[BUILD] 1176LN Rev D DIY

[Echo North]

Aha! Yeah! Jeez. That's totally it. I'm surprised it even worked for that long.

Ya that will do er'.  Glad you found it!

 

[JingleDjango]

What a careless error.  I hope you've marked up your shipping costs enough to make this worth your time!

 

[Echo North]

What a careless error.  I hope you've marked up your shipping costs enough to make this worth your time!

I like helping people. It's mostly fun and I usually learn something too.

 

[JingleDjango]

Well, thanks. Every stupid mistake along the way has opened my eyes to unfamiliar concepts. I'm having a great time with this, despite the frustrations.

 

[bdunard]

I was finishing up wiring my second compressor and my three 22 awg wire that is used to adjust the 2K pot for the meter is a bit short.  If I untwist the three wires it just makes it.  So my question is:

1.  Do these wires absolutely need to be twisted?

2.  If it does need to be twisted together...Where could I go locally to get 22 awg wire to match the wire in the kit?  Would Radio Shack wire work? 

Thanks!

 

[dbonin]

Really no need to twist those.  You should be ok

 

[bdunard]

Just finished my second Rev D and I have run into problems with calibration.

I set the 1kHz sine to .775 VAC on the input but when I move it over to the output I can't get the level much over 1.1 VAC with the output fully CW.  I have a REV D that is working so I checked the wiring against it and all looks well.  I also went through and checked my resistors and those too look right.  The unit powers up fine.  Any ideas where I should start my search?

 

[hymentoptera]

Just finished my second Rev D and I have run into problems with calibration.

I set the 1kHz sine to .775 VAC on the input but when I move it over to the output I can't get the level much over 1.1 VAC with the output fully CW.  I have a REV D that is working so I checked the wiring against it and all looks well.  I also went through and checked my resistors and those too look right.  The unit powers up fine.  Any ideas where I should start my search?

Did you 'center' the Qbias trimmer before installing? Meaning, did you confirm that it was at about half nominal resistance wiper to end lead?

Check your voltages against schematic w/ voltages?
http://mnats.net/files/1176REVD_VOLTS.pdf

 

[bdunard]

I did check all of my variable resistor settings.  I will go back and check qbias resistor in the morning. 

I should add that it does pass audio and sounds full bandwidth (just checked with a microphone and a preamp) but severely attenuated compared to my other Rev D.

Also, thanks for the votage schematic, I will check this as well.  Should these voltages be checked with .0775 VAC at the input?

I really appreciate the help!

 

[useme2305]

Should these voltages be checked with .0775 VAC at the input?

0.775 VAC

 

[JingleDjango]

Should these voltages be checked with .0775 VAC at the input?

0.775 VAC

At the bottom of the schematic there is red text reading:

REVISION D WITH TYPICAL VOLTAGES ADDED
TEST CONDITIONS:
FULLY CALIBRATED UNIT, NO INPUT, GR MODE, LEFT ON FOR 1/2 HR

 

[bdunard]

Should these voltages be checked with .0775 VAC at the input?

0.775 VAC

At the bottom of the schematic there is red text reading:

REVISION D WITH TYPICAL VOLTAGES ADDED
TEST CONDITIONS:
FULLY CALIBRATED UNIT, NO INPUT, GR MODE, LEFT ON FOR 1/2 HR

I can't do the first step of calibration because I can't get the output VAC hot enough to set the qbias so I'm not sure that I can get these readings on my Rev D.

 

[JingleDjango]

Right, I just meant to point out that these voltages correspond to 'no input', so you're signal generator should be turned off if you're checking against the values in that schematic.

 

[Echo North]

Low signal.

-make sure you're in bypass mode.
-check all of your wiring.
-check all of your components.

Another post coming...

 

[Echo North]

Figure out where you're not getting the gain. In bypass you basically have a 40dB mic pre.

Start with the input and output at 12 o'clock, attack in OFF position, 20:1.  Set you Qbias so you get pad 18 closest to 0VDC. Should be fully CCW. Inject you 0.775 VAC 1K signal into the input and again adjust it till you 0.775 VAC across input 2 and 3.

Again follow the schematic.

Set your DMM to AC and reference the 0V/CT on the main PCB power supply.

1. What is your AC @ the input transformer + on the in side? (should be smaller)
2. What is your AC @ the input transformer + on the out side?  (should be smaller)
3. What is your AC @ the main PCB input marked "+"  where the transformer comes in?  (should be very small like 0.085 VAC)
4. What is your AC @ + lead of C7 (should be WAY higher)
5. What is your AC @ -  lead of C7 (should be same)
6. What is your AC @ either lead of C8

Please post results.

Mike

 

[bdunard]

Figure out where you're not getting the gain. In bypass you basically have a 40dB mic pre.

Start with the input and output at 12 o'clock, attack in OFF position, 20:1.  Set you Qbias so you get pad 18 closest to 0VDC. Should be fully CCW. Inject you 0.775 VAC 1K signal into the input and again adjust it till you 0.775 VAC across input 2 and 3.

Again follow the schematic.

Set your DMM to AC and reference the 0V/CT on the main PCB power supply.

1. What is your AC @ the input transformer + on the in side? (should be smaller)
2. What is your AC @ the input transformer + on the out side?  (should be smaller)
3. What is your AC @ the main PCB input marked "+"  where the transformer comes in?  (should be very small like 0.085 VAC)

Mike,

I don't show any VAC between pad 18 and ground no matter where I turn the qbias.  Reading was 0 VAC.

As far as 1 & 2 go...
Not sure I understand where you want me to measure on the input transformer regarding inside and outside...also not sure what your saying it should be smaller than.

3.  Are you meaning the input or the output transformer?  I have 29.38 VAC where the input transformer comes in between CT and AC on both sides.

 

[bdunard]

I have set the compressors up side by side and have 1kHz at .0775 VACgoing into both of them. 
Front controls on both are:
Input and Output 12 o'clock
Attack off at full CCW position.
Release full CW
Ratio 20:1
Meter on GR

On both units I have .118 VAC at the input of the PCB (this is after passing through the tpad input and entering the PCB)  So I assume there is nothing wrong with the input wiring.  I do notice that referencing the  0VAC/CT pad and cap C7...I get a reading of 1.820 VAC on the good unit and .420 VAC on the bad unit. 

So is it safe to assume the problem is somewhere in the signal preamp section of the board?

 

[hymentoptera]

I don't show any VAC between pad 18 and ground no matter where I turn the qbias.  Reading was 0 VAC.

Multimeter should be set to volts DC when measuring DC at Pad 18.

 

[bdunard]

I don't show any VAC between pad 18 and ground no matter where I turn the qbias.  Reading was 0 VAC.

Multimeter should be set to volts DC when measuring DC at Pad 18.

Thanks for pointing that out...my own careless error.
After metering pad 18 I got it down to 0 VDC but I had to turn the qbias CW which seems to go against what Mike was saying.  If I have it full CCW I have about 1.119 VDC.

I know this is probably a stupid question but I'll ask anyway.  I'm not understanding the three test points (1,2,3) and where they are located on the PCB that Mike is asking me to test? 

I'm not sure what inside and outside mean...I'm sure this is a silly error on my part but I'm not getting it.

I've tested the input AC transformer outputs coming into the board and I have 29 VAC coming into the PCB on both sides.

I don't see any labels on the other transformer that suggest "+" or inside and outside...this probably what's throwing me off.

 

[hymentoptera]

Thanks for pointing that out...my own careless error.
After metering pad 18 I got it down to 0 VDC but I had to turn the qbias CW which seems to go against what Mike was saying.  If I have it full CCW I have about 1.119 VDC.

I know this is probably a stupid question but I'll ask anyway.  I'm not understanding the three test points (1,2,3) and where they are located on the PCB that Mike is asking me to test? 

I'm not sure what inside and outside mean...I'm sure this is a silly error on my part but I'm not getting it.

I've tested the input AC transformer outputs coming into the board and I have 29 VAC coming into the PCB on both sides.

I don't see any labels on the other transformer that suggest "+" or inside and outside...this probably what's throwing me off.

Audio Input Transformer. The small cylindrical can on the left hand side. There are input and an output pads on it's PCB. You're tracing the input signal as it enters the "in" side and again at the "out" side (Multimeter set to Volts AC), and on down into the PCB to try and find where the signal becomes quiet.