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

[Echo North]

You're measuring for AC there.

 

[Deejsirois]

You're measuring for AC there.

Right    lol

20:1 = 4.15  VAC
12:1 =2.06
8:1 =1.37
4:1=0.68

 

[Echo North]

Right    lol

20:1 = 4.15  VAC
12:1 =2.06
8:1 =1.37
4:1=0.68

Everything seems good. Super weird. 

- One of your release pot legs detach?  Happens pretty easily. 
- When you turn on GR how does your Q1 Gate voltage change?  From x to x?

Logging off for the evening....

 

[Deejsirois]

Everything seems good. Super weird. 

- One of your release pot legs detach?  Happens pretty easily. 
- When you turn on GR how does your Q1 Gate voltage change?  From x to x?

Logging off for the evening....

I will check the pot legs tomorrow. GR at Q1 gate goes from -1.276 to 0.364 when GR turned on...0.511 Fully CW

Thanks Mike!

 

[Echo North]

I will check the pot legs tomorrow. GR at Q1 gate goes from -1.276 to 0.364 when GR turned on...0.511 Fully CW

Thanks Mike!

So under the normal test setup, GR ON.  What is your AC and DC on either side of CR2 and CR3?

 

[Deejsirois]

So under the normal test setup, GR ON.  What is your AC and DC on either side of CR2 and CR3?

Input: 12 O’Clock
Output: 12 O’Clock
Attack: GR ON (fully CW)
Release: Full CW
Meter: GR
Signal: Sine 1kHz @ 0dBu (0.775 VAC across input + and -)

CR2                                                              CR3
0.699 and 0.0623 VAC              0.71  and  0.0625 VAC
-1.761 and  -1.41 VDC                --1.763 and -1.41 VDC 

Should I replace CR2 and CR3?

 

[ghiatorino]

Hi there, hi Mike
i am experiencing almost the same issue as Deejsirois.
I just finished a rev A build.
Units is calibrated and sounds as good as it should,
but..
when GR is engaged i have loads of distortion. Compression works, but sound is awful. Furthermore it seems that it's not catching transients as it should.
double checked usual stuff and found no build errors.
I have another Rev A. Using 5457 for both.
Looking at the output of the 2 units on a spectrum analyzer reveals that the spectrum is identical, except when engaging GR.
New units exhibits a high level of distortion over all the ratios. GR amount is the same.

Traced down the signal with a scope and i found a difference in the GR amp. The new unit has a clipped AC signal, right before entering CR3/CR4

I replaced all the GR amp transistors (using 2n5088) with no result. DC Voltages are correct. components value too.

I replaced  the R46 feedback resistor with a 50k pot and found a place where the same control signal passes undistorted. But only result was almost no compression.

Anybody experienced something like this?
Thanks for your time
Rino

 

[forgotteng]

I managed to put some caps in the wrong place and need to get a replacement but I am struggling to find them in stock in a lower quantity. Is there an exceptable replacement for the FK28C0G1H221J cap?

 

[Echo North]

Input: 12 O’Clock
Output: 12 O’Clock
Attack: GR ON (fully CW)
Release: Full CW
Meter: GR
Signal: Sine 1kHz @ 0dBu (0.775 VAC across input + and -)

CR2                                                              CR3
0.699 and 0.0623 VAC              0.71  and  0.0625 VAC
-1.761 and  -1.41 VDC                --1.763 and -1.41 VDC 

Should I replace CR2 and CR3?

Is this in 20:1?  Make sure you're in 20:1....re-check those DC measurements.

 

[Echo North]

Hi there, hi Mike
i am experiencing almost the same issue as Deejsirois.
I just finished a rev A build.
Units is calibrated and sounds as good as it should,
but..
when GR is engaged i have loads of distortion. Compression works, but sound is awful. Furthermore it seems that it's not catching transients as it should.
double checked usual stuff and found no build errors.
I have another Rev A. Using 5457 for both.
Looking at the output of the 2 units on a spectrum analyzer reveals that the spectrum is identical, except when engaging GR.
New units exhibits a high level of distortion over all the ratios. GR amount is the same.

Traced down the signal with a scope and i found a difference in the GR amp. The new unit has a clipped AC signal, right before entering CR3/CR4

I replaced all the GR amp transistors (using 2n5088) with no result. DC Voltages are correct. components value too.

I replaced  the R46 feedback resistor with a 50k pot and found a place where the same control signal passes undistorted. But only result was almost no compression.

Anybody experienced something like this?
Thanks for your time
Rino

The 5088's and 3707's that come with kit have different footprints. Did you just direct swap them?

 

[Echo North]

I managed to put some caps in the wrong place and need to get a replacement but I am struggling to find them in stock in a lower quantity. Is there an exceptable replacement for the FK28C0G1H221J cap?

We can send you some. Just fill out a missing parts form.

 

[Deejsirois]

Is this in 20:1?  Make sure you're in 20:1....re-check those DC measurements.

My bad. At 20:1

-5.86 and -1.43 for CR2

-5.86 and -1.429 for CR3

 

[Echo North]

My bad. At 20:1

-5.86 and -1.43 for CR2

-5.86 and -1.429 for CR3

Everything seems right.  You're using all of your own parts right?  I'd triple check the stuff you're using has the same footprints etc. 
Specifically transistors which all have different footprints.

We generally don't service non-stock builds but I could probably look at it.

Mike

 

[Deejsirois]

Everything seems right.  You're using all of your own parts right?  I'd triple check the stuff you're using has the same footprints etc. 
Specifically transistors which all have different footprints.

We generally don't service non-stock builds but I could probably look at it.

Mike

This build is the stock build...from the mouser cart from your website. The only substitutions I have made were Elna 100uf Caps. The transistors are the ones from the mouser cart.

 

[Echo North]

This build is the stock build...from the mouser cart from your website. The only substitutions I have made were Elna 100uf Caps. The transistors are the ones from the mouser cart.

I'm just not seeing any weird voltages.  You have your own enclosure right?  Those 3 mount LBrackets on the back are part of the grounding scheme and they need to be in there.

I'm stumped.

 

[Deejsirois]

I'm just not seeing any weird voltages.  You have your own enclosure right?  Those 3 mount LBrackets on the back are part of the grounding scheme and they need to be in there.

I'm stumped.

Yep, my own enclosure that works for all the other units except this one lol. I did my best to keep it right on par with yours to avoid headaches. I have even swapped this board into a different enclosure that I knew worked with Rev D and Rev F builds. The only thing I have NOT tried is switching out the release and attack assembly. Maybe I will give that a shot. At least I can eliminate that.

 

[Echo North]

Yep, my own enclosure that works for all the other units except this one lol. I did my best to keep it right on par with yours to avoid headaches. I have even swapped this board into a different enclosure that I knew worked with Rev D and Rev F builds. The only thing I have NOT tried is switching out the release and attack assembly. Maybe I will give that a shot. At least I can eliminate that.

Ya that's key to troubleshooting.  Swap out as much stuff to try and isolate the problem area.  Just not seeing anything weird.  Your Gate voltage swings super positive with compression, but that's a super hard place to measure because it's so high impedance and the meter is in parallel with it. 

Other than that we have a repair service, you'd just be sending in the PCBs.

Mike

 

[Deejsirois]

Ya that's key to troubleshooting.  Swap out as much stuff to try and isolate the problem area.  Just not seeing anything weird.  Your Gate voltage swings super positive with compression, but that's a super hard place to measure because it's so high impedance and the meter is in parallel with it. 

Other than that we have a repair service, you'd just be sending in the PCBs.

Mike

Time to CELEBRATE!!! Sweet Jesus, the REV A is working!!! Woohoo, I am not crazy and nor is Mike! Looks like my attack pot is faulty. All the leads are still connected, but that was the culprit. Man, that was driving me crazy. Thanks, Mike, for getting me on the right path!

 

[Echo North]

Time to CELEBRATE!!! Sweet Jesus, the REV A is working!!! Woohoo, I am not crazy and nor is Mike! Looks like my attack pot is faulty. All the leads are still connected, but that was the culprit. Man, that was driving me crazy. Thanks, Mike, for getting me on the right path!

Nice!

 

[Deejsirois]

Time to CELEBRATE!!! Sweet Jesus, the REV A is working!!! Woohoo, I am not crazy and nor is Mike! Looks like my attack pot is faulty. All the leads are still connected, but that was the culprit. Man, that was driving me crazy. Thanks, Mike, for getting me on the right path!

I guess I should have post-poned my victory dance. Distortion is back. Swapped out my ratio assembly, no luck. Swapped out the Orange Drop caps in the GR section because they were making noise when I tapped them...no luck. Swapped out the FETs...no luck. I already replaced the transistors in that section, but I will replace them one more time. If that doesn't work, then I think I will concede and pull the components out and build another REV D...this thing has been ridiculous. It was working perfectly fine for 2 days. Sometimes you just shake your head.