[BUILD] FET/500 Official Support Thread

[applespace]

I accidentally installed R16 and R54 around the wrong way.I have removed the trim pots, but in doing so a couple of the pads on the top of the circuit board have popped off with the legs. Can I fill the holes with solder and connections will still be made? Or is there another way to fix this? Hope I haven't ruined the board Many thanks for any advice.

 

[applespace]

I have replaced R16 and R54. But when powering on R36 fried. This happened the first time I powered the unit on. I thought it might have been because I had R16 and R54 switched, but there apears to be something else wrong.. Any suggestions?

I have gone through all components and I can't see anything else wrong or out of place.

I built a second unit that has been calibrated. The only thing I can see that is different is with 1 of the DIP-8s (IC-200 and IC-201) on the meter board. All 4 DIP-8s on the 2 meter boards say TL072CP. The working board has 1 x 29A8HTM TL072CP and 1 x 1AADGVM TL072CP, while the busted unit has 2 x 1AADGVM TL072CP. Is this something wrong?

Many thanks in advance.

 

[Echo North]

I have replaced R16 and R54. But when powering on R36 fried. This happened the first time I powered the unit on. I thought it might have been because I had R16 and R54 switched, but there apears to be something else wrong.. Any suggestions?

I have gone through all components and I can't see anything else wrong or out of place.

I built a second unit that has been calibrated. The only thing I can see that is different is with 1 of the DIP-8s (IC-200 and IC-201) on the meter board. All 4 DIP-8s on the 2 meter boards say TL072CP. The working board has 1 x 29A8HTM TL072CP and 1 x 1AADGVM TL072CP, while the busted unit has 2 x 1AADGVM TL072CP. Is this something wrong?

Many thanks in advance.

Those are just manufacture codes. Check that any damaged pads from the swap still have continuity to wherever they are supposed to connect.

https://help.hairballaudio.com/hc/en-us/articles/360048251974-Pad-and-Trace-Repair

 

[applespace]

Those are just manufacture codes. Check that any damaged pads from the swap still have continuity to wherever they are supposed to connect.

https://help.hairballaudio.com/hc/en-us/articles/360048251974-Pad-and-Trace-Repair

Following the trace lines on the under side I am getting continuity to all points they visually run to. I am getting the same continuity with the working and broken unit.

There looks to be a line emanating from R16 on the top side running towards the front. Due to capacitors, I can't see where it ends or get continuity while testing on the underside in that area. This is the same with the working unit, so both units appear to have the same continuity as each other in regards to R16 and R54.

Is there continuity I need to test on the top side? Do you have REV 3 board circuit diagram? Any further suggestions? Many thanks.

 

[metalmaz]

Hello there! I'm new to the thread but hoping for some help with a FET/500 rev D I purchased through Hairball -

I am getting a good clean signal through the finished unit, but I'm not getting any gain reduction despite several re-calibrations. Going through the Hairball Troubleshooting guide I can see this is most likely due to an issue in either the Signal amps section of GR side chain amp sections -

My voltage rails and Q bias measurements are all good, but my Signal preamp readings are all over the place compared to the expected readings after TP1:
TP1 = 0.100VAC
Q3 Base = 1.8V
Q14 Base = 0V
TP15 = 1.76V

Is anyone able to shed some more light on where I should be looking for an issue? I really was vigilant when placing components and checking their values etc. before soldering, and have gone back to check my joints and reflow the above transistors, given the pcb a good clean... so now I'm scratching my head with frustration while peering into the schematic

Cheers and any help at all seriously appreciated!
Rhys

 

[calaverasgrande]

ugh, why are the 1/4" parts listed on the BOM next to the 1/8th inch parts if they aren't going to work with the front panel? Now I have to decide between re-purchasing some very expensive parts or drilling out the holes larger. grrr.

 

[calaverasgrande]

Well so long as I am doing another parts run, what are you guys using for R78 the 5 Meg pot?
"308N5MEG" seems like an incorrect part no, since its for solder hooks not PC pin.
"308NPC5meg" should be the right way to make a part number for a 5 Meg with PC pins. According to the datasheet. Which is an academic exercise since nobody seems to stock either?
Is anyone else trying to source their own parts and finding this pot a little rare?

ps.I even looked for 4.7meg!

 

[jasonallenh]

I'm checking voltages and I'm seeing the qbias voltage only go from 0 to about -1.02v. There were shorts all over the pcb, especially around the grayhill switch that I had to clean up (I am helping a friend troubleshoot). Kind of stuck on where to look next.

 

[shxftctrl]

Hi Mike

I’ve already started Troubleshooting but noticed that my voltage rails are off. Not sure how and if to proceed from that?

“Test of voltage rails as explained HERE. I have 0.18 VDC on -V Out and 14 VDC on +VR.”

Secondly, I’m not sure I got the placements of TPs fully right based on the descriptions in your guide. Do you have a picture or an overlay where they are shown?

Thanks again

Did you ever figure out your issue? My -V Out looks alright but my +VR is reading 15 instead of 30.

 

[jasonallenh]

I'm checking voltages and I'm seeing the qbias voltage only go from 0 to about -1.02v. There were shorts all over the pcb, especially around the grayhill switch that I had to clean up (I am helping a friend troubleshoot). Kind of stuck on where to look next.

Bumping this only the one time, then I'm going to start replacing some 5088s

 

[calaverasgrande]

Well so long as I am doing another parts run, what are you guys using for R78 the 5 Meg pot?
"308N5MEG" seems like an incorrect part no, since its for solder hooks not PC pin.
"308NPC5meg" should be the right way to make a part number for a 5 Meg with PC pins. According to the datasheet. Which is an academic exercise since nobody seems to stock either?
Is anyone else trying to source their own parts and finding this pot a little rare?

ps.I even looked for 4.7meg!

nobody else going the DIY route on this?
Well if anyone else is thinking of doing that to save money. Don't. Almost all the parts are hard to find and expensive. I don't think I saved any money at all by going the 'cheap' route. Esp since I had to go back to Hairball for several parts anyway.

 

[jasonallenh]

I found a broken trace that was preventing 15v+ from getting to the necessary parts of the meter board. That's fixed but I still cannot get qbias voltage below -1v

 

[jasonallenh]

I am helping a friend clean up a Rev D build and there's been a number of issues to address. I feel like I'm getting closer, but I'm still not able to calibrate the unit. Here's a summary of what I've done/found so far:

-no +15v at the LED driver or TL072s this was a broken trace near the 10-pin header. v+ is correct throughout the meter board now

-reflowed everything, including some severe solder bridges at the grayhill switch. C21 had exploded presumably because of these shorts. Cap was replaced.

-Verified component placement against the RevD map and layout.

-Orange trafo wire was not soldered to the board. fixed.

-Couldn't set the ratio to 20:1 because the stops were never installed. I ordered replacements and installed them per the build guide.

-Compared all Q voltages to the schematic with the typical voltages listed. Nothing was way off, and I'm assuming minor discrepancies have to do with my unit not being calibrated.

-With Q1 installed, I cannot get above 2VRMS on output when feeding the .775 tone. With Q1 removed, there appears to be tons of gain. This would suggest an issue with Q1, BUT:

-QBias does not go below about -1.03VDC. With the trimmer all the way at each extreme, I can go from 0v to about -1.03. This does not change regardless of whether Q1 is installed or not. I removed Q1 and the behavior did not change.

The Qbias issue seems to be the main thing plaguing this unit, however the meter board also does not light up- no LEDS at all have come on since this was handed over to me, even though the voltages look good. I know I can send the unit in, but I want the experience of cleaning up a really jacked build. Would love some thoughts...not sure if @Echo North still watches this or not

 

[jkurzweg]

Reporting back on trying out 50k vs 100k vs stock 25k for the attack pot:---Doubling the value to 50k for a whopping 1.6 ms instead of .800ms ended up being the winner for me----I guess it's something to do with the fet and feedback nature of the compression for that to be plenty to let the front end of kick, snare, bass gt, acoustic guitar ,and vocals come through in a way I've wanted 1176s to do for years....(I often use somewhere between 10ms to 30ms on vca comps and some of my other fets like the adr Vocal Stressor and artistic comp+ etc ) -- If you've ever wanted a slower attack, I recommend the 50k, as to my surprise quadrupling the attack time with 100k was too slow and mostly unusable to me.

 

[applespace]

I have discovered that Q08-MPSWO6 and Q09-MPSW56 are faulty. Not sure of that's what fried the R36 resistor or they died when it fried.

What are these 2 NPN transistors for? I am wondering if they need to be matched in anyway across 2 different units? It's costly to source from Hairball directly these cheap parts so will need to source elswhere. Should I install a matched pair in my second working unit as well?

 

[egroys]

I have the 100Ω input slug on my blue Rev A and I find that my operating range is still microscopic, somewhere between 7-8 o'clock.
Would I need to go to 50ishΩ or 200ishΩ to reduce the gain even more? I'm not concerned with it being like the originals...

 

[egroys]

I have the 100Ω input slug on my blue Rev A and I find that my operating range is still microscopic, somewhere between 7-8 o'clock.
Would I need to go to 50ishΩ or 200ishΩ to reduce the gain even more? I'm not concerned with it being like the originals...

To answer my own question, a lower value accomplishes this. 50Ω made a very small difference and I ended up at 22Ω to have a broader operating range, for anyone interested in doing the same!

 

[noiro]

Having a problem with a REV.D FET/500. The compressor is working except that the signal is very muddy and louder, sound like a low pass filter signal almost. I check voltage and it's all good, was able to calibrate. Not sure where to look tho!