The parts we supplied are correct. Maybe its your DMM's battery?
[BUILD] CAPI FC526~500 Series~FET Limiter Kit~Official Support Thread
- Thread starter jsteiger
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Deadly Mix
Audio-engineer
I haven't encountered that before. Are you saying multimeters have trouble measuring high resistance as their batteries wear?
They are the correct resistors, according to the stripes. It's just the measurements that are out of the margin of error.
Like I said, I know the parts are good. I would suggest a fresh battery and see what happens. I just measured a bunch of parts and they are will within spec. Both of these are on reels so I suspect from the same batch.
OK, time to cast my lot in here. I'm attempting to go through the calibration process. Last night I was having a hard time getting readings consistently, so I figured it was cold solder joints somewhere. Touched that up, and now during the Q-bias setting process, I'm getting a little more output than expected (1.97 vAC/8.11 dbU). I'm also getting a quiet but audible hum when no test tone is applied, and I wonder whether that raised noise floor is contributing to my readings. These are my first three test point readings:
TP1: 6mV (nominal)
TP2: 121mV (a hair high)
TP3: 984mV (also a bit high)
Also, my TP9 is bang on at -10V, and I have the expected +/-15V on A3. I tested that 0252 in another module and it sounds fine there.
Is this device particularly sensitive to flux residue? I've cleaned it, but I don't feel like the flux remover I have is great. Tends to leave things kinda sticky. If not that, any other ideas where a hum might be coming from?
Also, for the benefit of posterity: I made a big mistake initially in this build, which was that I didn't notice that RV1 and RV2 aren't interchangeable, despite the fact that they have the same value. I flipped them, so neither trimmer was accessible. With difficulty, I managed to extract them and swap them. By turning RV1 as far clockwise as it will go, I can stop the meter lights from being illuminated, which I'll take as a sign that the part still works (I also measured them both before putting them back in, seemed fine). Anyway...don't be like me and do that if you're looking to build one of these.
TP1: 6mV (nominal)
TP2: 121mV (a hair high)
TP3: 984mV (also a bit high)
Also, my TP9 is bang on at -10V, and I have the expected +/-15V on A3. I tested that 0252 in another module and it sounds fine there.
Is this device particularly sensitive to flux residue? I've cleaned it, but I don't feel like the flux remover I have is great. Tends to leave things kinda sticky. If not that, any other ideas where a hum might be coming from?
Also, for the benefit of posterity: I made a big mistake initially in this build, which was that I didn't notice that RV1 and RV2 aren't interchangeable, despite the fact that they have the same value. I flipped them, so neither trimmer was accessible. With difficulty, I managed to extract them and swap them. By turning RV1 as far clockwise as it will go, I can stop the meter lights from being illuminated, which I'll take as a sign that the part still works (I also measured them both before putting them back in, seemed fine). Anyway...don't be like me and do that if you're looking to build one of these.
Here's my line of thinking at the moment: when the compressor is active but GR is off, the audio path is something along the lines of input transformer > A2 > A3 > output transformer (kinda educated guessing here). Since I know my A3 to be good, the question is whether I can detect the noise at TP1 or TP2. If I detect it at TP2 but not TP1, it suggests DTO5 as the likely trouble spot? I won't have time to play with this until later today or this weekend, but that's where my head is at right now.
Maybe I'm off base in thinking there's a problem here at all. I forgot that the input and output are both cranked to the gills. I put my Hairball FET/500 rev A in the rack and cranked its ins and outs all the way, and I'm getting about the same level of self-noise. Does a noise floor of about -47dBFS seem about right? Anyway, I guess I'll continue with the calibration procedure and see where I end up.
Edit: yeah, I think I was just psyching myself out about my measurements being a little higher than the guide says. I got it calibrated with no extra trouble and it's sounding great. Especially that ABI mode.
Edit: yeah, I think I was just psyching myself out about my measurements being a little higher than the guide says. I got it calibrated with no extra trouble and it's sounding great. Especially that ABI mode.
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museric
Member
Good to know! I have a pair of these in the box awaiting the soldering iron. I foresee much sonic tastiness in the results when assembled.
Watch those 2K trimmer pots. Put the front-facing one in the right spot, or you'll be cursing yourself. Also don't forget the DTO5...I got confused initially because the available build guide is for the old version that used three DOAs, and I also ordered a 553F at the same time and assumed it belonged to that, so I was confused why I had zero output until I looked at photos of some other builds and saw I was missing a crucial part. And obviously, triple-check resistor values and orientation for polarized components, yada yada.Good to know! I have a pair of these in the box awaiting the soldering iron. I foresee much sonic tastiness in the results when assembled.
The 526 is much more transparent sounding than my FET/500 rev A, which has sort of a crunchy vibe as part of the deal. Should be useful when I don't want to hear the compressor working.
museric
Member
Got it - thank you for the tips. I’ve a pretty strict setup method I use to verify parts (esp for complex kits), so I’ll make sure to stick to that, and pay close attention to said items.
