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

[grubbyliver]

Josh,
I don't see any schematic link but what you're describing basically sounds right, if you give up a pair of busses which will become your new 2 bus feeds then when you select bus 7/8 on the channel modules they feed the aca + bo directly.

Now it seems to me that it should be possible to send busses 1 - 6 into the 2 bus also by somehow taking an unbalanced feed from these busses somewhere and running these through some resistors and into the aca inputs also - may require running some wires between modules but should be doable, leaving you with a 32x6x2 desk. Surely overall summing would be improved by using aca+bo boards on the groups as well but that would be a much larger and more expensive task, indeed there may not be room enough inside your desk to do it.

On the old API desks, i think the 2 bus feed from the groups is taken after fader and booster amp but before the output transformer which may provide a less hot signal but I am not certain of this.

 

[JdJ]

Josh,
I don't see any schematic link but what you're describing basically sounds right, if you give up a pair of busses which will become your new 2 bus feeds then when you select bus 7/8 on the channel modules they feed the aca + bo directly.

Now it seems to me that it should be possible to send busses 1 - 6 into the 2 bus also by somehow taking an unbalanced feed from these busses somewhere and running these through some resistors and into the aca inputs also - may require running some wires between modules but should be doable, leaving you with a 32x6x2 desk. Surely overall summing would be improved by using aca+bo boards on the groups as well but that would be a much larger and more expensive task, indeed there may not be room enough inside your desk to do it.

On the old API desks, i think the 2 bus feed from the groups is taken after fader and booster amp but before the output transformer which may provide a less hot signal but I am not certain of this.

I must be asleep at the wheel as usual...  Hopefully I manage to get it attached this time.

Looking at the docs on ClassicAPI the topology doesn't look that different between the API and our PM2K.  I just can't decide whether to give up the sub-masters 7&8 as you mention above or to keep all 8 submasters (called programs on the schematic) and replace one of the "matrix" pairs with the 2-ACA.

Basically as I see it (from a routing perspective) if I go the way you say, I give up a pair of subgroups and have to do more wiring to get the subgroups (1-6) to feed into the new stereo bus (7 and 8) - but I gain the ability to send the individual channels directly to the stereo bus.  If I instead replace a matrix pair I keep all 8 submasters but have to route each channel through at least 1 of them to get to the stereo bus...

Decisions... 

 

[ramshackles]

Thinking about building this as a simple summing box for DAW output.

I thought about putting on/off switches after the mix resistors so that I could also treat it as an input selector for my monitors if need be.

However having, say, 16 switches for each pair of channels seems a very clumsy and time consuming switching method (consider needing to switch between a mix on channels 1-15 and some other source on channel 16 :S)

Is there a better way to do it??

Thanks..

 

[JdJ]

What about one switch and a bunch of relays?  Too expensive?

 

[ramshackles]

What about one switch and a bunch of relays?  Too expensive?

How would it work with just 1 switch?

 

[JdJ]

How would it work with just 1 switch?

Thinking a little bit more about it - it sounds like you just needed to switch between 2 sources in your previous post: 1-15 and 16 (alternate source).  Is that the idea?  If so (and here's where this goes beyond my knowledge) couldn't you switch the inputs between these two sources?  For example a L/R buss rail for 1-15 and a L/R buss rail for 16 (Aux input).  I'm not sure if the relays being on the inputs of the ACA would cause noise since they are before the summing amp - someone else will have to address that one...

Best of luck,

Josh

 

[ramshackles]

I think I will just have another couple of inputs that avoid the summing card altogether & just use a rotary switch between them to select after the summing...

 

[JW]

Hey Josh,

I think you should try to wire up the ACA in substitution of a pair of programs first so you can directly compare the difference between the original programs on the PM2K and the ACA. I don't particularly feel it's worth it to be running an entire mix through (a pair of the programs?) on the way to the ACA just so you can utilize two more mono busses. If I understand you right? (actually I'm thinking I'm not understanding you right because this would essentially be the same thing functionally, as you lose the independence of those 2 busses by forcing them to be assigned as the mains on the way to the ACA? Hmmmmm.



The way I plan to do it, I think, is to get (3 more?) ACA boards to substitute for the 6 remaining (mono) programs in the PM2K, and make those routable into the 2 buss ACA. You would have to hard wire these outputs on the back of the buss bar (straight into the main ACA-2), because I don't think there is a way to route a program to a program on the PM2K, without using the matrix (right?)

Anyway, you could run the remaining ACA's on the mixers +/-24V and use the existing yamaha opamps, which sound good anyway, and would save some cash, and you wouldn't need another power supply. Actually, you could do that for the main buss as well, but I sure do love those 2520's.  I'd like to know if the PM2K transformers could substitute too, at least at one stage.

I'd like to hear what Jeff thinks about this. Perhaps he will recommend using the inversion PCB instead for the other busses. But I'd like to retain the direct outputs (at full level) of the other program busses in the PM2k for stuff like bouncing (I'm on 8 track most of the time) Anyway, I'm just thinking out loud here. Probably all things you've already considered.

I think once you hear the difference between the PM2K Programs and the ACA, you'll want to be routing the input channels directly to the ACA, even if it means sacrificing two busses.

 

[JdJ]

Hey JW-

Yeah - after much cosideration and talking to Fletcher's tech we are going to use Programs 7&8.  The plan is to make it modular - combining 2 used master section frames, a P&G stereo fader as well as a regulator board for the power and some metalwork so the section can be plugged in to the old 7&8 Program spots.  Obviously we will have to route the connectors to the proper outputs & jacks in the body of the console still so it won't be true plug&play... 

I hadn't thought of using the existing DOAs but that is an interesting idea for when we do the other programs.  We already have some red dot 2520s for the first round.  Have you tried the Yamahas in your ACA?

I figure if we really are jonesing for the existing programs for submixing we can patch them in at the patchbay - we'll have to feed them back into channel inputs but it'll give us the option for a work around if necessary.

Thanks for the input!  PM2K's unite!!!

-Josh

 

[Fuccimain]

sorry if I missed this, but what is the ideal buss source impedance that feeds this ACA-Bo card?  I see on the classicapi  page it says signals should be routed thru 47k buss resistors, and the block diagram shows 2 INV-ACA cards feeding the ACA_Bo card.. so with 8 channels out of the INV on 47k buss resistors,. is the ideal Buss source impedance 5.8k?  thinking my buss source impedance will be around 2.35k, so I'm curious if/what I need to change to make the inputs on the ACA-Bo "happy" .is it feedback resistors that need to be modified?

does that make sense? sorry for nebbish question

s

 

[jsteiger]

A standard 2-ACA-Bo will easily sum 40 channels or so, all thru 47k bus R's.

 

[Fuccimain]

cool.

but is there an ideal load it wants on the input?

 

[globule_655]

Hi there !
Great thread ! Lots of really useful informations.

I still have a few questions though. I'm planning on building 2 things around the 2-ACA-Bo cards.

First, a summing box using the attached circuit for inputs (sorry for my poor drawing skills...). So my first question is : as this circuit uses the inverting input of the opamp too, I guess I wouldn't have to revert polarity at the output of the 2-ACA-Bo, am I right ? Stupid question I know but I just want to be sure I didn't misunderstood anything.

Next question is about my second build. I want to build a sidecar with mic pres (like 12 or 16 API312 pres), EQ based on the 553 schemo on Jeff's website but with 2 or 3 frequency per band (if at all possible, I'll ask when I build it), direct outs per channel driven by 325 cards with a fader, and 8 busses.

So, regarding buss assignement, can I just add a switch per busses on each channel, each one attached to a 47k summing R or does it require additionnal buffering ? Also where am I supposed to wire this ? Right after the fader and before the 325 card of after if and before output trafo ? Or maybe use a mult after the output trafo ?

Thank you very much !
Cheers !

 

[Chad.saxton]

I am building the 2-aca-Bo and I would like to incorporate a pan circuit.  Does this forum have an opinion on whether I use the dual gang pot method or the single gang pot method?

Thanks

 

[Coldsnow]

I'm using the booster side as makeup for a pultec filter.  With the 10k pot in front, anyone know what the input impedence of the booster side would be?  Would it be better to use a tpad after the transformer output? 

 

[Cosmonaut]

I'm working in a little sidecar with 8 modules from a Trident 65, and I'm planning on using the ACA board for the main L-R, but I have some doubts...the main one is what is needed for the the summing amp with main insert and master fader? It's ACA board, 4 DOA and 4 TX?

The second one is about the summing bus resistor, as I see in the schematics, the R from all busses is 12K(groups, main and auxes), but before this in the main, there is a pan circuit with a pot and a resistor in paralel with the wiper, should I take in account this pan circuit for the maths?

the schematic is on google drive, page 63 is the input circuit diagram.

https://docs.google.com/file/d/0B0LxNUBYfNL8OUFrNnYtQVcxaDg/edit

 

[jsteiger]

I'm working in a little sidecar with 8 modules from a Trident 65, and I'm planning on using the ACA board for the main L-R, but I have some doubts...the main one is what is needed for the the summing amp with main insert and master fader? It's ACA board, 4 DOA and 4 TX?

The second one is about the summing bus resistor, as I see in the schematics, the R from all busses is 12K(groups, main and auxes), but before this in the main, there is a pan circuit with a pot and a resistor in paralel with the wiper, should I take in account this pan circuit for the maths?

the schematic is on google drive, page 63 is the input circuit diagram.

https://docs.google.com/file/d/0B0LxNUBYfNL8OUFrNnYtQVcxaDg/edit

The 2-ACA-Bo will be what you need. You will have to adjust the feedback R and C of the ACA stage to work properly with your 12k bus R's but that will be no problem.

 

[Gachet]

Hi there

I have a few questions after reading almost all the post here.
What is the purpose of the two 2623 transformers? Looks like providing balanced output for insert and return is unbalanced.
Do I need those if just want an output fader with no insert point?

Can i use the input 2520 as a differential input amplifier(like in the 2520 brochure? I already have hot and cold separately summed in my config. 

Thanks

PS: jsteiger do you know when EA2503 will be back on stock?

 

[jsteiger]

Hi there

I have a few questions after reading almost all the post here.
What is the purpose of the two 2623 transformers? Looks like providing balanced output for insert and return is unbalanced.
Do I need those if just want an output fader with no insert point?

Besides balancing the ACA output, they also provide 6dB of gain and bring some "API tone". They can be skipped but you will have to adjust to make up the 6dB.

Can i use the input 2520 as a differential input amplifier(like in the 2520 brochure? I already have hot and cold separately summed in my config.

The PCB is not designed for this. It may be possible but you will have to check it out on your own.

PS: jsteiger do you know when EA2503 will be back on stock?

Should be today or tomorrow, from what I've been told.

 

[Gachet]

The PCB is not designed for this. It may be possible but you will have to check it out on your own.

Of course, I was asking about the topology. transformer or differential input.
I could also use the transformer before the aca input.

Anyway thanks for the quick answer.
Can't wait to place my order....