[BUILD] FET/500 Official Support Thread

[Echo North]

That helped! Thanks!

Also why does it work backwards? I thought the greens would have lit first from the top down.

The GR meter? It's like the anolog meter on the original. Starts at zero and moves down.

 

[alexgriva]

Hi Guys

I'm having an issue with GR meter calibration (Rev D). Looks fine when is 20:1. When I change to any other ratio the meter goes red/peak. Any idea?

 

[Blackdawg]

The GR meter? It's like the anolog meter on the original. Starts at zero and moves down.

Right, 0 being on top and -22 being on the bottom. Mine lights up at -22 first and goes up...

Also, been trying to calibrate. Nothing seems to change when trying to do the Q bias. Hell i can't even get it to output 2.75v even. Im getting 0.0168v max. And when i crank the input and outputs i only get 0.03v..

 

[Blackdawg]

figured out my problem. My outputs and inputs from the HP 8920A are BNC and i made cables from BNC to XLR. Had one of the wires going to ground not + & -

Edit: Damn. My VU meter trim pot does nothing. VR1.

I set the output to 4.88v and my peak LED is already peaked and lit up. Doesn't have enough in it at all to change it.  In fact if I change the output so the meter is reading in the green the pot only lowers it one LED.

Also, i can hit 45v output now..seems kinda high..

 

[Blackdawg]

Hello?? Any input? Very much would like these to work soon..

 

[robsn]

Hi,

I'm building a rev A stereo pair and can't calibrate the meters to -10 dB. What's the exact trimmer type of VR2? I can find 25 different 2kΩ bourns pots that would fit the footprint. Hope 2k will do the job.

Or would it make more sense to change either R222 or R223? I'm fully ccw on the pot.

Cheers, Rob

 

[Echo North]

Hi Guys

I'm having an issue with GR meter calibration (Rev D). Looks fine when is 20:1. When I change to any other ratio the meter goes red/peak. Any idea?

Give it some time to warm up, then use the zero adjust on the front to get the meter in the right spot. Should settle after 2-3 seconds on all ratios.

Mike

 

[Echo North]

Hi,

I'm building a rev A stereo pair and can't calibrate the meters to -10 dB. What's the exact trimmer type of VR2? I can find 25 different 2kΩ bourns pots that would fit the footprint. Hope 2k will do the job.

Or would it make more sense to change either R222 or R223? I'm fully ccw on the pot.

Cheers, Rob

The Rev F is a little finicky with the peak transistor.  DO you have any resistors in house? Lowering R203 should fix your issue.  Try something around 90Kish.

Mike

 

[robsn]

The Rev F is a little finicky with the peak transistor.  DO you have any resistors in house? Lowering R203 should fix your issue.  Try something around 90Kish.

Mike

Possibly something got mixed up here. I'm building a Rev A, not F and VR2 is the issue. R203 is around VR1.
But yes I do have a resistor set

Cheers, Rob

 

[Blackdawg]

Possibly something got mixed up here. I'm building a Rev A, not F and VR2 is the issue. R203 is around VR1.
But yes I do have a resistor set

Cheers, Rob

I think the tip for lower R203 was for me...but not sure..

 

[robsn]

Anyhow. On one unit I was fully ccw on both VR1 and VR2. So I made these adjustments on both. It's a stereo pair  ::

• I changed R203 from 22k0 to 24k0.
• I changed R222 from 1k2 to 1k8.

I can now calibrate the meters and both VR1 and VR2 pots are pretty much midway on both units.

I'd be extremely happy if someone who actually knows what he's doing could confirm that:

• I didn't make something completely stupid by changing these resistors i.e. it doesn't have any negative impact on any parts or the sound and I'm not outside the range of the voltage dividers total ranges (I hope this sentence makes sense).
  
• I didn't have to repeat setting the Q bias after changing these resistors 'cause I didn't 
• It didn't have an impact on the tracking adjust because I had to adjust it on one unit and it is fully ccw. I did't have to change it on the second compressor where I made the same resistor changes.

Cheers, Rob

PS get rid of that recaptcha stuff. It has stolen me like half an hour today and yesterday due to my inability to check street signs, connection timeouts and google accusing me of being a robot and not letting me select the loudspeaker symbol.

 

[Blackdawg]

Anyhow. On one unit I was fully ccw on both VR1 and VR2. So I made these adjustments on both. It's a stereo pair  ::

• I changed R203 from 22k0 to 24k0.
• I changed R222 from 1k2 to 1k8.

I can now calibrate the meters and both VR1 and VR2 pots are pretty much midway on both units.

I'd be extremely happy if someone who actually knows what he's doing could confirm that:

• I didn't make something completely stupid by changing these resistors i.e. it doesn't have any negative impact on any parts or the sound and I'm not outside the range of the voltage dividers total ranges (I hope this sentence makes sense).
  
• I didn't have to repeat setting the Q bias after changing these resistors 'cause I didn't 
• It didn't have an impact on the tracking adjust because I had to adjust it on one unit and it is fully ccw. I did't have to change it on the second compressor where I made the same resistor changes.

Cheers, Rob

PS get rid of that recaptcha stuff. It has stolen me like half an hour today and yesterday due to my inability to check street signs, connection timeouts and google accusing me of being a robot and not letting me select the loudspeaker symbol.

Im doing Rev F but i lowered my 203 to 98k and that got me good. Then i read your post and raised 222 to 1.4k as its all i had and that helped my VR1 pot too.

Im not the guy to tell you if that is going to cause problems though but i can't imagine it would. Just raised the resistance on the meter circuit.

Thanks for the tip too!

I have 1 calibrated before i switch R222. So i'll see after i change it if my q bias is different.

 

[Echo North]

I think the tip for lower R203 was for me...but not sure..

For Rev F's only.

 

[Blackdawg]

For Rev F's only.

Awesome.

Got mine all calibrated. Gonna use em tomorrow!

 

[jcgriggs]

Greetings,

Tried to post this yesterday, but got messed up by the Captcha stuff - apologies if it is a duplicate.

During de-soldering I lost the solder pad on the PCB for pin 5 of the input transformer on one of my Rev D builds (long story).

I looked at the data sheet for the part (http://library.hairballaudio.com/datasheets/3837.pdf), the schematic (http://mnats.net/files/FET-D500.pdf) and the PCB itself, but I can't work out where this pin should connect to.

Can someone tell me which other pad I could jump pin 5 of the input transformer to to restore the circuit?

Thanks,
  John

 

[Echo North]

Greetings,

Tried to post this yesterday, but got messed up by the Captcha stuff - apologies if it is a duplicate.

During de-soldering I lost the solder pad on the PCB for pin 5 of the input transformer on one of my Rev D builds (long story).

I looked at the data sheet for the part (http://library.hairballaudio.com/datasheets/3837.pdf), the schematic (http://mnats.net/files/FET-D500.pdf) and the PCB itself, but I can't work out where this pin should connect to.

Can someone tell me which other pad I could jump pin 5 of the input transformer to to restore the circuit?

Thanks,
  John

Pin 5 goes to the ground.  Same as pin 6 right beside it.  Just solder a jumper wire from pin 5 to pin 6.

Mike

 

[stevelawaudio]

Hi Everyone -
This is my first Fet/500/D build. Successfully built a Fet/Rack/A, which I'm loving!

Im having trouble getting my Gain Trims and VU to work. I successfully got the Q-Bias setup, but now when I move the Gain and VU  trim pots I have no movement of LEDs at all.
Ive been back across the bill of materials and cross checked things.. still no joy.

Where should i be starting my hunt.?

Cheers..
Steve.

 

[Echo North]

Hi Everyone -
This is my first Fet/500/D build. Successfully built a Fet/Rack/A, which I'm loving!

Im having trouble getting my Gain Trims and VU to work. I successfully got the Q-Bias setup, but now when I move the Gain and VU  trim pots I have no movement of LEDs at all.
Ive been back across the bill of materials and cross checked things.. still no joy.

Where should i be starting my hunt.?

Cheers..
Steve.

Are any of the LEDs lighting?

Are you passing signal?

Mike

 

[stevelawaudio]

Are any of the LEDs lighting?

Are you passing signal?

Mike

Hey Mike -

Yep, got signal in and out, and the LEDS are lighting. They just won't move with the trim pots. Turned the trims fully each way, and no luck/movement.

thanks mate!

S.

 

[stevelawaudio]

Are any of the LEDs lighting?

Are you passing signal?

Mike

Hey Mike -

just been across it with a DMM - found a few values that are correct in colour banding but are reading a bit low.
examples -
R207 (100k) is reading 72k
R216, R213, R215 (100k) are reading 80k
R227 (10k) is 5.3k...etc..
there are a few more reading low too..

thanks for your help!

S.