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

[murphster_matt]

Too All Guys having problems with TP2 during the first part of the calibration (Q-Bias) on a XFMR model and before you start scrutinizing your DT05 and resistors.....

DOUBLE CHECK YOU HAVE BRIDGED THE JUMPER ON RV7! (that little nugget costed me 4 hours)

I used logic pro x and the built in Test Oscillator plugin, output pointed towards the FC526.

0.0245 V = approx. -30dbu, measure with RMS voltmeter across Pin 2 & Pin 3 XLR out, adjust DAW out to get 0.0245 V and bypass all the patch bays and other crud

Good Luck, Mines Awesome Thanks Jeff!!

Matt

 

[daveriot]

i have two of the rev1 comps. one is working perfectly. the second unit tests spot on with all of the test points except in meter cal tp10 with 7dbu of GR in im getting -0.826 vdc and vr8 does not change this. meter is pegged . Ive gone through the cal several times to determine if i missed something and reread this thread.

any input would be appreciated!
thanks

 

[Mkinsella3]

Has anyone experienced having the Peak LED illuminating as soon as the module is plugged in?

And any issues with getting the MTR TP 11 to read the proper voltage?

 

[Mkinsella3]

Too All Guys having problems with TP2 during the first part of the calibration (Q-Bias) on a XFMR model and before you start scrutinizing your DT05 and resistors.....

DOUBLE CHECK YOU HAVE BRIDGED THE JUMPER ON RV7! (that little nugget costed me 4 hours)

I used logic pro x and the built in Test Oscillator plugin, output pointed towards the FC526.

0.0245 V = approx. -30dbu, measure with RMS voltmeter across Pin 2 & Pin 3 XLR out, adjust DAW out to get 0.0245 V and bypass all the patch bays and other crud

Good Luck, Mines Awesome Thanks Jeff!!

Matt

What do you mean by "Bridged" RV7 Jumper? I was told to leave that portion blank.

 

[jsteiger]

What do you mean by "Bridged" RV7 Jumper? I was told to leave that portion blank.

In the BOM it says RV7 is not used and to "Jumper it". On the PCB silkscreen for RV7 it says JUMP and theres a silkscreen line connecting the 2 pads to jump.

IF THIS IS NOT DONE FOLKS YOUR COMP WILL NEVER WORK.

 

[Mkinsella3]

So I am encountering an issue where as soon as I plug my module into my rack, the Red Peak LED illuminates, plugging in the module also causes the preamp next to it to peak even though there is no signal going into either module. Please give me any suggestions or ideas on how to fix this issue.

 

[jsteiger]

So I am encountering an issue where as soon as I plug my module into my rack, the Red Peak LED illuminates, plugging in the module also causes the preamp next to it to peak even though there is no signal going into either module. Please give me any suggestions or ideas on how to fix this issue.

Does the unit pass signal properly according to all of the Test Points?

 

[Mkinsella3]

So I am encountering an issue where as soon as I plug my module into my rack, the Red Peak LED illuminates, plugging in the module also causes the preamp next to it to peak even though there is no signal going into either module. Please give me any suggestions or ideas on how to fix this issue.

Someone please get back to me on this. I can't seem to get this issue to stop I've tried everything I can think of!

 

[jsteiger]

Someone please get back to me on this. I can't seem to get this issue to stop I've tried everything I can think of!

You never answered my question. Have you passed all audio Test Points? Is the unit properly calibrated? What 2520 style opamp is in it and who built it?

It is possible that the peak LED is illuminated and doing its job because you are clipping the unit but you have not given us any other info to go on.

 

[Mkinsella3]

You never answered my question. Have you passed all audio Test Points? Is the unit properly calibrated? What 2520 style opamp is in it and who built it?

It is possible that the peak LED is illuminated and doing its job because you are clipping the unit but you have not given us any other info to go on.

Sorry I didn't see your original response. I will do all the tests and calibration etc that I can later today and let you know.

 

[jsteiger]

Sorry I didn't see your original response. I will do all the tests and calibration etc that I can later today and let you know.

The peak LED is the last thing I would worry about. If your unit is not passing audio or is all jacked up, that could explain the peak LED. BUT one thing at a time.

 

[Mkinsella3]

Joe the only thing that's really throwing me off, is why would plugging in the FC526, cause the pre amp in my rack to also peak,  and have the vu meter and peak led indicate that the preamp is clipping???

 

[jsteiger]

Joe the only thing that's really throwing me off, is why would plugging in the FC526, cause the pre amp in my rack to also peak,  and have the vu meter and peak led indicate that the preamp is clipping???

Who's Joe?

I have no idea but once you verify that the FC526's audio path is OK or not, we'll get to that.

 

[Mkinsella3]

I didn't realize I needed to keep the VVR FET baggie so I no longer have it. Is there an average bias voltage range that should be seen at TP7?

 

[jsteiger]

I didn't realize I needed to keep the VVR FET baggie so I no longer have it. Is there an average bias voltage range that should be seen at TP7?

I keep records of them all so I can look that up BUT that is not how you bias the VVR FET. Its done by running audio signal and looking for the mentioned amount of dB loss. Have you followed the proper calibration instructions? No where in there do I say to bias that FEY by measuring the DC voltage.

 

[Bowener]

HI Jeff.

I have an interesting situation that a couple of posts have touched on here, but I don't seem the get resolution from the posts.  I've built several CAPI kits (love em all!), including  a couple of FC526 units.  Both the ones I built work perfectly.  This week, an online acquaintance sent me two FC526 units to calibrate for him.  First unit fired up great, and calibrated with no issues.  7db of gain reduction show 7 on the LED stack.  The second unit passes audio just fine, and I'm able to get 7 db of gain reduction after biasing the FET, but no matter what, the LED ladder is full on all the time.  With gain reduction off, I can get the first LED to come on as it should, but checking test point 9, I can never get the voltage positive, even after sweeping the entire range of the trimmer beside TP 9.  What could this be?  I'd love to fix this for this poor unfortunate fellow, as he's already spent a fortune on shipping, and sending him back one unit with non-functioning meters is not the outcome he expected.      Thanks, and keep up the fine work!

 

[jsteiger]

HI Jeff.

I have an interesting situation that a couple of posts have touched on here, but I don't seem the get resolution from the posts.  I've built several CAPI kits (love em all!), including  a couple of FC526 units.  Both the ones I built work perfectly.  This week, an online acquaintance sent me two FC526 units to calibrate for him.  First unit fired up great, and calibrated with no issues.  7db of gain reduction show 7 on the LED stack.  The second unit passes audio just fine, and I'm able to get 7 db of gain reduction after biasing the FET, but no matter what, the LED ladder is full on all the time.  With gain reduction off, I can get the first LED to come on as it should, but checking test point 9, I can never get the voltage positive, even after sweeping the entire range of the trimmer beside TP 9.  What could this be?  I'd love to fix this for this poor unfortunate fellow, as he's already spent a fortune on shipping, and sending him back one unit with non-functioning meters is not the outcome he expected.      Thanks, and keep up the fine work!

Highly possible he got the VVR and MTR FET's mixed up. If the pinch off voltage of the MTR FET is not more positive (closer to zero) than the VVR FET, it will never track.

FYI...MTR FET's are usually in the -1.1 to -1.4 range. VVR FET's are in the -1.4 to -1.7 range (when properly biased).

 

[Bowener]

Highly possible he got the VVR and MTR FET's mixed up. If the pinch off voltage of the MTR FET is not more positive (closer to zero) than the VVR FET, it will never track.

FYI...MTR FET's are usually in the -1.1 to -1.4 range. VVR FET's are in the -1.4 to -1.7 range (when properly biased).

Thanks for that tip Jeff.  I appreciate that you want to steer this kind of info to the support page so that other may benefit!    I'll quote your email response here for context:

"I would first verify that's what his problem is. One of the TP's is the VVR FET's gate. Depending on your DMM it can skew the reading but I would almost guess that you could check the good one and then check the bad one to see if they are close. I ship matched VVR FET's when someone orders a pair so they should only be off by no more than .005 volts."

So according to the docs:
"TP11 Gate lead of F4 the VVRFET"

So those readings are a good place to start...  I'll check back in when I'm back on the bench.  Thanks for the great service!

 

[santiagoclement]

Hi,

I am new building preamps and comp. I´ve just build an FC526 and I would like to know for the bias, how do I monitor the output level with my DMM,? I am using a Daw and a plugin for the sine wave at 1khz.

Thanks in advance.

Regards,

Santiago

 

[jsteiger]

I am new building preamps and comp. I´ve just build an FC526 and I would like to know for the bias, how do I monitor the output level with my DMM,? I am using a Daw and a plugin for the sine wave at 1khz.

I think it would be much easier and more accurate if you would monitor the output of the FC526 by going back into your DAW.