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

[jsteiger]

After installing the new pots post drop test. I re checked the audio path beginning with the transistors. The values you provided were close to my build. I then went back to the primary side of the transformer and found the signal not what it should be it appeared as if the transformer was loading the ckt. I reflowed the secondary side where there was almost no signal. No improvement. I then removed the transformer after which pin one had the correct amplitude. I hoped to check the transformer statically from the CA2622 schematic. I found 68 and 70 ohms on each of the primaries and 1.59K on the secondary. Should these values be representative of the listed 150/600 and 10Kohm printed. Thanks for the help.

No, the datasheet specs are AC impedance values not DCR measurements. Your DCR numbers are right in the ballpark for a normal transformer.

 

[toga]

Hi all,

intending to commence a build of the FC526 XFMR tomorrow. In the absence of a build guide for the updated XFMR model am I right in thinking I can still use Chunger's guide as a general aid? Anything to look out for in terms of particular difficulties associated with the build of the XFMR model?

All the best.

 

[jsteiger]

Hi all,

intending to commence a build of the FC526 XFMR tomorrow. In the absence of a build guide for the updated XFMR model am I right in thinking I can still use Chunger's guide as a general aid? Anything to look out for in terms of particular difficulties associated with the build of the XFMR model?

All the best.

Yes you can use it as a general guide. It is similar and easy overall in comparison.

 

[toga]

Yes you can use it as a general guide. It is similar and easy overall in comparison.

Many thanks.

 

[toga]

So my GND to opamps (-V and +V)  resistance readings checked out as did the 15V test when plugged in. The TP9 DC rail reading is at 10V. Audio passes and the meter functions (uncalibrated) but the audio is very distorted when unit is switched to the active position. I touched up the solder joints but resistors PR3 and PR4 burned out on powering up . Any thoughts? Does it sound like a problem with the DTO5?  The soldering of Transistor at Q5 was very poor and I was unable to remove it and replace.

All the best.

 

[jsteiger]

So my GND to opamps (-V and +V)  resistance readings checked out as did the 15V test when plugged in. The TP9 DC rail reading is at 10V. Audio passes and the meter functions (uncalibrated) but the audio is very distorted when unit is switched to the active position. I touched up the solder joints but resistors PR3 and PR4 burned out on powering up . Any thoughts? Does it sound like a problem with the DTO5?  The soldering of Transistor at Q5 was very poor and I was unable to remove it and replace.

All the best.

PR3 and PR4 are specially for the DTO5 so if they burned you have something wrong on that board. I would check for wrong facing diodes or misplaced transistors.

 

[toga]

To which board do you refer, DT05 or main? Many thanks.

 

[toga]

Diodes and transistors on DT05 all correctly positioned and aligned though Q4 is bodged. Being that initial test readings were good without opamps and unit appears to work correctly only with distorted audio, points to issue lying with the DT05? Happy to order a new DTO5 in the New Year.

 

[jsteiger]

PR3 and PR4 are specially for the DTO5 so if they burned you have something wrong on that board.

The DTO5 board.

 

[toga]

I'm replacing one of the Fairchild 2N5088 transistors on the DT05. Which to choose from? 

https://www.mouser.dk/Search/Refine.aspx?Keyword=2n5088

Thanks in advance.

 

[jsteiger]

I'm replacing one of the Fairchild 2N5088 transistors on the DT05. Which to choose from? 

https://www.mouser.dk/Search/Refine.aspx?Keyword=2n5088

Thanks in advance.

I ship Fairchild with the kits. I think ON SEMI bought them a while back. Most of the suffixes are different packing. Bulk, reel, etc.

 

[AndyKolp]

Hello all,

I'm having some issues straight away when trying to calibrating my FC256 XFMR with Litz compressor.

I'm supposed to have between +2.498V DC and +2.502V DC at the “top” of the the meter resistor string for the
LM339 comparators.

I measured 2.506VDC at this test point. Is this too far outside the range given? Will this effect accuracy of the meter? How do I bring this value to the proper level? Different resistor value somewhere else?

Thanks for any advice.

Andy

 

[jsteiger]

I'm supposed to have between +2.498V DC and +2.502V DC at the “top” of the the meter resistor string for the
LM339 comparators.

I measured 2.506VDC at this test point. Is this too far outside the range given? Will this effect accuracy of the meter? How do I bring this value to the proper level? Different resistor value somewhere else?

That should be fine Andy. I wouldn't call it a problem exactly.

 

[AndyKolp]

That should be fine Andy. I wouldn't call it a problem exactly.

Thanks, Jeff.

Calibration is complete as far as I'm able. Followed the guide several times until I believe I caught all of the steps that I missed in previous attempts. I will say that while the compressor sounds really good, the metering is SUPER sensitive. I'm running a simple drum loop for testing. Meter goes from no gain reduction to slamming 20dB reduction with very little action in between. I'm assuming I may have made a mistake as far as signal generator levels during calibration.

**Gain Reduction Meter Calibration**

3. Apply a 1kHz sine wave @ +7dBu to the input.

I assume that any dBu level mentioned as far as input singal in the cal guide needs to have the dBFS relationship of the interface deducted from your values?

So, a sine wave @ +7dBu from my signal generator in my DAW to theinput would really be -11dBu?
I believe I read elsewhere that this is also RMS level and NOT peak?

Is it also correct that monitoring the output level as mentioned in step 5  (adjusting the compressor output pot when looking for +7dBu output signal) does NOT have dBFS subtracted? Rather, I'd use the VAC of the signal when monitoring any output? In this case, +7dBu = 1.73VAC

I will say, I've learned a ton by working on this unit, which is always a good thing.

Thanks,

Andy

 

[Tschem]

Hello Jeff!
i have the same issues on both of my fc526-xfmr: in audio path i do not get the expected value on the test point T1:
input: 0,025V (-30dBu)
TP1: 0,01V instead of 0,0058V

Comp1: Seems like i'm "off" by the factor of 2
TP1: 0,01V
TP2: 0,254
TP3: 2,055V
Output: 1,014 V

Comp2: Same on the input but there some deviation between DTo5 output and TP2:
DTO5 input: 0,01V
DTO5 out: 0,250V
TP2 & TP3: ~0V
output: 0,009V

every pot full CW, RV2 full CW, DOA works, Litz wire xfmr connections exactly like here: http://www.capi-gear.com/catalog/images/gallery/2623/2623-1-L-specs.pdf

What could be the reason for getting 0,01V at TP1 on both units?
What could be the reason for the deviation on DTO5 output and DOA input?

thx a lot in advance
br, T

 

[jsteiger]

Could possibly be a DMM rounding thing? .0058 would round to .01. Not sure what meter you are using but if the rest of the circuit is correct on the first one I would say its your DMM.

On the 2nd one I'd say you have something wrong on the DTO5.

 

[Tschem]

comp1: at first i also thought about some kind of rounding, but that doesn't explain the other values.
input: 0,025V
TP1: 0,01V
TP2: 0,254
TP3: 2,055V
Output: 1,014 V

this deviates much from the values in the test point guide... 7.75dBu on the output means about 1,9V.
are these values still acceptable?

 

[420troll]

Hi I have just started calibration and Houston  we have a problem  

Test point data received..............

Sine wave at 1k @  0.024vAC into balanced input


Main pcb

TP 1 .      @ .    0v
TP 2 .      @ .    0v
TP 9 .      @ .    -10.01vDC

Meter pcb

TP 11 .  @ .      2.771
TP 5 .      @ .      2.572
TP 1 .      @ .      1.955




Maybe hi res pictures of a finished boards for reference?  Also schematics would be super helpful for me to be able to troubleshoot.
Thank you  for you time and what a fun and beautiful build design, with all parts accounted for. It means a lot to me

 

[jsteiger]

Scroll back to Reply #276 of this thread for TP1 problems.

 

[420troll]

Rob, TP1 is directly after the discrete follower which follows the input transformer. The only thing before that are the bypass relays.

Check the bottom of R71 for input + signal and bottom of R73 for input -. If you don't have audio there, your relays are not switching over properly.

If that is good, check the top of R42 which is immediately following the 2622's secondary.

If that is good then I would look at swapped transistors or something for Q1 and Q2.

R71 and R73 are good
R42 Not sure where to ground the O scope so using the ground point and no signal at R42