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

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Ok, nailed my problems.  I went through the board several times checking voltages, all was good.  Went through the calibration procedure a ridiculous amount of times and it still sounded dodgy.  Went over all the solder joints, look fine.  Checked most of the resistors, all in the right places.

The two issues that had me stumped which may be handy for others were:
* The cheap audio interface between my Mac and the 1176 caused me the biggest issue.  I was sending a test tone through it and when checking the pins on the lead with the DMM, it was reading .775.  Perfect.  However, as soon as I plugged it into the input of the 1176, it this dropped to around .130!  I didn't notice this straight away so when going through the calibration, it all wasn't really working right.  And when finished, everything didn't sound right (see my last post).  However, once I found this out, I had to go out of the Audio Interface into another unit to get the gain back up and once I had that going, calibration was much smoother.
* I had viewed the Mnats calibration videos before, but used a PDF from this thread (UREI KIT CALIBRATION 1176 V.A.pdf) which I downloaded and printed off, just to save having to pause the vid whilst calibrating.  However, this document was incorrect (or correct for a different version) and had me stumped until I watched the Mnats video again.  For the last calibration step (meter tracking), for the first half, it incorrectly states that once you've adjusted the input level to -10dB with compression on, turn the compression back off and adjust R55 (R71) to get the meter back to 0VU.  Of course, you should actually adjust the Output level and not R71 at all!

Anyway, that aside, I'm totally chuffed I managed to get this compressor built in my 1st go.  It's the first big project I've done in a very long while, so took my time.

It's sounding really great, I've run it through all sorts and so far, I'm liking the sound on room mics/overheads.  Vocals sound great.  And bass guitar.

Thanks everyone :)
 
remsouille said:
Hey there folks!
First of all, thank's a lot for all the great information here on this forum.
I just finished my first 1176 A build, and there's a problem with the gr part. My input and output work fine, the +4 and +8 on the VU as well. But: no compression, and VU doesn't work on GR mode (needle stays down). With pad 7 connected, there is a huge drop in output volume, and when out, I get the volume it seems I should get. I checked all the voltages against the mnats schematic, everything is fine EXCEPT in the GR meter driver section.
On Q11 I read about 2/3 volts on every pin, and then positive voltage on Q12 where It should be negative.... There is negative voltage coming all the way to r66 though, but out of R66 it's positive...
So I thought Q11 was fried, then replaced it, but nothing change. I don't actually think that the problem comes from the Gr meter section itself, cause if it did, it wouldn' affect the output volume the way it does, would it?
I think the problem occurs between Q10 and dot 7, but I checked continuity and wiring, and everything SEEMS fine.... Any measurements in this area from a working unit would be much much appreciated!

What is your bias voltage?  It's the DC voltage at Q1 gate.

Start there and we'll try and walk through this.
 
Echo North said:
What is your bias voltage?  It's the DC voltage at Q1 gate.

Start there and we'll try and walk through this.
Hey there

My DC at Q1 gate is 1,6V, no matter how much I turn the Qbias... I pulled the trimmer out and tested it, it seems to work fine...
If Q1 was dead, wouldn't the GR meter still work?

A couple other measurements, gr mode, 20 ration, compression off, no input:
-Pad 21: from -3,5 to -0,08 dialing from 4:1 to 20:1 This seems ok!
-Pad 22: No DC, no AC, no matter what...
-C7: 14 VDC in, 0 VDC out..... wtf? I'm I missing something here? Signal still goes in and comes out of the unit...

What do you think?

Thank's a lot!


 
Your DC at the Q1 gate (Qbias) needs to change (from 0VDC to about 2VDC) when you turn the trimer.  This voltage also feeds you GR meter section so you need to get this sorted.  Check your release pot wiring, specifically make sure you don't have the outside terminal wiring reversed.

C7 blocks DC from moving into the side chain and the signal line amp.  What you're seeing is correct.  Only AC should pass through that cap.  AC = Audio Signal.

With gain reduction ON, you should see an AC voltage at pad 22.

It comes from the output of C7 and feeds the ratio board voltage divider. R19-R22 (plus R78).  If you have say 2VAC (depending on your input signal) at C7 you'll see it fraction of it at pad 22 depending on the ratio selected.  Higher with 20, lower with 4.  You need to trace through that little voltage divider to see where you are losing signal.

Mike
 
Echo North said:
Check your release pot wiring, specifically make sure you don't have the outside terminal wiring reversed.

Damn... these were actually reversed... Sorry for that. But still, when I dial the trimmer, I can see the Q bias changing from 0 to -2,86V at pad 18, but at pad 7 I read from 13,17v to 12,95, and at Q1 gate,it sticks at 0,65 2,7 at Q11...
 
Something is most likely wrong with your wiring.  Double check all of your attack and release wiring.  The only thing between 18 and 7 is that attack and release pots.  Make sure you are measuring the gate...it's not the middle pin on the 5457.

Mike
 
Echo North said:
Something is most likely wrong with your wiring.  Double check all of your attack and release wiring.  The only thing between 18 and 7 is that attack and release pots.  Make sure you are measuring the gate...it's not the middle pin on the 5457.

Mike
Nope, I triple checked, everything around attack and release pots looks fine.... What should be my voltage at pad 19??
Thanks for your help, Mike!!
 
remsouille said:
Echo North said:
Something is most likely wrong with your wiring.  Double check all of your attack and release wiring.  The only thing between 18 and 7 is that attack and release pots.  Make sure you are measuring the gate...it's not the middle pin on the 5457.

Mike
Nope, I triple checked, everything around attack and release pots looks fine.... What should be my voltage at pad 19??
Thanks for your help, Mike!!

That's the output of the sidechain.  With no signal there should be a little DC that should change with ratio setting.  With signal and GR on you'll see more.  I'd have to check a working unit which I'm not near right now.
 
Read through the steve_h stuff earlier in this thread about the sidechain.

http://www.groupdiy.com/index.php?topic=29981.msg614590#msg614590

ready through all 3 or so pages.  Specifically the stuff on the voltages on page 69.
 
Echo North said:
Read through the steve_h stuff earlier in this thread about the sidechain.

http://www.groupdiy.com/index.php?topic=29981.msg614590#msg614590

ready through all 3 or so pages.  Specifically the stuff on the voltages on page 69.
Hey there,
I've been reading these posts for over a week now hahaha. I'm not with the unit right now, but from what I recall, my voltages at pad 21 are fine, dropping as I dial in the ratio buttons, but I'm getting positive DC at CR2 anode (as well as out of R52), again from what I recall, in the 14v range, which coincides with what I get at pad 7...
 
You're getting 14VDC at pad 7 with no signal?

That's really off.  Is your DCV at pad 21 negative?

Do all of these test with no signal and GR enabled.
 
Here are a couple measurements, compression ON, no signal:
PAD 7:
Attack all the way up: 14,2 VDC
Attack all the way down: 12,5 VDC

PAD 21:
20:1 : -5,5
12:1 : -3,1
8:1 : -2,4
4:1 : -1,6

out of R52 / anode CR2 : 15VDC

That's WROOONG... Maybe R52 is dead, I'm going to try to pull it out...
 
Check C19.  That may be dead/shorted.

I think that would cause the issue you're seeing.  Make sure it's installed correctly and not shorted.

Check C20 as well.
 
I haven't received my rev d kit yet but I am trying to figure out how to properly test the power supply? Should the unit be plugged in? Where do I attach the 2 probes on the meter? Thanks

Rich
 
RichardM said:
I haven't received my rev d kit yet but I am trying to figure out how to properly test the power supply? Should the unit be plugged in? Where do I attach the 2 probes on the meter? Thanks

Rich

Yes the unit needs to be powered as shown in the wiring guide with appropriate fuse. The power section has to power rails (+30VDC and -10VDC).  You set your DMM to DC V in the appropriate range (if it's not auto range) and place the common probe on the power transformer center tap.  Then test the +30V and -10V points labeled on the PCB with the other probe.
 
Just to make sure....

when there's no letter after a resistor value that is automatically R, correct?

For example: R69 is 820R (ohms) and R41 is 270 ohms - RIGHT?


sage
 
sage said:
Just to make sure....

when there's no letter after a resistor value that is automatically R, correct?

For example: R69 is 820R (ohms) and R41 is 270 ohms - RIGHT?


sage

Correct!
 
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