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

[frenkonio]

outside if it's disconnected.

It measures 16 ohm on one side and 52 ohm on the other one. I got one new inside a kit I still didn't built and measures the same. I'm going nuts with this ******* hpf on signal..

 

[Echo North]

It measures 16 ohm on one side and 52 ohm on the other one. I got one new inside a kit I still didn't built and measures the same. I'm going nuts with this f**king hpf on signal..

Are you sure you don't have a cable connection out of phase?

Did you remove the input?  Can you put the one from your other kit in and see if it fixes the issue?

Mike

 

[frenkonio]

Are you sure you don't have a cable connection out of phase?

Did you remove the input?  Can you put the one from your other kit in and see if it fixes the issue?

Mike

The cable seems ok visibly (you obviously mean the long black one inside the compressor, right?). I would try the other input trafo. Could it be something related to output trafo?

 

[Echo North]

The cable seems ok visibly (you obviously mean the long black one inside the compressor, right?). I would try the other input trafo. Could it be something related to output trafo?

No I mean your XLR in and out and patchbay  if you're using one.

Seems like your issue was happening around the input.  Try the other input you have then report back. Make sure the output is wired correctly.

Again bad transformers are VERY rare, almost never the causing the issue.  But possible, and many years ago I had a customer with this issue and it ended up being the input.

Mike

 

[frenkonio]

No I mean your XLR in and out and patchbay  if you're using one.

Seems like your issue was happening around the input.  Try the other input you have then report back. Make sure the output is wired correctly.

Again bad transformers are VERY rare, almost never the causing the issue.  But possible, and many years ago I had a customer with this issue and it ended up being the input.

Mike

Nope, the XLR cable is the same I used every time. And I tried it again with another REV. A and it works OK. The output trafo is wired ok too. I will report back after swapping the input transformer.

 

[Echo North]

Nope, the XLR cable is the same I used every time. And I tried it again with another REV. A and it works OK. The output trafo is wired ok too. I will report back after swapping the input transformer.

Sounds good.

 

[Deejsirois]

Project: REV A  v1.15

Issue: Qbias calibration. Cannot get 1 dB drop. Can't get any drop.

Audio passes (and sounds great btw). If I turn the Attack on, I gradually get more distortion from 4:1-20:1 (greatest distortion). I have read a bunch of other posts and your responses, so I did some testing.  The questions are from you Mike, albeit to other folk.

Try this:

Input/output: Mid Way
release/attack: full CW
Ratio: 20
Meter: GR

Feed and confirm a 0.775VAC 1K signal measuring between input XLR + and -.

No measure these TPs using chassis as your common.

TP22 - Measure for AC for all ratios and list them.
TP21 - Measure for DC for all ratios and list them.


Answer:

TP22- VAC TP21-VDC
0.556@20 -5.91 @20
0.365 @12 -3.39 @12
0.294 @8 -2.61 @8
0.217 @4 -1.81 @4


What is your V AC at pad 15 under the same conditions?

Answer:

TP15 VAC
0.946 @20
1.116 @12
1.378 @8
1.827 @4

TP15 with GR off = 3.15 VAC

What is it at the output XLR pin 2?

Answer:

8.05 VAC


With the FET out, what is your DC at the GATE pad of Q1 as you rotate the qbias from end to end?

Answer:

Q1 = -0.828 (Full CCW) and -1.428 (Full CW)


What is your DC range at pad 18 rotating the pot?

Answer:

-1.0 VDC (Full CCW) and -1.744 VDC (Full CW)



Voltages:

Q2: D= 8.44V ; G= 2.88V ; S= 4.61V

Q3: C= 14.95V ; B= 8.46 ; E= 7.87

Q4: D= 14.69 ; G= 2.33 ; S= 4.42

Q5: C= 26.47 ; B= 3.41 ; E= 2.87

Q6; C= 28.28 ; B= 2.872 ; E= 2.334



Q7: C= 15.20 ; B= 4.71 ; E= 4.16

Q8: C= 31.02 ; B= 15.20 ; E= 14.58

Q9: C= 17.98 ; B= 3.533 ; E= 2.966

Q10 C= 31.03 ; B= 17.98 ; E= 17.41



Q11: D= 26.25 ; G= -0.938 ; S= -9.14

Q12: C= 26.23 ; B= -9.14 ; E= -1.59

Q13: C= 24.67 ; B= -0.809 ; E= -1.40

 

[Echo North]

Project: REV A  v1.15

Issue: Qbias calibration. Cannot get 1 dB drop. Can't get any drop.

Audio passes (and sounds great btw). If I turn the Attack on, I gradually get more distortion from 4:1-20:1 (greatest distortion). I have read a bunch of other posts and your responses, so I did some testing.  The questions are from you Mike, albeit to other folk.

Try this:

Input/output: Mid Way
release/attack: full CW
Ratio: 20
Meter: GR

Feed and confirm a 0.775VAC 1K signal measuring between input XLR + and -.

No measure these TPs using chassis as your common.

TP22 - Measure for AC for all ratios and list them.
TP21 - Measure for DC for all ratios and list them.


Answer:

TP22- VAC TP21-VDC
0.556@20 -5.91 @20
0.365 @12 -3.39 @12
0.294 @8 -2.61 @8
0.217 @4 -1.81 @4


What is your V AC at pad 15 under the same conditions?

Answer:

TP15 VAC
0.946 @20
1.116 @12
1.378 @8
1.827 @4

TP15 with GR off = 3.15 VAC

What is it at the output XLR pin 2?

Answer:

8.05 VAC


With the FET out, what is your DC at the GATE pad of Q1 as you rotate the qbias from end to end?

Answer:

Q1 = -0.828 (Full CCW) and -1.428 (Full CW)


What is your DC range at pad 18 rotating the pot?

Answer:

-1.0 VDC (Full CCW) and -1.744 VDC (Full CW)



Voltages:

Q2: D= 8.44V ; G= 2.88V ; S= 4.61V

Q3: C= 14.95V ; B= 8.46 ; E= 7.87

Q4: D= 14.69 ; G= 2.33 ; S= 4.42

Q5: C= 26.47 ; B= 3.41 ; E= 2.87

Q6; C= 28.28 ; B= 2.872 ; E= 2.334



Q7: C= 15.20 ; B= 4.71 ; E= 4.16

Q8: C= 31.02 ; B= 15.20 ; E= 14.58

Q9: C= 17.98 ; B= 3.533 ; E= 2.966

Q10 C= 31.03 ; B= 17.98 ; E= 17.41



Q11: D= 26.25 ; G= -0.938 ; S= -9.14

Q12: C= 26.23 ; B= -9.14 ; E= -1.59

Q13: C= 24.67 ; B= -0.809 ; E= -1.40

Maybe a bad FET.  You got another you can try?  Or try putting Q1 in there and see if you can get the drop?

Mike

 

[Deejsirois]

Hey Mike,

Thanks for the quick reply. I have tried 3 so far, then I got thinking it must be something else. I have about 15 I can try, though.

Qbias affects my meter, but not my output. I have swapped FETs, tried several FETs. All of them affect the meter in Q11, but nothing dropping at output. Scratching my head on this for a while now.

 

[Echo North]

Hey Mike,

Thanks for the quick reply. I have tried 3 so far, then I got thinking it must be something else. I have about 15 I can try, though.

Are you just trying random 5457's?  The Rev A requires that Q1/11 very tightly spec'd in a small range.

Mike

 

[Deejsirois]

Yes, random. What's the tolerance on matching Q1/Q11 FETs for the REV A?

 

[Echo North]

Yes, random. What's the tolerance on matching Q1/Q11 FETs for the REV A?

They have to be matched yes, but it's more than that.  If your GATE voltage is limited to -1 to -1.75 VDC or whatever it is, you need a FET that will reach a 1dB drop in that bias zone.  It's a pain in the ass, we have special "Rev A" FETs here.

Mike

 

[Deejsirois]

I'll send you an email and get you to ship me a few. Thought I was going crazy.

 

[Echo North]

I'll send you an email and get you to ship me a few. Thought I was going crazy.

That's most likely what it is, based on the info you posted.

 

[Deejsirois]

I found a couple FETs that worked for the full calibration process, but the unit sounds terrible when the compressor is engaged...heavily distorted even at  almost no gain reduction. It's definitely clipping. I am assuming I should be looking in the GR Control amp, or do you still think this could be FET related?

 

[Echo North]

I found a couple FETs that worked for the full calibration process, but the unit sounds terrible when the compressor is engaged...heavily distorted even at  almost no gain reduction. It's definitely clipping. I am assuming I should be looking in the GR Control amp, or do you still think this could be FET related?

What brand are the FETs?  If they aren't Fairchild, I would suspect the FETs. I found non-FC FETs to be very different in their curves.

 

[Deejsirois]

They are Fairchilds. The other quirky thing is that the attack and release have almost no effect on the sound. I checked the attack/release pcb for continuity and resistance, shorts, flux, soldering, component values and nothing is off. That's why my brain just keeps going back to the GR control amp section, but  I have quadruple checked components and every test my brain can come up with. Thoughts?

 

[Echo North]

They are Fairchilds. The other quirky thing is that the attack and release have almost no effect on the sound. I checked the attack/release pcb for continuity and resistance, shorts, flux, soldering, component values and nothing is off. That's why my brain just keeps going back to the GR control amp section, but  I have quadruple checked components and every test my brain can come up with. Thoughts?

The GR amp really just converts your AC to a DC voltage.  Generally either it does that or doesn't.

-Check to see if your GR amp output is off. #4 here:
https://www.hairballaudio.com/blog/resources/post/fetrack-troubleshooting-guide

If somehow you had a transistor that was saturating I suppose you could see what you're seeing. Also make sure you don't have a 4.7K, 47K, 470K mix up in that section.

-Are you sure they are legit Fairchild's?  They haven't made them in years, there are a million counterfeits out there.

-Check to see if CR2/3 is damaged.

FYI, I'll be offline for a few days.

Mike

 

[Deejsirois]

The GR amp really just converts your AC to a DC voltage.  Generally either it does that or doesn't.

-Check to see if your GR amp output is off. #4 here:
https://www.hairballaudio.com/blog/resources/post/fetrack-troubleshooting-guide

If somehow you had a transistor that was saturating I suppose you could see what you're seeing. Also make sure you don't have a 4.7K, 47K, 470K mix up in that section.

-Are you sure they are legit Fairchild's?  They haven't made them in years, there are a million counterfeits out there.

-Check to see if CR2/3 is damaged.

FYI, I'll be offline for a few days.

Mike

Thanks again, Mike, for the response. As for the genuineness of the Fairchild FETs, I don't know. Starting to think they are likely not genuine at this point. I did all the stages in the troubleshooting guide for kicks and to be thorough.  I am a bit hot across the board on #4 GR Control Amp Output specs. 4.269 vs 3.63 (20:1) ,  2.11 vs 1.78  (12:1)  , 1.39 v 1.2  (8:1), and  0.686 vs 0.650 (4:1)

CR2/3 are good and working as expected.

No mixup with resistors either. I have a method so resistor mixup is not possible.
1. I organize the resistors from lowest resistance to greatest before I start.
2. I start with the lowest resistance resistor using the build map for location and DMM for value confirmation
3. Once resistor is in place, I double check location and value.
4. I scan through the build map for the same value and repeat.
It takes a little longer but I have never misplaced a resistor yet (because this method basically makes it impossible). But just to be safe, I reconfirmed all resistors again today and they are right.

So, ya, either I am overloading a transistor or the FETs are screwing with me...or both. I will place an order soon to eliminate the FETs.

Have a great weekend!

 

[Echo North]

Thanks again, Mike, for the response. As for the genuineness of the Fairchild FETs, I don't know. Starting to think they are likely not genuine at this point. I did all the stages in the troubleshooting guide for kicks and to be thorough.  I am a bit hot across the board on #4 GR Control Amp Output specs. 4.269 vs 3.63 (20:1) ,  2.11 vs 1.78  (12:1)  , 1.39 v 1.2  (8:1), and  0.686 vs 0.650 (4:1)

CR2/3 are good and working as expected.

No mixup with resistors either. I have a method so resistor mixup is not possible.
1. I organize the resistors from lowest resistance to greatest before I start.
2. I start with the lowest resistance resistor using the build map for location and DMM for value confirmation
3. Once resistor is in place, I double check location and value.
4. I scan through the build map for the same value and repeat.
It takes a little longer but I have never misplaced a resistor yet (because this method basically makes it impossible). But just to be safe, I reconfirmed all resistors again today and they are right.

So, ya, either I am overloading a transistor or the FETs are screwing with me...or both. I will place an order soon to eliminate the FETs.

Have a great weekend!

Those GR amp outputs look fine to me.  I would definitely get proper FETs, I'm guessing you have knock-offs.

Mike