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

[SIXTYNINER]

8)

 

[Johndcx]

Hey Jeff
I just got the first of your aca boards,my plan is to build a 24 ch summing mixer with them,I may use differant doas on each bank of 8 chs ....
I am a newb in builds so I am just getting my feet wet in this,I want to start with 2 chs and experment with   
Differant things..
So if I get a 2520 kit,2 2623's and 2 2503's will this get me going, +pwr supply??

 

[jsteiger]

Yes, as far as what I have at the store. You will need a stereo fader of some sort and the rest is just smaller bits like Molex connectors, some C's, some R's and a couple of diodes.

PS, I only have a few of the PC mount 2623-4's left on hand. Ed is doing another batch but it may be 5 or 6 weeks before I get them in.

Best, Jeff

 

[Johndcx]

The fader can be a pot like the one one the monitor out on the new 1604s?
Do you sell that bigger API style knob?
To have a balanced line in do I need trfos or can in go into the doa's , and as for panning per ch , how is that done with the Aca?
I hope to order those trfos this week if I can..
Thks

 

[Tubemooley]

I'll weigh in briefly on one of those questions. To get balanced line in, you can do transformer-balanced input with a line-level transformer. Or you can do what's called a balanced-transformerless amplifier or BTA. You can send a balanced signal into one DOA and then the output of that DOA can dump onto your summing bus. Go to Jeff's website and go to the documents section. Look for the API doc which shows different configurations of the 2520 amplifier. One of them is the BTA. DW.

 

[horvitz]

I'll weigh in briefly on one of those questions. To get balanced line in, you can do transformer-balanced input with a line-level transformer. Or you can do what's called a balanced-transformerless amplifier or BTA. You can send a balanced signal into one DOA and then the output of that DOA can dump onto your summing bus. Go to Jeff's website and go to the documents section. Look for the API doc which shows different configurations of the 2520 amplifier. One of them is the BTA. DW.

So, there is a bunch of discussion on page 3 of this thread on just this topic.  It would seem that in the case of electrically balanced outputs from whatever is plugging into this thing, that floating pin 3 is acceptable.  I've just got my 2-ACA together yesterday, so I'm doing a little testing here with just that.  Having some oddball results so far, but I'm fairly certain that it's my grounding situation (isn't it always?).

Of course, it would be rather nice to use an input transformer.  Jensen has a very good doc on this at http://www.jensen-transformers.com/an/an003.pdf.  But, that would get VERY pricey when you start getting up into lots of channels with this thing.  I had a look at the BTA layout in the doc on Jeff's web site, but it's a little hard to see so I'm not sure what to make of it.

 

[jsteiger]

...I had a look at the BTA layout in the doc on Jeff's web site, but it's a little hard to see so I'm not sure what to make of it.

Also take a look at the "API 325 Operation Ref." near the bottom right of the ref docs page. They have a much more clear description of a Balanced Differential Input Amplifier which is more or less the circuit that was used in the consoles. It is the same circuit that Tubemooley was referring too. He is psycho BTW and probably off his meds, so be careful!  Just kidding Dana you Q8 maniac!

As far as floating or connecting the Lo side to ground, it will probably be gear dependent. I do this with a few special patchbay cables that have pin 3 or Lo floating. By using a standard patch cable I am connecting pin 3 to ground within the PB jack.

Also, FWIW, within my console, the shield of almost every cable run is floating at the source and connected at the destination.

The fader can be a pot like the one one the monitor out on the new 1604s?

I am not exactly sure what they are doing on the 1608's. I would gather it is quite a bit different than the old desks. It is for a different purpose but could possibly work.

Cheers, Jeff

 

[horvitz]

As far as floating or connecting the Lo side to ground, it will probably be gear dependent. I do this with a few special patchbay cables that have pin 3 or Lo floating. By using a standard patch cable I am connecting pin 3 to ground within the PB jack.

Also, FWIW, within my console, the shield of almost every cable run is floating at the source and connected at the destination.

Makes sense to me - same thing we do in telecom.  Copper is always grounded on only one end in order to avoid group loops.

I think that I'll be ok with leaving the lo floating.  Seems to be working well in my testing so far.  Perhaps I'll put a small switch on the back on the case on the input to connect it to ground or not as needed.

 

[Johndcx]

Thks guys,I am still getting my head around the summing amp doa ins,do I need acas for left and right?
I want to have many stereo pairs with a few mono switches like the Dgr stuff.
The more I think about ,I don't need level controls that can all be done from PT,
I just want the clean discrete signal path to the iron for color?

 

[Tubemooley]

It is the same circuit that Tubemooley was referring too. He is psycho BTW and probably off his meds, so be careful!  Just kidding Dana you Q8 maniac!
Cheers, Jeff

That would be a big 10-4 good buddy. Psycho? That's an understatement. But I am taking my meds. I just wish my tin foil helmet did a better job of keeping those voices out of my head. DW.

 

[Tubemooley]

Go to that document which Jeff pointed to on his website... "API 325 Operation Ref." near the bottom right of the ref docs page. It's an 8-page .pdf. Go to page 3. That's the circuit right there. Balanced input to one DOA. Output goes to a transformer (of course) on a 325 card. For a clearer version of some of those API doc's, go here.... http://www.danalexanderaudio.com/api.html    .... Watch out..... His site gives these ***** pop-ups. Go down to "Op Amp 2520 #2" and look at Figure 4 Balanced Transformerless Amplifier. The 325 line amp has variable gain (with a pot) while the BTA shown in figure 4 is fixed gain of 20dB (set by the resistors). Plus the BTA has those 10k resistors on the inputs to load the source properly. Those two circuits are pretty similar. DW.

 

[Johndcx]

Thks Tubemooly
those links are very good, if I do the line amps I will need a card for allthat, then I am I want to add some pres to it if I am that far?
Will the 312 pcbs on here work?
Also think about having a neve type trsfo option out that could be switched??

 

[Johndcx]

I think the balanced line in doa is the way to go,I can then use different doa's for more sound choices,all with the same 2520 footprint...
Who on the board could make an 8 ch pcb for line input to 2520's?
And what kind of pwr supply is needed to run 32 or more doa's ?

 

[horvitz]

So, this thing is coming along quite nicely.  I have a perfectly working 2 channel mixer right now, with LCR assigns on each channel.  Just waiting for my switches to do the other 14 channels.

I do however need a little power advice.  I'm a PSU dummy, so I really don't know where to look for these things and my searching here and elsewhere hasn't yielded much.

People have designed and make available lots of power supplies for preamps which make +/- 16 or 24 and +48.  In fact, I have the real nice FiveFish 2448 supply running the thing right now for testing.  What I'd like to do though, is build a dedicated +/- 16 only supply for this project.  I also want it to be big enough to power the 2-ACA+Booster and 4 of the 4-ACA boards (although I'm only running 1 right now).

If anyone can point me in the direction of a PCB or something, I'd sure appreciate it!

  Brian

 

[jsteiger]

Good news Brian.  8)

Did you slug the switch to give you some sort of voltage drop when in the center position? This is possibly being handled in PT or ITB some way. Maybe you don't need this.

So, 4 Inverting ACA boards and a single 2-ACA-Bo card is 20 discrete opamps. Typically, a 2520 style amp will draw around 22-25mA when idle and around 50-52mA when driving a 600 ohm load. That's per rail. That has been my experience anyways. So worst case you will draw 52mA times 20 DOA's is 1040mA or just over 1A. I would gather any supply that will give you 1.2-1.5A will be fine. Actually, the DOA's on the Inverting ACA cards will never draw that much as they have a very small load. You may not find a dedicated 2 rail, bipolar PSU project around. There may be one but I don't recall seeing it. Not to pimp but you could always get a 51x PSU PCB and only build out 2 of the rails. Leave the rest of it unpopulated. Maybe someday in the future you could build out the other main bipolar rails for +/-16V or whatever. Same with the 48V section. Just don't build it. Just a thought.

Regards, Jeff

 

[Johndcx]

Hey Brian
are you using trsfos on inputs,or line cards?

 

[horvitz]

Did you slug the switch to give you some sort of voltage drop when in the center position? This is possibly being handled in PT or ITB some way. Maybe you don't need this.

What I did, was to put the 47k in back of the assign switch, so if it's assigned left it goes through one 47k, if right the other, and if center it hits both (and of course goes both ways).  I compared that to the way that PT handles assigning a signal hard side vs. center and it's almost exactly the same as far as level coming out.  Seems to work well.  Also if I for instance have one center and one left, I get the correct levels out the other side - I was worried about crosstalk, but this setup seems to address it well.

Also, if I have both channels center (or to the same side) and sum them it seems to have a very similar action to PT wrt to gain.  I should redo my tests and document the results.

So, 4 Inverting ACA boards and a single 2-ACA-Bo card is 20 discrete opamps. Typically, a 2520 style amp will draw around 22-25mA when idle and around 50-52mA when driving a 600 ohm load. That's per rail. That has been my experience anyways. So worst case you will draw 52mA times 20 DOA's is 1040mA or just over 1A. I would gather any supply that will give you 1.2-1.5A will be fine. Actually, the DOA's on the Inverting ACA cards will never draw that much as they have a very small load. You may not find a dedicated 2 rail, bipolar PSU project around. There may be one but I don't recall seeing it. Not to pimp but you could always get a 51x PSU PCB and only build out 2 of the rails. Leave the rest of it unpopulated. Maybe someday in the future you could build out the other main bipolar rails for +/-16V or whatever. Same with the 48V section. Just don't build it. Just a thought.

Pimp away! I actually have a 51x PSU built however it's going to power my 51x chassis.. if only someone could come up with some of those custom transformers

But seriously, that's not a bad thought.  Chances are that I'll end up going down that road since I think you're right, a dedicated 2 rail PSU project doesn't seem to exist.  I had considered making my own board and just umm.. borrowing 2 rails from one of the other projects.  I may not be a good PSU designer but I'm an excellent copier!  It's just kind of an expensive way to go.

And thanks for the advice on the total expected draw.  That would have been my next question.

  Brian

 

[horvitz]

Hey Brian
are you using trsfos on inputs,or line cards?

Neither, actually.  To keep things simple, I simply floated the lo on my balanced inputs.  I know that this won't work for everyone, but it's just fine for my application.

 

[jsteiger]

I myself see nothing wrong with this especially if you don't have really long cable runs. PRR has said many times around here that there is nothing wrong with unbalanced cable runs in a studio.

FWIW, the majority of the connections in my console are unbalanced. Maybe they did not have the same concerns back then with interference but my desk is pretty damned quiet, even now. Anyone who has built the 2-ACA-Bo knows that it is unbalanced busing. I know that balanced busing was one of the things that Paul Wolff introduced when he took over API.

Best, Jeff

 

[Johndcx]

The inputs will get a +4 balanced sig from a pro t, Brian have you seen how dangerous 2 bus does the switch? It's all stereo pairs and when you hit the switch it's 2 monos(for kick sn bass center voc)
So one bank of 8 would be all you need for mono switch 4 swt = 8 monos..
I want 24 because the more chs you sum out the better the results..
I am still not clear on how many ins per doa , the diagram show 8 ch per ?