[BUILD] FET/500 Official Support Thread

cspears · Feb 23, 2017

Hi Gang,
Just got my 500 Revision F soldered and am waiting on a jig to arrive to do more tests. For the meantime, I have some very obvious faults that I thought perhaps one of you kind folks might be able to answer:

1. The unit passes signal but doesn't compress when powered on and it doesn't pass any signal at all when the bypass is activated! The input and output knobs do change the volume, though.

2. I did power the unit on with a whole bunch of cables, (in lieu of the jig coming in the mail) and was able to trace the audio signal using the Marc Burnley technique until I arrived at R6 at which point the signal died and I couldn't hear it anywhere else on the board.

3. Visually, it looks like I connected the VR1 and VR2 backward though they only fit in one direction into the pcb (they are currently not changing the meters).

Anyways, apologies for my DIY nubeness and if someone has a quick solution to the bypass situation I would be very grateful. I attached a pic.

Echo North · Feb 24, 2017

cspears said:
Hi Gang,
Just got my 500 Revision F soldered and am waiting on a jig to arrive to do more tests. For the meantime, I have some very obvious faults that I thought perhaps one of you kind folks might be able to answer:
1. The unit passes signal but doesn't compress when powered on and it doesn't pass any signal at all when the bypass is activated! The input and output knobs do change the volume, though.

That's super weird. Double check all of the soldering around the bypass switch for shorts.

cspears said:
2. I did power the unit on with a whole bunch of cables, (in lieu of the jig coming in the mail) and was able to trace the audio signal using the Marc Burnley technique until I arrived at R6 at which point the signal died and I couldn't hear it anywhere else on the board.

This is in bypass mode where your signal dies?

That MAY indicate a FET issue. You could try removing Q1 and seeing if that allows your signal to pass.

cspears said:
3. Visually, it looks like I connected the VR1 and VR2 backward though they only fit in one direction into the pcb (they are currently not changing the meters).
Anyways, apologies for my DIY nubeness and if someone has a quick solution to the bypass situation I would be very grateful. I attached a pic.

That's fine. They will work fine like that. You're issue is probably no ouput or something else in the meter.

Mike

sebperry · Feb 26, 2017

Hi Mike,
I removed Q1 and the unit seems to be behaving pretty much the same. One thing I noticed that was weird was that at I turn the output pot clockwise I get no signal at all until it's turned about 3/4 to the right... If you have any other ideas please share, otherwise I think I will be sending it in for repair.

sebperry said:
I posted maybe a month ago about some issues I've been having calibrating my Rev D.

My problems all seem to stem from the output stage. I can't get enough signal out of the unit to calibrate properly. Most I can seem to get with Qbias maxed out is 1.367 VAC. And this is with the output pot fully clockwise.

The reason I think it's with the OUTPUT stage is because my input meters are in the red early on, but my output meters barely register until I turn the output pot fully clockwise.

I doublechecked all my resistors, questionable soldiers, I'm worried that the problem lies with the output transformer because I had some problems soldiering that one and it's not the neatest job (I trimmed some of the wires a little too short).

Are there any measurements I can take to isolate the issue?

Many thanks!

Hairball Audio said:
Try removing Q1 if you can. Carefully.

Then see what kind of output you get. You won't be able to adjust the Q, but this can confirm if there is an issue with your FET.

Mike

Echo North · Feb 27, 2017

That indicates and issue with your gain stages.

For now, keep the unit in GR Off and keep Q1 out. That way we can focus on just getting the gain stages working right.

Check all of your solder, components, and continuity in the two gain sections. Those parts are largely between the pots and output transformer. Especially make sure you don't have a bad joint, or something like a 470Ω and 470KΩ swapped.

Its the components in the top half of the schematic:
http://mnats.net/files/FET-D500.pdf

Mike

JoelCoteBergevin · Apr 2, 2017

Ok so my FET/500 rev D pair has been going strong for months but now I have a new chassis (Chameleon Labs 880 rack) and I'm having a weird issue.. I use the compressors as hardware inserts in my DAW and if I send a signal to FET #1, Fet#2's gain reduction meter is active (doing the same thing as FET #1) but the link 1/8 cable is NOT connected. I tried the compressors in every possible position in the chassis with the same result.

At first, I thought it had to do with the chassis (or some channel cascading embedded, but no) and after testing I realised it was not the issue. Because if I remove FET #1 from the chassis and send a signal to FET #1, FET#2's meter is not moving (which is normal since I send no signal through but only to where the #1 would be.

It's only really just the gain reduction meter. When I don't send a signal the unit #2, the knobs or output meter do nothing (which is normal), but the gain reduction meter is doing the exact same thing as on FET #1 (which is the only one getting signal)

In short: I only send a signal to one of my FET/500 but the other one (not getting signal) is showing the exact same gain reduction metering info. Like if they were linked, but they are not.

Thoughts?

Echo North · Apr 2, 2017

JoelCoteBergevin said:
Ok so my FET/500 rev D pair has been going strong for months but now I have a new chassis (Chameleon Labs 880 rack) and I'm having a weird issue.. I use the compressors as hardware inserts in my DAW and if I send a signal to FET #1, Fet#2's gain reduction meter is active (doing the same thing as FET #1) but the link 1/8 cable is NOT connected. I tried the compressors in every possible position in the chassis with the same result.

At first, I thought it had to do with the chassis (or some channel cascading embedded, but no) and after testing I realised it was not the issue. Because if I remove FET #1 from the chassis and send a signal to FET #1, FET#2's meter is not moving (which is normal since I send no signal through but only to where the #1 would be.

It's only really just the gain reduction meter. When I don't send a signal the unit #2, the knobs or output meter do nothing (which is normal), but the gain reduction meter is doing the exact same thing as on FET #1 (which is the only one getting signal)

In short: I only send a signal to one of my FET/500 but the other one (not getting signal) is showing the exact same gain reduction metering info. Like if they were linked, but they are not.

Thoughts?

Chassis pin 6s are surely linked. Look at the end of the FET/500 build guide.
If pin 6s are linked units are permanently linked.

JoelCoteBergevin · Apr 2, 2017

Thank you so much ! Makes a lot of sense since this lunchbox also has DB25 connectors (just like the newer API chassis). I should've checked into the build guide before asking the question.

However, from what I understand, in the chassis, channel 1 and 2 are stereo linked, same for 3 and 4, 5 and 6, 7 and 8, etc. But even if I rack the FET/500 in channel 1 for example and the second FET/500 in channel 5 for example, they appear to be linked anyway. Could it be that ALL channels are linked in my lunchbox? In that case should I just remove all 0 ohm resistors?

Echo North · Apr 2, 2017

JoelCoteBergevin said:
Thank you so much ! Makes a lot of sense since this lunchbox also has DB25 connectors (just like the newer API chassis). I should've checked into the build guide before asking the question.

However, from what I understand, in the chassis, channel 1 and 2 are stereo linked, same for 3 and 4, 5 and 6, 7 and 8, etc. But even if I rack the FET/500 in channel 1 for example and the second FET/500 in channel 5 for example, they appear to be linked anyway. Could it be that ALL channels are linked in my lunchbox? In that case should I just remove all 0 ohm resistors?

Could be yes. Just use an ohm meter and test the all pin 6's like at the bottom of the guide.

Unplug your unit for safety, no need to power it for the test.

Has to be that all pin 6's are linked.

Mike

Riverjetty · Apr 28, 2017

Hello All,

Little help--I just finish stuffing my fet/500 1176 rev. D from Hairball but neglected to set the trimpots at the get go. I am now callibrating, is this a problem?

Please help and thanks in advance,
rj

Echo North · Apr 28, 2017

Riverjetty said:
Hello All,

Little help--I just finish stuffing my fet/500 1176 rev. D from Hairball but neglected to set the trimpots at the get go. I am now callibrating, is this a problem?

Please help and thanks in advance,
rj

You can center the 20 turn trim pots by rotating them until you hear a little "click". That is the end. Then rotate back 20 turns in the opposite direction.

Mike

Riverjetty · Apr 28, 2017

Thanks Mike. Pardon--Which, out of the three, are the "20 turn trimpots?"

Thanks,
rj

Echo North · Apr 28, 2017

Riverjetty said:
Thanks Mike. Pardon--Which, out of the three, are the "20 turn trimpots?"

Thanks,
rj

The ones that seem to turn endlessly. The short square ones with the white plastic dials are single turn.

Riverjetty · Apr 28, 2017

Thanks, at this time, I'm only turning white screws or do I also turn the copper coloured screws to center position as well?

Echo North · Apr 30, 2017

Riverjetty said:
Thanks, at this time, I'm only turning white screws or do I also turn the copper coloured screws to center position as well?

Are you following the calibration videos in the build guide?

Generally you want to center all of the trimmers except the Qbias. You set that for max output to start.

Mike

12afael · May 20, 2017

I wonder if someone have a Mouser BOM for rev D or F ( or both)? I´m in the middle of doing one for revF .
I was trying to create a excel bom from the pdf but I have had problems with that. From text or excel file is easy but from the pdf is not.

best regards

TDJ · May 21, 2017

Hey guys! First time post so I'm sorry if this isn't the correct place, forgive my ignorance. I've searched and cant seem to find the solution to my problem. I just finished my 2nd Hairball blue stripe. I have a strange problem on my 2nd one - when I go from 20:1 to 4:1 it stops compressing. If I switch from 8:1 or 12:1 to 4:1 it compresses! So, there's something fishy about my 4:1 that I can't seem to figure out. Double check resistor values on my ratio board? Any help would be greatly appreciated. Thanks!

Echo North · May 22, 2017

TDJ said:
Hey guys! First time post so I'm sorry if this isn't the correct place, forgive my ignorance. I've searched and cant seem to find the solution to my problem. I just finished my 2nd Hairball blue stripe. I have a strange problem on my 2nd one - when I go from 20:1 to 4:1 it stops compressing. If I switch from 8:1 or 12:1 to 4:1 it compresses! So, there's something fishy about my 4:1 that I can't seem to figure out. Double check resistor values on my ratio board? Any help would be greatly appreciated. Thanks!

Bad solder joint or pad around those 4:1 resistors.

Is this 500 series or rack?

Mike

TDJ · May 22, 2017

Rack! I will reflow joints on the ratio board!

Echo North · May 22, 2017

TDJ said:
Rack! I will reflow joints on the ratio board!

Post any follow up to this thread:

https://groupdiy.com/index.php?topic=63600.0

mdmitch2 · May 23, 2017

Hey guys, I just built a pair of Fet500 Rev A's, and may be observing a little bit of strange behavior. On both units, when using VU trim to set the -10 LED, I don't get any change across the full range of adjustment (with the DMM reading 0.388 volts). The LED is in fact already at -10, and it just stays there. I noticed that if I lower the voltage with the output knob to 0.350 volts, then the LED drops down to -20 and I can then use the VU trim to bring it back up to -10. I'm using a Fluke 87v, and I double checked voltages with another DMM, and they match. Any thoughts?

Note, I built a Fet 500 when they first came out, and I don't remember having this issue, but I do think that the PCB has since been revised, so maybe this is normal?

Also, I noticed that the kit came with 2N3707 transistors for Q3, Q5, whereas the BOM states 2N3708. These seem to be pretty comparable, so I didn't worry about it....

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