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

[Echo North]

Would this be affecting the sound quality? I have nothing to compare it to so If it's just a low output I can deal with it. It seems to be working fine but I want it to be the best it can be and will send it in if you think it needs to be looked at.

Thanks!

It's just impossible to troubleshoot on the forum if values are changing, in this case pad 15.  It's either a bad connection or you're overlooking something in the setup/measurement.  Since it sounds like the unit still sounds good and the same as before, I suspect you might just be overlooking something in your set-up...which is super common since there are so many little details.

If you can, see if you're getting about 40dB of gain from the unit.  I don't know you're set-up, so you'll have to figure it out, but basically you want a -40dBu input and in GR OFF with both in/out maxed you should have about 40dB of gain. However, if you're new to this stuff it can be a little tricky.

Mike

 

[Diamondj421]

Something is making intermittent connection. You may need to safely wiggle some stuff in that section and see where the bad connection is.

Mike

Took your advice, wiggled some things around and realized that it was Q12/Q13. The heatshrink around it had loosened. Threw another piece of heat shrink over it, took a hair dryer to it and so far so good (knock on wood)

 

[Echo North]

Took your advice, wiggled some things around and realized that it was Q12/Q13. The heatshrink around it had loosened. Threw another piece of heat shrink over it, took a hair dryer to it and so far so good (knock on wood)

The heat shrink shouldn't cause it not to work, it just helps them share the same temp and track better.  It's more likely there is a bad joint there, or the original heat shrink was causing two leads to touch creating a short.

Mike

 

[Diamondj421]

The heat shrink shouldn't cause it not to work, it just helps them share the same temp and track better.  It's more likely there is a bad joint there, or the original heat shrink was causing two leads to touch creating a short.

Mike

You’re correct. Woke up today and the problem returned. Its definitely Q12 or Q13 though. Only problem is I don’t know how to fix it. I had to send it in for you to look at because I tried removing the old FETs (for some stupid reason) and destroyed the board around there. The leads on the FETs are too short for me to try connecting with jumpers. Any suggestions?

 

[Echo North]

You’re correct. Woke up today and the problem returned. Its definitely Q12 or Q13 though. Only problem is I don’t know how to fix it. I had to send it in for you to look at because I tried removing the old FETs (for some stupid reason) and destroyed the board around there. The leads on the FETs are too short for me to try connecting with jumpers. Any suggestions?

If you look at the top and bottom of the board, you'll see the traces that go from each Q12/Q13 pad to something else.  You need to prob the pads connected by that trace with your ohm meter and find out which pad is lifted (or trace is broken).  Once you identify it...we can figure out how to fix it.

Mike

 

[frenkonio]

I would triple check all of your capacitors values, particularly the small blue ones in the amp sections.

Report back.

Mike

Hey Mike sorry for the delay in the answer. I triple checked the blue ones, they're all correct. Same for the others. Where could I go next?

 

[Echo North]

Hey Mike sorry for the delay in the answer. I triple checked the blue ones, they're all correct. Same for the others. Where could I go next?

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

Look at step 2, amp stages.  Do it with like a 10K test tone and record your values, then do it agin with like a 200hz test tone. Then we can locate the stage where you lose your bass.

Mike

 

[frenkonio]

So, with an input of 0.775mVAC (0dBu) @1khz these are the results:

TP1: 0.110VAC
TP15: 1.80VAC
TP17: 0.260VAC
OUT TF: 4.71VAC

Doing the same measurements only changing frequency on the tone generator gives these results:

10Khz

TP1: 0.061VAC
TP15: 1.01VAC
TP17: 0.260VAC
OUT TF: 2.70VAC

100Hz

TP1: 0.110VAC
TP15: 1.80VAC
TP17: 0.260VAC
OUT TF: 4.70VAC

 

[Echo North]

So, with an input of 0.775mVAC (0dBu) @1khz these are the results:

TP1: 0.110VAC
TP15: 1.80VAC
TP17: 0.260VAC
OUT TF: 4.71VAC

Doing the same measurements only changing frequency on the tone generator gives these results:

10Khz

TP1: 0.061VAC
TP15: 1.01VAC
TP17: 0.260VAC
OUT TF: 2.70VAC

100Hz

TP1: 0.110VAC
TP15: 1.80VAC
TP17: 0.260VAC
OUT TF: 4.70VAC

You said you have no bass or no top end?  Looks like you have a high frequency roll off?

 

[frenkonio]

No bass frequencies

 

[Echo North]

You said you have no bass or no top end?  Looks like you have a high frequency roll off?

Do you have those 100hZ and 10K labels reversed?

 

[frenkonio]

Nope, from what I remember they're correct

 

[Echo North]

Nope, from what I remember they're correct

Well with that you have no HF. See how everything is lower under the 10K label?

Either way they should all be the same.  Could be something wrong with the input transformer, but honestly in thousands of transformers I've only seen freq response issues in like 2 units.  So it absolutely could be the tx, but I'm hesitant because your measurements are opposite to what you are hearing.

I would re-measure. If you get the same results, something is up with your measurement set-up.  If they are indeed the opposite way, confirm that R4 is 270Ω and not 270K or something.  Also confirm the value of R5, C22, C1.

If that is fine let me know. You might have a bad tx.

Mike

 

[SunkenCity]

Man I finished my second fet/rack a week ago and it calibrated the way it should have but today It didn't seem right.  I was setting it up for the stereo link on the drum buss but it was putting out a hotter signal than my other unit by alot.

I disconnected the link cable  and turned off the links but the level difference was still out of wack. I tried matching them but what they were compressing and putting out was completely different parts of the source. One unit was lowend information and the other highend.

I fed both units a 1k tone at 1.227 Vac  and switched the units to +4 metering input:24 output:24 4:1  attack fully counterclock wise but not off release fully clockwise. one unit shows 1/2 a db down from 0 Vu and the other shows +3 Vu with the exact same settings.

tweaking the unit to get it to match the level of the other with the output at 24, the input knob needs a bit more than a quarter turn lower from 24 to the dot between 36 and 48.

If I try to adjust the output with the input at 24 it needs 3 dots down.

Any ideas?





I've switched cables and re-calibrated both units the weird one twice. 

 

[Potato Cakes]

Is the problem the same when compressor is off (attack knob turned all the way down)? Aside from a bad solder joint or misplaced component, it could be the FETs in the hotter unit aren't being placed in inductance per the calibration procedure.

Thanks!

Paul

 

[SunkenCity]

When I turn the attack fully counterclock wise to the off position the needle on one unit jumps off scale fully to the right.  The other hot unit the needle is already fully to the right.

the hot unit if I back off the input to get the signal to 0vu then turn off the attack it doesn't change at all. If I back off the output to get the signal to 0 on the meter jumps fully to the right.

going thru the functions they have the same behavior meterwise when the hotter unit has it's output knob at the mark between 30 and 36. the input and output settings on the non hot unit are 24. The real problem is they are compressing  different parts of the same source. I tried just running  snare though them and can't get them to  act the same with  and without the link.

 

[Echo North]

When I turn the attack fully counterclock wise to the off position the needle on one unit jumps off scale fully to the right.  The other hot unit the needle is already fully to the right.

the hot unit if I back off the input to get the signal to 0vu then turn off the attack it doesn't change at all. If I back off the output to get the signal to 0 on the meter jumps fully to the right.

going thru the functions they have the same behavior meterwise when the hotter unit has it's output knob at the mark between 30 and 36. the input and output settings on the non hot unit are 24. The real problem is they are compressing  different parts of the same source. I tried just running  snare though them and can't get them to  act the same with  and without the link.

Did you buy them together?  Those output pots are 250K pots with a 20% tolerance.

Put them both at center and measure the resistance between the middle pin and on of the side pins for each unit.  See how off they are.  We can always send you a matching one.

Mike

 

[SunkenCity]

Originally yes then I sent them to you for repairs and you sent back fresh boards.  I'll measure the output pots but would that cause the units to be compressing  different frequencies of the the same signal and can't be adjusted to function the same?

 

[Echo North]

Originally yes then I sent them to you for repairs and you sent back fresh boards.  I'll measure the output pots but would that cause the units to be compressing  different frequencies of the the same signal and can't be adjusted to function the same?

I can follow your posts.

1. So this is all un-linked correct?
2. Is the unit you got repaired by us still working correctly?

Is this really just an issue with the one you build just now?

Mike

 

[SunkenCity]

Yes un-linked.

I'm really not sure which one is working correctly they both calibrate the way they should and compress.

The one you built is focusing on the top end on the signal.

The one I built has hotter output and is focusing on the low end on the signal.