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

[Echo North]

Been away for a week. So I checked the DC volts against the schematic and it seems like all are pretty close to where they're supposed to be. I didn't find any that were wildly different from the spec.

However I think I may have found a clue.  I was going around the board with a finger applying pressure and bit of wiggle to the caps and FETs seeing if I could find any loose/suspect connections that might have an impact on the meter. That's when I touched Q6 and said holy toledo that's hot. And that's when I remembered that Q6 is supposed to have a heat sync. I completely forgot to install it before power up.

Any chance I might have cooked the Q6 and that could be my problem?

Usually if Q6 has failed, R32 will be burned.

I would suspect something in your GR meter section which should be marked on the box.  Make sure you don't have your 100Ω and 2KΩ trimmer swapped.

 

[Echo North]

Hi guys-I just finished building my first Fet Rack, and I'm having trouble doing the calibration:

The first two calibration steps were successful and yielded the proper voltages, but now I'm stuck on the third step (adjusting the meter to reflect GR). It seems at this stage that the unit isn't compressing at all (no compression showing on the meter/the DMM/ or happening audibly,) but the unit IS passing audio through very cleanly.  The Q bias was set per instructions and R74 is showing 0 voltage across it.

Is there any obvious places to start with troubleshooting that you can think of (a problem with the attack/release board, a burned out FET unit...)? To reiterate-I have audio passing cleanly but no compression despite the Q bias being set per instructions. Thanks so much for the help.

If no GR, start with measuring the side chain voltages.

Set your unit to:
Input: 12 O’Clock
Output: 12 O’Clock
Attack: GR ON (Full CW)
Release: Full CW
Ratio: 20:1
Meter: GR
Signal: Sine 1kHz @ 0dBu

1. Using chassis as your ground reference, what is your AC V at TP22 for all 4 ratio settings.
2. Using chassis as your ground reference, what is your DC V at TP21 for all 4 ratio settings.

Mike

 

[Maxman]

If no GR, start with measuring the side chain voltages.

Set your unit to:
Input: 12 O’Clock
Output: 12 O’Clock
Attack: GR ON (Full CW)
Release: Full CW
Ratio: 20:1
Meter: GR
Signal: Sine 1kHz @ 0dBu

1. Using chassis as your ground reference, what is your AC V at TP22 for all 4 ratio settings.
2. Using chassis as your ground reference, what is your DC V at TP21 for all 4 ratio settings.

Mike

Hi Mike-Thanks so much for the quick response!  Here are the voltages I measured:

TP 22  @  20:1  --  .69VAC
                        12:1  --  .113
                        8:1    --  .07
                        4:1    --  .056

TP 21  @    20:1  --  -6.83VDC
                        12:1  --    -3.923
                        8:1    --    -2.839
                        4:1  --    -1.927
Thanks!
-Max

 

[nickcion]

Try removing the Q1 FET if you can...does that change the level?

Mike

hi mike. I've been MIA for a couple weeks doing an art installation.

I had no signal at T1. I just pulled Q1.. and now i have a tiny waveform coming through at T1.

 

[jgremlin]

Usually if Q6 has failed, R32 will be burned.

I would suspect something in your GR meter section which should be marked on the box.  Make sure you don't have your 100Ω and 2KΩ trimmer swapped.

R32 shows no sign of burns and still measures 38.7 ohm.

I haven't measured them yet but R44, R59 and R75 are all marked 202 so I assume they're all 2k. Excuse my ignorance but what do you mean when you say 'should be marked on the box'?

Although you weren't intending it for me, I went ahead and did the test you recommended for Maxman. With no input signal, here's my results.

TP21:
20:1 -6.79VDC
12:1  -3.89VDC
8:1    -2.81VDC
4:1    -1.90VDC

TP22:
20:1  0.000VAC
12:1  0.000VAC
8:1    0.000VAC
4:1    0.000VAC

Based on what Maxman is reporting, I'm guessing (well hoping really) all those zeros might be a clue?

 

[Echo North]

hi mike. I've been MIA for a couple weeks doing an art installation.

I had no signal at T1. I just pulled Q1.. and now i have a tiny waveform coming through at T1.

Set your unit to:
Input: 12 O’Clock
Output: 12 O’Clock
Attack: GR OFF
Release: Full CW
Ratio: 20:1
Meter: GR
Signal: Sine 1kHz @ 0dBu

With your DMM measure your AC at the following test points using the chassis as you reference (black probe).

-Input XLR +
-TP1
-TP15
-TP17
-Output Transformer BRN
-Output XLR +

 

[Echo North]

R32 shows no sign of burns and still measures 38.7 ohm.

I haven't measured them yet but R44, R59 and R75 are all marked 202 so I assume they're all 2k. Excuse my ignorance but what do you mean when you say 'should be marked on the box'?

Although you weren't intending it for me, I went ahead and did the test you recommended for Maxman. With no input signal, here's my results.

TP21:
20:1 -6.79VDC
12:1  -3.89VDC
8:1    -2.81VDC
4:1    -1.90VDC

TP22:
20:1  0.000VAC
12:1  0.000VAC
8:1    0.000VAC
4:1    0.000VAC

Based on what Maxman is reporting, I'm guessing (well hoping really) all those zeros might be a clue?

Is that with GR turned on? All zeros is normal with GR OFF. But not switched on.

Sorry I meant "marked on the PCB".

 

[Echo North]

Hi Mike-Thanks so much for the quick response!  Here are the voltages I measured:

TP 22  @  20:1  --  .69VAC
                        12:1  --  .113
                        8:1    --  .07
                        4:1    --  .056

TP 21  @    20:1  --  -6.83VDC
                        12:1  --    -3.923
                        8:1    --    -2.839
                        4:1  --    -1.927
Thanks!
-Max

Seems good.

With the same conditions, what is your AC at each ratio on the positive side (side without the stripe) of CR2 and CR3.

Mike

 

[Maxman]

Seems good.

With the same conditions, what is your AC at each ratio on the positive side (side without the stripe) of CR2 and CR3.

Mike

I'm getting zero volts AC across each positive side for all ratios.

 

[jgremlin]

Is that with GR turned on? All zeros is normal with GR OFF. But not switched on.

Attack full clockwise.

 

[Maxman]

Attack full clockwise.

Yep the attack is on fully CW.

 

[Maxman]

I can see a small amount of voltage is quickly sent across CR2 and CR3 when I push in the buttons (.5 volts) but the meter quickly rests on Zero VAC

 

[Echo North]

I'm getting zero volts AC across each positive side for all ratios.

Something is wrong in the GR AMP section then.  Go through that box carefully.  Check every trace, component, joint.

Mike

 

[jgremlin]

Ok here's what I've done.
1. Since I ran it for a while with no heat shield on Q6, I ordered replacements and replaced Q6. I know I probably didn't have to, just trying to be thorough.
2. I retouched every trace in the GR control amp section plus any others I could find that looked wonky.
3. Seeing that there are 3 holes where CR10 goes, I pulled out CR10 and ordered a replacement. I then read that the outer holes are what I should use (which is what I had in the first place), installed a replacement 1N914 in outer holes of CR10.

When I powered up and tried to retest volts at tp21/tp22 it seemed like I had some volts going on. But something wasn't right. So I went back to do all the calibrations from scratch. I verified 0.775VAC at the input pins. But the output pins were all over the map as I moved the output knob.

Unmuted the output and sure enough I've now got myself a nice little noise maker. With nothing on the input, I get radio frequency interference type tones through most of the sweep of the output knob. But near the top of the travel of the knob it switches over to an oscillation noise with the frequency going up as I raise the knob more.

Recording of the noise during up/down knob sweep here: https://soundcloud.com/juliet-hotel/1176-noise-1/s-mPZvG

So feeling pretty stupid but puzzled where to look to find the source of the noise.

 

[Echo North]

Ok here's what I've done.
1. Since I ran it for a while with no heat shield on Q6, I ordered replacements and replaced Q6. I know I probably didn't have to, just trying to be thorough.
2. I retouched every trace in the GR control amp section plus any others I could find that looked wonky.
3. Seeing that there are 3 holes where CR10 goes, I pulled out CR10 and ordered a replacement. I then read that the outer holes are what I should use (which is what I had in the first place), installed a replacement 1N914 in outer holes of CR10.

When I powered up and tried to retest volts at tp21/tp22 it seemed like I had some volts going on. But something wasn't right. So I went back to do all the calibrations from scratch. I verified 0.775VAC at the input pins. But the output pins were all over the map as I moved the output knob.

Unmuted the output and sure enough I've now got myself a nice little noise maker. With nothing on the input, I get radio frequency interference type tones through most of the sweep of the output knob. But near the top of the travel of the knob it switches over to an oscillation noise with the frequency going up as I raise the knob more.

Recording of the noise during up/down knob sweep here: https://soundcloud.com/juliet-hotel/1176-noise-1/s-mPZvG

So feeling pretty stupid but puzzled where to look to find the source of the noise.

There are only 2 holes for CR10.  There may be a via close by. That is a small hole that allows a trace on opposite sites of the PCB to connect through the PCB.

Have you done this:

Set your unit to:
Input: 12 O’Clock
Output: 12 O’Clock
Attack: GR OFF
Release: Full CW
Ratio: 20:1
Meter: GR
Signal: Sine 1kHz @ 0dBu

With your DMM measure your AC at the following test points using the chassis as you reference (black probe).

-Input XLR +
-TP1
-TP15
-TP17
-Output Transformer BRN
-Output XLR +

That will tell you where your signal is dying.

Also we offer flat rate repair on those.

Mike

 

[jgremlin]

Configured as indicated in previous post and with 0.775 VAC measured between input XLR+ and XLR- I get the following using chassis as ground.

Input XLR+                          .438VAC
TP1                                    63.9
TP15                                  60.5
TP17                                    5.72
Transformer Brn          59.0
Out XLR+                        55.6

 

[Echo North]

Configured as indicated in previous post and with 0.775 VAC measured between input XLR+ and XLR- I get the following using chassis as ground.

Input XLR+                          .438VAC
TP1                                    63.9
TP15                                  60.5
TP17                                    5.72
Transformer Brn          59.0
Out XLR+                        55.6

You sure you have 60.5VAC at 15 and 5.72VAC at 17?

That's super weird.

 

[jgremlin]

You sure you have 60.5VAC at 15 and 5.72VAC at 17?

That's super weird.

Yep. Just double checked.

 

[Echo North]

1. Check you DC V bias at PAD 18.  Rotate the pot. You should have between 0 VDC and about -2.9VDC.  Set it at the most negative position (about -2.9 VDC).

2. Make sure your GR OFF. Confirm your pad 22 is shorted to ground (chassis).

Try the AC test as described above again. Do you get anything different?

Mike

 

[jgremlin]

1. Check you DC V bias at PAD 18.  Rotate the pot. You should have between 0 VDC and about -2.9VDC.  Set it at the most negative position (about -2.9 VDC).

Ok a few dumb questions.
Is this still with a 1k test tone?
Rotate which pot? R59?

2. Make sure your GR OFF. Confirm your pad 22 is shorted to ground (chassis).

GR is definitely off. How do I confirm tp22 is shorted to ground? Ohms setting?