[BUILD] New FET/RACK Official Help Thread - Please read first post!

kingofspain2 · Sep 23, 2018

Hairball Audio said:
Those are not part of the ground system. So I doubt it's the caps. I would make sure a connector or L-braket PCB mount hasn't become loose.

Mike

checked all screws, some weren't continuous but remedied through tightening, scraping and sanding screw holes, however ground hum persisted. Diagram shows where ground hum is present, R28 to Q4 is significantly diminished however. C1 has capacitive aleration to amplify ground hum when touched, scratching can be heard when connection between C1 and R8 is touched. Acceptable noise levels only achieved when hand is wrapped around C1 in rack mount.

Orange drop mod on unit #2 went off with no hitches...just stuck with this problem on #1. Did everything the same on both units...

BackToThe80s · Sep 28, 2018

Hello,
I started building a Fet Rack revision A from HAirball.
I install the corresponding parts for the power supply (except the active link).
When I realize my test I have the good value to the ground, however I do not find the following values: (+ 30VDC and -10VDC)
When I decide my multimeter "mastercraft 052-0060-2" on 200m and that I test my -10v I find about -9.6 and when I test the 30v and my multimeter to settle on 2000m I find about 255. That it is the problem?

scott2000 · Sep 28, 2018

BackToThe80s said:
Hello,
I started building a Fet Rack revision A from HAirball.
I install the corresponding parts for the power supply (except the active link).
When I realize my test I have the good value to the ground, however I do not find the following values: (+ 30VDC and -10VDC)
When I decide my multimeter "mastercraft 052-0060-2" on 200m and that I test my -10v I find about -9.6 and when I test the 30v and my multimeter to settle on 2000m I find about 255. That it is the problem?

.... You should have the meter set to 200 to check for the 30v//// not 2000m (2000milivolts..ie 2v)......

You really shouldn't be goofing around with power supplies yet if I'm reading right.....

....... I thought you were in an electronics course??? ???

but 255mv isn't good obviously if that's what it is....

BackToThe80s · Sep 28, 2018

scott2000 said:
.... You should have the meter set to 200 to check for the 30v//// not 2000m (2000milivolts..ie 2v)......

You really shouldn't be goofing around with power supplies yet if I'm reading right.....

....... I thought you were in an electronics course??? ???

but 255mv isn't good obviously if that's what it is....

My multimeter was dysfunctional I used the one from my school today and the results were completely different. Actually it is necessary to adjust it on 200m but I found no values when I was settling on the previous one.
So I took my measurements again, the multimeter set over 200m and the values I find are:

- For the Ground: 0.2
- For the -10: between -10 and -14
- For the 30v: between 30 and 45v.

The multimeter is not super quality and its accuracy is +/- (0.5% + 5)

Is that correct after you?

Thanks for your help.

alex_dempsey · Sep 30, 2018

Hello,

I was finally able to get both of my Rev A 1176s into (almost) functioning condition. They both seem to compress fairly normally, besides the circuit being pretty hot, but I'm having a problem with the ratios. When I select each of the different ratios, it doesn't seem to have an effect on the audio. Theres like maybe a 1dB difference on the meter and when I pass audio through there is really no audible difference between the ratios. I've double checked the resisters on the ratio card and they all look pretty much correct (pre modification) to what the circuit is looking for. Any ideas of where to look for issues?

Thanks.

Alex

clcmusik · Oct 3, 2018

Hi, I need help trying to troubleshoot my 1176 Rev D. New Version

I have three units in total, One completely calibrated and working like it should. The other two are a bit strange.

First unit with problems. Q1 is distorting at the source pin, and from then on the circuit has distortion on most of the resistors. I'm not able to calibrate the Q-Bias either. It keeps Skipping around.

From what I understand I'll need to replace Q1 & Q11 both. Correct me if I'm wrong ?

The Second Unit, I'm not sure what's wrong. I can calibrate the Q-Bias and I have audio passing through the circuit but the meter is stuck to the left, far left.
The only time the meter moves is when the power cord has been pulled out. The meter does work on the other units. How do I find out what's wrong with this unit?

Regards
Mo

TillM · Oct 3, 2018

clcmusik said:
From what I understand I'll need to replace Q1 & Q11 both. Correct me if I'm wrong ?

The Second Unit, I'm not sure what's wrong. I can calibrate the Q-Bias and I have audio passing through the circuit but the meter is stuck to the left, far left.
The only time the meter moves is when the power cord has been pulled out. The meter does work on the other units. How do I find out what's wrong with this unit?

Regards
Mo

Yes Q1 and Q11 need to be matched.

The Transistors for the Meter are Q12 and Q13. They also need to be matched.
So as far as I understand, the meter just works, when you turn the compressor on.
Make a small test. Take your DMM and go into the continuity tester mode.
On side to the ground the other side to TP11 or TP10.
Your Meter should move very fast to the right. Do it shortly, cause the meter went crazy.
But this is a good method how you can find out, if the meter is okay.
How many volts do you have at TP11 and TP10 ?

Echo North · Oct 7, 2018

BackToThe80s said:
My multimeter was dysfunctional I used the one from my school today and the results were completely different. Actually it is necessary to adjust it on 200m but I found no values when I was settling on the previous one.
So I took my measurements again, the multimeter set over 200m and the values I find are:

- For the Ground: 0.2
- For the -10: between -10 and -14
- For the 30v: between 30 and 45v.

The multimeter is not super quality and its accuracy is +/- (0.5% + 5)

Is that correct after you?

Thanks for your help.

They're bouncing around in that range? That is super weird.

Echo North · Oct 7, 2018

alex_dempsey said:
Hello,

I was finally able to get both of my Rev A 1176s into (almost) functioning condition. They both seem to compress fairly normally, besides the circuit being pretty hot, but I'm having a problem with the ratios. When I select each of the different ratios, it doesn't seem to have an effect on the audio. Theres like maybe a 1dB difference on the meter and when I pass audio through there is really no audible difference between the ratios. I've double checked the resisters on the ratio card and they all look pretty much correct (pre modification) to what the circuit is looking for. Any ideas of where to look for issues?

Thanks.

Alex

Compression is pretty subtle, and ratio is not something you see on your meter.

Look the troubleshooting guide and measure your pin 21,22, and GR Amp output as instructed in that guide.

That wil tell tell you a lot.

Mike

Echo North · Oct 7, 2018

clcmusik said:
Hi, I need help trying to troubleshoot my 1176 Rev D. New Version

I have three units in total, One completely calibrated and working like it should. The other two are a bit strange.

First unit with problems. Q1 is distorting at the source pin, and from then on the circuit has distortion on most of the resistors. I'm not able to calibrate the Q-Bias either. It keeps Skipping around.

From what I understand I'll need to replace Q1 & Q11 both. Correct me if I'm wrong ?

The Second Unit, I'm not sure what's wrong. I can calibrate the Q-Bias and I have audio passing through the circuit but the meter is stuck to the left, far left.
The only time the meter moves is when the power cord has been pulled out. The meter does work on the other units. How do I find out what's wrong with this unit?

Regards
Mo

The first one seems like it has an error in the first gain section.

The second either has a side-chain or meter GR amp issue. Start with the troubleshooting guide and the voltage charts linked with in it.

Mike

YoDudeRock · Oct 7, 2018

Hi ,
Need a little help with a Rev D. I recently built 4 units, but 1 of them isn't acting right.
Here's what's happening. On the "Null Adjust" calibration step, I discovered the voltages weren't right.
Adjusting R75 is getting me 1.40v DC (full CCW) and 0.00v DC (full CW). 0v DC on R75 should be somewhere around 12 o'clock. What have I done?

Not sure if this is helpful, but here's these individually.
TP10 = 10.06v DC
TP11 = 9.34v DC

Thanks!!
Chris Trentham
Ready To Rock Audio

Echo North · Oct 8, 2018

YoDudeRock said:
Hi ,
Need a little help with a Rev D. I recently built 4 units, but 1 of them isn't acting right.
Here's what's happening. On the "Null Adjust" calibration step, I discovered the voltages weren't right.
Adjusting R75 is getting me 1.40v DC (full CCW) and 0.00v DC (full CW). 0v DC on R75 should be somewhere around 12 o'clock. What have I done?

Not sure if this is helpful, but here's these individually.
TP10 = 10.06v DC
TP11 = 9.34v DC

Thanks!!
Chris Trentham
Ready To Rock Audio

Are you able to calibrate it even though you're at the end of the trimmer?

Could be Q12/13 miss matched a little.

YoDudeRock · Oct 8, 2018

Hairball Audio said:
Are you able to calibrate it even though you're at the end of the trimmer?

Could be Q12/13 miss matched a little.

A reading of 0vDC, R75 (at full CW) puts the VU meter fully to the right. FYI, turning R75 all the way to CCW puts the VU needle all the way to the left, so from the perspective of just looking at the VU, it appears to be working right, but the voltages between TP10 and TP 11 aren't right. IT DOES seem that if I adjust R75 to where it normally lands after a perfect calibration, it IS in the correct range on the VU meter, but the DC voltage between TP10 and 11 is about .70v DC. What have I done. Haha! I thought I was getting pretty good at these. Good to stay humble, I suppose.

I will check into Q12 and Q13 a little more. I matched the closest HFE between 28 2N3707's, so they should be pretty well matched. Gonna try reheating the solder joints first. Maybe I have a slight short between on of them?

Thanks,
Chris

Echo North · Oct 8, 2018

YoDudeRock said:
A reading of 0vDC, R75 (at full CW) puts the VU meter fully to the right. FYI, turning R75 all the way to CCW puts the VU needle all the way to the left, so from the perspective of just looking at the VU, it appears to be working right, but the voltages between TP10 and TP 11 aren't right. IT DOES seem that if I adjust R75 to where it normally lands after a perfect calibration, it IS in the correct range on the VU meter, but the DC voltage between TP10 and 11 is about .70v DC. What have I done. Haha! I thought I was getting pretty good at these. Good to stay humble, I suppose.

I will check into Q12 and Q13 a little more. I matched the closest HFE between 28 2N3707's, so they should be pretty well matched. Gonna try reheating the solder joints first. Maybe I have a slight short between on of them?

Thanks,
Chris

Check for shorts, bad joints, maybe a lifted pad. One of the transistors may have crapped out. Usually you can check the voltages around them to test that, or replace them.

YoDudeRock · Oct 8, 2018

Hairball Audio said:
Check for shorts, bad joints, maybe a lifted pad. One of the transistors may have crapped out. Usually you can check the voltages around them to test that, or replace them.

Mike,
I forgot to mention and it's significant, the ratio switch appears to do absolutely nothing. No left or right needle bounce like normal. I tried the ratio switch from the other working unit, no difference no movement.

I went over all transistors, they all seem normal except Q12 and Q13, they are around 13v at the collectors.
I changed them with another matched pair of 2N3707's, no difference.

I don't know if this is any help, but I noticed, with the unit powered on, measuring resistance from one side of R67 to the other is 3.9K ohms, on the working unit I have here, it's around 5M ohms.

Chris

Kroc · Oct 15, 2018

Hi!! I just finished building the Rev D kit (In about three consecutive days... I'm now dreaming of solder. Lol).

We're noticing some issues that we're having trouble locating: when no ratio buttons are pushed in, it passes audio. But the moment I push in any ratio button, the sound is distorted and without any low end, and there's weird static noise when turning the output pot (no noise when it isn't being turned. However, it functions cleanly and normally without a ratio selected). We did all the calibrations several times over (and were able to complete it normally), but the meter also seems to just get pinned to the right during regular operation in GR metering mode (+4 and +8 metering work as expected). I can't tell if the compression circuit is working at all or not.

We made sure to triple-check the directionality of components, and measured each resistor with a multimeter before installation. If you might be able to point me in the right direction, it would be much appreciated!

Attached is a photo of the PCB for reference. (I can post a photo of the ratio/metering/power side too if helpful also)

Cheers,
Dan

kingofspain2 · Oct 16, 2018

It's not the L Bracket PCB mount... any ideas? I feel dumb.

kingofspain2 said:
checked all screws, some weren't continuous but remedied through tightening, scraping and sanding screw holes, however ground hum persisted. Diagram shows where ground hum is present, R28 to Q4 is significantly diminished however. C1 has capacitive aleration to amplify ground hum when touched, scratching can be heard when connection between C1 and R8 is touched. Acceptable noise levels only achieved when hand is wrapped around C1 in rack mount.

Orange drop mod on unit #2 went off with no hitches...just stuck with this problem on #1. Did everything the same on both units...

Echo North · Oct 17, 2018

Kroc said:
Hi!! I just finished building the Rev D kit (In about three consecutive days... I'm now dreaming of solder. Lol).

We're noticing some issues that we're having trouble locating: when no ratio buttons are pushed in, it passes audio. But the moment I push in any ratio button, the sound is distorted and without any low end, and there's weird static noise when turning the output pot (no noise when it isn't being turned. However, it functions cleanly and normally without a ratio selected). We did all the calibrations several times over (and were able to complete it normally), but the meter also seems to just get pinned to the right during regular operation in GR metering mode (+4 and +8 metering work as expected). I can't tell if the compression circuit is working at all or not.

We made sure to triple-check the directionality of components, and measured each resistor with a multimeter before installation. If you might be able to point me in the right direction, it would be much appreciated!

Attached is a photo of the PCB for reference. (I can post a photo of the ratio/metering/power side too if helpful also)

Cheers,
Dan

https://www.hairballaudio.com/blog/resources/post/fetrack-troubleshooting-guide

Start here. Report back.

Echo North · Oct 17, 2018

kingofspain2 said:
It's not the L Bracket PCB mount... any ideas? I feel dumb.

The ground plane has continuity to the chassis?

Check your Q bias voltages...maybe one got shorted out in the solder job.

https://www.hairballaudio.com/uploads/pdf/fet_rack_d_v1.14_voltages.pdf

Kroc · Oct 17, 2018

Hairball Audio said:
https://www.hairballaudio.com/blog/resources/post/fetrack-troubleshooting-guide

Start here. Report back.

I just noticed that I had put CN2 on the ratio PCB backwards!! #Facepalm (I thought I had triple-checked everything)
Which certainly explains some of the gremlins. I'm hoping everything will work properly once reversed. Unfortunately I don't have access to a solder sucker for a couple of days to fix it. I will report back once I have.

With that in mind, at the moment, these are my measurements from the troubleshooting diagnostics:

- Q bias range is 0 to -3.02 at fully cw via tp 18
Amp Stages
- TP1: 0.068
- TP15: 1.31
- TP17: 0.288
- Output Trnf BRN: 0.005
- Output XLR: 5.320 VAC
GR Control Amp:
- 20:1 = 0.009 Second day's measure: -1.0 and creeping (I think I measured incorrectly the first time)
- 12:1 = 0.009
- 8:1 = 0.008
- 4:1 = 0.003. Second day's measure: -1.6 and creeping

GR Control Amp Output Voltages:
- All low
GR Control Amp Threshold Voltages:
- 4:1 = -1.194
- 8:1 = - 1.152
- 12:1 = -1.036
- 20:1 = -0.57 and dropping

Cheers,
Dan

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