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

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Sintech, looks really cool!

I've found that fooling about with it in different ways has shown me a lot.  I'm getting REALLY close to dead quiet on mine.

Since the last time, I've made an input/bus board.  I proto'ed a version using 5532 op amps, but elected to go with THAT 1200.  It works really well!  It's SO much better since I don't float the Lo input anymore, and have a good way to round up and deal with the grounds.  Also, I'm not running cables all around hell and back to assign LCR via switches, but rather doing it with relays on the board.  I'm rather proud of this part, being the relative noob that I am :)

I actually found that some portion of my noise is coming from the Bo section.  If I go direct out from the 2-ACA, it's much quieter.. actually near to the level of the whole unit just being unplugged.  There's just a bit of hum left, which I'm thinking is in my power supply - not sure how to fix that.  I may actually just leave it this way since without the booster I'm actually at unity, which is all I really need in my application.  I had mine set up so that we get -6 from the 2-ACA to BO (I think - it's grounding the lo output from the 2-ACA as per Jeff's schemo) and then the BO was just making that 6db back up again.  No fader involved.

Although, I'd really like to tear apart the BO and see why it's noisy, just because it's bugging me!

So, my ground scheme looks like this:

input sig gnd -> star ground
input/bus board to 4-ACA -> shields grounded to at output from input board only, not at ACA
4-ACA to 2-ACA -> shields grounded at output from 4-ACA only
2-ACA to Bo -> shield+lo to ground at input side of Bo
Bo to XLR -> shields grounded at output side of Bo

Actually, as I write that all down, I notice that at the Bo is the only place where I ground the shields at the input side, rather than the output side.  I guess it helps to say it out loud!  I'll give a shot the other way 'round.

So, so close :)

Let me know what you end up with, Sintech.  I'd love to compare notes.
 
Hey guys,

Just reading all of this info and I'd like to start up by building a 4 Channel Inverting ACA and a 2 Channel ACA & Booster, and start with only 2 or 4 line inputs.

I was hoping to use Martin's EZ1272 line input boards for the input channels, but the panning and the connection from the output of those into the inverting ACA is what confuses me.  Can someone fill me in a bit on this?

Thanks!
Sig
 
horvitz said:
Jeff, a question for you.. You mention that your bus cables have the shield to ground on both ends.  Is the shield in those cases the actual audio ground?  As in, a single conductor cable using the shield to carry the ground.  In my case, I used a two conductor cable for each channel and have tried running the grounds in a number of different configurations, all with roughly the same effect.  The shields however, are connected to nothing on either end.  I figured the run was so short (maybe 12" ea) that it didn't matter.

I basically have the grounds from all 16 channels bussed together at the LCR assignment switches.  Kinda wondering if this is the wrong approach entirely.  You can see what I've done in the attached picture.  The two terminal blocks on the far left receive the ground for each channel and then you can see it bussed across the bottom to the outputs, which go to the 4-ACA.

It's funny, you can get everything working and then it's the audio-101 junk that trips you up!  I'm hoping that some fresh eyes will see something that I'm not.. one of those things where I need to not think about it for a few weeks and then come back to it and all of a sudden the problem is obvious.

LCR_back_sm.jpg

What is this board, and how do I get one...?

Thanks!
Sig
 
Siegfried Meier said:
What is this board, and how do I get one...?

You don't want one!  Although if you're dying for a marginally useless piece of board, I have two extras that I'll be happy to send you for the postage.  Then you can throw them away instead of me.

I'm not familiar with Martin's input board, but it sounds like if it's got a L and R output for each channel, just strap a 47k on each of those, and then bus 8 of each into the 4-ACA inputs.  If you look at my crappy bus board, you can certainly see where it does just that - 8 on the top, 8 on the bottom, and each can be assigned L, R, or both, where they go through a 47k and then bussed out to the right.

  Brian
 
I think it's just too late for my brain to process anything...

Martin's boards are just line input boards, so they only have a balanced mono out, not L or R...

So you're suggesting that your board is unnecessary?  I am just not understanding at all how or where I would place a pan pot after the (channel ie. line input board), and how that signal would get to the ACA board. 

Please someone help me understand how this all comes together...

Thanks!
Sig
 
Sig,

I am not sure how Neve use to do it but, if you take an unbalanced signal from Martin's line boards to a dual 10k linear pot, slugged with a couple of 2.2K R's(season to taste for -dB point when at center), connect each wiper to a 47K bus R, then connected all the bus R's to the inputs of the ACA, keeping Left and Right separate. That is pretty much it.

best, Jeff
 
Ok, so I should NOT be using the Neve line output transformer then?  Too bad, since it's a big part of the sound...would this still work if I did balance it?

Can you please explain what "slugged" means...I've not heard this term before.

There isn't a simple drawing someone has for all the connections, is there?

Sorry, just trying to get this all to make sense.

Thanks!!
Sig
 
Sig,

Maybe some of the Neve experts would chime in on where to take the signal that you send to the pan pots. API does did it before the output tranny. The output tranny was for Channel Direct Out only, not for the panned-bused signal.

Here is a post with some details on what I have done. I also see some Geoff Tanner and New York Dave info that I found.

http://www.groupdiy.com/index.php?topic=33007.msg402242#msg402242

Best, Jeff
 
Thanks for the info!

Is anyone using these relay boards to handle mute (or perhaps even solo?) in their homebrew consoles?

http://classicapi.com/catalog/product_info.php?cPath=102&products_id=195

Wondering if I should pick up a bunch, and how exactly they would be wired up.

Thanks!
Sig
 
Siegfried Meier said:
Thanks for the info!

Is anyone using these relay boards to handle mute (or perhaps even solo?) in their homebrew consoles?

http://classicapi.com/catalog/product_info.php?cPath=102&products_id=195

Wondering if I should pick up a bunch, and how exactly they would be wired up.

Thanks!
Sig

Anyone know?
 
it's possible to use the one relay per channel for both mute and solo - solo is just "enable mute on all other channels that don't have solo depressed"...

that's how the JLM PM2000 solo in place mod works - it works well on my board. you'll need a "solo bus" etc might take some thinking and legwork.

 
Hi Jeff !
i'm planning to buy the 2-ACA boards to upgrade my tascam M3500,
and i need to evaluate the costs,
are the 4 transformers needed or can i build the 2-ACA with 4 opamps
and only the 2 2503 ?
As my inserts are unbalanced, i thought it's possible not to use the 2623-4,
is it correct ?
best regards,
francois
 
pacemaker said:
Hi Jeff !
i'm planning to buy the 2-ACA boards to upgrade my tascam M3500,
and i need to evaluate the costs,
are the 4 transformers needed or can i build the 2-ACA with 4 opamps
and only the 2 2503 ?
As my inserts are unbalanced, i thought it's possible not to use the 2623-4,
is it correct ?
best regards,
francois
Francois,

Yes, you can build it without the 2623-4's. The only issue you have is that the signal will need to be flipped 180 degrees again. The 2520's in the ACA stage are inverting. This inverting back is typically done with the 2623-4 transformers.

The 2503's could also be replaced with 2623-1's to save a little money. That was the config on the 2488.

IMHO, part of the color/sound of the entire circuit is from the 2623-4's. You will be eliminating some of the API color by not using the 2623-4's. Just a thought...

Cheers, Jeff
 
ok,
now i understand that the 2623-4 not only balance the signal before the fader
but also flip phase after the inverting amps,
Ok i will save a few more bucks and order the whole things.
As i would like to order all parts at once from your shop
(BC/vishay eletrolytic caps etc... )
How do you proceed for sending the BOM for 2-ACA ?
regards,
francois
 
Typically when I ship I send them so I don't forget. The only other things that I have for this build on hand are the DOA sockets and the (4) BC 470uF caps. The rest is pretty simple stuff.
 
Yes, a pair of 10uF/25V and also a pair of 220uF/16V. I don't carry those at the store. You will find that they are expensive. Make sure you get the 138 series.
 

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