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

[jsteiger]

3nity, I myself am not intimately familiar with the Amek Einstein. Are the program buses balanced or unbalanced? The old API summing is unbalanced. What are the bus R's? It almost doesn't matter as you can adjust the feedback R and C in the first ACA stage to accommodate. Many guys have done that and mentioned here on this thread.

Hope that helps. Jeff

 

[tgauge]

Hello Jeff,
I have two questions regarding the 2-ACA-BO...

1. Because the 2-ACA-BO is unbalanced and my proposed summing network will be balanced, would you suggest a) that I rework the plans for the summing network to be more compatible (i.e. de-balance every input as they enter the summing box), or b) sum balanced and then de-balance the output signal right before it goes to the 2-ACA-BO?  I'm assuming B would be best, easiest, and cheapest (saves a lot of money to de-balance 2 channels than 32) but I wanted to get your input on it before I started.

2. Do you have a mailing list or anything of the sort to notify your customers of when products arrive (i.e. the EA-2503)?  I was waiting on it to come in, and then I went back to the page and the date was pushed out.  I'm just checking, otherwise it is not problem to just back on the 2nd...

Thank you Jeff!  I'm really looking forward to this project!

-TG

 

[brennyb]

jeff just a quicky the 2aca board outputs are balanced, the booster channel inputs are unbalanced. To the bo channel do you drop the common and take the + from aca to the BO side as well as the - aca to the Bo side (connecting aca + output to + bo input & -ACA output to the C bo input)?

 

[jsteiger]

Yes correct. If you look at the fader schemo in the support docs, that is basically what it show...minus the fader of course.

 

[JW]

Jeff, wow. I had no idea this was even out there until yesterday. Seems like it would be perfect for my Yamaha PM2000.

I attached a copy of the PM2000 schematics. If anyone is so inclined, I have a couple questions.

I'd like to be summing in total 32 input channels and 6 mono busses.
For the input channels, it appears I would just pick a pair of the existing program (main) buss sends and connect the input channels to the ACA after the main program buss bar.
My summing resistors appear to all be 33K.

For the other six busses in my console (second schematic) I think it would be easiest to take the signal right before it goes into the matrix amplifier. There is a switch right before the output transformer, which would be very convenient, and I don't really use the matrixes on the PM2K anyway.

Do you guys think this is a good approach? What would the adjustments need to be on the ACA to provide for the 33K bussing resistors if any?

This would be SO awesome. It would totally kill  2 birds with one stone in that it would allow me to finally sum my busses to the 2 mix without having to use the matrix amps (this is a strange peculiarity that Yamaha came up with) and also work around the non-discrete IC summing that's in the busses right now.

EDIT:Well, here's a word file w/ the schematics pasted on it. They were too big to upload the whole thing. If anyone wants to host a link, or just wants me to email them a copy of the full PM2K schemos I got 'em.

 

[brennyb]

just a quick question, between the 2 aca channel and the booster should the 10k fader/pot be logarithmic rather than linear?

 

[jsteiger]

just a quick question, between the 2 aca channel and the booster should the 10k fader/pot be logarithmic rather than linear?

Either will function but you will want log.

 

[JW]

I just ordered the 2-ACA board. Can't wait.

Does anybody see any problems with using the +/-24V rails in my console if I use diodes in series on both rails to drop the voltage on the way into the 2520 opamps (down to the +/-16V to  +/-18V operating range?)

Also, Jeff, regarding the Excel chart on pg.7 of the thread, if I type 33K in the RF box (that's what my buss resistors are) and 47pF in the Cf box, I'm getting a Cutoff frequency of about 102K. Does this sound about right? Just making sure I'm using that handy excell chart right.

 

[JW]

Okay, most of the parts are in the mail. Yes!

I'm bumping my last questions though. And asking one more. Does anybody have a recommendation for a really tight tolerance 10K stereo pot? I've decided to just use a pot with a knob since my fader throw length on my console is obscenely long (130mm) and it would require some ugly modifications anyway to use a P&G.

 

[JW]

Jeff,

My above math is incorrect.

Can you tell me if this is correct?

If I'm following correctly, with the equation Gain=Rf:Rs, with Rs at 33K, and Gain at -.6, I'm getting 19.8K for Rf.

If adjust Rf a little to 19.5K, and then use a 68pF cap, I'm getting a cutoff frequency at 120K
Is this correct?

(Edit: Wait, I'm confused as to whether I'm changing R9 and R12 as well? )

Also, concerning my question about dropping the voltage going into the the opamps with diodes in series, I guess I'll just try it and see. How tight does the tolerance need to be between the +/- voltage rails?


Sorry for my question bombardment. I am learning slowly. . . . .

 

[jsteiger]

Jeff,

My above math is incorrect.

Can you tell me if this is correct?

If I'm following correctly, with the equation Gain=Rf:Rs, with Rs at 33K, and Gain at -.6, I'm getting 19.8K for Rf.

If adjust Rf a little to 19.5K, and then use a 68pF cap, I'm getting a cutoff frequency at 120K
Is this correct?

(Edit: Wait, I'm confused as to whether I'm changing R9 and R12 as well? )

Also, concerning my question about dropping the voltage going into the the opamps with diodes in series, I guess I'll just try it and see. How tight does the tolerance need to be between the +/- voltage rails?


Sorry for my question bombardment. I am learning slowly. . . . .

I get 19660 ohms for feedback R so I'd use a 19k6 which is a standard value. Yes, 68pF for the feedback caps C11 and C15. You only need to change R10 and R13. Leave R9 and R12 as they are.

I think if your rails are within .75 volts of each other you will be fine. Dropping the voltage is a different subject in itself. I am pretty sure you can find tons of info if you do some searching.

Cheers, Jeff

 

[JW]

Thanks Jeff.

One more quickie question.

If I understand the schematic correctly, on the 2-ACA-BO, the polarity is being flipped first by the 2623-4 transformer, then flipped back again by the 2503 on the booster side? 

I guess what confused me about this was reading about the implementation (and title) of the 4 Channel Inverting ACA card. I'm not using that card, only the 2-ACA, but it seems that that card flips the polarity as well? Or am I wrong about that? A polarity flip X 3 is obviously going to end up with a reverse polarity in the end.

 

[jsteiger]

Thanks Jeff.

One more quickie question.

If I understand the schematic correctly, on the 2-ACA-BO, the polarity is being flipped first by the 2623-4 transformer, then flipped back again by the 2503 on the booster side? 

I guess what confused me about this was reading about the implementation (and title) of the 4 Channel Inverting ACA card. I'm not using that card, only the 2-ACA, but it seems that that card flips the polarity as well? Or am I wrong about that? A polarity flip X 3 is obviously going to end up with a reverse polarity in the end.

Both sections of the card (ACA and Booster) are using the inverting side of the respective opamp. The polarity is being flipped back by each stage's output transformer.

When using the 4 channel inverting board (if combining a large # of inputs) I flip the polarity at the output of the ACA section (post 2623-4), which is essentially leaving it since it was already flipped back to in phase by the ACA's opamp which is the second inverting stage. So, technically 4 flips.

Hope that makes sense! That is some hard stuff to try and type so it makes sense! 
Jeff

 

[JW]

Unbelievable!

Finished installing the ACA in my console yesterday. Easily the best modification I've ever done to anything.
I can't believe it worked perfectly right away, as well. Somehow my grounding scheme worked perfectly on first try.

For right now I'm using my consoles +/-24V rails to power it, and using 4 Hardy 990C's. I haven't even tried the 2520's yet, until I figure a better way to drop the voltage than 1 pair 317/337 regulators.

Anyway, thank you thank you thank you Jeff! I can't believe how alive and defined everything is now. It's really encouraging hearing the emotion/realism of old tracks that I KNEW went down, but somehow was partially lost when summed through the console's previous 2 buss. I realize I actually recorded those tracks pretty well after all! 

 

[jsteiger]

Awesome news JW! Congrats on your success!

Hey, nothing at all wrong with staying on 24V and running the 990C's. Killer opamps for sure. Who knows, you may go thru all the work to drop the voltage and find out you prefer the higher voltage rails with the 990C's. IIRC, Whistlerock has 918's that will also run on 24V rails.

Best, Jeff

 

[TimRandolph]

Hello!

I'm new here. Been lurking around for quite a while though.

I'm interested in building some submixers for my unbalanced gear (keys, fx).

Was thinking about using the ACA board for summing, and something like this for the mixer circuit:

( taken from http://www.all-electric.com/schematic/simp_mix.htm )

I would like 16 mono inputs.

I'm getting a fairly good sense of what is required by reading this thread, but I have some questions on the exact values / circuit.

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.

So the resistors after the pan pot should be 47k...

The pan circuit recommended above specifies a dual 10k linear as opposed to the single 10k in the schematic. I assume the dual-pot circuit lessens the insertion loss? By "slugged" does that mean the the 2.2k resistors go from the "input" of each pan pot to the wiper?

In the schematic shown, there are 10k resistors between the blocking cap and the pan pot... do these remain necessary with the dual-pot pan circuit? If so, what would the proper values be?

I'm guessing that keeping the blocking cap would be a good idea.

And, finally, what would be the proper value for the level pot? Would a linear or audio taper be appropriate?

Forgive all the basic questions. Obviously just learning about all this mixer stuff. Big thanks to Jeff for making these boards available!

Tim

 

[Jannee]

Hi Guys! I thought I'd share with you our exciting project.

I got a MS Audiotron Multimix modular console which was used as a monitor mixer in finnish National Opera during 1992 to 2007. The console has 16 input channel's and 16 aux sends. No channel faders or master bus whatsoever... The Mic Pre's on this are top-notch with Lundahl input trafos and simple eq.
These custom build desks were used in theatres all over scandinavia and europe too. The company went down in late 90's and no one was able or willing to continue to manufacture the se wonderful consoles any longer. You can still find them here for a reasonable price and they are being modified for ob preamps and summing mixers.

The fun thing is that I all so got a huge AMS Neve Logic 2 digital console from Opera's studio too. Now running that thing in a studio these days would be a nightmare and trying to sell that 300 kg of nowadays worthless gear wouldn't make any sense, so I thought we'd tear it apart and use the really solidly build body as a frame for our modular analog MS Multimix console.

Here's some pictures of the parts and pcb's:
www.wolf.fi/multimix

So... I've been thinking of doing the 2 ACA master bus mod for this baby. Other mod will be direct outputs.
We only need 6 auxes so we will have plenty of space in the AMS frame, which luckily happens to take the aux, buss and fader modules just fine, only the input modules need a little metal work.

Allthough I have a technician taking care of the build I would appreciate your input or ideas on the build.

Cheers,

Janne Huotari
Flow Recording Studios
OULU, Finland

 

[skidmorebay]

Hello all,
I've been building a stand-alone active summing amplifier based on the JLS-Inv and ACA pcbs from ClassicAPI. I've got a hybrid studio with no console - my goal with this is to be able to sum up to 16 drum tracks through the ACA, to give them some analog vibe, and to allow me to strap a compressor and EQ across the entire drum bus.

Anyone see any issues with this signal path?
DA converter>47K resistor>JLS-Inv(left channel to one side, right channel to to other)>right side of Classic ACA-bo>10k stereo fader>right side of ACA>Left and Right xlr's>monitor controller, AD converter, etc.

I am sending a mult of the final output to a pair of VU meters. Power is coming from a Five Fish PSU kit. I am not connecting the jumper between the two sides of the JLS pcb, so one side cover the L channel, one side covers the R. It all goes in a 2U rack case with DB25 in's and 2 xlr outs.

I was going to unbalance the line in signal by floating the low side. Basically I was going to solder eight positive legs at a time to a turret board post, solder the 47k resistor across to the opposite post, and then send one wire into an input of the JLS pcb. Ditto for the rest of the channels until I have 16 stereo pairs going in.

Anybody see a reason that wouldn't work? Much thanks!
JSmith

 

[jsteiger]

If I am following you correctly, it sounds like it should work. Are you buffering the feed to the VU's? You will want to do this with a cheap dual chip of some sort.

 

[skidmorebay]

Thanks for taking a look. Yes, I am using a kit from JLM audio to buffer the VU's:
http://www.jlmaudio.com/shop/index.php?_a=viewProd&productId=19

I've found that when you are working semi- in the box, analog summing adds a subtle but noticeable amount of spaciousness and presence. I will probably use this box mostly for drums, and send the drum mix into another summing amp I already have along with other mix elements. It gets me a little closer to having multiple busses in the analog realm like I would if I had a console. Someday...

There are a few good summing amps on the market (Dangerous Music, Tube Tech, Black Lion). I think your ACA circuit would make a great equivalent kit for the DIY world.
JS