[BUILD] FET/500 Official Support Thread

[Echo North]

Hi Mike, yes, I saw pulsing on diode 4 of the main pcb. I've also triple checked that the Qs on the meter PCB and that the 2 regulators and one transistor are correctly placed.
I will try to probe the board again but please let me know if pulsing on diode 4 is strange and if you have any idea about that.
Thanks

Super weird.

D4 is just a protection diode for the main rail.  It should not be pulsing AC or DC.

 

[ubermetal]

It was Q6! I replaced it, and it's running perfectly again. Thanks a million, Mike!

No it shouldn't fail with the supplied sink.  More likely a bad part.  If it's even Q6.

Mike

 

[Echo North]

It was Q6! I replaced it, and it's running perfectly again. Thanks a million, Mike!

Nice.

 

[warmtape]

Super weird.

D4 is just a protection diode for the main rail.  It should not be pulsing AC or DC.

Another very strange aspect is that if, while the unit is turned on, I apply pressure with my finger to the meter board directly on top of the 1/8" jack from the top of the board (so the pressure is being applied not to the jack itself but to the underside of the jack where it's soldered (since the 1/8" jack is soldered from above as opposed to the rest of the components on the board)) then the audio does not pulse but seems to go through smoothly. Once I stop applying pressure there the pulsing starts again. The soldering there seems fine. I noticed this entirely by accident, but does this happen to shed any light on what might be happening?

 

[Echo North]

Another very strange aspect is that if, while the unit is turned on, I apply pressure with my finger to the meter board directly on top of the 1/8" jack from the top of the board (so the pressure is being applied not to the jack itself but to the underside of the jack where it's soldered (since the 1/8" jack is soldered from above as opposed to the rest of the components on the board)) then the audio does not pulse but seems to go through smoothly. Once I stop applying pressure there the pulsing starts again. The soldering there seems fine. I noticed this entirely by accident, but does this happen to shed any light on what might be happening?

You're probably just grounding the noise.

 

[emmanuel_szczygiel]

Hi Mike,

I just finished my FET/500 Rev D but i made some mistakes during the building which prevents it to works well. I reversed R540 and R086 and on the meter board i reversed VR1 and VR2  :-\

After putting them back in the right place here are the symptoms when I send a 1kHz sin wave (0.775 VAC) : I hear the signal BUT the volume is low with some noise. When INPUT knob and OUTPUT knob are fully clockwise I measure about 0.65 VAC at the output of the compressor. Furthermore when I turn Q Bias nothing happens.

Can you tell me which components I probably damaged by inverting the trimmers?

Thank you in advance for your precious help

Manu

 

[Echo North]

Hi Mike,

I just finished my FET/500 Rev D but i made some mistakes during the building which prevents it to works well. I reversed R540 and R086 and on the meter board i reversed VR1 and VR2  :-\

After putting them back in the right place here are the symptoms when I send a 1kHz sin wave (0.775 VAC) : I hear the signal BUT the volume is low with some noise. When INPUT knob and OUTPUT knob are fully clockwise I measure about 0.65 VAC at the output of the compressor. Furthermore when I turn Q Bias nothing happens.

Can you tell me which components I probably damaged by inverting the trimmers?

Thank you in advance for your precious help

Manu

It's highly unlikely anything is damaged unless you damaged a pad or trace removing them.  It sounds more like your gain amp stage just isn't working. Or possibly your qbias.  Do you have away to probe the circuit while it powered? Like an extender jig, or chassis big enough that you can remove the slots on the right and get in with a probe?

 

[emmanuel_szczygiel]

It's highly unlikely anything is damaged unless you damaged a pad or trace removing them.  It sounds more like your gain amp stage just isn't working. Or possibly your qbias.  Do you have away to probe the circuit while it powered? Like an extender jig, or chassis big enough that you can remove the slots on the right and get in with a probe?

Thanks for your answser Mike.
Yes I can probe the circuit while it powered. Are there any tests points to identify where the problem comes from?

 

[Echo North]

Thanks for your answser Mike.
Yes I can probe the circuit while it powered. Are there any tests points to identify where the problem comes from?

For all measurements, use the positive terminal of D4 for your GND reference.

1. Measure your Q1 DC V at the gate...what is the most negative you can get it?
2. Measure your AC V with a 1KHz 0dB signal at C7 (either pad) and output transformer brown lead. Control set mid way, GR off.

Mike

 

[Echo North]

Hi Mike!

I built 2 units of 500/Rev D. So far so good... It's working properly, but for 2 things.

1st is the VU meter... I can't get to set -10 on the calibration process... The VR2 almost does nothing to the VU behavior...

Likely something on the meter PCB.  Swap the two meter PCBs and see if the issue follows the meter PCB. If so you'll need to go through and check every component for value and orientation and re-dlow and suspect solder joints.

The other thing is about the stereo link... when I plug the p2 cable in both units, one of the units reacts really weird. GR meter gets pinned to -9 varying a lil bit and it acts very weird, not properly. Any ideas?

Also, I kind of didn't understand how it works... It sums both sidechains? Or it's about the settings I do at one of the units that controls the other one?
Sorry for the newbie question... But it'd help me a lot to clarify this!

I'll come back with pics of the st link issue and maybe upload a video of the calibration thing...

Thanks very much!

I wouldn't worry about it until you can get the one unit properly calibrated.  This issue is probably caused by the first issue.  We're the FET'S in both units matched with each other?

Yes they are summed...your release will be doubled so you can set one to super fast and the other as needed. Set the rest of the controls the same and then trim them to match GR and output level...they'll be a little off because of tolerance.

Thanks,

Mike

 

[guismarquesrj]

Likely something on the meter PCB.  Swap the two meter PCBs and see if the issue follows the meter PCB. If so you'll need to go through and check every component for value and orientation and re-dlow and suspect solder joints.

I wouldn't worry about it until you can get the one unit properly calibrated.  This issue is probably caused by the first issue.  We're the FET'S in both units matched with each other?

Yes they are summed...your release will be doubled so you can set one to super fast and the other as needed. Set the rest of the controls the same and then trim them to match GR and output level...they'll be a little off because of tolerance.

Thanks,

Mike

Gonna test it tonight (here in Brazil!) and get back to you asap...

About the matched transistor, I think yes, as I bought 2 units together and I remember it was labeled "matched" or something like that....

but just to be sure, what transistor are u talking about? the (Q200) 2n5088 on the meter board?

Thanks VERY MUCH for the support, Mike

 

[Echo North]

Gonna test it tonight (here in Brazil!) and get back to you asap...

About the matched transistor, I think yes, as I bought 2 units together and I remember it was labeled "matched" or something like that....

but just to be sure, what transistor are u talking about? the (Q200) 2n5088 on the meter board?

Thanks VERY MUCH for the support, Mike

I was talking about the 2N5457's Q1/Q11 on both units should be 4 way matched.

 

[emmanuel_szczygiel]

Hi Mike,

While it's powered, here are my results :
Between D4 and Q1(gate) : -1.33DCV (this value doesn't change)

With 1kHz signal, control set mid way, GR off :
Between D4 and C7 : 0.014ACV
Between D4 and brown lead : 0.31ACV

Thanks,
Manu

For all measurements, use the positive terminal of D4 for your GND reference.

1. Measure your Q1 DC V at the gate...what is the most negative you can get it?
2. Measure your AC V with a 1KHz 0dB signal at C7 (either pad) and output transformer brown lead. Control set mid way, GR off.

Mike

 

[Echo North]

Hi Mike,

While it's powered, here are my results :
Between D4 and Q1(gate) : -1.33DCV (this value doesn't change)

With 1kHz signal, control set mid way, GR off :
Between D4 and C7 : 0.014ACV
Between D4 and brown lead : 0.31ACV

Thanks,
Manu

Carefully remove Q1, set it aside.

Do you pass signal now?

Mike

 

[emmanuel_szczygiel]

Hi Mike!
Good news, I finally discovered that one of my audio cables that I used for calibration was damaged!
So, I started the calibration again, (the amplification seems ok) BUT other problems appeared...
- Q-bias does not react when I turn it (as much on the output voltage as on the leds).
- The led220 "SLAM" is constantly on, even when the bypass is engaged.
- Led211 to led219 reacted in a strange way during the beginning of calibration.

My hypothesis comes from the TL071 which controls this series of LEDs (211-220). Indeed, I had indicated that I had reversed R540 and R86, after that Q11 was replaced because it was damaged. The sensitive TL071 could also be affected by the inversion of the trimmers. What do you think?

Let me know
Many thanks (and Merry Christmas!)
Manu

Carefully remove Q1, set it aside.

Do you pass signal now?

Mike

 

[mcrowe]

I've managed to clear up most of the issues I've had with my FET/500 build, but the GR meter is still flummoxing me. The slam LED stays lit all the time, and the -22 LED also stays very faintly lit all the time. The meter doesn't seem to react to program material. When I apply power, the GR meter goes up and down through its full range a couple of times very quickly, so the LEDs are working, at least. I've checked for continuity in the areas around IC204 as well as around IC1 on the main board, and everything seems OK. Can you offer any advice?

 

[Echo North]

I've managed to clear up most of the issues I've had with my FET/500 build, but the GR meter is still flummoxing me. The slam LED stays lit all the time, and the -22 LED also stays very faintly lit all the time. The meter doesn't seem to react to program material. When I apply power, the GR meter goes up and down through its full range a couple of times very quickly, so the LEDs are working, at least. I've checked for continuity in the areas around IC204 as well as around IC1 on the main board, and everything seems OK. Can you offer any advice?

Make sure the IC on the main board is correct. It should be a 071 not 072.  We had a few kits ship with 072's.

Mike

 

[mcrowe]

The IC is an 071. I just put the meter on it and I'm showing 15VDC on the pin carrying the VU signal and about 13VDC on the pin carrying the GR signal. Is that expected?

 

[emmanuel_szczygiel]

Hello Mike,
Did you see my last message? (Below here)
Thanks

Hi Mike!
Good news, I finally discovered that one of my audio cables that I used for calibration was damaged!
So, I started the calibration again, (the amplification seems ok) BUT other problems appeared...
- Q-bias does not react when I turn it (as much on the output voltage as on the leds).
- The led220 "SLAM" is constantly on, even when the bypass is engaged.
- Led211 to led219 reacted in a strange way during the beginning of calibration.

My hypothesis comes from the TL071 which controls this series of LEDs (211-220). Indeed, I had indicated that I had reversed R540 and R86, after that Q11 was replaced because it was damaged. The sensitive TL071 could also be affected by the inversion of the trimmers. What do you think?

Let me know
Many thanks (and Merry Christmas!)
Manu

 

[Echo North]

Hello Mike,
Did you see my last message? (Below here)
Thanks

I doubt you damaged the IC from the trimmers.  Maybe it's just bad from heat or static.  I would check every joint and trace.  If you're swapping our parts it's really easy to lose a pad.

Everything else works?

Mike