[BUILD] CAPI FC526~500 Series~FET Limiter Kit~Official Support Thread

Ok, sounds like there's non-linear stuff happening with the ratio/threshold, maybe even one of those funky 'S' curve knees that a few comps produce. 

Slightly off topic but related. Dorks like me will find this fascinating! SSLTech explains ABI things nicely. http://prorecordingworkshop.lefora.com/topic/3841871/All-Buttons-In-1176#.VX3dvWAVqFJ

Jeff,
I'm having problems with the calibration section.
My signal generator only goes down to 0.1 volt, so I don't think it can generate anything less than -26dBu,
I tried to use a computer generated signal, but my fluke DMM readings are jumping around and I don't know if I can trust it.
Sorry to be so technically challenged, is there a louder level that could be used to calibrate?
Thanks,
-Steven

steveau said:

Jeff,
I'm having problems with the calibration section.
My signal generator only goes down to 0.1 volt, so I don't think it can generate anything less than -26dBu,
I tried to use a computer generated signal, but my fluke DMM readings are jumping around and I don't know if I can trust it.
Sorry to be so technically challenged, is there a louder level that could be used to calibrate?
Thanks,
-Steven

Click to expand...

You should be fine at -26dBu. Just keep in mind that all levels stated will be 4dB hotter. This is only during the first few steps (VVR adjustment & audio path dbl check). I chose -30 because one can safely run both pots wide open and not worry about anything clipping.

Jeff, et al

Howdy. I am having some issues with calibration on both of my units. When I feed aprox -30dB (-.024v) in to test the audio path I am getting the same voltage reading at TP1. At TP3 I have 2.898v.

I have a 1731 in the receiver slot and red dots in the other two opamp slots. All three opamps work well in my VP28.

Seems obvious that something is wrong with my audio path but I am no expert on these and am not sure where to start trouble shooting. Any suggestions would be greatly appreciated.

Thanks!

tctonn said:

Jeff, et al

Howdy. I am having some issues with calibration on both of my units. When I feed aprox -30dB (-.024v) in to test the audio path I am getting the same voltage reading at TP1. At TP3 I have 2.898v.

I have a 1731 in the receiver slot and red dots in the other two opamp slots. All three opamps work well in my VP28.

Click to expand...

So you get appx 24mV AC at TP1 with 24mV AC signal at the input? Try different opamps in the receiver spot. If it persists, post a pic of the group of R's between the receiver amp and the output transformer.

jsteiger said:

tctonn said:

Jeff, et al

Howdy. I am having some issues with calibration on both of my units. When I feed aprox -30dB (-.024v) in to test the audio path I am getting the same voltage reading at TP1. At TP3 I have 2.898v.

I have a 1731 in the receiver slot and red dots in the other two opamp slots. All three opamps work well in my VP28.

Click to expand...

So you get appx 24mV AC at TP1 with 24mV AC signal at the input? Try different opamps in the receiver spot. If it persists, post a pic of the group of R's between the receiver amp and the output transformer.

Click to expand...

BINGO! Thanks for the quick reply Jeff. I swapped out a couple opamps and touched up a couple dodgy solders and everything works perfectly. I don't know exactly what was wrong but I don't care now because this thing is great. Thanks again!

'Chung has been making some progress on the build! He has 2 sets of pics up in the 2nd and 3rd post of this thread.

I'm setting up the build for my pair and I'm doing sorting sheets. Just noticed a possible minor error on Chung's beautiful pics. I believe the white metallized polyester C6 & C7 caps are labeled '•22J63' and not 'n22J100' (which is the C5 cap). I'll PM Chung in case he doesn't see this.
Edit: Chung's inbox is full, and I wasn't able to reach him thru his homepage, so perhaps Jeff could alert him?

to clarify, on C6 and C7, just ignore the "22n j100" to the right of chungs sort sheet, his marking of ".0 22uf 63v" on the left is correct.
Jeffs build guide and the PCB Bom are great. I just grab the bag he suggests in the BG, then grab whatever resistor hits my fingers? put it on my MM, look at his PCB Bom that lists values( in low to high order), read the position of the value in hand, and stick em in till their gone.
It seems the step of organizing with sheets is a waste for me because my obsessive nature will not allow me to NOT put the part on my MM just before I install it haha

that said, Chung's build threads are legendary!

btw, i also suggest building in pairs, it's like double checking yourself as you go 

Jeff, I remember reading somewhere that when soldering a couple of transistors you switch between them to not overheat. This is the first time I'll  solder ICs directly to the PCB. Are those sensitive to heat too? Make sense using the same method?

Unit7 said:

Jeff, I remember reading somewhere that when soldering a couple of transistors you switch between them to not overheat. This is the first time I'll  solder ICs directly to the PCB. Are those sensitive to heat too? Make sense using the same method?

Click to expand...

Yes they are and I use the same alternating method for them.

Jeez Jeff, this kit, build wise, is my fav so far. Everything fits perfectly and it looks super neat. Kudos.

I have a problem w calibration. Everything measured and seemed perfectly by the book until the final stage at step 8 of the GR meter calibration. I noticed that the action of RV8 isn't 'backwards' as described, resulting in (I believe) that when toggling GR on/off and trimming RV1 and RV8 accordingly, the measurements gets more and more off. Anything obvious comes to mind?

BTW, I have the Litz version (triple checked the wiring..)

Cheers
Paul

Unit7 said:

I noticed that the action of RV8 isn't 'backwards' as described, resulting in (I believe) that when toggling GR on/off and trimming RV1 and RV8 accordingly, the measurements gets more and more off. Anything obvious comes to mind?

Click to expand...

This part of the build is a little odd and hard to describe. RV8 does not work backwards but the entire procedure is conceptually "backwards". If you are getting farther away, then turn RB8 in the opposite direction.

Unit7 said:

when toggling GR on/off and trimming RV1 and RV8 accordingly, the measurements gets more and more off.

Click to expand...

I have not been able to return to mine, but this part seems to match my last attempt.  Regardless of rotational direction, the instructions specify an order in which you set each voltage, and doing exactly that, one after another, made the opposite measurement get further away when returned to, until the trimmers maxed out.  Maybe the directions need a rewrite.  I'll be re-trimming to the mid points and trying again whenever I can get to it. 

jsteiger said:

Unit7 said:

I noticed that the action of RV8 isn't 'backwards' as described, resulting in (I believe) that when toggling GR on/off and trimming RV1 and RV8 accordingly, the measurements gets more and more off. Anything obvious comes to mind?

Click to expand...

This part of the build is a little odd and hard to describe. RV8 does not work backwards but the entire procedure is conceptually "backwards". If you are getting farther away, then turn RB8 in the opposite direction.

Click to expand...

Ahh I get it! The manual says:
"This can be a little tricky since it works opposite of how you might think", which I thought referred to how the RV8 trimmer behaves, because that trimmer is mentioned in the previous sentence. But it's just a description of a little backwards procedure overall.

So Doug, if you read it the same way I did: If (when) you get an off value with GR on, just blindly turn the RV8 a couple of turns in the 'wrong' direction, making the measurement even further away from the target 2.245V. Then switch GR off and adjust RV1 to 2.487V. Keep doing that and you'll get closer and closer.

I did that and was able to get one unit perfect and the other almost, because the RV8 hit the bottom and I settled for 2.489V with GR off and 2.235V with GR on. The meter behaves, but Jeff would you say that is close enough, or is there something funky about the RV8 hitting the bottom?

Going to play with these now!

emrr said:

the turning was specific to the correct direction to hit the voltage listed for the step at hand.

Click to expand...

Exactly what I did at first. But you shall not aim for the listed voltage when trimming the RV8 (GR on), instead trim further away. Then, because of the interaction trimming the RV1, with every step you'll get closer instead of the opposite.

Unit7 said:

I did that and was able to get one unit perfect and the other almost, because the RV8 hit the bottom and I settled for 2.489V with GR off and 2.235V with GR on. The meter behaves, but Jeff would you say that is close enough, or is there something funky about the RV8 hitting the bottom?

Click to expand...

I think that is a little funky. There should be plenty of room on both trimmers to cal the meter in perfectly.

jsteiger said:

Unit7 said:

I did that and was able to get one unit perfect and the other almost, because the RV8 hit the bottom and I settled for 2.489V with GR off and 2.235V with GR on. The meter behaves, but Jeff would you say that is close enough, or is there something funky about the RV8 hitting the bottom?

Click to expand...

I think that is a little funky. There should be plenty of room on both trimmers to cal the meter in perfectly.

Click to expand...

Thanks Jeff! Played with them for a while (GOOD SH*T MAN!!!) and they seem to sound/behave very similarly, so I'll probably have to get back to this more later. But now, while at it, any suggestion on where to start looking except go over all solder points?

Yes that and R's behind the Grayhill switch and around the IC opamps.