[BUILD] 1176LN Rev D DIY

[bbona68]

Hi, folks at Hairball!

I've just completed my build of 1176 Rev D. Lots of fun, lots of learning! And now a slight frustration.

The unit powers on, meters work, audio passes through, unit compresses, attack and release work, ratios work, unit sounds good. Great!
BUT...
I'm having trouble calibrating Q Bias (have not tried subsequent cals). Turning Q Bias in R59 leads to no changes. I've tried both Hairball and Mnats cals. No effect. It seems I can turn it forever in either direction and it will never make a difference or have a detent. Is that how it is supposed to be?
if this is any clue:
Following the 0dbu at 1kHz procedure (0,775 VAC across pins 2 and 3 on XLR in), with meter in +4, the signal pins my needle at about 42 in my front pannel's Input Scale. GR is pinned in the red even if input knob is set fully CCW.

 

[dbonin]

Hi, folks at Hairball!

I've just completed my build of 1176 Rev D. Lots of fun, lots of learning! And now a slight frustration.

The unit powers on, meters work, audio passes through, unit compresses, attack and release work, ratios work, unit sounds good. Great!
BUT...
I'm having trouble calibrating Q Bias (have not tried subsequent cals). Turning Q Bias in R59 leads to no changes. I've tried both Hairball and Mnats cals. No effect. It seems I can turn it forever in either direction and it will never make a difference or have a detent. Is that how it is supposed to be?
if this is any clue:
Following the 0dbu at 1kHz procedure (0,775 VAC across pins 2 and 3 on XLR in), with meter in +4, the signal pins my needle at about 42 in my front pannel's Input Scale. GR is pinned in the red even if input knob is set fully CCW.

This is odd.  When wired correctly, with the input off (full CCW) there should be no signal to peg the needle.
Does the same thing happen when you click the attack knob into the "off" position and set the meter switch to +4?  There should be no signal present with input fully CCW unless you have wired something incorrectly.

Follow the input signal through the t-pad to where it connect to the PCB after the transformer - you should see the AC rise and fall relative to your input knob position, falling to zero volts when fully CCW.

 

[bbona68]

Ok, Hairballers,

First of all, thanks for the prompt answer the day before yesterday.
My unit was "working" but I had 2 fuses blown in 10 minutes. So I've been doing some checking on my wiring. Everything seems to be OK,

EXCEPT

I noticed my wiring to the VU meter PCB is different from what is shown in FIG 5-44, particularly how the red/blue twisted pair is wired. That image shows (from top to bottom) white, black, green, orange, BLUE, RED wires on that PCB.
BUT
The text just above FIG 5-38 says the order should be white, black, green, orange, RED, BLUE (I quote "solder the blue wire from the meter board pad X" AND "next solder the red wire from the meter board pad Y").

I followed the WRITTEN instruction (and I am having problems with calibrating).
Should I have followed the FIG 5-44 PICTURE instead?

 

[Echo North]

Ok, Hairballers,

First of all, thanks for the prompt answer the day before yesterday.
My unit was "working" but I had 2 fuses blown in 10 minutes. So I've been doing some checking on my wiring. Everything seems to be OK,

What fuse are you using.  Should be a 350mA-500mA slo-blo.

EXCEPT

I noticed my wiring to the VU meter PCB is different from what is shown in FIG 5-44, particularly how the red/blue twisted pair is wired. That image shows (from top to bottom) white, black, green, orange, BLUE, RED wires on that PCB.
BUT
The text just above FIG 5-38 says the order should be white, black, green, orange, RED, BLUE (I quote "solder the blue wire from the meter board pad X" AND "next solder the red wire from the meter board pad Y").

I followed the WRITTEN instruction (and I am having problems with calibrating).
Should I have followed the FIG 5-44 PICTURE instead?

I'll have to look at that.  But the orientation of blue and red at the PCB is irrelevant.  Meaning either way is fine.  Blue should go to X and pin 2 for consistency with the schematic.

What are you calibration issues?

Were you able to get the q-bias set?  If not read here:

http://groupdiy.com/index.php?topic=29981.msg724759#msg724759

R80 in that Rev A post is R35 on the rev D.  Trace it, find where your bias is dying.

 

[tlh]

Hello, I hope that I have posted in the correct place for some help on my Rev D build.  After some frustration with a bad transformer, I have completed the build of my 1176, but have not been able to get through the last calibration step.  Also, I have noticed some strange behavior.  My unit does not compress even though I was able to set the Qbias. I have checked the side chain ( Gain Reduction ) section for voltages and they are very close even though I have not completed calibration for example, 13.7 instead of 13.53 like on the mnats schematic. My power supply is correct at 30 vdc and -9.75 vdc, but I get no signal drop at all in the third calibration step when I switch my attack on.  In fact, nothing happens at all.  The unit passes sound, but does not compress audio. Input and output work but gain seems a bit weak.  The meter seems to work fine as I can get through meter calibration.  Hopefully someone can work with me to get the problems solved so I can enjoy the compressor.  Any help much appreciated, Thank you

 

[Echo North]

Hello, I hope that I have posted in the correct place for some help on my Rev D build.  After some frustration with a bad transformer, I have completed the build of my 1176, but have not been able to get through the last calibration step.  Also, I have noticed some strange behavior.  My unit does not compress even though I was able to set the Qbias. I have checked the side chain ( Gain Reduction ) section for voltages and they are very close even though I have not completed calibration for example, 13.7 instead of 13.53 like on the mnats schematic. My power supply is correct at 30 vdc and -9.75 vdc, but I get no signal drop at all in the third calibration step when I switch my attack on.  In fact, nothing happens at all.  The unit passes sound, but does not compress audio. Input and output work but gain seems a bit weak.  The meter seems to work fine as I can get through meter calibration.  Hopefully someone can work with me to get the problems solved so I can enjoy the compressor.  Any help much appreciated, Thank you

Go back and read the "ericfergus" exchanges with me a few posts ago in this thread.  You need to measure your Pad 21/22 voltages. 

You also need to confirm you're no teething compression at the output to ensure it's not a meter issue.  To do that measure AC V at pin 2 and there of the output and see if you get a drop when you switch from GR off to GR on.

 

[tlh]

Thank you for the quick reply.  The voltages are as follows:
Pad 22  AC  -  20:1  =  .070,  12:1 = .043,  8:1 = .030 and 4:1 = .021

Pad 21 DC - 20:1 = -9.75, 12: 1 = -9.75, 8:1 = -9.75 and 4:1 = -1.99  ( ? )

Pad 19 DC - 20:1 = -0.976, 12:1 = -0.976, 8:1 = -0.976 and 4:1 =  -2.1 jumps and settles down to -0.976 

Hope these help and thanks again -  oh, and there is no ac voltage drop on the output when GR is switched in or the attack knob is turned on

 

[JuniusRecordingCo]

I, too, am just finishing up my build and am having trouble at the "Gain Reduction Meter Tracking Adjustment" step: the meter and voltage out the output do not change with the Attack control coming in and out.

I've attempted to be diligent and follow the previous instructions measuring voltages:

Pad 22 AC
20:1 103mV
12:1 48mV
8:1 32.8mV
4:1 24mV

Pad 21 DC
20:1 -6.78V
12:1 -3.80V
8:1 -2.68V
4:1 -1.74V

Pad 19 DC
20:1 -1.09V
12:1 -1.09V
8:1 -1.09V
4:1 -1.09V

R64 (no input signal): -9.77V, -6.78V
R63 (no input signal): -6.78V, -3.80V
Pad 21 (no input signal): -3.80V

R78 (with input signal): 1.578VB, 0.187V
Pad 21 (with input signal): 0V

....and I just blew my fourth fuse. One held out for a long time, but the others seem to blow (or were faulty) immediately. That seems to occur when I turn the Meter switch to the "Off" position. But it's not consistent.

 

[Echo North]

I, too, am just finishing up my build and am having trouble at the "Gain Reduction Meter Tracking Adjustment" step: the meter and voltage out the output do not change with the Attack control coming in and out.

I've attempted to be diligent and follow the previous instructions measuring voltages:

Pad 22 AC
20:1 103mV
12:1 48mV
8:1 32.8mV
4:1 24mV

Pad 21 DC
20:1 -6.78V
12:1 -3.80V
8:1 -2.68V
4:1 -1.74V

Pad 19 DC
20:1 -1.09V
12:1 -1.09V
8:1 -1.09V
4:1 -1.09V

R64 (no input signal): -9.77V, -6.78V
R63 (no input signal): -6.78V, -3.80V
Pad 21 (no input signal): -3.80V

R78 (with input signal): 1.578VB, 0.187V
Pad 21 (with input signal): 0V

....and I just blew my fourth fuse. One held out for a long time, but the others seem to blow (or were faulty) immediately. That seems to occur when I turn the Meter switch to the "Off" position. But it's not consistent.

Did the Qbias adjust meant go well?  Sounds like you're Qbias may not be right.  Is that Pad 22 with a signal?

Fuses should be 350mA-500mA slo-blo.

 

[Echo North]

Thank you for the quick reply.  The voltages are as follows:
Pad 22  AC  -  20:1  =  .070,  12:1 = .043,  8:1 = .030 and 4:1 = .021

Pad 21 DC - 20:1 = -9.75, 12: 1 = -9.75, 8:1 = -9.75 and 4:1 = -1.99  ( ? )

Pad 19 DC - 20:1 = -0.976, 12:1 = -0.976, 8:1 = -0.976 and 4:1 =  -2.1 jumps and settles down to -0.976 

Hope these help and thanks again -  oh, and there is no ac voltage drop on the output when GR is switched in or the attack knob is turned on

You're pad 21 voltages are WAY messed up.  You need to get that sorted.

Check all of the PAD 21, Pad 18, Ratio PCB, and Attack/Release wiring.  Something is wrong.

 

[Alexwfm]

Hi Friends, sorry for bumping the message but still after hours of google research I still didn't understand what is the 6th position on the ratio rotary switch for..
Does actually anyone know? it connects pad 7 to one of the central pins.
thanks in advance,
Alex

 

[tlh]

Hmm,  really stumped here.  I have checked the ratio board including resistance on each of the resistors and all seems normal.  I have tripled check the wiring and it seems correct as well.  That said, what could be the problem as the voltages are clearly whacked?  The voltages are within tolerance on the side chain section of the pcb according to MNATS schematic.  Where else should I look?  Thanks for your help

 

[Echo North]

Hi Friends, sorry for bumping the message but still after hours of google research I still didn't understand what is the 6th position on the ratio rotary switch for..
Does actually anyone know? it connects pad 7 to one of the central pins.
thanks in advance,
Alex

Does the rotary have adjustable stops so you just eliminate that position?

 

[Echo North]

Thank you for the quick reply.  The voltages are as follows:
Pad 22  AC  -  20:1  =  .070,  12:1 = .043,  8:1 = .030 and 4:1 = .021

Pad 21 DC - 20:1 = -9.75, 12: 1 = -9.75, 8:1 = -9.75 and 4:1 = -1.99  ( ? )

Pad 19 DC - 20:1 = -0.976, 12:1 = -0.976, 8:1 = -0.976 and 4:1 =  -2.1 jumps and settles down to -0.976 

Hope these help and thanks again -  oh, and there is no ac voltage drop on the output when GR is switched in or the attack knob is turned on

You're pad 21 voltages are WAY messed up.  You need to get that sorted.

Check all of the PAD 21, Pad 18, Ratio PCB, and Attack/Release wiring.  Something is wrong.

Pad 21 is sets the threshold.  It's a negative voltage that increases as you switch ratio buttons from 4 to 20.  If you're threshold is at -9VDC you'll never get any compression.  I don't recall the exact measurements, but the pad 21 voltages should be more like (roughly):

4:  -1V
8:  -2V
12:  -4V
20:  -6V

Open the schematic:
http://mnats.net/files/1176REVD_VOLTS.pdf

See where the -10VDC rail connects to the point between R35 and R64.  That's the pad 20 wire.  That wire carries the -10VDC to the ratio board.  The it connects to R61, R62, R63, R64.  This is the voltage divider that sets that pad 21 voltage.

If 20 is selected (switch on the far right) that -10DC voltage goes through R64 then through the switch down to point 21 (via the 21 wire).  So only 1 resistor, it only decreases a little to say -6VDC.

If 4 is selected (switch on far left) then that voltage travels through R61, R62, R63, R64 before going down to pad 21.

Start in ratio 4 and trace that DC voltage up from the wire, across those 4 resistors and back down the pad 1 wire and see why it's not dropping.  If the voltage is present but not dropping, the circuit likely is not complete.  If you have voltage, but no drop....you don't have flowing current.

Mike

 

[JuniusRecordingCo]

Did the Qbias adjust meant go well?  Sounds like you're Qbias may not be right.  Is that Pad 22 with a signal?

Fuses should be 350mA-500mA slo-blo.

I'll need to get new fuses before I can re-calibrate. The Mouser cart for the Revision D kit has 250mA fuses, which is what I ordered. Should I step up to something over 350mA?

Thanks for the help. Really appreciate it!

 

[Echo North]

Did the Qbias adjust meant go well?  Sounds like you're Qbias may not be right.  Is that Pad 22 with a signal?

Fuses should be 350mA-500mA slo-blo.

I'll need to get new fuses before I can re-calibrate. The Mouser cart for the Revision D kit has 250mA fuses, which is what I ordered. Should I step up to something over 350mA?

Thanks for the help. Really appreciate it!

Ya sorry I need to fix that.  350mA is better.

 

[Alexwfm]

Does the rotary have adjustable stops so you just eliminate that position?

it says so on the mouser page, http://uk.mouser.com/ProductDetail/Alpha-Taiwan/SR2921F-0206-19R0B-E9-S-W/?qs=%2fha2pyFaduhD8I4lhbuO7y7JCfYBkOfcNKb1PSAeQkdC3ssy0l9S7A%3d%3d
tho, I can't figure out how since there is no tab to stop the rotating element..

 

[Echo North]

Does the rotary have adjustable stops so you just eliminate that position?

it says so on the mouser page, http://uk.mouser.com/ProductDetail/Alpha-Taiwan/SR2921F-0206-19R0B-E9-S-W/?qs=%2fha2pyFaduhD8I4lhbuO7y7JCfYBkOfcNKb1PSAeQkdC3ssy0l9S7A%3d%3d
tho, I can't figure out how since there is no tab to stop the rotating element..

Ya it has adjustable stops.  I've never built a rotary, maybe someone can chime in, or see if there is a data sheet with a hint on it.

 

[tlh]

Thanks Mike for your post, I traced out the DCV from pad 20 through the ratio board and still have not solved the problem.  There maybe more than one problem here as with the ratio board completely disconnected ( entire board out of circuit ) there is approx. 2volt DC on pad 21.  If 21 is the return voltage line, there should be no voltage on pad 21 if it is disconnected from the ratio board right?  I am continuing to troubleshoot, but find it very odd that there is voltage at pad 21 with the ratio board completely disconnected from the circuit.  Also, I can't seem to find any errors on the ratio board under study.  The resistor values seem correct ( pulled a leg on each and checked with DMM ) and I can't find any bad traces.  Could it be that DC feedback from pad 21 is fouling up the correct operation of the circuit?  Oh, one other anomaly, there is -9.75 VDC on each side of resistor 64.  I pulled the leg on R64 and tested it to make sure that it was the correct value and also checked for bad solder joints and or traces, to no avail.  Needless to say, I am pretty stumped here.  There should be a 3VDC drop across R64 and there is not.  I am continuing to study the schematic and pcb traces, but could you confirm that there should not be any VDC on pad 21 unless the ratio board is connected and supplying voltage from pad 20.  There must be a serious solder bridge, but as yet I haven't found it.  Also, I checked the diodes in the GR section and they appear correct as well.  Please help...

 

[JuniusRecordingCo]

Did the Qbias adjust meant go well?  Sounds like you're Qbias may not be right.  Is that Pad 22 with a signal?

OK. Got new fuses. Let's re-do the Q Bias calibration. Here's my blow-by-blow:

1.) Confirmed:
Input = “24″ mid rotation
Output = “24″ mid rotation
Attack = full CCW (switched to off position)
Release = full CW
Compression ratio = 20:1
Meter mode = “GR”
Q-bias adjustment = full CCW

Applied a 1kHz test tone and am reading 0.776VAC at input XLR pins 2 and 3.

2.) Moved DMM to Output pins 2 and 3. Get reading of 4.66VAC. Need to turn DOWN output to reach 2.75VAC.
3.) Turned Q Bias trimmer CW until DMM reads 2.44VAC on the Ouput pins 2 and 3.

So, seems to have worked? Now, I'm going to perform the remainder of the calibration again, too.

Discrete Meter Circuit/Null Adjust went smoothly. After setting the Zero Adjust Pot correctly, the DC voltage across R74 was 0.00V. So, the previous calibration seems to have held.

Gain Reduction Meter Tracking Adjustment

Applied the test tone again, and am reading 4.16VAC at pins 2 and 3 of the Output. Need to turn way down to get 0.775VAC (about at "48"). Got through the first 7 steps (listed here: http://www.hairballaudio.com/blog/d_assembly/revd/calibration/ )--but turning the attack knob full CW makes no change at the output VAC or the meter reading from when it's set to fullCCW (off).

I'm assuming I should see some change at the meter, correct? To check that the meter is responding at all, instead of a steady test tone, I ran a drum loop through. With the Input control all the way up, the meter did show some movement when the kick drum hit.

Now, I'll return to Pad 22 readings, with input signal applied (without input signal, all VAC readings are 0):

20:1 0.080VAC
12:1 0.036VAC
8:1 0.024VAC
4:1 0.017VAC

So. I'm a bit stumped, again.