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

jsteiger said:

Looks doable. I see 12k bus R's on the input channel skiz.

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Would it just be a matter of changing these to 47k?

Funnily enough I have a allen and heath system 8 as well(MKII though), however mine is in a very sorry state. I've toyed with the idea of stripping out the buss section and making my own 8 channel summing mixer with the 2-aca-bo.

gar381 said:

Humner said:

What is the lowest voltage the DOA's can operate? I have a few PSU's I've built off of the 7815 and 7915 chips

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Hey Hummer

If your using gar2520 or gar1731 DOAs...  a PSU based on 7815/7915 will work fine. (+15v/-15v)

Best..

GARY

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Cheers, I think I'm going with gar2520

Humner said:

....Would it just be a matter of changing these to 47k?....

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No, do not change what is there. You would just have to adjust the feedback R and C of the ACA stage. There is some talk a few pages into this thread on what to do.

jsteiger said:

Humner said:

....Would it just be a matter of changing these to 47k?....

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No, do not change what is there. You would just have to adjust the feedback R and C of the ACA stage. There is some talk a few pages into this thread on what to do.

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sorry, you are right, I do remember reading about this eariler on in the thread.

Aniol1349, if youh ave the 168 desk, you may have some room above the buss section for the aca boards. I have the 1616 desk and there is no room for anything.

Well I have only one PSU here that delivers 16V and a 280hz hum can hardly be PSU related right? The PSU part is located behind a shield that is soldered to the ground... I didn't seem like PSU noise.. More like a leaking cap.
Or maybe a ground loop but if it disappeared it's weird.

Concerning the pot, can someone tell me how to wire it properly? 

Aniol1349, if youh ave the 168 desk, you may have some room above the buss section for the aca boards. I have the 1616 desk and there is no room for anything.

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I do have the 16 16 version, well I'm still waiting for it's arrival so I will have a look into it soon..

meanwhile I'll have a good read of the thread

thomasdf said:

Well I have only one PSU here that delivers 16V and a 280hz hum can hardly be PSU related right? The PSU part is located behind a shield that is soldered to the ground... I didn't seem like PSU noise.. More like a leaking cap.
Or maybe a ground loop but if it disappeared it's weird.

Concerning the pot, can someone tell me how to wire it properly?

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Hey Thomas, can you post some pictures or your board or explain in more detail how you wired your summing box? I'm thinking of doing a similar thing. Basically 24 inputs (coming from my soundcard/tape machine), using two inverter boards (6 channels into each op amp), and then going down to the ACA board with the master outputs.

area8 said:

I'm positive that some of Jeff's ACA buyers must be building summing boxes to be used with DAWs, etc., as opposed to being part of a larger mixing console.

I'd love to see any pics of your work. They don't have to be pretty, just have to use the ACA board(s). I'm looking for ideas.

I've already built the boards, and keep struggling with how to rack this up - I keep vacillating back & forth between a really simple L & R summing box with few or no controls (simple 2bus, separate L&R inputs) to a (Neve 8816-like) mixer with pan & level controls, etc. I plan to use buffered VU meters on the 2bus, whichever way I go.

Anyway - anybody want to share?

Thanks,
Frank @ Area8

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hey frank i have just finished a build as you mentioned in your post for summing the 8 sub busses of my soundcraft 500 mixer i will be posting pics up later this week after a little snagging and testing. i'm also willing to post up my circuit and block diagrams although a bit rough for some more insparation. Although i can not offer full support for the build i'll do what i can now and then they may be a good starting point.

Just a quick question to all: the soundcraft 500 has a balanced output impedance of 600 ohms i believe. would i need to place termination resistors across pins 2 and 3 (+ & -) on the XLR  inputs to a passive summing network prior to the 2-aca board?

and the same question for the outputs after the 2aca bo implemented in the way of jeff's block diagram for layout?

any help on this would be very much appreciated.

Brendan.

Hey Thomas, can you post some pictures or your board or explain in more detail how you wired your summing box? I'm thinking of doing a similar thing. Basically 24 inputs (coming from my soundcard/tape machine), using two inverter boards (6 channels into each op amp), and then going down to the ACA board with the master outputs.

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hey there!!!

i have the system 8 too (1616 mkII). i really loved working on this board 10 years years ago especially EQs then it goes into cellar. now im restoring it and upgrades would be great.

first thing is to finish the GDY51 PSU. i have the dual VPR version with one rail +/-15v for the board and the other +/-16v for my GDY51 rack...

im thinking of upgrading the master/summing section too. i dont need the mixers control room, talkback or something else (all done with rme mixer). just EQ, summing and routing the busses will be done on the mixer.

i imagine a ACA summing would be graet 

theres really no place inside the board - BUT i dont need the monitoring 16 channels. removing the PCBs is easy. this is enough to fit the ACA thing.

Hi all,
A while back I made a stand-alone 16ch summing box basically following the block diagram on Jeff's website for the ACA project. (sound card>47k resistors> JLS-Inv>ACA/Bo>patchbay). Cold side of the signal is floated at the sound card.

Could anyone take a look at this small schematic and proofread it for me? This is my very first attempt at drawing a circuit and having a custom pcb made. Just beginning to learn a little bit about using Eagle...

I wanted to clean up the input to my box a little bit with this tiny board. It just allows me to use a through hole db25 connector and provides pads to solder in the buss resistors. (Less messy wires....) It also allows me to have outputs 7&8 be summed to mono.
I will add channels 9-16 to this circuit by basically duplicating what I have here. My main question is if I handled the mono-ing of channels 7&8 correctly. From what I gathered from this thread, sending the L and R through their own 47k resistors is correct. But what about placing a resistor ahead of these two resistors for a 3db drop? What value would that be?
Any feedback would be really appreciated.
thanks!

Here's my take on a stand-alone summing amp based on Classic API's ACA circuit...it's an 8, soon to be 16 channel summing amp.

I was having some noise issues with connecting my balanced audio interface into the unbalanced JLS-Inv/ACA circuit. I took a shot at putting together a set of THAT 1200 line receivers on a perfboard, and that made it a lot quieter. Eventually I would like to have a pcb made for that (and lose all the messy wiring...). It's set up for 8 input channels. I would like to do another set of chips for 8 more inputs soon. Channels 7 and 8 are each routed to both channels for mono tracks.

For the fader, I found a balanced stereo 10K Valab 23 step pot (http://www.ebay.co.uk/sch/m.html?_nkw=valab+stereo&_sacat=0&_odkw=&_osacat=0&_ssn=vintage_audio_lab.
Using another pair of THAT 1200's I was able to send the balanced feed from the 2623-4 transformers through the pot, then out to the 1200's to unbalance before going into the ACA booster stage. That made it quieter still.

Also in the mix are a power supply from Five Fish, VU's from Hairball, VU buffers from JLM Audio, and a handy "ProtoBoard-3U-Conn" from Mouser which comes set up with a set of holes for a DB25 pcb mount connector. I used a 4PDT switch to allow for pre- and post- ACA booster metering. Dan at Collective Cases made the case for me.

Fun.
It sounds sweet. It definitely adds a little spaciousness and weight to the drum tracks I've run through it so far.

So I bought a used aca 2 bo racked in a case as a summing bus in varying degrees of condition and after having it for several months am finally getting around to fixing and Rewiring it. I've always loved the API sound and am excited about getting it finished.
I went with 20k bus resistors and with Jeff's help recalculated the FB resistor and caps. I'm self informed from the internets diyer so excuse my ignorance. R3,8,11,14 were not stuffed on the board. Are these needed and what do they do? I was trying to source a good dual deck non stepped pot in the US under $25 and there seem to be a lot of options. I have an alps rk27 dual 50k on hand, could this work if I change r1 and r5 or will my fader throw give less than desirable results. On grounding I decided to use some spade lugs to a central point so I can disconnect one by one for testing. So dsub gnd to star, summing network to aca bus gnd to star and aca 2 bo to star. Where would be the best mounting point of aca 2 bo to use for this or should I gnd all of its mounting points and use one to connect to the other grounds. Seems to defeat the term star ground at that point. Thanks for any help on this old thread.

Hello,

can i use the 2-ACA in replacement of the summing amp, post fader amp and balanced output amp in the master section of a soundcraft delta 200. The board is powered +/-17V.
Will i keep the monitor section fully functional ? (Regarding to the schem i guess yes, but i'd like to be sure).
What do you think of this mod ? Is t stupid to use 2 really differents electronic designs in a same board ?
This board is usable but in my sense the master section is not good enought to be use to sum my mixes thru. In the other hand i use api-sh style pre's for recording, i really love them, musician friends too (i exclusively record 90's indie rock/shoegaze). would it be an improvement in my api-sh sounding quest ?

Thanks,
Guillaume

bubble said:

Hello,

can i use the 2-ACA in replacement of the summing amp, post fader amp and balanced output amp in the master section of a soundcraft delta 200. The board is powered +/-17V.
Will i keep the monitor section fully functional ? (Regarding to the schem i guess yes, but i'd like to be sure).
What do you think of this mod ? Is t stupid to use 2 really differents electronic designs in a same board ?
This board is usable but in my sense the master section is not good enought to be use to sum my mixes thru. In the other hand i use api-sh style pre's for recording, i really love them, musician friends too (i exclusively record 90's indie rock/shoegaze). would it be an improvement in my api-sh sounding quest ?

Thanks,
Guillaume

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some posts above ive had the same idea, but havent done it... i dont want to risk my boards health so im going out of my master insert out into a high quality preamp or whatever im patching in there (at the moment its a stereo 1084 neve clone EQ from bluzzis project, im loving very much). i think its the safe way and i like what i hear in comparison to the boards master amp (tl72 i suppose).

Its an idea. I do this kind of thing with a passive mixer. But the idea here is to replace the summing amp to improve summing in the desk. The summing amp is before the master insert point.

And regarding the schematic, in this way u doesn't have the cr section usable cuz you disconnect the output amp that feed the control room section. Right ?

bubble said:

And regarding the schematic, in this way u doesn't have the cr section usable cuz you disconnect the output amp that feed the control room section. Right ?

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yes but perhaps you could feed a master stem of your DAW via the DA converter to the return of the insert. e.g. the RME totalmix can do this without latency if you are on rme system... for sure summing is not improved

if the soundcraft has direct outs for each channel you can sum with passive circuit and make up gain amp.

because after hearing some opinions about a system in a system like aca summing in a existing board i found it too dangerous. but perhaps im wrong and its a good improvement... if you try let us know the result! itxs exiting for sure

yes but perhaps you could feed a master stem of your DAW via the DA converter to the return of the insert. e.g. the RME totalmix can do this without latency if you are on rme system... for sure summing is not improved

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I can do that with my motu system but as you say summing is not improved.

if the soundcraft has direct outs for each channel you can sum with passive circuit and make up gain amp.

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no direct out and in this case, no pan and bus assigns.

Just want to improve the summing quality of the desk to make it usable in a mixing setup. There's a lot of mods for the old soundcraft line, but the aca seems to be a really good way to change the desk in something at my taste. Just d'like to know if it's suitable and if it's a real improvement.

I'm in a similar boat to JW back on page 11 with a Yamaha PM2000.  Those familiar with the console know the strange signal flow: input channels assignable to->  8 mono programs which can be mixed individually to-> 8 matrix summing amplifiers/outputs.  All programs and matrixes are currently mono.

My wish would be to replace one pair of matrixes (matricies?) with the 2-ACA-Bo as well as 1 pair of programs.  Ultimately I'd like to be able to keep the programs assignable for subgroup duties.  I understand the JW replaced a pair of the program summing amps with the ACA and it worked well.  The downside is that to use this as his 2buss he now has no subgroups.

I don't understand how much gain is being added in each stage that I'd like to replace.  My other concern is that I will have to loose a bunch of switching/functionality to shoehorn these things into an existing circuit. 

If anyone wouldn't mind, it'd be great to have a second, third fourth set of eyes on the schematic/block diagram.  The output buss resistor is 33k which in not on the attached schematics.  It is a 32 channel desk BTW.

Should I be looking at the Inv-ACA for the program (subgroup) duties (to keep gain at unity) and the 2-ACA-Bo for the 2 buss?

Sorry for so many questions...

Many thanks in advance!

Josh

I'm in a similar boat to JW back on page 11 with a Yamaha PM2000.  Those familiar with the console know the strange signal flow: input channels assignable to->  8 mono programs which can be mixed individually to-> 8 matrix summing amplifiers/outputs.  All programs and matrixes are currently mono.

My wish would be to replace one pair of matrixes (matricies?) with the 2-ACA-Bo as well as 1 pair of programs.  Ultimately I'd like to be able to keep the programs assignable for subgroup duties.  I understand the JW replaced a pair of the program summing amps with the ACA and it worked well.  The downside is that to use this as his 2buss he now has no subgroups.

I don't understand how much gain is being added in each stage that I'd like to replace.  My other concern is that I will have to loose a bunch of switching/functionality to shoehorn these things into an existing circuit.

If anyone wouldn't mind, it'd be great to have a second, third fourth set of eyes on the schematic/block diagram.  The output buss resistor is 33k which in not on the attached schematics.  It is a 32 channel desk BTW.

Should I be looking at the Inv-ACA for the program (subgroup) duties (to keep gain at unity) and the 2-ACA-Bo for the 2 buss?

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I hear you as I'm also in a similar boat, looking to add 2 bus functionality to an old Allen and Heath mod3 console (16x8, modular, discrete), I'm still weighing up the pros and cons. inv acas would be great as a solution for the busses except that as they are not intended for this purpose there would be no fader or sends on the groups. It might be possible to modify the boards to do this but it starts to get messy with wires all over the place, grounding etc

Right now I'm considering starting with adding Jeff's aca +bo board and working backwards from there - building a new monitor section and perhaps stealing a pair of busses from the aux, (or from power distribution and wire them separately instead) to use as stereo bus feeds. Ideally - 1 aca bo board per pair of groups on our desks!  then sum them through resistors into the master aca. Still working it out but I would like to keep the 8 groups and just add the 2 bus if possible.

inv acas would be great as a solution for the busses except that as they are not intended for this purpose there would be no fader or sends on the groups. It might be possible to modify the boards to do this but it starts to get messy with wires all over the place, grounding etc

Right now I'm considering starting with adding Jeff's aca +bo board and working backwards from there - building a new monitor section and perhaps stealing a pair of busses from the aux, (or from power distribution and wire them separately instead) to use as stereo bus feeds. Ideally - 1 aca bo board per pair of groups on our desks!  then sum them through resistors into the master aca. Still working it out but I would like to keep the 8 groups and just add the 2 bus if possible.

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Yeah that's what I can't figure out - how do I utilize the group faders with an inv-ACA and then go to the ACA-bo for stereo buss summing.  Or do I need the ACA-bo's for the groups too?  Seems like it'd be way too much gain that way around.  Perhaps they can be run at unity some how?  This stuff is over my head...


That's my plan as well - backwards from the stereo buss.  I'm going to replace two of the matrix busses (7 & 8) with a 2-ACA-bo and send all of the programs to it.  The programs have a "on-off" switch right before they hit the matrix buss so I should be able to pick them off there - right where it says "to matrix post" in the attached schematic above if anyone cares to check it out.