summing mixer with Aca Booster

[ilfungo]

Hi
I want to build a 24 channel passive summing mixer with Aca Booster summing amp.
Suggestions?
Thanks!

 

[keefaz]

ACA means Active Combining Amplifier, so not passive 

 

[ilfungo]

Thanks keefaz
And what I need to do a simple summing mixer with ACA Booster?
Schematics?
Thanks!

 

[gato]

Ilfungo, look here: http://www.capi-gear.com/catalog/images/gallery/PCBs/inverting_ACA/Block-diagram.pdf

 

[ilfungo]

Yes I've seen it but where I can find the schematics?
Thanks!

 

[keefaz]

I think most people use these cards to replace the summing amplifier section in an existing mixer.

If you start from scratch, define your requirements (input gain trim, fader buffer, pan etc..) then use 47k as summing resistors value. Depending on mixing sources and requirements it could be as simple as one opamp per channel
(opamp balanced input -> 47k resistor -> mixing bus -> ACA amp)

 

[ilfungo]

Thanks Keefaz!
Just one question.
I want to use 312 mic amp, for line amp I can use the same board but directly into DOA?
Thanks!

 

[alexc]

Simple summing ..  with just a L assign switch, and a R assign switch .... for each input works quite well with makeup gain provided by a pair of standard 312 style mic pres .

The '312 mic pres' provide classic 'non inverting' gain  block to a passive summed input - including a transformer balanced version. Nothing fancy, just 'voltage summing' with gain makeup.

You could also take that summed input - including a transformer balanced version, to an  'inverting' gain block - the classic, again API,  'ACN' for active combining network.

Sometimes called 'current summing' or 'virtual earth summing' - it's somewhat different to  'voltage summing with gain makeup'.

For low-ish channel counts with very spartan 'facilities' per channel, 'voltage summing with gain makeup' can be awesomely satisfying in sound quality - the 'simple is best' approach.

For anything more than low channel count with only assignment switches, the ACN method is the way to go.  Facilities like gain, variable panning, variable fading, solo etc  .... ACN is pretty much the only way.

Fortunately, ACN *with* a lotsa 'facilities' can be insanely high quality ... modern mixer manufacturers do this every day for very little investment, these days

Personally, I like a combo of 'simple' stuff and modern stuff.

DIY builds lend themselves well to passive, old style 'voltage summing' ...  less is best  approach.

ANything that needs 'facilities', modern small mixers work very well indeed.

I like the 'cluster' approach - a bunch of modern sources making modern stems into some classic mixing, feeding the mastering chain.

Works really well in the 'live room studio' context.

 

[alexc]

I have a bunch of DIY channels ..  preamp + eq +compression  chains

They feed a 'voltage summing with gain makeup' simple sum box. It provides basic mojo tres plus.

Also into that voltage sum box, I feed outputs from a Yamaha 03D small digital mixer.

The Yamaha  handles things like drum machines, keyboards, effects units, basic mic pres,  talk-back mic, as well as 10 digital returns from my audio interface.

The built in effects engines and mixing facilities are very comprehensive  and sound great  ... .

Combining the digitial facilities with the authentic analog sound from the DIY builds  makes for the best performance and cost ratio 

Add in to that the power of DAW facilities, which lend themselves well to simple, classic summing  - DAWs have all the awesome ness of digital processing with plugins ..

One can put together a system that is unthinkably flexible and with quality as required ...  for quite modest investment .. compared to when I was a youngster in the audio world ..  late 70s early eighties  8)

 

[ilfungo]

Thanks alexc!!!
This is the Idea I want to realize....

 

[lachlan.vercoe]

I have a couple of these Inv-ACA boards I'd like to make a small summing box with.

Basically for tracking two sources, combining them into 1 mono output (no pan needed).
This would be placed after the mic pre, and then using a 2623 tfmr to balance the outputs.

I'd only really need level and phase flip on each input, at which point would you suggest implementing this?
After the DOA? At the input?

Thanks in advance.

 

[ilfungo]

Hi
I'm trying to understand if for line input I need a separate pcb from mic preamp or I can just use something like this.
I could use the same idea in 312 mic preamp?
Thanks!

 

[Floti]

No expert here, but you can use the 2520 to unbalance the signal without going through the 2622 like in the 536/528 or you can use a U-Pad like CAPI does on the VP28 and make the line signal go through the 2622.

 

[ilfungo]

Thanks Floti
Just a U PAD directly to input transformer?
thanks!

 

[abbey road d enfer]

Lots of shooting in the dark here!
Before trying to put together "name" hardware, I would suggest googling "passive mixer schematic" and read, in particular
http://sound.whsites.net/articles/audio-mixing.htm
has enough theory to put you in the right direction without foggying the issue with complicated math.

 

[ilfungo]

Thanks abbey road d enfer!

 

[orangerec]

So, I'm trying to revive this 24x2 summing mixer. I'm finally going to finish this project (thanks covid?). Here's my signal flow: out of my Apollo 16>line xfrmr(600ohm out unbalanced)>pan pot(10kpan from CAPI) or LCR switch, 47k ohm buss resistors>CAPI ACA. My question is, do I have to worry about crosstalk between channels with a LCR switch or panner or the ACA a virtual earth (VE) design? 

https://www.capi-gear.com/catalog/images/gallery/pots/BI/Passive-pan-pot-network.pdf
https://www.capi-gear.com/catalog/images/gallery/PCBs/2-ACA-Bo/2-ACA-Bo-Block-diagram.pdf
https://capi-gear.com/catalog/images/gallery/PCBs/2-ACA-Bo/CAPI-2-ACA-Bo-Rev-B.1-schematic.pdf

 

[abbey road d enfer]

My question is, do I have to worry about crosstalk between channels with a LCR switch or panner or the ACA a virtual earth (VE) design? 

The ACA is actually a VE summing amp. You shouldn't worry too much about x-talk.