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

geardude said:

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?

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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. 

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?

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

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

jsteiger said:

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

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

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.

Are you 100% sure the FET is not conducting?

jsteiger said:

Are you 100% sure the FET is not conducting?

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

Is your DMM set to AC volts?

geardude said:

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

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

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

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

geardude said:

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

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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?

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

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.

geardude said:

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.

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Yes its the DTO5 area.

geardude said:

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.

Click to expand...

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.

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!!

geardude said:

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!!

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

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!