[BUILD] FET/500 Official Support Thread

[Echo North]

Hey!

First off, thanks so much for what you do.

I just finished building the FET/500 Rev D. I did the calibration and everything is sounding great, but I can't seem to get the orange LED to light up... If soldered and re-soldered...

Can an LED be bad? Any suggestions on fixing this??

You could test the LED with a DMM (check google for methods), see if it's dead.

LED's (and all semi-conduuctors) are sensitive to static electricity and heat when installing. Also, see if either pad is lifted.

Mike

Thanks for responding. It seems like it is fried. How do I purchase a replacement?

And a follow up question.

The attack and release knobs feel much more lose compared to the other pots... Is there a better way to secure them better?

Mouser# WP132XND

Loose like rotational?  Part of issue with that circuit having 4 different pots, and no manufacture that makes all 4 values well for a decent cost.

Mike

 

[junomat]

Hey!

I am looking at switching out the knobs for the FET500 to look more like the original 1176 knobs....

Can I use the knobs here?
http://www.hairballaudio.com/catalog/parts-store/knobs/3a5a-style-small-skirted-knob (for the input/output)
http://www.hairballaudio.com/catalog/parts-store/knobs/fet-small-knob (for attack/release)

Will there be enough room?

 

[Echo North]

Hey!

I am looking at switching out the knobs for the FET500 to look more like the original 1176 knobs....

Can I use the knobs here?
http://www.hairballaudio.com/catalog/parts-store/knobs/3a5a-style-small-skirted-knob (for the input/output)
http://www.hairballaudio.com/catalog/parts-store/knobs/fet-small-knob (for attack/release)

Will there be enough room?

Probably not for the bigger one.

I would use these the second link or these:
http://www.hairballaudio.com/catalog/parts-store/knobs/fet-style-miniature-knob-18-shaft

Mike

 

[junomat]

Thanks. So no mini skirted input/output knobs exist?

 

[Echo North]

Thanks. So no mini skirted input/output knobs exist?

Not that we sell or that I know of.

 

[MChammer]

I am having problems with my FET/500. Everything works except for the attack. Also my gain reduction slam led at the top of the compressor is lit when it is not in slam mode? Is this problem just a calibration error?

Any help would be appreciated.

-Michael

 

[Echo North]

I am having problems with my FET/500. Everything works except for the attack. Also my gain reduction slam led at the top of the compressor is lit when it is not in slam mode? Is this problem just a calibration error?

Any help would be appreciated.

-Michael

The GR meter is like the original in that it will drift a little from supply to supply (Lunchbox) and even with heat. After it's been in the rack and settled in you want to adjust that with the zero adjust on the front panel to get it back to "0".

The 1176 attack is super fast. Real fast. It's 20 MICRO seconds to 800 MICRO seconds. That's 0.00002 to 0.0008 seconds. If you want less attack you may want to consider a larger attack pot.

Mike

 

[junkface]

ok, finally got my extension jig together to have a look at my F. I hooked up my .775 vac 1k signal and realized it is actually passing signal, it just seems really low and GR at most settings (or off) doesn't effect it at all. with input and out put at 12 o'clock I'm getting .15 vac at the output. Then I noticed that it seems to function fine when it's in slam mode, whether the GR off button is engaged or not. Doesn't that slam position just send it through R22, R2, and R24-26 as it would for the other ratios? double checking R23...

hey mike, et al,
was having a problem with my fet 500 (rev F). built and calibrated it up and it was working fine for the few days I first used it. came back from a trip and now it's not passing signal anymore unless it's in bypass. decided to double check all the soldering and in the process mucked up a solder pad for the input xfo. according to the data sheet though, pin 2 (also 3,7) is not connected, which looks in line with the schematic. am I correct that I can just disreguard pin 2 or do I need to jumper it somewhere?
if that's not the issue then I'm waiting for a 500 jig to arrive so i can start signal tracing...

Bummer.

Ya pin 2 is not connected. Let us know what you find in the signal trace.

Mike

 

[Echo North]

ok, finally got my extension jig together to have a look at my F. I hooked up my .775 vac 1k signal and realized it is actually passing signal, it just seems really low and GR at most settings (or off) doesn't effect it at all. with input and out put at 12 o'clock I'm getting .15 vac at the output. Then I noticed that it seems to function fine when it's in slam mode, whether the GR off button is engaged or not. Doesn't that slam position just send it through R22, R2, and R24-26 as it would for the other ratios? double checking R23...

hey mike, et al,
was having a problem with my fet 500 (rev F). built and calibrated it up and it was working fine for the few days I first used it. came back from a trip and now it's not passing signal anymore unless it's in bypass. decided to double check all the soldering and in the process mucked up a solder pad for the input xfo. according to the data sheet though, pin 2 (also 3,7) is not connected, which looks in line with the schematic. am I correct that I can just disreguard pin 2 or do I need to jumper it somewhere?
if that's not the issue then I'm waiting for a 500 jig to arrive so i can start signal tracing...

Bummer.

Ya pin 2 is not connected. Let us know what you find in the signal trace.

Mike

Let's measure some stuff.  Start by measuring DC V at the gate of Q1 and see what you can get when you rotate the qbias pot.  Your common/reference will be the anode side (+) of D4.

 

[junkface]

I get -2.6 V DC at ful CCW, trimming up to 0 at full CW

 

[Echo North]

I get -2.6 V DC at ful CCW, trimming up to 0 at full CW

That's good.  Keep it at -2.6 for now. That will pinch off the FET. 

No with the FET gate at -2.6 feed a 1k 0dB signal into the unit. GR OFF, 20:1, attack/release full CW, in/out at 12 o'clock. What is your AC voltage at either pad of C9?

Mike

 

[junkface]

2.67 VAC

 

[Echo North]

2.67 VAC

That's good.

Double check your resistor values and cap values/orientation in the output stage. It's in the upper between the 100K pot and the output transformer.  Double check your resistors in SW2C and SW2D.

http://mnats.net/files/FET-F500.pdf

Mike

 

[junkface]

man it musta just been a cold joint somewhere  : . double checked everything you mentioned, all the values and orientations were correct. pulled a couple leads to double check I wasn't reading  suspect resistor values backwards and reflowed everything that looked even remotely questionable. now it's workin fine! thanks for your help, if nothing else it's given me a much better understanding of this schematic and pcb layout.  you're the best mang!

 

[martin bluenoise]

Hi guys!

I've got and use a rev A for well over a year and I really like it.

I'm having an issue though. The input pot has gotten scratchy. Only as I turn it. Is this a symptom of something gone wrong during the build or is it just dust? If it's dust, how do I clean it? Contact cleaner?

Thanks a million in advance! 

 

[Echo North]

Hi guys!

I've got and use a rev A for well over a year and I really like it.

I'm having an issue though. The input pot has gotten scratchy. Only as I turn it. Is this a symptom of something gone wrong during the build or is it just dust? If it's dust, how do I clean it? Contact cleaner?

Thanks a million in advance!

If those get dirty they get real noisy. Because it's the input pot, any noise is amplified.

We'll send you a new one if you want to replace it.

Mike

 

[MChammer]

I already sent a message to the hairball audio site but I wanted to see if anyone had some suggestions on here. I was calibrating the revision d fet 500 today and the GR meter LEDs were not working properly. Multiple LEDs were lit. For example -9, -7, -3, -2, and -1 would be lit. I have it on the default so only the top LED should be lit. The output is correct when changing from GR off to GR on, only the LEDs seem to be wrong. Any help would be appreciated. I have compared this meter board to a previous working version and I can't find my mistake.

-Michael

 

[Echo North]

I already sent a message to the hairball audio site but I wanted to see if anyone had some suggestions on here. I was calibrating the revision d fet 500 today and the GR meter LEDs were not working properly. Multiple LEDs were lit. For example -9, -7, -3, -2, and -1 would be lit. I have it on the default so only the top LED should be lit. The output is correct when changing from GR off to GR on, only the LEDs seem to be wrong. Any help would be appreciated. I have compared this meter board to a previous working version and I can't find my mistake.

-Michael

The GR Meter also has some circuitry down on the main PCB. Everything around IC1:
http://mnats.net/files/FET-D500.pdf

Have a look at all of those parts including the trimmer value.

Re-flow joints if all else fails.

Mike

 

[MChammer]

So far I have found out that the problem is not the meter board. The meter board works with my Rev. A perfectly. I re-soldiered many of the joint and the problem still occurs

 

[Echo North]

So far I have found out that the problem is not the meter board. The meter board works with my Rev. A perfectly. I re-soldiered many of the joint and the problem still occurs

Right, much oh that circuit is on the main PCB around and including IC1.

Mike