[BUILD] 1176LN Rev D DIY

[Echo North]

Hey guys! First time post  ;D Nice to e-meet yall!!

So I'm having a problem with output level. I've completed my build, and all of my calibration/tests - which all went immaculately. (Those distant sounds you all probably heard were my gigantic sighs of relief.)

I tried passing some vocals through my box, and my output level seems to be really low, so I have to push the level in my DAW window to get any sound. The sound I do get is still pretty low, distorted and has a ton of hiss. I've gone through my board and all of my solder points are solid (I think!), and my tests all went well, so this is my confused face:  :-\

Haalllpp!!!!!

Most likely an issue somewhere in the signal or line amp stage.

Start by doing all of your testing with the unit in GR OFF (attack full CCW) that will eliminate a good bit of the circuit and we can focus on getting the gain stages working right.

I sent you an email about testing the DC conditions around the transistors.  Another thing you can try is testing signal at the various gain stages of the unit and see where things go south.

Easiest way to check for signal is to use a DMM set to read AC volts.

Turn the attack pot to the GR off position. Set your input and output to mid rotation and your release fully CW.  Feed the unit a 1kHz, 0dB signal (0.775VAC).  Confirm you have 0.775VAC between input pins 2 and 3.  Now follow the signal using ground and you common reference point (where you put the black lead).  You can attach it to ground at the 0V/CT terminal at the PCB power supply.

Measure the VAC against ground at:

1. T-Pad input + (should be about half of 0.775)
2. T-Pad output +  (should be even smaller)
3. Input transformer primary + (should be the same as step 2)
4. Input transformer secondary + (getting smaller)
5. At the Input + terminal at the main PCB (should be roughly 0.06 to 0.09VAC)
6. C7 + pad (should be much larger now, around 2.0 VAC)
7. C7- pad (should be the same as  #6)
8. Blue wire on output transformer (should be a large VAC number)

Report back. That will help determine where the signal is dying.

Mike

 

[dacapitan]

Someone please help!

I built my 2-1176 stereo unit using Mnats Rev D boards and the stereo kit from Hairball, the unit works fine but I noticed it is experiencing some hum problems at 100hz (-55db) - attached is an image with the output turned fully CW - 1 at 29.2V and one at 30V

I am using the separate Little  PSU board from Mnats so I did not populate each section of the PCBs. I found this thread http://groupdiy.com/index.php?topic=51062.0 where someone was experiencing the same problem as I was, which was narrowed down to the drop out voltage of the LM317 in the PSU where trimming the 30V rail down to around 28V seemed to get rid of the 100hz hum, so I tried this and the 100Hz hum went away too - the problem is that this gives the unit reduced headroom and introduces distortion when hitting the compressor hard. So I replaced the LM317 with a LDO LM1086 regulator which was suggested to get the unit working at 30V without the hum, but this did not resolve the problem so I have trimmed the unit to 29.2V as this is the highest I am able to get it without the 100hz hum interfering - but still not 30V

I dug through the thread and saw that a ground wire from the centre wire between -10/+30 was being used so I took this to star ground which I hoped would solve it but it had no effect.

My questions are

- is 29.2V close enough to 30V or will I be missing headroom?
- is the general noise level (around -100db) shown in the for the lower 29.2V at a normal/acceptable level?
- is this likely to be a PSU issue and I should look at populating the power section of each board separately?
-is this a likely a grounding issue somewhere?

If anyone could please help me figure this out I would be very greatful!

 

[Echo North]

- is the general noise level (around -100db) shown in the for the lower 29.2V at a normal/acceptable level?

I'm familiar with the dual build at all, but I can tell you 29.2V should be totally fine. Anything within a volt is good.

Mike

 

[dacapitan]

- is the general noise level (around -100db) shown in the for the lower 29.2V at a normal/acceptable level?

I'm familiar with the dual build at all, but I can tell you 29.2V should be totally fine. Anything within a volt is good.

Mike

Thanks for your reply Mike - I am the guy who sent you that email today BTW - I really appreciate your reply. I tried to find Mnats email address, but it seems that all roads point to this thread/forum!

So 29.2V is acceptable, thats good news, with a bit of finer tweaking I managed to get it up to 29.52. Here is an image of the unit at 29.52V - the output is on full - is this noise floor normal for this level? Apologies, I'm just not familiar with what the norm or benchmark is (the before image @ 30V is in the previous post)

Thanks

 

[mgalimbe]

I forgot to mention that I have .278vav at the input pad on the  main pcb

Check all of your components in the box labeled "Signal Preamp".  Make sure you have the R values right, like you don't have a 56K or 560K mixed up.  Check everything super close.

Check the DC V in that section against these values:
http://mnats.net/files/1176REVD_VOLTS.pdf

Mike

Mike

All of my resistors are of the correct value. Where should I go from here.  I forgot to mention that I should probably know how to do this but I'm not too sure how or where to check the DC voltage. ex what pins should I be testing and do I need the unit plugged in or just run a signal through it. Thanks

 

[cfleming1989]

Most likely an issue somewhere in the signal or line amp stage.

Mike, thanks so much for this. Here are my resistor values for the top half:

Q2:
    E .537
    C 1.782
    B 1.045

Q3
    E 1.165
    C 11.53
    B 1.784

Q14
    E 10.92
    C 29.73
    B 11.53

Q4
    E .434
    C 4.77
    B 1.024

Q5
    E 2.768
    C 25.62
    B 3.299

Q6
    E 2.25
    C 27
    B 2.768

How do those values look? I'm also having 2 very weird problems:

1) R4/24/25/28 all are definitely the correct resistor values, however when I put them in the board and measure them, they measure something completely different (13, 1.38M, 1.38M, and 1.634K respectively).

2) I was getting around .178V at my T-pad input, so I rewired my input and now I'm getting 54V in the input section of the T-Pad????

Thanks guys for all of your help, looking so forward to getting this figured out.

 

[Echo North]

Most likely an issue somewhere in the signal or line amp stage.

Mike, thanks so much for this. Here are my resistor values for the top half:

Q2:
    E .537
    C 1.782
    B 1.045

Q3
    E 1.165
    C 11.53
    B 1.784

Q14
    E 10.92
    C 29.73
    B 11.53

Q4
    E .434
    C 4.77
    B 1.024

Q5
    E 2.768
    C 25.62
    B 3.299

Q6
    E 2.25
    C 27
    B 2.768

How do those values look? I'm also having 2 very weird problems:

1) R4/24/25/28 all are definitely the correct resistor values, however when I put them in the board and measure them, they measure something completely different (13, 1.38M, 1.38M, and 1.634K respectively).

2) I was getting around .178V at my T-pad input, so I rewired my input and now I'm getting 54V in the input section of the T-Pad????

Thanks guys for all of your help, looking so forward to getting this figured out.

Voltages look ok.

1) You have parallel resistances on the PCB so that changes the resistance.  You either need to lift a leg of the resistor or calculate the  parallel resistance.  Probably not an issue since your DC V's look ok.

2) That's imposible. Has to be a measuring error.

Now you need to trace the signal level as described in my last post.

Mike

 

[Echo North]

I forgot to mention that I have .278vav at the input pad on the  main pcb

Check all of your components in the box labeled "Signal Preamp".  Make sure you have the R values right, like you don't have a 56K or 560K mixed up.  Check everything super close.

Check the DC V in that section against these values:
http://mnats.net/files/1176REVD_VOLTS.pdf

Mike

Mike

All of my resistors are of the correct value. Where should I go from here.  I forgot to mention that I should probably know how to do this but I'm not too sure how or where to check the DC voltage. ex what pins should I be testing and do I need the unit plugged in or just run a signal through it. Thanks

Try this:

http://groupdiy.com/index.php?topic=20058.msg769979#msg769979

 

[mgalimbe]

Thanks Mike I've already done this my findings are below. Here is my original post:

Hello,
i am at the first step of calibrating my compressor using the Hairball audio way.  The problem is that I'm not getting a voltage reading at the output xlr.

I have a signal and reading coming to the input xlr  (.775vac).

I measured the voltage to the input and ground pad on the board and with the input knob at 48 I'm getting 0v and at input 0 I'm getting .875 v. so it seems to be working to here.

I visually checked the wiring from the meter board and input transformer to the output and it is wired fine. 

I'm just not too sure what I should be looking for from here (i.e. what to test and what I should be seeing for readings).

I'm assuming that I shouldn't have the unit plugged in for this step and will not plug it in for testing unless someone recommends that I do so.

Thank in advance for any help.

ok because I'm impatient I tried the mats version of calibrating the Qbias and what I noticed is that my bias pot isn't doing anything so I probably overstressed it so my question now is if this bias pot is broken would that explain why I'm not getting a signal to the output xlr using the hairball method of calibrating the q bias?

time to order some pots!

I doubt it's the trimmer. Even with a damaged trimmer you's see output.  Your signal is dying at some point likely do to a misplaced component, damaged component, or wiring.

Easiest way to check for signal is to use a DMM set to read AC volts.

Turn the attack pot to the GR off position. Set your input and output to mid rotation and your release fully CW.  Feed the unit a 1kHz, 0dB signal (0.775VAC).  Confirm you have 0.775VAC between input pins 2 and 3.  Now follow the signal using ground and you common reference point (where you put the black lead).  You can attach it to ground at the 0V/CT terminal at the PCB power supply.

Measure the VAC against ground at:

1. T-Pad input + (should be about half of 0.775)
2. T-Pad output +  (should be even smaller)
3. Input transformer primary + (should be the same as step 2)
4. Input transformer secondary + (getting smaller)
5. At the Input + terminal at the main PCB (should be roughly 0.06 to 0.09VAC)
6. C7 + pad (should be much larger now, around 2.0 VAC)
7. C7- pad (should be the same as  #6)
8. Blue wire on output transformer (should be a large VAC number)

Report back. That will help determine where the signal is dying.

Mike

Hi Mike Here are my findings

input xlr=.776vac
Tpad in+=.775vac (not half of input xlr)
Tpad out+=.276vac
Input trans. Pri +=.275
Input Trans 2nd+= .278
I have nothing on either pin(+or-) of c7.
nothing on blue wire of output transformer.

 

[Echo North]

You've either got something wrong in that first signal amp stage or a wiring error withx your output pot.

With the unit on and no signal, measure the DC V of the transistor leads in the "Signal Preamp".

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

Q3 and Q4.

Triple check your output wiring. What is the resistance in ohms between C7 - and ground (0V in the power supply)?

Mike

 

[JingleDjango]

I got a new PCB and all new components for it, except for one standard resistor and the 100Ωtrim pot which were out of stock on Mouser. I salvaged those from the wonky old board. Stuffed the board in an evening, everything went quick and problem-free. I'm in the middle of calibration.

At the tracking adjust stage, I'm trying to set R44 to show a 10dB drop, however, engaging the compression dropped the signal at the output from 2.44 vAC down to ~0.525vAC, not to 0dBu (0.775vAC).

Step 5 in the instructions states, "readjust the output level control for "0dBu" if necessary."

Am I supposed to readjust the output control in this way every time I switch the compressor on and off and make my adjustments, or am I meant to let it be after the first go?

Thanks!

 

[JingleDjango]

Or does this mean I need to recalibrate the qbias? I guess I'll try that now regardless.*

 

[Echo North]

Or does this mean I need to recalibrate the qbias? I guess I'll try that now regardless.*

Don't mess with stuff you already set! Just repeat step 6 and 7.

http://www.hairballaudio.com/blog/resources/post/calibration

You have to go back and forth with GR on and off to dial in the drop.

Mike

 

[Echo North]

If you have a little less than 0dB with GR ON increase the output. Then GR OFF and adjust the input to +10 dBu. Back and forth till its close.

 

[JingleDjango]

Thanks! I'm glad I abandoned the previous board. It must have been full of mistakes from being over my head from the beginning. I was confident in my wiring. This board took a couple hours to put together and it's working from the first go. Thanks for all your help over the past while.

 

[JingleDjango]

How would you go about taking measurements of attack and release response? With a scope? I don't have one but I've been eyeing a piece of oscilloscope software for OSX. Not sure what the disadvantage of software vs hardware is.

 

[Echo North]

How would you go about taking measurements of attack and release response? With a scope? I don't have one but I've been eyeing a piece of oscilloscope software for OSX. Not sure what the disadvantage of software vs hardware is.

Specs are covered in the original manual. Measurement is an enormous can of worms. Search around there is a thread or two in this forum.

Release is pretty audible, attack is pointless since it's 0.000002 sec - 0.0002 sec. 

 

[cfleming1989]

Now you need to trace the signal level as described in my last post.

Mike

Hey Mike!

So I've rewired my input (again), and just sat down to do VAC measurements. I measured .775 V at pins 2 and 3 (black lead on 2, red on 3), and I plugged it in.

Internal side of the input XLR (pins 2/3): .304 V
Input of the TPad: .153 V
Output of TPad: .061 V
Input transformer input: .061 V
Input transformer output: .049 V
Input terminal PCB: .049 V
C7 pad + : fluctuates a whole lot?
C7 pad - : .879 V
Blue wire: 2.425 V

It seems like things are a little low from the input jack, but progressing nicely from there? Is it the input jack??

Thoughts??? Thanks again for all your help!

 

[Echo North]

Now you need to trace the signal level as described in my last post.

Mike

Hey Mike!

So I've rewired my input (again), and just sat down to do VAC measurements. I measured .775 V at pins 2 and 3 (black lead on 2, red on 3), and I plugged it in.

Internal side of the input XLR (pins 2/3): .304 V
Input of the TPad: .153 V
Output of TPad: .061 V
Input transformer input: .061 V
Input transformer output: .049 V
Input terminal PCB: .049 V
C7 pad + : fluctuates a whole lot?
C7 pad - : .879 V
Blue wire: 2.425 V

It seems like things are a little low from the input jack, but progressing nicely from there? Is it the input jack??

Thoughts??? Thanks again for all your help!

Once you established the input level between pin 2 and 3, what did you put your black probe on as a reference for the rest of the measurements?  0V on the power supply?

If you're getting a ton of fluctuation you have some oscillation in your first amp stage on in the output wiring.

Mike

 

[cfleming1989]

Now you need to trace the signal level as described in my last post.

Mike

Hey Mike!

So I've rewired my input (again), and just sat down to do VAC measurements. I measured .775 V at pins 2 and 3 (black lead on 2, red on 3), and I plugged it in.

Internal side of the input XLR (pins 2/3): .304 V
Input of the TPad: .153 V
Output of TPad: .061 V
Input transformer input: .061 V
Input transformer output: .049 V
Input terminal PCB: .049 V
C7 pad + : fluctuates a whole lot?
C7 pad - : .879 V
Blue wire: 2.425 V

It seems like things are a little low from the input jack, but progressing nicely from there? Is it the input jack??

Thoughts??? Thanks again for all your help!

Once you established the input level between pin 2 and 3, what did you put your black probe on as a reference for the rest of the measurements?  0V on the power supply?

If you're getting a ton of fluctuation you have some oscillation in your first amp stage on in the output wiring.

Mike

I put the black lead on the 0V CT on the PCB. How would I be getting fluctuation? Faulty soldering of parts in the PCB? How should I address that?

EDIT My oscillation goes in and out, sometimes I get a solid reading at both pads at C7, sometimes I don't. I don't know if that helps..

Also the lower input level to the PCB is a problem right? Getting .04V instead of .06-.09?

As always thanks man!