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

[JW]

This question concerns the "booster" boards that Jeff also has available. I wasn't sure where to post so thought I would here.

I'm trying to make a 4 channel 312 mic preamp out of one of these boards.

On these boards, there is one CR1 and and one CR2 diode for the main DC power rails supplying all 4 opamps.  And there are 10R resistors in series on the main DC rails locally (close to each 2520)

I can see the other mods I need to make to make it into a 312, but do I need these 10R resistors to isolate each 2520? And is the value (10R) good for a mic preamp?

Just asking because they aren't there on say, a single channel of CAPI VP312.

 

[boji]

If you short out your system, you'll be happy a 10 ohm resistor took one for the team instead of your opa.

 

[orangerec]

So, I'm trying to revive this 24x2 summing mixer. I'm finally going to finish this project (thanks covid?). Here's my signal flow: out of my Apollo 16>line xfrmr(600ohm out unbalanced)>pan pot(10kpan from CAPI) or LCR switch, 47k ohm buss resistors>CAPI ACA. My question is, do I have to worry about crosstalk between channels with a LCR switch or panner or is the ACA a virtual earth (VE) design and I don't have to worry? Thank you.

https://www.capi-gear.com/catalog/images/gallery/pots/BI/Passive-pan-pot-network.pdf
https://www.capi-gear.com/catalog/images/gallery/PCBs/2-ACA-Bo/2-ACA-Bo-Block-diagram.pdf
https://capi-gear.com/catalog/images/gallery/PCBs/2-ACA-Bo/CAPI-2-ACA-Bo-Rev-B.1-schematic.pdf

 

[boji]

do I have to worry about crosstalk between channels with a LCR switch or panner or is the ACA a virtual earth (VE) design and I don't have to worry?

Yes aca's use virtual earth, but you should always be concerned about crosstalk. 

A solid return reference and PSU is a must, as well proper shielding both in wire runs and overall design.

 

[orangerec]

Thanks boji! Yes, I'm using the CAPI floor power supply. As well, proper shielding is always good practice. Another question: I'm leaning toward the LCR switch for a simpler design. All i could find is a 3 position 4 pole switch. Am I right in assuming that I could still use it as a single pole, ignoring the others? Also should I go for a shorting or non shorting switch? Here's a link to the switch if you're inclined? Thanks again!

https://www.mouser.com/ProductDetail/Alpha-Taiwan/SR2511F-0403-19R0B-E9-S-W-159?qs=8%252Br4Hz5Xir%2FmSW9A%252BgefJA%3D%3D

 

[boji]

Am I right in assuming that I could still use it as a single pole, ignoring the others?

Yes, but might as well double-up poles. Btw I'd move questions like these off the ACA support thread.

 

[znjamznjam]

Ok, I just finished standalone summing mixer with capi aca. I have hem simple as can make. Sound is same or even better than my SPL MixDream. Its little bit more open from mid to high. Not much more difference. I have build mine arround 500€ and SPL is 1000€.

 

[znjamznjam]

Foto 2

 

[znjamznjam]

Foto 3

 

[znjamznjam]

Foto 4

 

[znjamznjam]

foto 6

 

[shortyboyboy]

Hello! I was looking to add this to my Trident 65 master section. I am wondering if it can be mounted in the board and if it needs to be hooked up to the psu. I apologize if my questions seem amateur. Thanks for reading!

 

[skidmorebay]

Question about populating the 4-Channel Inverting ACA pcb's. I'm using these for pre-summing 32 channels in groups of 4 before going into the ACA-Booster pcb. (I know the ACA-Booster can sum this channel count, but I just want the additional pass through more discrete electronics.)
Jeff's description of the 4-channel Inverting ACA pcb in the CAPI store says "By using 28K feedback resistors, the discrete opamps will provide no additional gain within the console's 2-mix signal path (unity)." But the schematic actually shows 47k resistors and 27pf caps in the feeback path. The ACA section of the ACA-Booster pcb uses 28k and 47pf.

If I'm going for unity gain through the 4-Channel Inverting ACA's, should I go with 47k/27pf in the feedback path for the 2520's, or 28k/47pf which is what the ACA stage of the ACA-Booster pcb uses?
thanks,
JS

 

[Potato Cakes]

Is the summing before the ACA done passively with a resistor network? The schematic shows 47k as that provides the make up gain needed for eight channels of summing via resistors (20log(1/8) = -18.06dB), which is how it would be implemented in a console build. If you didn't need any gain, then 28k for the feedback would give you unity through the circuit.

Thanks!

Paul

 

[skidmorebay]

Paul,
Thanks, I think that finally went into my brain. Yes, I'll have eight channels per inverting ACA, through 47k resistors.

I can see now why the ACA's on the ACA-Booster card that comes after use 28k, since they aren't summing multiple sources. Just curious - what makes that stage -2db?

 

[Dimitree]

hello everyone, I'm wondering if using INV-ACA and ACA Booster modules it is possible to build a simple "mixing console", I mean 24 channel mono Line inputs with Pan, faders and mutes, + 4 subgroups and 5 or 6 aux channels (for external FXs), and a master LR fader.
I guess it is possible but I still don't understand how many, and which, modules would I need

 

[AW]

Hi everyone
I was thinking of adding the CAPI 2-ACA-Bo to my Tac Scorpion I, can anyone tell me exactly where this would be inserted. I want to install it inside the board itself if possible.
I have schematics of my board so I could take a partial screen shot of the area where it can be connected if someone wants to look at it.

Thanks Tony

 

[JW]

So, if the N channel transistors are not used (no mute or talkback) can't I just bypass them on the schematic? I couldn't find a certain answer for this in the thread. I know Jeff recommends having them in there and grounding the gate if the mute function is not used, but why? Can't I just jumper over them?

 

[jsteiger]

So, if the N channel transistors are not used (no mute or talkback) can't I just bypass them on the schematic? I couldn't find a certain answer for this in the thread. I know Jeff recommends having them in there and grounding the gate if the mute function is not used, but why? Can't I just jumper over them?

Yes just jumper over them. Its been mentioned in the past.

 

[danielchodges]

Hello,

I am working on adding an eventual 4 more of these in my console, to handle the 8 group/record busses. Several years back I modified my master section to use the capi ACA card and have been thrilled with the results.

My question is, how many of these can be "daisy chained" for power? Additionally, if in total I have 5 of these in my console (a sound craft 500, with the "medium console psi"), am I risking overtaxing my power supply?

Thanks for any insight.

- Daniel