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

[Basti]

Hi DIYers!

I've read so many forumpost the last week but i just cant find something similar to my problem...

So i have finished building the Rev D Hairball Kit(V1.11) and wanted to start the calibration,
in fact i made all 3 steps.
As i bypassed the test oscillator afterwards the 1KHz Signal jumped out of my speaker,
meaning there is definitely something wrong with my build... (Signal passing through, but too quiet)

So i checked every resistor and generally everything if its in place and in the right direction ->
everything is fine

i tried to recalibrate, didn't help

but i noticed some strange things:

-The Input and Output knob doesn't make the oscillator signal louder or quieter in my DAW and Speakers
-I hear the Signal out of my Outputtransformer when the output knob is turned heavily up
-I'm not quiet sure but i think the unit distorts the signal more than it should
-Signal is obviously passing through, but much too quiet

What are your suggestions?
Cold Solderjoint? Have i bridged somehting?

greetings from Austria

 

[Echo North]

Hi DIYers!

I've read so many forumpost the last week but i just cant find something similar to my problem...

So i have finished building the Rev D Hairball Kit(V1.11) and wanted to start the calibration,
in fact i made all 3 steps.
As i bypassed the test oscillator afterwards the 1KHz Signal jumped out of my speaker,
meaning there is definitely something wrong with my build... (Signal passing through, but too quiet)

So i checked every resistor and generally everything if its in place and in the right direction ->
everything is fine

i tried to recalibrate, didn't help

but i noticed some strange things:

-The Input and Output knob doesn't make the oscillator signal louder or quieter in my DAW and Speakers
-I hear the Signal out of my Outputtransformer when the output knob is turned heavily up
-I'm not quiet sure but i think the unit distorts the signal more than it should
-Signal is obviously passing through, but much too quiet

What are your suggestions?
Cold Solderjoint? Have i bridged somehting?

greetings from Austria

Ya definitely something wrong. Audible signal out of the output tx is normal.

With the input and output midway and GR off (20:1) what your output level at each end of the qbias adjustment.

Mike

 

[Diamondj421]

Hey everyone!
Hope you're all having a great new year! I posted this on a different topic and never heard back. Let's see how this goes... I got my 1176 Rev D back from Mike a few months ago and I LOVE it.  One thing that I'm curious about though is whether or not I may need to recalibrate it. I was printing a vocal with it on (Input at 40, output at 6, 4:1 Ratio, Attack fully CW and Release at 5) and the amount of gain reduction seems rather extreme for the low input setting. The source signal was fairly low between -12dB to -10dB and the needle was floating around -10 to -20dB of gain reduction.  Doesn't seem like it really leaves me anywhere to go. haha. Could the adjustment pots have gotten shaken around during delivery or is this reading typical? I'm sure DDM readings would help but I figured I'd ask before taking it out of the rack and removing the top.

Thanks in advance!

 

[Basti]

Ya definitely something wrong. Audible signal out of the output tx is normal.

With the input and output midway and GR off (20:1) what your output level at each end of the qbias adjustment.

Mike

I'm not sure how to measure that...
from point 18 to the ends of the poti?

 

[Echo North]

I'm not sure how to measure that...
from point 18 to the ends of the poti?

At the XLR +/- test point.  AC.  What range do you get as you rotate the qbias under those conditions.

 

[Echo North]

Hey everyone!
Hope you're all having a great new year! I posted this on a different topic and never heard back. Let's see how this goes... I got my 1176 Rev D back from Mike a few months ago and I LOVE it.  One thing that I'm curious about though is whether or not I may need to recalibrate it. I was printing a vocal with it on (Input at 40, output at 6, 4:1 Ratio, Attack fully CW and Release at 5) and the amount of gain reduction seems rather extreme for the low input setting. The source signal was fairly low between -12dB to -10dB and the needle was floating around -10 to -20dB of gain reduction.  Doesn't seem like it really leaves me anywhere to go. haha. Could the adjustment pots have gotten shaken around during delivery or is this reading typical? I'm sure DDM readings would help but I figured I'd ask before taking it out of the rack and removing the top.

Thanks in advance!

Maybe not.  There are a few things going on.

One is that the input t-pad on the original units has a very unique taper.  Not very common today.  Our taper is a little different which just means the input runs hotter quicker. So instead of getting that classic compression setting at 30 (Dr. Pepper)...it's more like 36-40 .

Also the meter, while good, is not like they used to make them or like an equivalent meter costing around $110.  It does overshoot a little. When you combine that with medium to slower release settings, you'll see heaver compression. Especially at 4:1 which has a lower threshold.

Hope that makes sense.

Mike

 

[Basti]

At the XLR +/- test point.  AC.  What range do you get as you rotate the qbias under those conditions.

Ah okay! sorry for the dumb question mike! had to sleep a night over this 

okay i have: 0,25 VAC to 9,36 VAC

thank you for taking time!

 

[Echo North]

Ah okay! sorry for the dumb question mike! had to sleep a night over this 

okay i have: 0,25 VAC to 9,36 VAC

thank you for taking time!

That seems normal.

What is the issue again?  Just that the signal is too quiet?  Are you able to get through all of the calibration steps?

 

[Basti]

That seems normal.

What is the issue again?  Just that the signal is too quiet?  Are you able to get through all of the calibration steps?

Yes, the signal is way too quiet... may it be the preamp section, not pushing the signal enough?

Calibration steps are no problem..

 

[Basti]

Yes, the signal is way too quiet... may it be the preamp section, not pushing the signal enough?

Calibration steps are no problem..

okay, spent some time now with the unit
checked the voltages with mnats schematics

preamp sections looks good except of Q3 instead of 12,58 V i have 11,77 v
Q14 has 11,14 V instead of 12 V

i dont know how much its allowed to differ..

biggest problem is the gain reduction driver..
nothing is near the Voltages
Q11 gets only 6 V instead of 10,56 V
and i Cant understand why, resistors are good

Trying to build a audio probe next week and seek on

Any Tipps or suggestions so far?

 

[Echo North]

okay, spent some time now with the unit
checked the voltages with mnats schematics

preamp sections looks good except of Q3 instead of 12,58 V i have 11,77 v
Q14 has 11,14 V instead of 12 V

i dont know how much its allowed to differ..

biggest problem is the gain reduction driver..
nothing is near the Voltages
Q11 gets only 6 V instead of 10,56 V
and i Cant understand why, resistors are good

Trying to build a audio probe next week and seek on

Any Tipps or suggestions so far?

You're signal looks good an strong with no GR.  There has to be something misplaced in the GR amp, bad semi, bad solder joint...something weird in there.

It sounds good and loud with no GR correct?

 

[Basti]

You're signal looks good an strong with no GR.  There has to be something misplaced in the GR amp, bad semi, bad solder joint...something weird in there.

It sounds good and loud with no GR correct?

I think i should have mentioned this earlier^^
The signal has the same low level -> bypassed or in gain reduction
Is that good to isolate the issue?

 

[Echo North]

I think i should have mentioned this earlier^^
The signal has the same low level -> bypassed or in gain reduction
Is that good to isolate the issue?

Hmmmm.  I would check your signal/patching coming into the unit.  You mentioned that under the conditions I mentioned, your unit was as loud as 9.36VAC before setting the bias?  That is an output of over 20dBu which is LOUD.  Even with the 1dBu qbias roll back you should be fine unless this output is all HF oscillation.

You're having no issue setting the qbias?

 

[junkface]

Remove the shunt then measure R44, the trim pot, while at either extreme.

it goes from 0 to 0.1dcV

 

[mnats]

it goes from 0 to 0.1dcV

A trimmer is a variable resistor, so try measuring its resistance...

 

[junkface]

A trimmer is a variable resistor, so try measuring its resistance...

it's working correctly, 0k up to 4.8k at full trim. had a 2k per the BOM, (measuring up 0 up to 1.8k) but put a 5k in there when I changed R75 out for 5k too.

 

[mnats]

it's working correctly, 0k up to 4.8k at full trim. had a 2k per the BOM, (measuring up 0 up to 1.8k) but put a 5k in there when I changed R75 out for 5k too.

What this part of the circuit does is compare the voltage at the base of Q12 with the voltage at the base of Q13. The voltage at the base of Q12 will vary with gain reduction since Q11, the FET, sees the same input at its gate as Q1, the FET that is doing the audio gain reduction.

So let's take a step back. Did you measure and confirm all resistor values before they were soldered in place? If not, have you done a visual confirmation of resistor values in the GR Meter circuit after it was built? Right now I cannot see how changing R75's value would change the voltage produced at its wiper unless other values were incorrect. *edit: Yeah, of course it would.

 

[junkface]

So let's take a step back. Did you measure and confirm all resistor values before they were soldered in place? If not, have you done a visual confirmation of resistor values in the GR Meter circuit after it was built? Right now I cannot see how changing R75's value would change the voltage produced at its wiper unless other values were incorrect. *edit: Yeah, of course it would.

Always measure before soldering, but JIC I just measured and confirmed all resistors in the GR Meter Driver amp. then rechecked earlier calibration steps, still having the same issue. It's compressing fine, sounding great, the meter just shows way too much GR, even when there is no actual reduction being applied to the signal (although the compressor is engaged on the attack switch).

 

[mnats]

Always measure before soldering, but JIC I just measured and confirmed all resistors in the GR Meter Driver amp. then rechecked earlier calibration steps, still having the same issue. It's compressing fine, sounding great, the meter just shows way too much GR, even when there is no actual reduction being applied to the signal (although the compressor is engaged on the attack switch).

With the unit on, set the meter switch in GR, ratio to 20:1 and the attack knob fully counter clockwise, no input, tracking adjust shunt removed, starting with the front panel meter zeroed. We'll assume the voltage across R74 is around 0.00VDC as you had measured when you did the meter null calibration but you may want to verify.

With your multimeter set to DC volts and the negative probe on the chassis, measure the voltage at the base of Q13. Measure the voltage at the base of Q12. Now measure the voltage at the base of Q13 while R75 is at each extreme. Please report your voltages.

 

[junkface]

With the unit on, set the meter switch in GR, ratio to 20:1 and the attack knob fully counter clockwise, no input, tracking adjust shunt removed, starting with the front panel meter zeroed. We'll assume the voltage across R74 is around 0.00VDC as you had measured when you did the meter null calibration but you may want to verify.

With your multimeter set to DC volts and the negative probe on the chassis, measure the voltage at the base of Q13. Measure the voltage at the base of Q12. Now measure the voltage at the base of Q13 while R75 is at each extreme. Please report your voltages.

Across R74 with shunt in "normal" position is -0.1dcV or so
Q12 base: -1.95 dcV
Q13 base: -2.06 dcV

R75 FULL CCW
Q12 Base:-1.95 dcV
Q13 Base: 0 dcV

R75 FULL CW
Q12 base: -1.96 dcV
Q13 base: -3.52 dcV