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

[jsteiger]

BUMP

Lot's of folks here trying to find a way to calibrate ITB, myself included! Want to order the new version as there's no THD calibration, but I don't want to bite off more than I can chew. Having watched the hairball compressor calibration video's and understanding the the basic principles behind analog  dbu &  digital dbfs and it's relativity to you're interface/AD daw  etc... it's all a bit much. Care to chime in DIY Gods?

Its just some simple math and depends on your DAW reference level. For example, if your system is -18dBFS = 0dB, then just offset my -30dBu numbers by -18 so you would use -48dBFS. For the +7dBu level you would use -11dBFS and of course for 0dBu it would be...you guessed it -18dBFS. 

 

[geardude]

EDIT I SWITCHED UP the 470 RESISTORS: PROBLEM SOLVED!

Thanks Jeff, got all the numbers sorted out and written down now thanks! Just built a pair and testing with Rogue 5 op amps and I'm getting the same results on both.... Preflight I get -9.96v DC at TP9 & +2.49DC @ MTR point 11 so looking good there.

 
however upon  flipping to active after turning all the knobs to their respective positions I noticed no led's light up, and  I get a signal drop not an increase to +7.75

STEPS

So is it possible I've flubbed both builds audio path, and need to go on to the testing points now?

 

[jsteiger]

You will have to use the test points guide and trace thru the audio path. Maybe something went sideways on the DTO5 amps...

 

[jsteiger]

Please post a pic of the top of the PCB for one of these.

 

[geardude]

Please post a pic of the top of the PCB for one of these.

Sure thing here's a link including Test Tone settings + Dt05
https://www.dropbox.com/sh/kdhtmnl9ekghx9t/AADTpgihw2YvpSdha_xjQlSZa?dl=0

 

[jsteiger]

You can (and should) confirm that what you think is 0dBu from your signal generator actually measures 0.775mV AC with probes between XLR pins 2 and 3 of the output of your convertors or what you are using for a signal generator.

Your TP1 results look close but things go south at TP2. That tells me its something with the DTO5 or surrounding circuity.

 

[jsteiger]

Are you 100% sure the FET is not conducting?

 

[geardude]

Are you 100% sure the FET is not conducting?

I believe so turned rv2 fully CW till it clicks. I'll confirm the output with the Dmm here shortly.

 

[jsteiger]

Is your DMM set to AC volts?

 

[jsteiger]

I believe so, In auto range mode and switching to manual for me I'm getting the same readings

Attach a pic of the DMM as you are using it.

 

[geardude]

Ok so after much finagling and clearing everything in totalmix fx( a nightmare btw) I'm finally getting the proper signals out of both generators.

Changed cubase signal settings to -9 as that's my +4dbu


Attached pics with settings. Going to go ahead and continue with trace point measurements. More posts to follow

 

[geardude]

Alright so finally working out all the kinks at confirming that I'm getting 1.219v whilst sending a 0db signal out at -9dbfs. not .775mv


Sending the 1kz out at -39dbfs and flipping to active:

TP 1: 9.5mv
Tp 2: 1mv
Tp 3: 6.9mv

 

[jsteiger]

Alright so finally working out all the kinks at confirming that I'm getting 1.219v whilst sending a 0db signal out at -9dbfs. not .775mv


Sending the 1kz out at -39dbfs and flipping to active:

TP 1: 9.5mv
Tp 2: 1mv
Tp 3: 6.9mv

OK so change your output lower by 4dB so you get 0.775mV. That would be -13dBfs. Your offset will be 13dB below my specific -30dBu.

For this test, do you have a known good 2520 amp installed and is the module under power? Connected to a rack or extension jig?

 

[geardude]

Alright will do thanks jeff! And yes with a rogue 5 I have other known working gars around too. And yes under power through the extension jig

 

[geardude]

Ok at -34

Tp1  6 mV
Tp2  .7mV
Tp3  4.2mV

Are all signs pointing to the dto5? I can also try another op amp though brad's rogue 5 is brand new.

 

[jsteiger]

Ok at -34

Tp1  6 mV
Tp2  .7mV
Tp3  4.2mV

Are all signs pointing to the dto5? I can also try another op amp though brad's rogue 5 is brand new.

Yes its the DTO5 area.

 

[jsteiger]

Ok at -34

Tp1  6 mV
Tp2  .7mV
Tp3  4.2mV

Are all signs pointing to the dto5? I can also try another op amp though brad's rogue 5 is brand new.

I just zoomed in on your pics and I can see that you have mixed up some R's. Not sure of the extent but I for sure see that R28 should be a 470k and you have a 470R in that position.

 

[geardude]

Oh wow well that's what I get for using my old dmm- was going to go over all the resistors here after dinner! Nice catch!!

 

[jsteiger]

Oh wow well that's what I get for using my old dmm- was going to go over all the resistors here after dinner! Nice catch!!

There are also 47k's on the build so you gotta be careful.

 

[geardude]

So as previously mentioned,  I flubbed  and swapped those on BOTH modules...having accidentally switched 470R and 470K resistors.  Double checked the other close looking resistors (47k & 470R) to confirm they are correct as well.  Firing them up and now I'm finally getting proper readings at the trace points.

They are as follows

Tp1:    6 mV AC
Tp2:    119mV AC
Tp3    958mV AC

Alright so looks like I'm good to go ahead with calibration!

Thanks Jeff, when I'm in nashville a Beer is on me!