[BUILD] FET/500 Official Support Thread

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FarisElek

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Oct 26, 2019
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HA! I found a Green LED in my parts drawer and it's the same size so I went for it to be over with this build. It's perfect! It ain't red but it works.
It ain't pretty on the inside near the LEDs, perfect everywhere else. Had a really hard time with some old lead cutters that I've permanently retired.

I am so unbelievably happy with this compressor now. I've already tracked drums with it on the kick. Absolutely crazy.
 

FarisElek

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Oct 26, 2019
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428
Fuzz Face said:
Man you were supposed to clip the LED leads before you solder to the board!  ;)

I know. I was building it away from my tools and I didn’t have tweezers to hold the LED’s to the board to to the pcb while soldering, so I kept one lead long enough that I could hold it bent up while soldering one side. It went wrong once but I thought I could get away with it again and it happened again 😓. I should have just been patient and waited til I had access to my tweezers.
 

zarndyhoff

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Feb 17, 2016
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Location
Christchurch, New Zealand
Hi!

Just built my two Rev Ds. (actually these are the third and fourth I've built over the years).

First unit worked perfectly, calibrated perfectly, straight away.

Second unit, everything fine during calibration until the bit where you repeat the four steps. When GR Off is engaged, nothing changes - the AC output doesn't change regardless of where the switch is positioned..

Any ideas? I've been through and re-flowed all the solder joins on the meter board, but I haven't gone over the resistors yet... dreading that part. It's pretty tidy. I'll add a photo. Can you see any issues?
Thanks!
 

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Echo North

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Seattle, WA
zarndyhoff said:
Hi!

Just built my two Rev Ds. (actually these are the third and fourth I've built over the years).

First unit worked perfectly, calibrated perfectly, straight away.

Second unit, everything fine during calibration until the bit where you repeat the four steps. When GR Off is engaged, nothing changes - the AC output doesn't change regardless of where the switch is positioned..

Any ideas? I've been through and re-flowed all the solder joins on the meter board, but I haven't gone over the resistors yet... dreading that part. It's pretty tidy. I'll add a photo. Can you see any issues?
Thanks!

https://help.hairballaudio.com/hc/en-us/articles/360048613813-Common-Build-Errors-and-Troubleshooting-Techniques

and

https://help.hairballaudio.com/hc/en-us/articles/360048218173-FET-500-Troubleshooting-Guide
 

novisplit

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Oct 16, 2013
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Having the same VR2 issue as a lot of folks. Any official fix for that? double checked all my values. rebiased 6 times now.

Meter also seems to be way hotter than VU meter in protools. Other than that it's working great.

Please help!!!
 

FarisElek

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Oct 26, 2019
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428
Does using a linear psu for the 500 series such as the CAPI floor box psu bring the 500 series unit closer to the fet rack in character?
 

noiro

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Oct 22, 2011
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FarisElek said:
Does using a linear psu for the 500 series such as the CAPI floor box psu bring the 500 series unit closer to the fet rack in character?

I'm buidling them both rack and 500 series, basically i don't see much of a difference but what I notice is that each of them are unique, even two rack with active link aren't exactly doing the same work, it's the beauty of the analog world, like us they are all unique in my view.
 

noiro

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Oct 22, 2011
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hasanova said:
On a side note:
After calibrating "Unit#1" I put everything together. I noticed that a leg of R72 might be touching a #4 nut and/or 1/4" standoff. When I checked it with a DMM, it was so. Solved it by adding a bit of tape to the 1/4" standoff and #4 nut.

Hi man, I'm not sure if this is a good idea, it maybe suppose to touch, but it is very odd that it does that to my two last build as well REV F, not certain if i saw that before, R72 is shorting with the whole frame as well. it goes to ground, but in the schematic it does not?  any idea Mike?
 

asstrochris

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Aug 13, 2020
Messages
1
Wondering if anyone can help with what should be a simple question? Just finished a FET/500, everything seems great, calibration mostly went fine for both, except for the VR2 "VU Trim" pot doesn't seem to adjust the lowest level. Second LED stays lit no matter of the setting on the pot. Any ideas welcomed, thanks!

Also, here's all my test measurements for the meter:

1: 1.22 VAC 10: -15.55 VDC
2: 1.52 VAC 11: 1.5 VAC
3: +7.12 VDC 12: 1.2 VAC
4: -8.02 VDC 13: +1.39 VDC
5: -.501 VDC. 14: +2.04 VDC
6: -1.115 VDC 15: +.78 VDC
7: -14.22 VDC 16: +15.38 VDC
8: -12.5 VDC 17: +2.5 VDC
9: +15.38 VDC. 18: +.05 on, +1.15 off (.7 LED1) VDC
 
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zarndyhoff

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Joined
Feb 17, 2016
Messages
11
Location
Christchurch, New Zealand

and

Thanks for this reply! I figured it out ages ago - I think I had swapped a 10 k ohm with a 10 ohm resistor. Both units have been working perfectly for a year and sound fantastic.
 

Sweetfoot

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Jan 12, 2017
Messages
2
I built a rev D kit, got it all calibrated, and started using it for some mixes. It's been great for a week or so, but today the output suddenly got super hot. Previously, the input an output seemed to have a reasonable range across their rotation, but now the output goes from zero to completely blown out within like 5 degrees of rotation, while the input pot still functions as expected. Any Idea why this might happen? Did my q bias drift as the circuit burned in?
 

Sweetfoot

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Joined
Jan 12, 2017
Messages
2
I built a rev D kit, got it all calibrated, and started using it for some mixes. It's been great for a week or so, but today the output suddenly got super hot. Previously, the input an output seemed to have a reasonable range across their rotation, but now the output goes from zero to completely blown out within like 5 degrees of rotation, while the input pot still functions as expected. Any Idea why this might happen? Did my q bias drift as the circuit burned in?
Update: The super loud output is intermittent. On the day I first posted, It occurred for a few minutes, then went away for a few minutes, then came back for the rest of the day. Since that day though, the unit has been sounding normal.
 

magnusp71

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Sep 23, 2021
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Location
Denmark
Hi all
I am in the proces of calibrating my Hairball FET/500 but have reached a dead-end before even getting started :/

Gear:
Logic Pro DAW
Apogee Duet 2 interface (Userguide)
Lindell Audio 503 lunchbox (Specs here)
Brymen 867 DMM (SPECS here)
Soundskulptor XT500 lunchbox connector extender (LINK)

Input to FET/500:
I am sending a 1kHz 0dB signal to the input from Logic Pro's Test Oscillator through my one of my Apogees balanced outputs via a mono-jack to XLR cable. By adjusting the level to approx -10dB in Logic, I measure 0.775 VAC and 1kHz on pin 2 and 3 on the XLR at the lunchbox input. So far so good.

Output from FET/500:
The knobs are set as instructed in the video. I have connected the lunchbox output to the Apogees input 1 via a XLR-cable. However, for some reason I have a zero voltage reading between the XLR pin 2 + 3 on the output of my lunchbox and thus cannot proceed with calibration.

What I have tried so far:
  • As a test, I've tried to record whatever is on input 1 of the Apogee, and this is indeed a 1kHz sinus-signal (however with some "bumps" as seen on picture below").
  • Measuring output between pin 1+3 and 1+2 - also 0 VAC.
  • Measuring directly on the pins of the lunchbox - also 0 VAC.
  • Measuring on the measuring pins of the XT500 connector (COM and OUT+) - also 0 VAC.
  • Test of voltage rails as explained HERE. I have 0.18 VDC on -V Out and 14 VDC on +VR.
What I can see:
  • LED1 and LED2 working.
  • Green LED number 4 from bottom on Meter PCB lights up when powering on the unit and stays on.
What I can hear:
  • I have attached a sound clip from a vocal signal, that I tried to send through the FET/500 while twisting the input/output knob a little. Weird.
I truly hope that someone is able to guide me in the right direction :)

Pictures:
Input cable.
IMG_7405.JPG
Tone generated in Logic Pro.
IMG_7408.JPG
Input on lunchbox.
IMG_7409.JPG
Input measured.
IMG_7410.JPG
Cable between lunchbox output and Apogee interface
IMG_7411.JPG
Output on lunchbox:
1634293348381.jpeg
Output measured:
1634293378671.jpeg
FET/500 Output recorded to Apogee input in logic (signal strength can be modulated with FET/500 output knob).
1634293449086.jpeg
The FET/500:
1634293594728.jpeg
IMG_7424.JPG
Thank you in advance!
Br, Magnus
 

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