[BUILD]CAPI 2-ACA-Bo~Official Support Thread

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andow

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Wow, just discovered this and am really interested! Anybody tried it in a Trident 80?

How many channels can be summed with this board? I guess there shouldn't be a limit, but I'm wondering why there is a cascaded summing in the block diagram?  ???
 

znjamznjam

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Hy

Can be used balanced inputs with this board?
Out of daw via RME fireface, to resistors board to capi 2-aca-bo stereo out balanced via RME in DAW.

thanks in advance
 

jsteiger

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znjamznjam said:
Hy

Can be used balanced inputs with this board?
Out of daw via RME fireface, to resistors board to capi 2-aca-bo stereo out balanced via RME in DAW.

thanks in advance
Yes it can be done. I kinda depends on the interface. The cold leg will likely need to be grounded. Some electronic devices don't like this, some don't care.
 

znjamznjam

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Hy
i have heard that signal from resistor board is too weak. After resistor board signal becomes a microphone signal and it is too weak for input in aca board. Is that correct?
If so I can put an input transformer in between to increase signal to correct input level for aca?
Is that correct.
For Chanel's inputs I will use passive summing resistor board van Ian.
This is idee rme out to passive summing resistor board out to 2 aca board

Thanks in advance
 

jsteiger

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znjamznjam said:
Hy
i have heard that signal from resistor board is too weak. After resistor board signal becomes a microphone signal and it is too weak for input in aca board. Is that correct?
If so I can put an input transformer in between to increase signal to correct input level for aca?
Is that correct.
For Chanel's inputs I will use passive summing resistor board van Ian.
This is idee rme out to passive summing resistor board out to 2 aca board

Thanks in advance
I am not really sure what "resistor board" you are talking about. In a  typical application, 47k bus resistors are used and they are fine with the rest of the 2-ACA-Bo built as we suggest.
 

znjamznjam

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Hy
Something like this one

https://groupdiy.com/index.php?topic=52068.msg665350#msg665350

 

Potato Cakes

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znjamznjam said:
Hy
i have heard that signal from resistor board is too weak. After resistor board signal becomes a microphone signal and it is too weak for input in aca board. Is that correct?
If so I can put an input transformer in between to increase signal to correct input level for aca?
Is that correct.
For Chanel's inputs I will use passive summing resistor board van Ian.
This is idee rme out to passive summing resistor board out to 2 aca board

Thanks in advance

The first stage DOAs on the board do the make up gain for the signal loss after the summing network. The second set is for a fader insert.  The console I installed mine in uses 10k for bus resistors and there is no issue with gain. I've also built a unit using the recommended 47k resistors also with no issue. The only way I can see you having problems is if you are not feeding line level to the summing network.

There are several passive style summing contraptions such as DB25 to two (2) XLRs and the end user is usually instructed to plug it into a preferred preamp for the tone of their liking, but that probably has more to do with the fact that most consumers of pro audio gear won't have, want, or know how to build a dedicated gain circuit for summing.

In conclusion, build one and just follow the instructions. They're awesome.

Thanks!

Paul
 

eternal slang

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Hi all,

I just realized my console PSU is unipolar and would need the -24 rail to power AM10 on the ACA board.
How would you guys do it? Should I use a separate PSU?

Thanks !

Fabien
 

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fragletrollet

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Hello Jeff,

I've noticed that in your ACA schematic you list 47k feedback R, while in the ACA/BO, on the ACA side you list 28k.
I've built a summing mixer with 2520 receiver stages, 47k bus R's and following the ACA/BO schematic, 28K bus resistors in the ACA/BO (47k in booster with a 10k switch). What gain should I expect at the output of the 2503?

How would the gain change with 47k in the ACA?


Thanks and all the best,

 

groselicain

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Wondering if anyone has had any problems from the fader connection between the ACA and Booster sections. I'm using a 1k pot with the 47.5k resistors and wired as the schematic shows. I even emailed Jeff and he confirmed it was correct. Both sides operate correctly when used individually, but there's something very wrong when they're joined by the fader.

To be more specific, the noise floor is untenable with the fader at minimum. As I raise it, the noise goes away but the signal is completely distorted. If I disconnect the ACA output negative, my noise issues are no longer as problematic but I lose gain, and of course I can't get by without the shield on the BO input side. Any ideas?
 

boji

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Might help to draw out your connections.

I've only done some testing, but did not experience any noise issues using a 10k fader.
I used insulated standoffs to mount pcb to console frame. For ACA tx outs, cold legs were tied to console agnd and fader low.

Edit (just read your edit): I've tied both ACA and BO unbalanced input coms to agnd, chassis pins only for use as cable screen.
 

groselicain

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boji said:
Might help to draw out your connections...
I've tied both ACA and BO unbalanced input coms to agnd, chassis pins only for use as cable screen.

https://drive.google.com/file/d/1_11YdpihPsTDgYgHhCyLLN2ius4CJV8G/view?usp=sharing

Here's a picture of what I had. Couldn't get everything in the shot, but yellow and purple run to BO input positive and shield, respectively. When you say you tied BO input common to audio ground, are you saying you did it in addition to connecting the fader common to it? I apologize if I'm not following. Thanks Boji.
 

boji

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If all four units are working fine independently, then it's likely a connection issue.

Looks like you might be feeding Bo into ACA?!? (can't tell since picture is cropped).

Signal should go ACA 2520---> 2623---> Fader--->2520 booster---->2503

 

groselicain

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boji said:
If all four units are working fine independently, then it's likely a connection issue.

Looks like you might be feeding Bo into ACA?!? (can't tell since picture is cropped).

Signal should go ACA 2520---> 2623---> Fader--->2520 booster---->2503

Oh my goodness. Thank you so, so much. I sent these exact same pictures to Jeff and I guess he just never looked at them. With the outputs of each section for left and right being flipped on the board, I should've guessed that the signal flow would be flipped from right to left in the same way—but then again, I never looked at the damned silk screen either.

Thank you Boji, you just fixed everything. I owe you.
 

fragletrollet

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Can I substitute the 33uf PC caps for 47 uf?

Can I turn a Inverting Aca board into 4x fader boosters/output transformer drivers, by omitting c4 and jumping r4, and changing R2 to 47R .5W and use 2503 transfomer? What difference does the R2 (inv aca board) or R8 (ACA/BO board) play in the circuit, and could I use the 2623 instead (keeping 100R for R2?)

 

boji

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Can I substitute the 33uf PC caps for 47 uf?
Going from memory, if the 47's are going to power pins you should be fine.

Can I turn a Inverting Aca board into 4x fader boosters/output transformer drivers
Yeah should be simple value swaps. Again going from memory, R2 sets gain giving +10db in-hand, whereas aca nfb value would be unity with 2623 providing a +3dB boost.

Edit: Jeff sells 1x4 PCB aca's that could be repurposed for make-up gain.


 

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