DIY%2D670%2Dtranny/1-edc.jpg)

New Trafos
(http://kaada.no/DIY/DIY%2D670%2Dtranny/1.jpg)


------------------------------



Edcor :
(http://kaada.no/DIY/DIY%2D670%2Dtranny/4-edc.jpg)

And here with the new Trafos
(http://kaada.no/DIY/DIY%2D670%2Dtranny/4.jpg)



It should be taken into consideration that a lower ratio on the inputtranny gives a lower volume in - which is more gentle on the rest of the circuit. But interestingly enough, the output volume was almost as loud.




With full Gain I now have virtually no noise or hum. Only a modest 60Hz peak at -96dBu on right side and a -106dBu on left side.



As for the sound, the results are self explanatory
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: radiance on June 24, 2010, 02:31:15 PM
So are these 40Hz and 2K test signals (sine's) we're seeing here?
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: inputoutput on June 25, 2010, 06:03:10 AM
sinustones. The results looks kinda the same in all frequencies.

Title: Re: the pimp / mod the Poor Man 660 thread
Post by: inputoutput on July 01, 2010, 07:02:39 AM
Stumbled upon a page with sample testrun through the Analogue Tube AT-101 (Fairchild 670 Recreation). http://ronansrecordingshow.com/2010/06/analogue-tube-at-101-the-fairchild-670-recreation/  Hope Ronan Chris Murphy, who run the site, and the musicians at play, thinks it's ok that I borrowed his soundsamples.  I ran the files through the PM670 to see how it came out.   This is just a fast run-through.  Don't make a review out of this, cause there are so many factors at play....! Compared to the wonderful AT-101 I would say that the Poorman tightens the bottom end, and the midtone sounds harder. 

I have been using the PM670 A LOT throughout the last year, with great joy,  mainly because of its uniqueness.  The clue is to know what it's good at, and what not.  Like, if you run a clean piano piece through it will probably sound nothing but horrible, but a more low-fi'ed piano track might sound just wonderful (as long as the inputgain is not set to high.)

Here are the files (one with bypass, one PM670 and one AT-101) http://www.kaada.no/DIY/PMSHOOTOUT.zip

Title: Re: the pimp / mod the Poor Man 660 thread
Post by: Ronan Chris Murphy on July 01, 2010, 06:25:59 PM
Hope Ronan Chris Murphy, who run the site, and the musicians at play, thinks it's ok that I borrowed his soundsamples.  I ran the files through the PM670 to see how it came out.   This is just a fast run-through. 

Hey, that is cool that you did this. You definably have my permission, For those that are just going to download the files here and do not visit my site, I just want to acknowledge the musicians on the samples who I did not pay anything for the use of their music in the shoot out:

In order the audio samples contain clips of:
Jibilian/Setar http://www.garyjibilian.com (http://www.garyjibilian.com)
Tay Zonday http://tayzonday.com/ (http://tayzonday.com/)
Terry Bozzio http://terrybozzio.com/ (http://terrybozzio.com/)
Kathleen Blackwell www.kathleenblackwell.com (http://www.kathleenblackwell.com)
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: opacheco on June 20, 2011, 12:12:23 PM
(http://i8.photobucket.com/albums/a22/analag/Back2-1.jpg)

A lot of money, time and effort. I have enough tubes to re-tube it three times. As much as I love it, I wouldn't build another one...too much work.

Analog,

I see your proyect....man that is incredible!!...Do you have info or Instruction in order to do a unit like this(your own instructions)??
How about the sound?

Thanks a lot for your time.
Opacheco.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: analag on June 20, 2011, 01:18:27 PM
This was built and fine tuned years ago and as for the sound, I took it to the NY group meet and the guys rather liked it a lot  ;). It  would be a combination of PCB and point to point wiring. Power and output transformers would have to be custom. It's a big project but the sound is worth it I suppose.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: opacheco on June 20, 2011, 01:44:21 PM
This was built and fine tuned years ago and as for the sound, I took it to the NY group meet and the guys rather liked it a lot  ;). It  would be a combination of PCB and point to point wiring. Power and output transformers would have to be custom. It's a big project but the sound is worth it I suppose.

Analog, Thanks for you response!

Do you have the schematic that you used for it?....how about the internal pics, do you have some internal pics?

Thanks for your time
Opacheco.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: analag on June 21, 2011, 10:55:45 AM
(http://i8.photobucket.com/albums/a22/analag/Chassis3.jpg)
(http://i8.photobucket.com/albums/a22/analag/DSCF4613.jpg)

I have go dig around to find the internal pics. These are all I could find. I took the second pic about five years after I built the thing.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: opacheco on June 21, 2011, 12:40:07 PM
(http://i8.photobucket.com/albums/a22/analag/Chassis3.jpg)
(http://i8.photobucket.com/albums/a22/analag/DSCF4613.jpg)

I have go dig around to find the internal pics. These are all I could find. I took the second pic about five years after I built the thing.

Analag,
Nice pictures!!, really good unit!
how about the schematic for this unit?....do you have a copy?

Thanks
Opacheco.
Title: how to add the M/S to the pm670?
Post by: creal on December 26, 2012, 11:04:47 PM
HI All,
i like to know if it's possible and how to add the M/S to the pm670 like the original fairchild?
I use the edcor transformer.
Title: Re: the pimp / mod the Poor Man 660 thread
Post by: prescott on December 27, 2012, 12:06:54 PM
Hello!

My 6k4p tubes just arrived :)
Please help me how to connect the pins to triode mode!
I've read the post about it, but not 100% clear...
Pin 1 is for grid, 3-4 heater, but dont know the others... :-\

Thanks!
Peter
Title: Federal AM864/ Vari-mu stereo linking? Re: the pim /mod the Poor Man 660 thread
Post by: Rompstomp89 on November 29, 2016, 04:27:14 PM
There's been no mention of stereo linking method to date, and it's not on the PM schematic. The Fairchild simply ties the two control voltages together.  Here's some food for thought.

Many limiters use diode isolation to ensure dual mono and stereo operation match in timing. The Fairchild fails to correct for this, for better or worse. As is, in the original design, if you toggle between linked and unlinked the time constants will change because of the nature of paralleling networks. We do not have the complexity of time constant switching found in the Fairchild, so it's not as if I'm suggesting we alter something that already mimics exact original operation. As far as I can tell, the only thing possibly changed by addition of diodes is the relatively minor need to overcome the diode voltage drop through additional drive on the threshold control. 

NONE OF THIS HAS BEEN ATTEMPTED IN THE FIELD WITH A PM660!

Here's a comparison of the mono Collins 26U-1 with the stereo 26U-2 for example.  This is not to be taken as a cookie-cutter drop-in, given the differences in design.  The Collins being the more common type of side chain driven from a high impedance source with fairly high bias voltages present, and the PM660 being a side chain driven from a low impedance source with fairly low bias voltages present.   The Collins manual describes the 1N459's as preventing feedback into the 1 mfd caps, to avoid increase in attack time from effective lowering of 1 mfd value. 


(http://farm4.static.flickr.com/3007/2771971717_e76b746cff_o.jpg)

The unattached connection from the 0.01 cap below runs to the link switch, then to the other identical side chain and audio channel. 
 (http://farm4.static.flickr.com/3108/2772818784_97a4faf058_o.jpg)


Could this idea be brought in to a pair of Federal am864 builds?  Ive been thinking about adding a link function and not sure of the best way to implement it.  Any thoughts would be great!!!

Title: Re: the pimp / mod the Poor Man 660 thread
Post by: justinheronmusic on December 09, 2018, 06:41:52 PM
At the moment I've got on channel modified and the other stock for a quick possibility to compare.
I wil certainly stop my research now for today (I've got children to pimp ... sorry, to wash  ;D)
So, about 8ms attack time and 300ms release time : remove R17, shunt (or not it's not important here) R18, shunt C4 and change the pot (RV7) for a fixed 1M resistor.  :D

Listen, compare, it's really different !!! A lot quicker than stock, and maybe clearer, but I'm not sure I must perfect my settings between the two... I want to be sure they sound close without compression but I won't have time enought today to do this...

See ya later  ;)

Hey Lolo-M,

 So after using tons of bus compression, I am pretty sure the quoted mod is what I am after - about 8ms of attack time, and 300ms of release. I am, however, still a bit of a newb when it comes to the lingo of things. How exactly do I shunt C4? Would I take it out and replace it with a wire?

 Also, I am curious if there is a way to have about 8ms attack with variable release?