[BUILD] 1176LN Rev D DIY

[madmark_dj]

I just finished my second build and I'm noticing that there's pops and noises when I turn the Input/Output knobs...  :-\ :-\ :-\ Any idea what could be causing this problem?

Thanks

Edit: Here's an addition to the described problem: The meters (set on +4)  are moving when the crackles occur... Here's a short video showing the behavior: https://www.dropbox.com/s/pgsmt5hk8kpgb7r/1176%20Crackle.mov?dl=0

 

[madmark_dj]

Bump... Anybody?

I just finished my second build and I'm noticing that there's pops and noises when I turn the Input/Output knobs...  :-\ :-\ :-\ Any idea what could be causing this problem?

Thanks

Edit: Here's an addition to the described problem: The meters (set on +4)  are moving when the crackles occur... Here's a short video showing the behavior: https://www.dropbox.com/s/pgsmt5hk8kpgb7r/1176%20Crackle.mov?dl=0

 

[lalalaetc]

Apologies, I realize there are a few simultaneous topics going on here...
So I received my new t-pad (which was, in fact faulty before).  A few quick questions:

When beginning the calibration process, I can't get my output above .037VAC. This is with the output pot full clockwise... So here is where I start poking around for problems...

This is going to sound like a silly question, but shouldn't I be able to hear tone at both PCB input terminals with my signal tracer when in circuit? When removed from the circuit, I have signal at both sides of my input tx secondary (quite low, as expected). When connected to the PCB, I get an amplified signal on the hot side, and no signal on the cold side. Voltage as measured between both input terminals of the PCB is .116VAC.

On a possibly related note, should I be getting continuity between the PCB input terminals and chassis ground (13 ohms on the hot leg, 0 ohms on the cold)?

I've checked all voltages at each transistor, and everything appears to be within range (aside from the GR meter driver section but on an uncalibrated unit).


Thanks for all of your help!
Wyatt

 

[dbonin]

Apologies, I realize there are a few simultaneous topics going on here...
So I received my new t-pad (which was, in fact faulty before).  A few quick questions:

When beginning the calibration process, I can't get my output above .037VAC. This is with the output pot full clockwise... So here is where I start poking around for problems...

This is going to sound like a silly question, but shouldn't I be able to hear tone at both PCB input terminals with my signal tracer when in circuit? When removed from the circuit, I have signal at both sides of my input tx secondary (quite low, as expected). When connected to the PCB, I get an amplified signal on the hot side, and no signal on the cold side. Voltage as measured between both input terminals of the PCB is .116VAC.

On a possibly related note, should I be getting continuity between the PCB input terminals and chassis ground (13 ohms on the hot leg, 0 ohms on the cold)?

I've checked all voltages at each transistor, and everything appears to be within range (aside from the GR meter driver section but on an uncalibrated unit).


Thanks for all of your help!
Wyatt

The first calibration step is the critical step - without the q-bias set correctly most of your signal will likely be going to ground, hence the low output.  Given no other issues that is likely the cause of your low output.

You are on the right track tracing the signal from the input, past the input transformer.  Are you sure your input signal is at the recommended level to start with?  .775 VAC  Where the input t-pad  connects to the PCB terminals one leg goes to ground, the other carries the AC signal. 

Start at the point where the input transformer enters the PCB - apply your .775V / 1khz test signal and measure the voltage as you increase the input pot (t-pad) from full ccw  to full cw  - (if you used terminals for the wiring, disconnect them)
- you should be seeing somewhere around .340 AC coming OUT of the input transformer, with t-pad turned full cw with the leads disconnected from the pcb - this should fall to ZERO volts as you turn the input knob fully off.
-  let us know what you find.

 

[dbonin]

Bump... Anybody?

Likely DC  where there should be only signal AC....

Check your caps for polarity and be sure you have them seated correctly.

 

[mnats]

This is going to sound like a silly question, but shouldn't I be able to hear tone at both PCB input terminals with my signal tracer when in circuit? When removed from the circuit, I have signal at both sides of my input tx secondary (quite low, as expected). When connected to the PCB, I get an amplified signal on the hot side, and no signal on the cold side. Voltage as measured between both input terminals of the PCB is .116VAC.

On a possibly related note, should I be getting continuity between the PCB input terminals and chassis ground (13 ohms on the hot leg, 0 ohms on the cold)?

Please have a look at the schematic. Earlier, you measured 14.3 Ohms on the transformer secondary. If wired according to the instructions on my website, main PCB ground will be connected to the chassis at one point. Note carefully what you are measuring and what parallel resistances are present.

Now you should have your answer to the previous question as well. Assuming you've left your signal tracer ground connected to chassis you're measuring the potential between chassis and PCB ground which are connected to each other.

 

[lalalaetc]

To everyone who lent their advice: Thank You! I was able to get my it aligned and finished today.

The odd thing that I kept coming upon in my measuring and trouble shooting, was that my issue seemed like a bit of a moving target. I would get different readings and behavior from day to day. It turned out that not only did I have a bad t-pad (which was easy enough to diagnose/replace), I had an intermittent ground from the input transformer to chassis, and a short from signal to ground under the shrink-wrapped end of one of my shielded cables.
I noticed the intermittent input tx ground yesterday, and added a jumper cable from pin to chassis so I won't have to rely on the mechanical connection of the tx pcb.

After that, still no luck in calibrating.

Luck would have it that when I fired my unit up for testing today, everything was working well enough to align. Fortunately, I was able to make it through this process just far enough to diagnose what I suspect was one of my primary problems all along. I noticed some intermittent crackling and drop-outs of my signal, so I start poking around. It turns out that under the shrink-wrapped end of the shielded cable running from the PCB to output pot, I had a short to ground. This, I suspect, was the source of my intermittent headaches all along! I snipped the end, rebuilt, and all is well!

Again, thanks to all who helped along the way. I truly appreciate it, and wish you all the best.

Wyatt

 

[babaorum]

Probably the gain reduction meter circuit? I know it's not calibrated, but have you checked voltages against the schematic linked in the FAQ which is in turn linked from the first post of this thread?

Actually I just re-build the ratio meter pcb to be sure it's ok, I'll test again after wiring.

I have another question : I wish to wiring the GR off option into my GR knob, How do I have to do that please can you tell me the needing wiring for that ?

Thanks,

 

[JW]

My unit has an issue where if you boost the output volume all the way, it goes into current limiting or something. I'm sure if that's the right term, but the volume cuts out significantly when the output is boosted nearly all the way.

Has anybody had that symptom before?

It sounds fine otherwise. Actually with the amount of gain available, it makes it so I probably don't need that last amount of boost, but it concerns me.

 

[Echo North]

My unit has an issue where if you boost the output volume all the way, it goes into current limiting or something. I'm sure if that's the right term, but the volume cuts out significantly when the output is boosted nearly all the way.

Has anybody had that symptom before?

It sounds fine otherwise. Actually with the amount of gain available, it makes it so I probably don't need that last amount of boost, but it concerns me.

Might be going into a HF oscillation. That is usually related to messy/unshielded wiring. Particularly from the meter to the output XLR.

Mike

 

[ffarrell]

HI all

Clarification on power Transformers for a  Mnat stereo D build and a Mnat stereo F build.

Will the Y236207 work for both builds?  its 30 / 30  50va

thanks
fvf

 

[Echo North]

HI all

Clarification on power Transformers for a  Mnat stereo D build and a Mnat stereo F build.

Will the Y236207 work for both builds?  its 30 / 30  50va

thanks
fvf

You really only need the 30VA 25/25.

If you get the 50VA is just a bigger size for an extra 20VA you really don't need. It doesn't hurt to have extra VA though.  You can use the 30/30 but it's just more work for the regulators and zeners.

Really you only need the 25/25. It regulates to over 30V DC.

Mike

 

[JW]

Might be going into a HF oscillation. That is usually related to messy/unshielded wiring. Particularly from the meter to the output XLR.

Mike

Thanks Mike. I shielded the wires that goes from the meter board to the XLR, but that didn't change anything. I've included a picture of my unit.

It's a dual 1176. It started it's life as a dual G1176 of the last mnats variety. So, essentially a rev F/G. I eventually replaced both front ends with the Altran transformer and the T pad so then I had two Rev F's.

I figured how hard is it to just breadboard the output circuit for a Rev D, so the one on the right side in the pic is actually a hacked G1176 that has been turned into a Rev D. I tapped the circuit at wiper of the output pot. You can see the little bread boarded circuit in the back by the EA 5002 transformer.  Anyway, I've checked and rechecked and I built the circuit right. I think it's likely it has something to do with the meter, since the meter is from the G1176 (ic driven) and this is the part of the circuit I understand the least with all the switching. Not sure if there is a ground that needs to be added somewhere in there?

I can easily go back and make it a Rev F again, but I'm digging the sound A LOT. So I'd like to get this working if possible.

Moving the wires to the meter and ratio boards around while it's powered on doesn't really seem to have much of an effect. 

If anybody has done the tape machine bias trick where you feed it a low frequency tone (10 HZ or so) , and then adjust bias for when the 'rocks' are making the minimal rumble, that's what the sound is like when I crank the output all the way up. It sounds like the rocks. And like I mentioned it cuts the volume when it gets to full output boost, like it's compressing actually but never lets go until I roll the volume back down.

Any other ideas? I followed the shielded wire advice exactly according the build instructions for the Mnats G1176 document fwiw, since this  was a G1176 to start with,  except now there is a shielded wire that runs from the meter board along the front of the unit, then makes a right turn and heads toward the back to the XLR.

 

[ffarrell]

HI Mike thank you,
I had ordered it by mistake but I am using it in a stereo build so that was prob. my reasoning. 

one other question.  with the old rev boards the BOM for the F output pot calls for a 100K ,  your site has 250K pot for the D output pot.  should I use the 100K or use a 250K for the F ver. 2.2 build? 


thanks
fvf

You really only need the 30VA 25/25.

If you get the 50VA is just a bigger size for an extra 20VA you really don't need. It doesn't hurt to have extra VA though.  You can use the 30/30 but it's just more work for the regulators and zeners.

Really you only need the 25/25. It regulates to over 30V DC.

Mike

 

[Echo North]

HI Mike thank you,
I had ordered it by mistake but I am using it in a stereo build so that was prob. my reasoning. 

one other question.  with the old rev boards the BOM for the F output pot calls for a 100K ,  your site has 250K pot for the D output pot.  should I use the 100K or use a 250K for the F ver. 2.2 build? 


thanks
fvf

Definitely a 100K for the Rev F.  Mouser has them.

 

[Olegarich]

Hey DIY Friends. Just finished 1176 REV D with parts from Hairball Audio.
All works well,  I jus calibrated the compressor -  all is set well.
Noticed one thing -  on the output XLR PIN2 (Hot) i have a wave form but on the out XLR PIN 3 (cold) I have no sound or just verry little, is that normal? Blue cable goes to PIN2 - which all is good, and red cable from transformers goes to PIN3 and i have no sound there,  is that normal?
PS. Yellow and orange cables on out transformer  (5002) are twisted and soldered.

 

[Olegarich]

Anybody?

 

[mnats]

Hey DIY Friends. Just finished 1176 REV D with parts from Hairball Audio.
All works well,  I jus calibrated the compressor -  all is set well.
Noticed one thing -  on the output XLR PIN2 (Hot) i have a wave form but on the out XLR PIN 3 (cold) I have no sound or just verry little, is that normal? Blue cable goes to PIN2 - which all is good, and red cable from transformers goes to PIN3 and i have no sound there,  is that normal?
PS. Yellow and orange cables on out transformer  (5002) are twisted and soldered.

It has been discussed before. The question is - pin two has a waveform in relation to what?

The only valid output from a balanced XLR connector is pins two and three.

 

[Olegarich]

On pin 2 I'm i have a signal but on pin 3 there is no signal, is that ok? is output of this compressor is balanced and I have to get signal on pin2 and on pin3 ?

 

[mnats]

On pin 2 I'm i have a signal but on pin 3 there is no signal, is that ok? is output of this compressor is balanced and I have to get signal on pin2 and on pin3 ?

Please answer the question I posed above. It should provide a solution.