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

[gbesouchet]

Thanks, Jeff!

Please list it!
I'm thinking about making it 8 stereo ins and 8 mono ins. For the mono's I just need to split the input to 2 different 47k resistors, one to each 4-Inv ACA, is that right?

Regards,

Gabriel

 

[jsteiger]

Yes that is correct.

 

[living sounds]

EDIT:

Everything works now and sounds great! Turns out the faders were to blame, also fixed the feedback R and C as described here.  8)

 

[JW]

Hey Jeff,

Just hypothetically speaking . . .

Let's say I have 8 channels of Yamaha PM1000 input strips that I want to turn into a simple mixer on the cheap. Now, let's say I have 4 600:600 output transformers, and also a bunch of Yammie discrete opamps (These opamps are from the Pm2000 and run on +/-24V) However, my power supply for the input strips is +48VDC. It's huge though, a 3A supply. So there's a ton of current available.

I've already built the ACA buss for my big mixer, and I love it. I'm just wondering if there's a way I can make it work for a little portable discrete 8X2 with a not so standard B+ and some different transformers.

Hmmmm.

 

[GVK]

hi.

Could I use the 2 ACA Bo to add some analog color to the stereo bus of my ITB mixes?
I'd be feeding it from the balanced output of my DAW's two channel USB interface.

How much color could I actually add to a mix this way? 
I guess I'd have to hit the transformers fairly hard to make a difference... a result that's not perceivable would be pointless.

Could the circuit then directly drive a pair of active speakers & headphone amp, and be suitable to patch back to the interface so I can capture mixes back into the DAW for file export?

Cheers - S

 

[Dr_J]

Hi Jeff,

I just thinking about the next projects going for 
I came up with the idea of a little rack mixer, 4 to 2 or two times 2 to 1.
(Pre mixing some mic preamp signals before going into the DAW).

Then i stumbled over your "Classic Inv-ACA", could he do the job?
Is there a way to add some (mixing) pot faders as well?


ROCK-ON!

 

[JayDubrek]

Dr-J... Hakanai is releasing a 4 input version of his 'stereotype' board in the White Market. This will drive four faders and is designed to sit in front of the ACA....  Hope this helps!
Jay

 

[kante1603]

An ACA-BO might be even better because you can have a master fader (or pot) then.

Best,

Udo.

 

[Dr_J]

Hi,

thanks for pointing me to the Hakanai boards; looks good.

ROCK-ON!

 

[darnell]

Hey all,

Just putting the finishing touches on populating my pcbs.  Wanted to ask a couple questions.  I've already bugged Jeff (who is always extremely helpful) but maybe someone has done this already.

I am looking to build a 16 ch summing mixer with the 2aca-bo on the end, and 4 of the 4ch aca inverting boards.  The idea is to have a 2520 on each input that sums to the 2aca board.  I was thinking just populate 4 4ch boards so I end up with 8 left and 8 right.  I think this would essentially be what is going on with the API 7800/8200 without all the panning/level/mutes, which i don't need.  Is that correct?

With that in mind, would I need the 47k input resistors if I'm only sending 1 signal per 2520 on the 4ch boards?  Or can I just go straight out of my Lynx to a TRS jack with the - floating (or grounded)  to the input of the 4ch aca? Jeff said balancing the inputs might be unnecessary if I'm not doing long runs, and my PB for my Lynx will be a few inches above this summing mixer. 

Also, should I just input my 4ch ACA boards (ch1-4)output into the other 4ch ACA board (ch5-8) via the aux in area to get 8ch per side? it seems like that would tie all the 47k summing resistors to 1 buss point to send to the input of the 2aca-bo. 

Anyone who did this, please feel free to chime in.  I have 2 of the 4ch boards populated and my 2ch aca-bo is ready too, so im going to try to get things going in the next couple days. 

Thanks in advance.

Daryl

 

[jsteiger]

Yes you still need the bus R's. They can't be eliminated.

 

[darnell]

Yes you still need the bus R's. They can't be eliminated.

Thanks Jeff!!!

I was trying to avoid bugging you again with more questions. Thanks for once again helping out.

Ill be ordering more 4 ch boards in a couple days.

Daryl

 

[skidmorebay]

Hi,
I configured an ACA board with THAT line receivers as an eight-in/two-out summing amp, using four gar2520's. It's worked fine for a while. I just acquired four API 2520's date-marked 2010. Strangely, I get frequent intermittent left or right channel drop outs and occasional pops with the API's. I've checked the power supply rails, and both are at +/- 16V.
I re-installed the gar2520's one at a time, but the problem didn't go away until all of the API's had been removed. Hard to believe that all four API's would be defective. Is there any reason that gar2520's would work fine in this circuit but API 2520's wouldn't?
thanks!
JS

 

[jsteiger]

Not to my knowledge. They should be interchangeable. I would go thru the real 2520's one at a time and see if some or all are bad. Maybe someone sold you some faulty ones?

 

[AUDIO-ON]

Hi there!
I want to build a basic Mixer with the Hakanai Input Boards, 16 channels, and the 2 aca Bo as Summer. My question is about implementing a Monitor controller and headphone amp. The booster has 3 outputs. 1 output as master output. The other output could feed the monitor controller. Is it suitable to feed an passive attenuator without compromising the main output? I think the outputs are transformer isolated? Where can I feed the headphone amp and a VU meter? The -6db output? Or shall I feed the monitor fader from the mult output from the aca board and feed another booster for the monitors?
Thanks,
Rafael

 

[living sounds]

I love my 2-ACA with APP992 op amps on the mix bus. 

But I've got a question regarding the circuit: What's the role of the parallel resistor and cap before the transformers? A cap by itself would be obvious - blocking DC - but the low value resistor kind of defeats that purpose, doesn't it?

 

[kante1603]

I love my 2-ACA with APP992 op amps on the mix bus. 

But I've got a question regarding the circuit: What's the role of the parallel resistor and cap before the transformers? A cap by itself would be obvious - blocking DC - but the low value resistor kind of defeats that purpose, doesn't it?

I would be interested too,maybe Jeff can shine a light on it?
Meanwhile a little question on the APP992: Do you run it from +/-16vdc or the higher +/-24vdc?
I'd like to do some experiments with them too since I made some very good experiences in my other builds.
Wondering if the ACA/BO is safe to use with higher supply voltages.


Thanks in advance,


Udo.

 

[jsteiger]

But I've got a question regarding the circuit: What's the role of the parallel resistor and cap before the transformers? A cap by itself would be obvious - blocking DC - but the low value resistor kind of defeats that purpose, doesn't it?

Well, keep in mind that the 2-ACA-Bo is a replication of what API did in my console. From what I have gathered, the R in parallel with the output coupling cap forms an RC filter to help flatten out the bottom end. Also from what I have found, this was first added to the 550 EQ by Wally Heider in the early '70's. Wally hacked in a 47R in parallel with the 400uF coupling cap before the 2503. This RC then started showing up in the output stage of many other API circuits. Typically, there is very little DC offset especially in the ACA or booster circuits. The actual DC voltage at the opamp's output will drop over the parallel R (easy to measure). It is typically less than 80mV so will be even less when it reaches the output transformer's primary (Ohms law). If there is a major problem and you have a spike in DC offset, the 47R will usually smoke due to the uber high current across it so the output trafo will still be protected. Many of the 512C's and EQ's have charred evidence of this burnt 47R. 

If you are using something other than an API style 2520 or 1731, I would suggest measuring the DCV after the RC to make sure you don't have anything higher than 80-100mV.

 

[kante1603]

Aha,great,thanks for the explanation Jeff!


Best regards,


Udo.

 

[ppa]

But I've got a question regarding the circuit: What's the role of the parallel resistor and cap before the transformers? A cap by itself would be obvious - blocking DC - but the low value resistor kind of defeats that purpose, doesn't it?

Well, keep in mind that the 2-ACA-Bo is a replication of what API did in my console. From what I have gathered, the R in parallel with the output coupling cap forms an RC filter to help flatten out the bottom end. Also from what I have found, this was first added to the 550 EQ by Wally Heider in the early '70's. Wally hacked in a 47R in parallel with the 400uF coupling cap before the 2503. This RC then started showing up in the output stage of many other API circuits. Typically, there is very little DC offset especially in the ACA or booster circuits. The actual DC voltage at the opamp's output will drop over the parallel R (easy to measure). It is typically less than 80mV so will be even less when it reaches the output transformer's primary (Ohms law). If there is a major problem and you have a spike in DC offset, the 47R will usually smoke due to the uber high current across it so the output trafo will still be protected. Many of the 512C's and EQ's have charred evidence of this burnt 47R. 

If you are using something other than an API style 2520 or 1731, I would suggest measuring the DCV after the RC to make sure you don't have anything higher than 80-100mV.

APP992 has an input offset voltage that rarely goes over 15mV and it is however under 25-30mV