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

[JW]

Jeff,

Are the 2503 transformers wired as 600 ohm output? Just curious. I'll need to go back and do another test, but I was feeding an LA 2A with one side of the ACA the other day and it seemed like maybe it wasn't playing nice, but I may be wrong. . . .

 

[jsteiger]

No, 1:2 so more like 300 ohms. Should be fine driving a 600 ohm device.

 

[thomasdf]

I am in the process of building a second version of my summing box. The summing is passive thru 47K bus resistors and then the stereo mix goes into the ACA, a Alps Blue 10K stereo pot acting as a master fader, and in the booster section.
Only the right side is working properly...

I am 100% sure about the overall wiring (summing to the ACA, ACA to the master fader, master fader to the Booster section, Booster section to the output) as I doubled checked it and everything is fine.

I have swapped the 2520 around, the capacitors between L and R on the ACA module... Resistors look and test OK...

So I am confused here, because that d*** left side of the ACA is not working...

I know that you guys may not be of a big help without actually seeing the unit in front of you but who knows, maybe I have forgotten something...
Still have a 60hz mains hum but that is not my main concern for the moment

EDIT : It is now working. For some reason I had to add 2 straps near the output transformer but it is fine now.
Still need to get rid of that mains hum!

 

[mitsos]

Hi guys, I am getting my hands on an old TAC scorpion and have an ACA-BO (the mixer + booster pcb) that I want to "splice" into one of the groups, so that I can use the ACA for mixing and use the stock TAC module for fader/insert/mute/etc.  I think I figured out the patch points ok according to the schematic and will use shielded cable for this, but I noticed the channels have 10K summing resistors.  I assume I should change the feedback R for unity, would this be 10K?  I know I'd have to change the cap as well...

thanks!

 

[mitsos]

hmm, from what I gather, API used 47K bus resistors, so with 28K that gives a gain of 0.59.  To get this with 10K bus resistors I'd need 5.9K feedback R and 220pF cap to keep the -3dB point at 122KHz... guess I'll try this out and see what happens.

 

[Jannee]

My mixer runs from 15 volts power rails, do you think it would be ok for gar2520 op amps in the ACA?

Janne

 

[jsteiger]

Yes that will be fine.

 

[JW]

Anybody got a recommendation for a high quality stereo potentiometer for the ACA? I was using I believe an Alpha pot for awhile, and it's starting to get scratchy. I don't really need a fader, just a nice high quality pot.

And, Jeff I wonder if you might suggest a tweak? I really like the sound of the board, when said pot is opened up pretty wide. The problem is, when I push the inputs on my board, which I also like to do a bit, it starts to clip my converters. Do you have a suggestion as to where to remedy this, so as not to change the sound of the ACA much, but so I can have it opened up pretty wide, and not be clipping my converters?

Maybe a little more resistance somewhere? Perhaps just a different volume pot,? which is why I started this thread.

 

[jsteiger]

Well, I think any changes to the circuit will alter the way is sounds to some degree. It may take some experimentation to see what alters it the least or in a way you can handle. You could use a balanced u-pad after the final outputs. You could also increase the input series R's in the booster stage. The ones following the insert point and fader.

 

[JW]

Just replying concerning my issue a couple posts ago. Sort of an oh-duh moment. I got a new stereo pot for the ACA, one of these: http://www.partsconnexion.com/product7384.html

It solved my gain staging problem. I get the same wide full range sound no matter where the level is set with this pot. I think I had a crappy carbon stereo alpha pot from the parts drawer in there prior.

So, my advice is, don't skimp on your mixers main output pot/fader! I makes a huge difference.

 

[Olegarich]

I bought console where is installed Aca2 summing system. Inventors and booster. Today I've been reparing channels and something happened to summing ( I might damaged it with channel drop or something else). Left channel doesn't work. I need schematics and other documents if there is any. ON web page there is writen that documents are sended to mail with purchase but I've purchased it from other guy (with console) and it's hard to find him now. Could you please send documents to [email protected]

 

[Olegarich]

hey guys. how you guys resolved afl or solo button thing? i mean now when aca installed afl button doesnt work in my case. in my console afl doing 2 things. first it lets sound to pass in threw it routing and secondly it turns on relay on master section that plugs from mix source to afl source. any ideas?

 

[jsteiger]

You could probably adapt the talkback function of the 2-ACA-Bo card to your solo bus signal. I assume your AFL sends those channels to a separate solo bus or pair of buses? You will need to see about the logic for that. There will be a logic bus for AFL. You will have to see the state of that bus when solo is off and when it is activated.

 

[Olegarich]

yeah it sends afl to separate bus. when it off there is no signal coming in to that bus and when its on then signal goes threw that bus and also same switch turn on relay on master section. so how connection should look like?

 

[jsteiger]

Well, actually this should probably be done after the 2-ACA-Bo card. This type of switching would be in the control room module part of the board. The 2-mix signal would typically not be interrupted.

Are you using a monitor controller of some sort, after the 2-ACA-Bo?

 

[skidmorebay]

A simple question:
What is the purpose of the 47K bus resistors? Are they involved in setting the input impedance, or something else?
I am summing eight channels through my ACA. Is 47K the value I should be using there for such a small channel count?
thanks!
JS

 

[Olegarich]

hi
no im not using any monitor controller it goes straight back to the convertor.
by the way how you find which input resistor (47k mostly)
is best choise for your console? i mean how this procedure looks like?

 

[jsteiger]

47k is just what API used in the vintage consoles. I think that was so subgroups could be assigned or switched off with very little load change to the channel booster amp.

 

[gbesouchet]

Hi there,

First post on this thread (though I think I read it all):

I'm planning on building a 24 channel summing, 2 inverter boards, 1 ACA-Bo, so, 12x2520s.
Is it possible to use Classic API floor power supply for it? Is it too overpowering?

Cheers!

 

[jsteiger]

Roughly speaking, twelve 2520's would be in the neighborhood of 300mA per rail. A Dual VPR PSU will deliver 3A per rail so way overkill IMHO. I have a small 2 rail PSU that is good up to 1A. I need to get them listed at the store.