[BUILD] FET/500 Official Support Thread

[Houroftower]

I do see how my descriptions could be confusing and sincerely appreciate your responses.
I'm going to proceed with a video and the measurement you requested tonight after work.

By Pin 1, I assume you mean the one labelled "GR Sig"?
I do not have an oscilloscope. I am using a DMM.

 

[mnats]

I do not have an oscilloscope. I am using a DMM.

I'm guessing you have a computer with an audio input. I hear there is software...

Not directed just to you but I do much better when my questions are answered so please try.

 

[Gosha Usov]

Hi, Just finished building Fet/500 Rev A. Got to the first stage of calibrating and my Qbias trim does not adjust the levels turning all the way clockwise or counterclockwise. Is this a faulty trim pot or are there any other components that could cause this.

 

[mnats]

Hi, Just finished building Fet/500 Rev A. Got to the first stage of calibrating and my Qbias trim does not adjust the levels turning all the way clockwise or counterclockwise. Is this a faulty trim pot or are there any other components that could cause this.

There is no way to know from your description. Have you read the troubleshooting FAQ linked from the first post of this thread? If not, you may want to start there...

 

[Houroftower]

I'm guessing you have a computer with an audio input. I hear there is software...

Not directed just to you but I do much better when my questions are answered so please try.

I wasn't aware that a PC and audio input could be turned into an oscilloscope, I'll certainly look into it. I should have worded my last message better -- I only meant to say that I am limited to the use of a multimeter at the moment.

 

[Hynek]

Hello--

Is there a fine gentleman here with a well calibrated FET500RevD v2.0 who could measure a few DC voltages relative to AGND (neg probe on the input TRF shielding can might be easiest) for me?
I'm having some difficulties calibrating the stereo pair I bought from Hairball. More specifically the GR meters.

All three voltages are easily readable off of the 10-pin SIL that connects the two boards.
I'm interested in:
- pin#3 (I understand this is supposed to be -9V)
- pin#1 (Sig) @ 0dB of GR
- pin#1 (Sig) @ 9dB of GR

My Sig @ 9dB of GR goes negative - i.e. below REF LOW of IC204 - which concerns me.

Thanks a lot

 

[mnats]

Hello--

Is there a fine gentleman here with a well calibrated FET500RevD v2.0 who could measure a few DC voltages relative to AGND (neg probe on the input TRF shielding can might be easiest) for me?
I'm having some difficulties calibrating the stereo pair I bought from Hairball. More specifically the GR meters.

All three voltages are easily readable off of the 10-pin SIL that connects the two boards.
I'm interested in:
- pin#3 (I understand this is supposed to be -9V)
- pin#1 (Sig) @ 0dB of GR
- pin#1 (Sig) @ 9dB of GR

My Sig @ 9dB of GR goes negative - i.e. below REF LOW of IC204 - which concerns me.

Thanks a lot

I would never describe myself like that, but I'm happy to post measurements since I have a prototype handy. For what it's worth I can't recall any significant differences to the v2.0; IIRC this was the first version where we'd sorted all the bugs out.

Pin 3: -8.8v
Pin 1, GR off: 1.14v
Pin 1, 9dB of GR: 0.46v

Hope that helps.

 

[Hynek]

I would never describe myself like that, but I'm happy to post measurements since I have a prototype handy. For what it's worth I can't recall any significant differences to the v2.0; IIRC this was the first version where we'd sorted all the bugs out.

Pin 3: -8.8v
Pin 1, GR off: 1.14v
Pin 1, 9dB of GR: 0.46v

Hope that helps.

Many thanks, mnats--

Yep, all's good on my end except when slowly increasing Input in GR mode there's a point where the GR meter takes a sudden plunge and my Sig goes through the floor even though the audio side measures and sounds fine. At this point I'm pretty certain both of my Q11 are shot as everything around IC1 looks good.

It took me days of reviewing my soldering to figure it out as I was hesitant to believe both units had the same component failure. Wild luck would have it though.

 

[mnats]

Many thanks, mnats--

Yep, all's good on my end except when slowly increasing Input in GR mode there's a point where the GR meter takes a sudden plunge and my Sig goes through the floor even though the audio side measures and sounds fine. At this point I'm pretty certain both of my Q11 are shot as everything around IC1 looks good.

It took me days of reviewing my soldering to figure it out as I was hesitant to believe both units had the same component failure. Wild luck would have it though.

That sounds unlikely. If you have built two simultaneously there is a possibility an error was duplicated in each. Still, it wouldn't take long to swap out each FET to prove your hypothesis.

 

[Hynek]

That sounds unlikely. If you have built two simultaneously there is a possibility an error was duplicated in each. Still, it wouldn't take long to swap out each FET to prove your hypothesis.

Bought as a pair but built consecutively.

Can't disagree with it being unlikely but there doesn't seem to be all that much to that part of the circuit and I've measured and value verified everything to death. Mike is kindly sending another pair of 5457s so I'll know end of the week what my hypothesis amounts to.

 

[Hynek]

That sounds unlikely. If you have built two simultaneously there is a possibility an error was duplicated in each. Still, it wouldn't take long to swap out each FET to prove your hypothesis.

Thanks for your assistance. Both babies work as a charm and sound very nice.

If anyone cares for a few observations I made through the build

- for my situation 1k5 for R222 worked better than the supplied 1k2, with 1k2 I ended up maxing out VR2 when calibrating
- google for something like "SPDT 1P2T 2 Position 3 Pin PCB Slide Switch" if you wish to have dot/bar modes selectable solderlessly
- I consider standoffs for the meter board a must especially if you plan on ever using the stereo link, you will be pushing on the meter board with the 3.5mm TSR jack that is only held in place by the 10-pin SIL connector, if your top side standoff interferes with any heat sink you may have on Q6 then at least fit the bottom side standoff, it is mechanically the more crucial of the two anyway
- aesthetically, you may prefer to cut the pot shafts shorter and grind the pot nuts smaller to make them fit and hide in the bottom of the knobs, it will allow you to slide the knobs closer to the front panel and only leave a small gap which you may find pleasing to the eye

 

[mnats]

Thanks for your assistance. Both babies work as a charm and sound very nice.

The issue was the FETs as you thought it was?

If anyone cares for a few observations I made through the build

- for my situation 1k5 for R222 worked better than the supplied 1k2, with 1k2 I ended up maxing out VR2 when calibrating
- google for something like "SPDT 1P2T 2 Position 3 Pin PCB Slide Switch" if you wish to have dot/bar modes selectable solderlessly
- I consider standoffs for the meter board a must especially if you plan on ever using the stereo link, you will be pushing on the meter board with the 3.5mm TSR jack that is only held in place by the 10-pin SIL connector, if your top side standoff interferes with any heat sink you may have on Q6 then at least fit the bottom side standoff, it is mechanically the more crucial of the two anyway
- aesthetically, you may prefer to cut the pot shafts shorter and grind the pot nuts smaller to make them fit and hide in the bottom of the knobs, it will allow you to slide the knobs closer to the front panel and only leave a small gap which you may find pleasing to the eye

Thanks for the suggestions. For what it's worth, I never intended the meter to be used in bar mode as it pushes the current consumption too close to the maximum spec. Should have left the pads off but they were on the proto and never got removed. Standoffs are on my BOM and I agree are required. Using the heatsink I did one fin just needs to be bent to clear the top one. I'd love to have a milled panel and custom nuts but that would push the price up too much! Please post a pic of your solution if you get a chance.

 

[Hynek]

The issue was the FETs as you thought it was?Thanks for the suggestions. For what it's worth, I never intended the meter to be used in bar mode as it pushes the current consumption too close to the maximum spec. Should have left the pads off but they were on the proto and never got removed. Standoffs are on my BOM and I agree are required. Using the heatsink I did one fin just needs to be bent to clear the top one. I'd love to have a milled panel and custom nuts but that would push the price up too much! Please post a pic of your solution if you get a chance.

Yes. It was the FETs and I'm pretty sure I heat-damaged them when soldering. I've gone through spools of solder in my day but I admittedly did a hasty job this time. Looking back, I very much did the best I could to smoke them. Soldered at my "do it all" temperature which I would have still gotten away with had I not soldered all pins at a time and, to make things worse, I pushed the transistors pretty deep which left only short leads to dissipate heat on its fatal march to end the FET's life.

Towards the end of my several days of diagnosing the problem I was confident it was the FETs. Mike was kind enough to send both pairs so I just replaced all four and calibration was a breeze.

As far as bar vs dot, reducing current through the LEDs takes one resistor swap. Naturally, that will also reduce the meter brightness. Anyone who loves the bar mode and is concerned about maxing out supply may want to consider that.

I had no standoffs included in my kit and I quickly resolved to buy some after seeing what I was up  against from mechanical standpoint.

The supplied circular double-disc sink was not a great selection as it was not only interfering with the added standoff but also gently sticking out of the overall footprint of the module. Nothing two minutes on a grinder couldn't fix. I ended up grinding the side of the standoff itself a tad too to reconcile the whole territory dispute.

What I did with the nuts was nothing artistic. I just ground all corners making the hexagon a 12-sided shape small enough to get absorbed by the knob.

I will post photos as soon as the mini switches show up in the mail and I can finally call the whole thing finished.

Impressed with the sound so far!

 

[useme2305]

https://www.youtube.com/watch?v=Gcmoc6XUo6I

is this behavior in BAR mode correct? i mean, the fact that all leds are lit when no gain reduction is happening and unlighting downwards as the gain reduction increases? kinda weird. or is this normal?
it's basically reverse of what i expected it to be and i just wanna know if this is intended.

 

[Hynek]

The issue was the FETs as you thought it was?Thanks for the suggestions. For what it's worth, I never intended the meter to be used in bar mode as it pushes the current consumption too close to the maximum spec. Should have left the pads off but they were on the proto and never got removed. Standoffs are on my BOM and I agree are required. Using the heatsink I did one fin just needs to be bent to clear the top one. I'd love to have a milled panel and custom nuts but that would push the price up too much! Please post a pic of your solution if you get a chance.

OK, it's all done and dusted.

This first picture shows the added nylon standoffs. A 6mm one on the bottom between the L-bracket and the main PCB, and a 20mm in between the PCBs. I also used 6mm standoffs on top instead of just nuts after I repeatedly bumped into one of the electrolytic caps on the meter PCB when trying to insert the module into the rack in between two other modules. This way the standoffs will take the beating instead.

You can also see the trimmed output transistor sink. More importantly, and I admittedly didn't do a great job of capturing that detail, the sink also has a chunk ground out of it on the side facing the standoff. The standoff itself is gently shaven too. That gave me a decent size gap but not enough to use aluminum standoffs and risk fatal issues.

I would have loved to actually screw the bottom standoff to the L-bracket as that would further stiffen the structure and the thread is already there but I didn't find any place to source the correct screws. Drilling the hole in the L-bracket just deep enough may also prove to be more challenging then what it looks like.

 

[Hynek]

The issue was the FETs as you thought it was?Thanks for the suggestions. For what it's worth, I never intended the meter to be used in bar mode as it pushes the current consumption too close to the maximum spec. Should have left the pads off but they were on the proto and never got removed. Standoffs are on my BOM and I agree are required. Using the heatsink I did one fin just needs to be bent to clear the top one. I'd love to have a milled panel and custom nuts but that would push the price up too much! Please post a pic of your solution if you get a chance.

...this one shows the trimmed pot nuts to make way for the knobs to sink deeper on the shafts and closer to the face plate.

The little metal bit in the forefront isn't dirt, it's a piece I made that's the same shape as the negative space that's missing from the ratio selection switch shaft. I use it every time with builds that have that issue. A little bit of work but it makes the knob sit a lot nicer when tightening the set screw.

 

[Hynek]

The issue was the FETs as you thought it was?Thanks for the suggestions. For what it's worth, I never intended the meter to be used in bar mode as it pushes the current consumption too close to the maximum spec. Should have left the pads off but they were on the proto and never got removed. Standoffs are on my BOM and I agree are required. Using the heatsink I did one fin just needs to be bent to clear the top one. I'd love to have a milled panel and custom nuts but that would push the price up too much! Please post a pic of your solution if you get a chance.

...and finally with the knobs on and a better view of the added micro switches to select between the LED meter modes.

Now let's make music!

 

[Rickstar44]

Hello
I just purchased three FET/500 Compressors and am very happy with the kits, one problem.. I am a novice builder and started with the Rev A build. I have been over the build sheet and schematic sheet several times and cant seem to find anything out of place. all my solders seem to be good, every cap and diode and relay in the right direction. I could use some advise on next step "short of sending it to hairball and pay the $100 to fix it" the PK light stays lit and the GR light will not work. Trying to calibrate and no signal out to my DIMM. I have a Purple sweet 10 rack, Pro tools 12 with the signal generator set to 1000Hz  -18dB, Fluke 179 Meter. If there were more discussions I would be happy to  keep plugging along but....
Thanks

 

[sebperry]

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!

 

[Echo North]

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!

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