CAPI 2-ACA-BO in a Soundcraft 200b

[jstark]

Hey y'all,

just finished up installing a CAPI master section in my Soundcraft 200b:

Installation was pretty painless.  Everything is sounding great...still ironing out a couple issues: the meters now seem a bit off, and there is now a strange spot at about 15% fader where things actually get louder.

If anyone is interested in any details or more pics, please let me know.


cheers,
David

 

[living sounds]

This looks very interesting, any more information? 

 

[gar381]

Pics PLEASE !!

GARY

 

[jstark]

glad this is of interest!


the first step was moving the stock chassis gnd connection and installing the standoffs:




next I test fit the board and tested to make sure it was passing signal without smoke release.  (also a nice shot of Gary's excellent DOAs):




removed the stock fader wiring, soldered in new fader connections, and the lifted one leg of both LK1 and LK2 and connected these to the ACA input:




I tried the stock feedback R value first, but this was turning square waves into sine waves by 10kHz.  This turned out to be the easiest way to fix that:




after vacillating for a while on how to connect the booster outs, I decided to take them directly to the XLRs on the stock output PCB.  Thus, the signal gets "backfed" into the headphone amp through CON2.




here's the schematic with mods:




It sounds great!  I think I'm still going to tweak the ACA feedback R again: I used some resistors I had on hand, so I ended up on the low side of the stock gain, which has me pushing faders farther than I'm used to.


(thanks gar381 and jsteiger for such great contributions!)


peace.
david.

 

[gar381]

Nice David !!

This is a wonderfull upgrade for your 200b

Use a cheap 25 turn trimmer for your feedback R.
This will let you nail your fader pos.

ALso try a 990c DOA in the summing pos. to
see what you think. Mike (hairball) makes a very nice 990c kit
if you need a source.

GOOD JOB!!

Best

GARY

Having looked at your schemo a bit closer, A few things to try.

Place your fader in between the summing amp and line driver stages of Jeff ACA pcb
and bypass the socuncraft fader amp.
Also try tieing your  -ACA out to audio gnd.

 

[living sounds]

Interesting! So this is a kit from classicapi? How much DC does it put out (in my 200b the entire signal path is free of DC blocking caps)? How did measurements change, how did the sound change?

 

[jstark]

Use a cheap 25 turn trimmer for your feedback R.
This will let you nail your fader pos.

great idea!

Having looked at your schemo a bit closer, A few things to try.

Place your fader in between the summing amp and line driver stages of Jeff ACA pcb
and bypass the socuncraft fader amp.
Also try tieing your  -ACA out to audio gnd.

yeah, I should have spent some more time on that schematic; it's sorta misleading, I suppose.  basically, everything between LK1/LK2 and SW1 has been cut.  the master faders are sitting between the ACA and booster, as you suggest.  When I get some free time, I intend to play around with different grounding schemes.  (although I suppose I should implement Mr. Ciletti's mod first...).

Interesting! So this is a kit from classicapi?

indeed: http://classicapi.com/catalog/product_info.php?cPath=22_46&products_id=403

 

[living sounds]

This looks pretty straight forward, I'm tempted.  The EA 2623-4 seems to be permanently out of stock, how did you get it?

And again, how does it sound compared to the stock arrangement?

As for grounding, the star mod is good, but what's even better (though a lot of work) is to also isolate the audio ground from the pwr/decoupling ground. This cleared up the sound quite a bit, and also lowered noise/hum (again).

 

[CalGTR]

This looks pretty straight forward, I'm tempted.  The EA 2623-4 seems to be permanently out of stock, how did you get it?

It will eventually come into stock again. Jeff Steiger (CAPI) would know better, of course.  If you are not patient enough to wait, or if you have a shorter-term need, there's no reason why you can't wire up an appropriate tranny (perhaps another version of the same 2623, or maybe 2503, or CMOQ-2 (Cinemag), or whatever) off-board.

 

[lachlan.vercoe]

Thanks for this thread, huge help as I just installed one into my 200b along with the grounding mod.

Everything is working perfectly  on mine but I’m curious if you ever managed to correct your faders being off after putting the 2-ACA-BO in?