[BUILD] 1176LN Rev D DIY

[JingleDjango]

You are correct about the PCB input voltage.

On R14 I get 0.021VAC on the far leg, toward the edge of the PCB.  .009VAC on the the leg closer to Q4. I can't tell from the schematic but I assume the leg closer the transistor is the one connected.

Edit: I meant Q3, not Q4

 

[Echo North]

Verify your DC voltages are correct against this schematic w/ voltages.

http://mnats.net/files/1176REVD_VOLTS.pdf

Measure for DC and use the CT for your reference probe again.

Check that signal pre section carefully.

Mike

 

[JingleDjango]

Between R8 and R9 I have 1.07VDC vs 1.05VDC on the schematic linked.

0.514VDC on the leg of Q2 connected to R18 and 1.008VDC on the opposite leg. These values obviously don't match the diagram so I'm not sure if I should stop there or keep going.

 

[JingleDjango]

Values around Q3 are closer to the ones specified, but don't match exactly. Between Q14 and C7 I have 11.6VDC rather than 12VDC. Not huge differences but my values are consistently lower than specified.

 

[Echo North]

Values around Q3 are closer to the ones specified, but don't match exactly. Between Q14 and C7 I have 11.6VDC rather than 12VDC. Not huge differences but my values are consistently lower than specified.

That's fine.

Reflow your solder joints in those sections and look for any lifted pads.

I'm about to be offline until Tuesday.  Keep looking for something in that section and I'll check in with you when I'm back.

Good luck!

Mike

 

[JingleDjango]

Thanks again. Pretty great support for a kit that's ostensibly sold with none. I know that I need to do my own tooling around anyway for this to be the learning experience I want out of it.

 

[hymentoptera]

JingleDjango,

If I had to take a wild guess, sight unseen, from the info you've provided, I would think you might have R59 "Q BIAS ADJ" turned too far to the one direction. It's a multiturn trimmer so it swings about 20 full turns in total. Make sure you don't have it turned all the way to one side which could cause the Q1 JFET to be turned fully on and to dump all of your input signal to ground instead of just -1dB. The goal here is to calibrate it to -1dB.

Just a thought. Try turning the Q bias trimmer all the way to one direction, test voltages at R8/R9 junction again, then if it's still too low, turn that trimmer all the way in the opposite direction about 20 turns and try that.

DBonin's youtube videos are a great place to learn more about the qbias calibration if you haven't watched them already.

 

[JingleDjango]

Thanks, hymentoptera. I'll try that soon.

 

[dbonin]

@JingleDjango

According to your photo,  your output pot is wired incorrectly.
Check out the side by side attached photo...

...then review mnats guide again for the output pot:
http://mnats.net/1176_reva-d_hairball_wiring_output_zero_pots.html

I hope this helps and good luck!
Don

 

[JingleDjango]

dbonin, thanks for taking the time to carefully look over my photos. I'm finishing a recording project and haven't had time to troubleshoot this at all yet. Next week I hope to delve back in. I'll address the wiring of that then.

Thanks again.

 

[milomofo]

Hey, I am new to this forum and also new to DIY audio, I have spent a while searching around on here and have not found any similar issues to the one I am having, so I decided to make this post to see if anyone could help me.  This is my first project and it was all going so well until I reached step two of the calibration process. I have followed the MNATS and Hairball guide for this step to the letter.
Ok so I managed to set the QBias all DMM readings were fine at the input .775v and output 2.44v after adjusting the bias pot.

Then I proceeded to step 2 and managed to zero the meter and  the null adjust and get the reading of R74 to 0.02v... then a few seconds later the meter wigged out all the way to left to -20 so I decided to go back to step 1 and input signal 1k at .775v and now my output is 0.380v any ideas what this could be?  :-[

Any help would be much appreciated. I am building the device as a part of my dissertation for university (first DIY audio project)  I am looking into whether DIY audio can provide a low cost sonically robust alternative to expensive commercial outboard my idea Is to build a clone of the 1176 and test it against the software emulations and the original Urie device.

I am also new to this forum so i'm not sure whether i'm even positing this in the right place, I have searched the boards up and down for this particular problem to no avail.

 

[Echo North]

Hey, I am new to this forum and also new to DIY audio, I have spent a while searching around on here and have not found any similar issues to the one I am having, so I decided to make this post to see if anyone could help me.  This is my first project and it was all going so well until I reached step two of the calibration process. I have followed the MNATS and Hairball guide for this step to the letter.
Ok so I managed to set the QBias all DMM readings were fine at the input .775v and output 2.44v after adjusting the bias pot.

Then I proceeded to step 2 and managed to zero the meter and  the null adjust and get the reading of R74 to 0.02v... then a few seconds later the meter wigged out all the way to left to -20 so I decided to go back to step 1 and input signal 1k at .775v and now my output is 0.380v any ideas what this could be?  :-[

Any help would be much appreciated. I am building the device as a part of my dissertation for university (first DIY audio project)  I am looking into whether DIY audio can provide a low cost sonically robust alternative to expensive commercial outboard my idea Is to build a clone of the 1176 and test it against the software emulations and the original Urie device.

I am also new to this forum so i'm not sure whether i'm even positing this in the right place, I have searched the boards up and down for this particular problem to no avail.

Hmmmm.  I would start by checking your DC voltages as described here:
http://mnats.net/files/1176REVD_VOLTS.pdf

These voltages are for a fully calibrated unit so some in the meter section might be a little off, but compare and see what you find then report back.

Mike

 

[JingleDjango]

I have some time in the next two days and hopefully I can get this guy a little closer to finished. I'll start by re-flowing the pre-amp section of the board and address the wiring of that pot.

 

[JingleDjango]

So. . .

I started combing over the PCB looking for cold joints and re-flowing every pad for good measure. Apparently when I was populating the board I neglected to solder one of C1's leads, but I did trim the lead with the rest which made it easy to miss.

Now I get a reading of:

1.38VAC Between CT and C7 + lead
1.71VAC between CT and C7 - lead
0.25VAC between CT and XLR output pin 2.

 

[JingleDjango]

So the voltage between the output and the CT is clearly out of whack still, though a signal is present.

Here is the output pot. I think the wiring is correct now.

 

[hymentoptera]

Is there a change at output XLR when turning the output knob?

 

[JingleDjango]

I did notice an increase in voltage if I turned the knob up. The reading given is for 24, dead center, as you're instructed to have it for calibration. I also tried turning R59 to either extreme to little or no effect.  Maybe I should try routing the output back into my interface to see what it sounds like.

 

[JingleDjango]

Okay, here's the scoop.
>I'm running the test tone (1kHz) out from Ableton Live through a line out from my Focusrite Saffire Pro 40 at  ~0.775VAC (closer to 0.78VAC).
>into the input of my compressor unit
>feeding the output back into the interface. I believe that using a TRS plug like I have into the XLR/1/4" jack will bypass the mic preamp.

I get an audible signal back, which I'm taking as a sign of progress, though this whole endeavour is starting to try my patience! Can't wait to get it working. . .

The signal is very quiet. 0.18-0.20VAC. Despite being this low, the signal also sounds distorted.

I'm keeping the input dial set to 24.
If I turn the output down to 48, the distortion is no longer audible but the signal is so low I have to really drive the gain on the input and turn up my monitors to hear it.
Between 30-24, the signal is distorted but audible, increasing in volume as I turn the dial.
There is an abrupt step up in volume (and distortion) when the dial hits 18.

I don't know if this is relevant, but if I hit the off switch while the tone is going, there is an abrupt jump up in volume before the machine runs out of juice and it fades to silent.

Does this help anyone interpret my signal at all?

 

[Cockola]

HELP! Why is my unit suddenly distorted?
Built it a couple of years ago.  It's worked beautifully until today
What should I check?

 

[JingleDjango]

A couple more details:

I've tried toying with R86  (dist. trim) but that doesn't address the distortion. I found this partially lifted pad. This is the red conductor from the shielded one conductor line that runs between the output pot and the ratio board.

Seems like this must be part of the problem.  Does this defect seem consistent with the problems I'm having? I don't know where to begin repairing a lifted pad on a PCB like this that's insulated by a solder mask.  Any guidance is appreciated. Thanks.