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

[john lommock]

We switched the orientation to make replacing the lamp easier. Go with the arrow on the PCB you have.

Thanks for the clarification! For posterity, here's a photo of the correct orientation of the lamp board for PCB version 2.01

 

[Jan_M]

Hi everyone I could use some help with a REV A build.

Built up the power supply and went to test and got:

+3.6 VDC at CR8
-3.6VDC at CR9


Double checked L bracket - ok

Double checked components on main pcb

Checked for continuity between yellow wire pad on CN1 to ground - ok

Traced ac power from IEC up to CN13 and got the neutral ac voltage at white and blue pin and live ac voltage at black and red pins. I’m assuming this part is correct.

I would also like to double check the AC voltages coming into main pcb from the power transformer anyone know what readings I should expect?

Any idea on what else I should be checking.

Thanks for your help.

 

[john lommock]

Hi everyone I could use some help with a REV A build.

Built up the power supply and went to test and got:

+3.6 VDC at CR8
-3.6VDC at CR9


Double checked L bracket - ok

Double checked components on main pcb

Checked for continuity between yellow wire pad on CN1 to ground - ok

Traced ac power from IEC up to CN13 and got the neutral ac voltage at white and blue pin and live ac voltage at black and red pins. I’m assuming this part is correct.

I would also like to double check the AC voltages coming into main pcb from the power transformer anyone know what readings I should expect?

Any idea on what else I should be checking.

Thanks for your help.

Maybe this will help: https://www.hairballaudio.com/uploads/pdf/fet_rack_a_v1.14_voltages.pdf

 

[Jan_M]

Maybe this will help: https://www.hairballaudio.com/uploads/pdf/fet_rack_a_v1.14_voltages.pdf

Thanks John I must have missed this before.

I had a look but need the AC volts at P2 and P4 (orange wires) from the power transformer. I was trying to follow some of the troubleshooting steps from earlier in the thread but didn’t see what the correct expected voltages should be.

 

[Natethekill]

i thought i had posted before, but i guess not.
I finished my rev A build not too long ago, but while trying to calibrate it, ive been running into problems.


as im doing step 3 of the calibration, with input control maxed out only 1.3VAC at output, where 2.44VAC
is where i wanna be, but i cant get any more juice out of it. Feeling super defeated here

 

[Dominique Poinçot]

Hello everyone,

I've just finished building my first 1176 Blue Stripe Rev. A 1.15, and did the calibration.

I've noticed that my 0 on the GR meter doesn't stay fixed while the unit is on, it was going towards the red part, very slowly over a couple hours.

I adjusted it a couple of times with the zero trim on the front.

Today at startup, it had gone left this time, not by much, but how come ? Is this normal ?

Thanks a lot

 

[Ricardus]

Question:

I have built 2 of these, Rev D. Builds went great, and the calibrations seemed to go great as well.

So I get all parts of the cal dialed in, and the meter is in GR mode and is at zero, everything is great, the sun is shining, birds are chirping, etc...

Then I turn them on the next day, they fire up, and the meter is at +1. This has happened to me twice now. anyone else? Is this just a temp stabiliziation thing?

Also, what does your meter do when it's in "all buttons in mode"?

 

[fractal33]

Question:

I have built 2 of these, Rev D. Builds went great, and the calibrations seemed to go great as well.

So I get all parts of the cal dialed in, and the meter is in GR mode and is at zero, everything is great, the sun is shining, birds are chirping, etc...

Then I turn them on the next day, they fire up, and the meter is at +1. This has happened to me twice now. anyone else? Is this just a temp stabiliziation thing?

Also, what does your meter do when it's in "all buttons in mode"?

Both of those questions are answered here on the FAQ

Just built a Rev D with orange drop together a month or so ago. Love it!

Cheers

 

[Ricardus]

Both of those questions are answered here on the FAQ

Just built a Rev D with orange drop together a month or so ago. Love it!

Cheers

So the meter is supposed to slam to the right in ABI mode, but will it damage the meter in any way?

 

[Echo North]

So the meter is supposed to slam to the right in ABI mode, but will it damage the meter in any way?

Yes it is supposed to slam right and no it will not damage the meter.

 

[davidjohn]

I've just finished pulling my hair out on this one. I built a FET Rev D and cannot work out why I am getting a very low voltage reading on the input XLR despite measuring the correct 0.775VAC from the input cable.

I've verified ~30V at CR8 and -10V at CR9. I've verified voltages from the DC voltage chart are all correct EXCEPT the readings for Q12 and Q13, which are almost double. However, I don't understand how this affects the input XLR voltage since it seems like there's a lot of circuitry in between that appears to be working correctly.

I've re-flowed the solder joints. I also built a 2nd unit, which is working correctly. I've compared various test points between the two and am getting the same voltages.

I'm at a loss with this and don't know what to test next. I would appreciate some guidance.

Thanks,
Dave

 

[tommythecat_80]

Hi,

Just finished my first Rev A. Power supply works and managed to calibrate the Q-bias. The problem is the GR meter which doesnt show signs of life, sits on the far left. Any advive where to start finding the problem?

Cheers
Tommi

 

[tommythecat_80]

Hi,

Just finished my first Rev A. Power supply works and managed to calibrate the Q-bias. The problem is the GR meter which doesnt show signs of life, sits on the far left. Any advive where to start finding the problem?

Cheers
Tommi

I’m answering to myself I managed to wake up the needle just checking the wiring, maybe the wire to meter board was loose. However, the needle only moves on +8 and +4 buttons but on GR, needle is still on far left and the meter trim pot doesnt do anything.

The unit passes signal and compresses and sounds fantastic! The problem still is the metering…

 

[davidjohn]

I've just finished pulling my hair out on this one. I built a FET Rev D and cannot work out why I am getting a very low voltage reading on the input XLR despite measuring the correct 0.775VAC from the input cable.

I've verified ~30V at CR8 and -10V at CR9. I've verified voltages from the DC voltage chart are all correct EXCEPT the readings for Q12 and Q13, which are almost double. However, I don't understand how this affects the input XLR voltage since it seems like there's a lot of circuitry in between that appears to be working correctly.

I've re-flowed the solder joints. I also built a 2nd unit, which is working correctly. I've compared various test points between the two and am getting the same voltages.

I'm at a loss with this and don't know what to test next. I would appreciate some guidance.

Thanks,
Dave

Does anyone monitor this board anymore? Seems like the activity is almost zero :-(.

 

[Echo North]

I do not. I do support through the site now.

https://help.hairballaudio.com/hc/en-us
I'd check the resistance between input + and - to make sure you don't have a dead short. The resistance should be low but not 0-10Ω low.

Mikw

 

[Dominique Poinçot]

Hi all,

I just finished my second Rev A build, and everything went without a hitch including calibration, until I tried passing audio through...

Eveything seems to work but there is a HUGE distortion no matter the settings.

The tape supposed to keep the 2N3707 pair together for Q12 and Q13 failed in the packaging, so I had to guess which ones to pair.

This is my best bet, but I wanted your insight before comitting to changing them ?

My first build worked like a charm right away.

Thanks

Dom

EDIT : It was just a bad solder joint on C22's ground, the unit sounds great. I'm still worried about the matched transistors, should I still replace them ?

 

[noiro]

got back a damage rack rev D, doing testing point get 0.100 vac on tp1 but nothing on the next 4 points, q2,q3,q14 and tp15. any idea here? perhaps some dead transistor?

 

[Echo North]

Damaged Q1 or you have no bias voltage at the Q1 gate. You should see -1 to -2 VDC at the gate. if you have 0VDC either the FET is bad or more likely there is an issue between that Gate and the negative rail (attack/release/ratio boards).

Mike

 

[noiro]

Came back totally damage in transport, since that I always put form in between the pcb and the top /bottom, had both front input and output pots wreck as well. get -2.3vdc at the gate of q1

 

[Echo North]

That's a good voltage. What's the DCR between the Source and Drain of Q1?