[BUILD] 1176 Rev A - Back to the beginning...

[ER]

Weird calibration on step 3. So I finished my second Rev a but the difference is this one used the 1.25 PCB and I stuffed all the mods (whereas my other one was the previous PCB version) To get the 10db drop (first part in VU MODE) the input knob was almost full CW and the output knob was about 3/4 CCW.  Oddly, increasing the IP knob with the compression circuit activated still caused the gain to increase. And the only way to get the 10dB drop was as I stated earlier.

Having said that, the unit operates and compresses fine. I tested it out against other working units all all is good. I'm just wondering if anyone else experienced this with the modded 1.25 PCB? I thought it strange.

 

[Randyman...]

Are you using matched Q1/Q11 transistors?  And are you using 3707's or 3708's?

My 1.2.5 Rev A's work perfectly (after swapping a misplaced resistor in the GR Control Amp) and are fairly consistent to each other with regard to gain reduction (Q1/Q11 from Hairball and I used 3708's)...

Did you use the most current Ratio Board resistor values from Hairball, and you heeded the mnats updated schematic/BOM (the 1.2.5 PCB has a few mistakes on the silkscreen which are corrected in the online documentation)?

 

[ER]

Yeah,  q1 & q11 come matched from hairball. I also put in the resistors that were incorrectly screened before I did anything else so I wouldn't forget - including the modded ratio board values. Also using 3708's.

The thing is, the unit sound great and seems to be working perfectly, I'm just scratching my head over the input/output pot orientation to get that 10dB drop. It seemed weird. Do you remember yours during that step?

 

[Randyman...]

This will obviously depend on the amplitude of the input signal.  I fed around +8dBu @ 1KHz into my unit, and (recalling from memory) my IP Gain ended up around 2:00-3:00 for -10dB GR @ 20:1.

Are you positive the Bias was set properly (-1dB of static GR)?  And you used a very small signal for the Bias setting (you must be sure you are below the threshold for an accurate setting).

8)

 

[ER]

You used that much eh?

That's probably the difference. I used .775v which is like -4dB. And yes my q bias and all that is perfect. Unit is working fine as I said, just curious about that thing.

 

[barclaycon]

I've been building a couple of 1176's recently and have got some parts left over which I've put in Black Market.

 

[snooty]

I just built two Rev A's, and have the same problem with both.  Resistor R32 39ohms, is burning up within 5 secs of powering up.  I know I should have a smaller fuse in there, and hopefully haven't caused more damage.  1/2 amp fuse is obviously too big, I'll get smaller ones today.

I built the power supply first before populating the rest of the boards, tested 30v & -10 at the right test points.  All electrolytics have the correct polarity, & all transistors have the correct orientation.  

Any ideas?  -Actually I think I might have discovered the problem, I believe my OT wires are hooked up wrong. I was going off the "1176 -Rev A Wiring_on-off---m.gif".  The traces on the board listing the proper colors are covered by the screw terminals.  I'll try again tonight.  I'm at work so can't 100% confirm.

Using MNATS 1.2.5 boards.

 

[phatmateo]

ER. I always had problems calibrating the meter in step 3.  I have the version 1.0 pcb with the suggested mods.  I ended up getting frustrated and just calibrating the meter to about 7 or 8 db reduction.  My unit compresses like it should, but something is funky with the meter that I never figured out

 

[kazper]

I just built two Rev A's, and have the same problem with both.  Resistor R32 39ohms, is burning up within 5 secs of powering up.  I know I should have a smaller fuse in there, and hopefully haven't caused more damage.  1/2 amp fuse is obviously too big, I'll get smaller ones today.

I built the power supply first before populating the rest of the boards, tested 30v & -10 at the right test points.  All electrolytics have the correct polarity, & all transistors have the correct orientation.  

Any ideas?  -Actually I think I might have discovered the problem, I believe my OT wires are hooked up wrong. I was going off the "1176 -Rev A Wiring_on-off---m.gif".   The traces on the board listing the proper colors are covered by the screw terminals.  I'll try again tonight.  I'm at work so can't 100% confirm.

Using MNATS 1.2.5 boards.

I believe your output transformer mis wired is exactly your problem...

 

[snooty]

Yep!  I had the output transformer wired completely wrong.  Glad it was such an easy bone-headed problem...

Both 1176 Blue Stripes calibrate and sound very good.  Since I built two, I'm going to replace as many of the Sprague OD caps as possible with sozo caps on one comp and compare.  I'll report back if there is a difference.  I like the Sozo's better in my guitar amps, never been a fan of the Sprague OD's in guitar amps unless its just one or two used.  Of course this isn't a gtr amp...but I can't help but tweak a bit!  After all the mustard caps were used in the old Neve's, so I'll give them a try.

Last night I worked on some mixes using my Purple mc77 & the Blue Stripes...different flavors with the Blue Stripes more aggressive & brighter with a harder knee.  The Purple sounds great though...I doubt I'll be selling it.  Hats off to Purple!

 

[MicDaddy]

whew.. 

Started at 9am this morning on a blank Rev A 1.2.5

It's 7:53pm and I just finished stuffing 1 board (with exception of 2N5457s)

I'm waiting on the chassis, and then to see how much damage control is needed  ??? (hopefully not much)

I'm familiar enough with the layout I believe I could knock one of these out in nearly half the time if I pushed myself.  Every move made was with my IPC as well as QC hat on.

Want to thank those of you up front for all the help in troubleshooting, and documenting errors and problems.  It's shed light on issues I might not have otherwise double checked.

Thanks to Mnats for the pcb and the layout, boards look great!

 

[Rellister]

All of you who made this possible -  a wonderful project.
Might be way over my head, but can't keep my hands off.

Have to say I'm truly impressed by the skill level in this forum.
Most of you will be headhunted by some high-end manufacturer at some point, dont let capitalism fool you ;D

Enough a-kissing.

Ordered PCBs from mnats, hopefully a kit from Mike before end of the month.

Being a newbie a couple of questions arises, sorry if some are already answered/obvious;

According to the org. schematic, the SNR 125-216 used 1/2W 5% resistors, I guess these was carbon comp.
Will the material of resistors affect sound in any way, if used in the audio path? R5,R6,R7 etc.. (I already ordered 1/4W 1% MF's)  :-\
Will my 1/4Ws burn...?

Can anyone point me in the right direction towards making good choices when it comes to components? I understand theres some room for experimenting here, but that doesnt exactly fit my skill level at this point. Been looking at some of the other BOMs here, but apart from physical size, voltage requirements etc, theres still a jungle, of caps, especially. Do one make decisions solely out of experience, or any other factors? Im not after the "right" components, just some direction in how to choose.

Thanks all!

Rune

 

[evilcat]

Hi Rune !

Yes, originals 1176 used carbon comp resistors. Some says that they have more mojo but are noisier than carbon film, less mojo less noise, than metal film, even less mojo and less noise.
I didn't have experiment diff' kinds of resistors. An easy way is to take the Shopping Cart from Hairball Audio (thanks again Mike !) and then you changed for your taste. Me, I put carbon comp on the signal path and metal film 1 or 2 % on the power and meter sections. Take more trimmers than needed, they break easily.
What I made too is to put the transistors on sockets, then I tried 5088 and 3708 kind : they really sound different ! Here's a thread I made where I explain my experiments and links for sound samples :

http://www.groupdiy.com/index.php?topic=40154.0

Hope I helped !
Good luck on your build,
Ben.

 

[Stagefright13]

Well my rev A is still using unmodified schematic etc. Original page one stuff. Mostly carbons for everything I had that wise. Orange drops. And is ripping. Little smoother than the rev D on top end but still has that sound I like. Have 4 rev D mnats going strong but this has it's place trust me. It will be a choice and it will will win A lot. Depends. ")

No mods for me so far. Touchy? input knob? Wouldn't even know I turn and listen. It's a different compressor. Works for me. Always has since built.

John

 

[MicDaddy]

Got her all finished tonight!!   ;D

I've only begun discovering its' character, have found from nice and subtle to very thick and gritty, lovin' it!!

Has anyone noticed a drift in the VU meter?  This has barely burnt in, possibly it will loosen up some over time?

Thanks again everyone!!  

If you've posted a picture in this thread I've used it as a reference, thanks to all of you!

Thanks to those of you who had problems that posted them, and those of you that helped sort those with issues.

Been lucky to only pop one 250mA slowblow and smoked the light from Hairball (didn't like the ac rail )  Going LED

 

[tmuikku]

...
Has anyone noticed a drift in the VU meter?  This has barely burnt in, possibly it will loosen up some over time?
...

Looks great! I've got two channel unit and meter drifts on the other one, don't know why.. When in GR mode, the needle doesn't go to 0 but droops more and more since last calibration.

 

[Rob Flinn]

Did you leave the unit on for an hour before you calibrated it ?  It is normal for the meter to move around a bit in the 1st hour when it is switched on.

 

[tmuikku]

Did you leave the unit on for an hour before you calibrated it ?   It is normal for the meter to move around a bit in the 1st hour when it is switched on.

Not for an hour no. Have to do this with next calibration.

 

[Rellister]

Evilcat, Stagefright;
Thanks for helpful info. Ben - excellent samples, that puts some sound on words
Off to farnell for more parts!


Rune

 

[Randyman...]

Quick Q:

I got my Rev A's working just fine, but an astute forum member pointed out that I swapped C1 in the preamp and C8 in the line amp.  They are both the same value, but one is an Orange Drop and one is a WIMA.  Would this cause any observable change in the audio?  Pic:



Opinions before I attempt to swap them back?  I'm really digging the Rev A's "as-is" - but I really don't know how this cap swap would affect the sound (if at all)?

Thanks!  8)