[BUILD] 1176 Rev A - Back to the beginning...

[mnats]

Apparently there were no problems with the unit after all, I just did not understand the process.

It's hard to understand how you could get TP10 at -0.5V as you previously reported even with the worst case miscalibration. I tried with my unit and the best I could do was 2.5 Volts. Are you certain there was nothing wrong?

For the next person, do not necessarily be alarmed if your voltages are off prior to all of the calibrations.

This might be why it says at the bottom of my schematic with voltages "TEST CONDITIONS: FULLY CALIBRATED UNIT, NO INPUT, GR MODE, LEFT ON FOR 1/2 HR" in red!

 

[frazzman]

Apparently there were no problems with the unit after all, I just did not understand the process.

It's hard to understand how you could get TP10 at -0.5V as you previously reported even with the worst case miscalibration. I tried with my unit and the best I could do was 2.5 Volts. Are you certain there was nothing wrong?

For the next person, do not necessarily be alarmed if your voltages are off prior to all of the calibrations.

This might be why it says at the bottom of my schematic with voltages "TEST CONDITIONS: FULLY CALIBRATED UNIT, NO INPUT, GR MODE, LEFT ON FOR 1/2 HR" in red!

Hi mnats,

Sorry to hijack your post...
I'm trying to source some of your excellent small variable psu pcbs... I've purchased them through your page many times in the past... Since your board sales now go through hairball i haven't seen the boards available there... Any chance you have any laying around , or plan for Mike to stock them ? They are very useful for dual channel projects . Thanks in advance

 

[Dissler89]

I'm having some problems with the first calibration step.

As it is written I am sending a 1khz 0.775 AC reference voltage out of my daw.
I have made sure that the voltage being sent is this by simply using my DDM and measuring pins 2 and 3 on the XLR.

I now proceeded to measuring the voltage again from the Input XLR inside the casing with the XLR connected, sending 1khz at 0.775AC

The voltage seems to have dropped a considerable amount. Down to 0.114 AC.

I suspected that this may have been some wiring issue to the input XLR. So I decided to resolder. However the Voltage is not changing.

I'm now assuming the the internals of the XLR may have been damaged. Is this a feasible idea? or could something else be going?

Thanks in Advance. 

 

[Unit7]

As it is written I am sending a 1khz 0.775 AC reference voltage out of my daw.
I have made sure that the voltage being sent is this by simply using my DDM and measuring pins 2 and 3 on the XLR. 

Where did you read that? Reading the calibration chapter at Hairball assembly guide to me it seems quite clear that you should have .775 at the input XLR of the unit, not from your DAW. This to 'include' the 600Ω input impedance. It's described very well imo even for a electronics noob like me.

 

[Dissler89]

Where did you read that? Reading the calibration chapter at Hairball assebly guide to me it seems quite clear that you should have .775 at the input XLR of the unit, not from your DAW. This to 'include' the 600Ω input impedance. It's described very well imo even for a electronics noob like me.

"Apply a 1 KHz O dBu signal to the input and confirm with your DMM between pin 2 and 3 of the input XLR."

I can now see that I interpreted the sentence wrongly.
English is unfortunately not my first language.
Thanks!

 

[Unit7]

Where did you read that? Reading the calibration chapter at Hairball assebly guide to me it seems quite clear that you should have .775 at the input XLR of the unit, not from your DAW. This to 'include' the 600Ω input impedance. It's described very well imo even for a electronics noob like me.

"Apply a 1 KHz O dBu signal to the input and confirm with your DMM between pin 2 and 3 of the input XLR."

I can now see that I interpreted the sentence wrongly.
English is unfortunately not my first language.
Thanks!

Neither my mother tongue. And yes, that sentence could be misleading, but to me it's clear it's just referring to the instructions in the first part of the calibration instructions:
'There’s another problem.  The FET Compressor has a very low nominal 600Ω input impedance.  Generally we want our input impedance (FET Compressor) to be at least 10x the source impedance (signal generator) to avoid impedance loss.  With an input of 600Ω, this is rarely the case.  Generally sending 0 dBu from your generator will result in a lower level at your input due to this impedance loss.

Confused?  There is a simple fix for all of this.  When asked in the calibration steps to send a 1K at 0 dBu signal to the input, use your DMM to measure the AC voltage between lug 2 and 3 of the input XLR.  Adjust your signal generator until you see 0.775VAC between pin 2 and 3.  When you see 0.775 VAC between pin 2 and 3, you have 0 dBu at your input.'

Of course even the most accurate instruction could be misread, but I have to say Mike's guides are pretty brilliant. For beginners like me I believe the trick is just not to rush, read everything 'til you really get it and then proceed with the build. I read the PSU chapter at least 5 times before feeling confident enough to start assembling.

 

[David RP]

I found some alternative calibration videos on you tube. Worth a look.
They may have been posted here before so forgive me

Q Bias trick to get it right
http://www.youtube.com/watch?v=9yECKyklD0o

Step 1 Q bias
http://www.youtube.com/watch?v=0Uuk1Y7M2D8

Step 2 Discrete meter calibration
http://www.youtube.com/watch?v=lRStwXwmBUw

Step 3 Meter tracking
http://www.youtube.com/watch?v=pgSWfsEzU40

Tip if you cant get the meter to zero adjust in GR mode
http://www.youtube.com/watch?v=PScAEEriE-Q

BTW I like the tape over the zero adjust hole to prevent scratching the panel

 

[Flanger]

Hi,
I assembled the compressor and went to do the calibration step, and realized something is wrong. My issue is that I am measuring VAC between pins 2 and 3 of the output XLR to do the Q bias step and as I'm adjusting the pot it is having no effect on the voltage.
My other issue is that my VU meter is not showing any signal.
I'm new at this kinda stuff and would appreciate any help you guys can give me on narrowing down what the problems could be.
Thanks

 

[Echo North]

Hi,
I assembled the compressor and went to do the calibration step, and realized something is wrong. My issue is that I am measuring VAC between pins 2 and 3 of the output XLR to do the Q bias step and as I'm adjusting the pot it is having no effect on the voltage.
My other issue is that my VU meter is not showing any signal.
I'm new at this kinda stuff and would appreciate any help you guys can give me on narrowing down what the problems could be.
Thanks

If there is no signal at the output, switch the attack to gain reduction off, then try and trace your signal throughout he amp stages to see where it dies.

Do you have and AC at main PCB pad 15 with the in and out midway and a 1K 0dB signal on the input?

 

[Flanger]

The signal is getting from input to output. I just tried the Q bias calibration again and it seems there must have been a problem with me or my DMM because the adjustment is working fine now. I've made it, but I am still having some trouble with my VU meter. It simply seems disconnected, it won't show any signal and the needle won't pop up when on the GR setting. It's likely there's a short or a disconnect somewhere, any ideas on where I should begin checking with the DMM? I'm a little hazy on how the VU fits into the signal flow.
Thanks a lot for the help!!

 

[All Ears]

I've just finished a pair of these units and they pass audio etc but I'm wondering about this measured voltage -

Q4 source voltage: 4.2v  (measured same on both units)

I saw a few other posters also had voltages around the 4v mark rather than the nominal 6.6v marked on mnats schematic.

My question is:
- Will there be any effect (distortion, clipping etc) from having this slightly low source voltage @ Q4 ?

Cheers 

 

[Winetree]

Can I use a .01uf wima poly film cap on the attack pot instead of the .015uf cap.

 

[dbonin]

Can I use a .01uf wima poly film cap on the attack pot instead of the .015uf cap.

I would give it a try, yes - should be fine.

Cheers,
-Don

 

[bcaldiy]

Hey guys,
I finished the revA bluestripe build, at calibration stage,
I completed the first two calibration steps but could not get the adjustment with the input to drop to a low enough voltage for stage 3 (meter tracking adjustment)… I got sick of trying to complete step 3 and passed audio from my daw and found the thing seemed to work and had a day of testing it out and it sounds good,
so today I decided to try and go back to step one with my calibration and meticulously redo it to try and be able to complete the meter tracking calibration,
Q-bias went fine again, but now the step 2 discrete metering calibration will not work properly, originally when I did it i remember the meter went easily into negative DC with the null adjust and meter adjust pot and I just zeroed in on 0 VDC between TP10 and TP11…
now the null adjust and meter adjust pot won't allow me reach negative voltages between TP10 and TP11, it only achieves 0 VDC with the adjust pot full CCW…
any ideas what might be the issue?
thanks for your time!
cheers
Ben

 

[skidmorebay]

I love using my pair of REV A's on my drum bus, but I wish they had a high-pass filter in the sidechain so they didn't respond so strongly to the kick drum.
Does anyone know how to implement this? Even a simple RC filter set for 80 or 100hz that I could switch in and out would be awesome. Any ideas?
thanks.

 

[BenHer]

Hey everyone,

Thank you for your kind insight, this is my first comp as well as first time posting here.  I searched the previous posts for this same issue and didn’t quite run across the same problem, forgive me if I overlooked it.


I built the Rev A blue stripe,  and the only ratio that works is the 20:1.  (Which sounds fantastic)
The rest of the ratio buttons still pass signal through, although very hot, and quite distorted.  So it sounds more like a distortion pedal than a compressor.

I checked for obvious signs: cold solder joints...etc, even had it in with a pro tech who overlooked the wiring and schematics and it checked out well with him.

Thoughts?????

Thank you so much for any help you can offer

Hi everyone,
Has Anyone found a solution to this? I'm having the same problem. I'm only getting 0.147 V at pad 22 @ 10db reduction 20:1, and 0 volts at any other ratio. I'm using a rotary switches wired for "slam mode". I built a rev D at the same time and it's doing the same exact thing. I've checked the switch wiring about 10 times. It looks right when compared to the mnats pics. Any help would be much appreciated.
Thanks
-Ben

 

[Indecline]

Just did a fun 1176 shoutout, figure I'll share the results

6176 (compressor only): The baseline for the test. Modern and thick sound, very slight roll off of on top. Everything to be loved on this unit.

Urei Rev. F: more clear than the 6176. Extended top end not quite as thick in the lows.

Purple Action: noticeably different sound. More aggressive in the upper mids, not quite as thick as the lows.

Distressor 1176 mode: slightly punchier than the rest. Frequency response is flat overall

Rev. A: slightly thicker than the 6176 with more high end rolled off. Otherwise very similar sound to the 6176.

Overall I liked the Rev. A the best with the 6176 just behind that. They both sound very similar with the Rev. A losing a bit of the top.

Super impressed with the shootout  8)

 

[madscientist]

Hello all,

I've been working on building a Rev A 1176 using the Hairball Kit.  I've got everything together, but when I went to calibrate it, the Q-bias adjustment is having zero effect on the output voltage.  I'm just looking for help with some troubleshooting steps to figure this out.  Though I'm quite handy with a soldering iron, I am very much a noob at this.

So far, I have double checked all the resistors and solder connections.  I have also verified that the Q-bias trimmer is working properly. 

In my impatience, I sent some audio through the unit.  Everything appears to be working.  The input and output controls functions as does all of the compressor and meter functions.  The output is very thin and tinny though.  There is essentially zero bass response.

Once again, any direction that could offered to start the troubleshooting path would be greatly appreciated. 

Thanks!

 

[Echo North]

Hello all,

I've been working on building a Rev A 1176 using the Hairball Kit.  I've got everything together, but when I went to calibrate it, the Q-bias adjustment is having zero effect on the output voltage.  I'm just looking for help with some troubleshooting steps to figure this out.  Though I'm quite handy with a soldering iron, I am very much a noob at this.

So far, I have double checked all the resistors and solder connections.  I have also verified that the Q-bias trimmer is working properly. 

In my impatience, I sent some audio through the unit.  Everything appears to be working.  The input and output controls functions as does all of the compressor and meter functions.  The output is very thin and tinny though.  There is essentially zero bass response.

Once again, any direction that could offered to start the troubleshooting path would be greatly appreciated. 

Thanks!

You have the output transformer connected correctly with the two remaining wires shorted together?

You need to complete the Qbias adjustment.  You need to follow the -DC bias voltage and see where it dies.

Open the schematic now....

http://mnats.net/files/1176REVA_125_VOLTAGES.pdf

See in the lower right where it says "-9.85V"?  That's the negative rail.  R80 and R60 are a voltage divider.  R60 is connected to ground at one side and R80 is connected to the neg rail at one side.  In the middle is some negative voltage between 0 and -9.85 based on the ratio of those two resistors.  At the point where they meet you'll see roughly -2.5 to -3V DC.  If you don't that's a problem with that divider.

That voltage then goes through the R59 drummer and is further trimmed by that trimmer.  You should see the voltage change at pad 18 based on rotating the trimmer. If you don't, trimmer is bad.  Pad 18 is wired to the release pot.  The side with the resistor...see that.  Follow that voltage through there where is goes to the attack pot next , the leg w/o a resistor or cap, then get's wired to back to the main PCB (pad 7 I think).  Your error is probably in that wiring.

Trace that voltage, see where it dies.  It always should be negative in reference to ground.

Mike

 

[Mr.Franky]

Hey,

So I built my new Rev A kit. When I powered it on however, R32 started smoking. I immediately turned it off.

I already built a rev A before, but it has never worked. It's always given this terrible distortion (even in bypassed). If I remember correctly, I have also replaced R32 there because it was looking funky.

I planned on building a new (good) rev A so I could check my old one for mistakes.. but this one does seem to have problems as well. We've checked all the voltages before, we've checked all the resistors on color code, we've checked all wiring... nothing seems to be out of place, nothing seems to be shorted.. Any ideas?  :-\

I'm Europe based if that says anything..

(Also I have built 2 rev.D kits but they've been working and sounding beautifully from the start. I have no idea why my 2 rev A (V1.2.5) kits seem to be giving problems. The same problems apparently, although I haven't tested if my new rev A hs the same terrible distortion as my previous one. Maybe there is some kind of mistake in the Rev A assembly guide or anything?  :-\ I'm running out of ideas)

http://tinypic.com/r/23uokcp/8

http://tinypic.com/r/33412qo/8

Also, at the 30V test point I'm getting 29.69V and at the -10V i'm getting -9.71V. In my other rev A kit these values are also correct.