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

Hi, It now works but has hum. After much trial and error I found that when I disconnected the inputs from the buss the hum and noise disappeared.

I had found a point on the old master module where the L R buss (1 2 ) entred and disconnected that from the cct. But as I said it did not work. How do people usually go about tapping the buss? Should I take the feed after the buss resistor on an input module instead? How important is shielding at this point? Must L and R be independently shielded?

stuartpre said:

Hi, It now works but has hum. After much trial and error I found that when I disconnected the inputs from the buss the hum and noise disappeared.

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This sounds like a ground issue of some sort.

I had found a point on the old master module where the L R buss (1 2 ) entred and disconnected that from the cct. But as I said it did not work. How do people usually go about tapping the buss? Should I take the feed after the buss resistor on an input module instead? How important is shielding at this point? Must L and R be independently shielded?

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I am not sure how your console is but if there is a backplane, you should be able to just tap into the L/R bus tracks somewhere near the mid point of all of the channels. This will be basically right after the channels bus R's. I would keep the L/R cables separate if possible and shield them.

Hello,
To Jeff, or anyone else who has the knowledge:
I have a Trident Trimix which I want to add this board to.  My question is about the bus resistors.  On my board, the pan outputs feed all the buses and mix bus with 12k resistors.  Can I just swap those out with 47k for the ACA or should I modify the ACA itself?  And if so, I know how to solder and follow instructions, but I don't know the math to adjust the R C values...a little help in that direction would be awesome!  Also, the Trident supply runs on 18v, which should be good for all the DIY DOAs out there (planning on building some 990s), but how will that affect headroom/ response?  I imagine it will be better than the three TLO 71s the trident uses in it's summing blocks...
Thanks,
Brendan

Drumbreak said:

Hello,
To Jeff, or anyone else who has the knowledge:
I have a Trident Trimix which I want to add this board to.  My question is about the bus resistors.  On my board, the pan outputs feed all the buses and mix bus with 12k resistors.  Can I just swap those out with 47k for the ACA or should I modify the ACA itself?  And if so, I know how to solder and follow instructions, but I don't know the math to adjust the R C values...a little help in that direction would be awesome!  Also, the Trident supply runs on 18v, which should be good for all the DIY DOAs out there (planning on building some 990s), but how will that affect headroom/ response?  I imagine it will be better than the three TLO 71s the trident uses in it's summing blocks...
Thanks,
Brendan

Click to expand...

I would not recommend changing the bus R's. Just adjust the feedback R's on the ACA section of the 2-ACA-Bo. For 12k I would go with 7k15 and 200pF or 220pF for the feedback cap. The increase in voltage rails will slightly increase headroom but its negligible.

Cool, thanks Jeff!
Cheers!
Brendan

Ok, so I've got the ACA up and running and it sounds great!  Well, out of the main outputs...
My problem now is integrating the new ACA into the monitoring path of my board.  When I take the signal off the + side of the Booster Out Mult, it sounds like the whole frequency response is shifted up: it has no low end above about 200 and the high end is piercing and noisy.  My uneducated guess is that there's a impedance mismatch happening between the ACA and the monitor amp section...?
The ACA replaces a similar circuit in my master section that uses two TL071s for summing amps and another as a post fader booster.  What's now missing in the new ACA is the monitor buffer and line amp.  The buffer, which mults right off the main XLR output is a TL071 at unity gain followed by a TL071 that adds gain (6db, I think) and feeds the monitor section which, surprise! is a few TL071s...I should mention that the whole internal busing in the Trimix is unbalanced and I might not be making the proper connection by just feeding the monitor bus with the + side of the Main Out, but that's my understanding of the unbalanced input of the internal bus.  The solution I'm thinking is to make a small board that replicates the monitor buffer circuit as is done in the original master section, but I'm hoping that's not necessary- there was plenty of gain in the monitors, it just sounded shitty.  Do I need a bus resistor?  The original buffer has a 12K feeding the output to the monitor amp.
Thank you all for your time and help!

just getting around to building this. My fader is 5k, so what value should I use for R1 and R5?

byron

I'm running into a problem when I installed this in my TAC Scorpion II. I only have the ACA section hooked up right now for summing. The left side is much louder and the right side is much quieter than it should be. I've swapped in 6 different opamps with the same results. The low end is completely gone as well. It sounds like a high pass at about 500hz.

My PSU is +\-17V, but a DMM reads +16V -17v at the pcb.

Not sure where else to go here. I've spent around 11 hours checking the wiring and component placement over and over. No cold solder joints.

Both sides are unbalanced with the + connected, shield connected at one end, and the - disconnected.

Feedback resistors and caps changed to 5.9k and 220pf to work with the 10k summing resistors.

I've verified that it is the summing stage by recording directly from an insert (before the monitor section).


EDIT:  The strangest thing is happening. When I connect the negative out of the right ACA to ground, the left side of the stereo tracks goes to normal volume and the right side gets really loud. It no longer has a big lack of low end.

Connecting the negative left ACA out to ground makes no difference  is right is already connected. If it is not, then it lowers the volume of the left channel to be correct, but the right stays small.

I'm also noticing with this latest update that panning works in the opposite direction than it should, but it is definitely wired correctly on the left and right sides.

Are you sure you don't have any shorts?

I remember when I finished my ACA-BO and found I was frying one of the 10ohm power resistors because I had a solder bridge on one of the 47uf caps (that come after the 10ohm resistors). I remember the pads for the 47uf caps being quite close, so a solder bridge shorting one(or more) power rails to GND is a possibility. The 10ohm resistor was doing its job (otherwise I may have fried my opamps/PSU instead!).

It could be that you have fried one of the resistors the first time powering it up and didn't notice and now the error continues?

Eitherway, check your 10ohm resistors, look for any black soot to indicate its been fried(but also check the resistors, with a multimeter). if you find one then check your soldering for you 47uf caps.

Hi,

I just bought a Speck M72 line level console and I'm working on a switchable summing design using inverting ACAs and the 2 ACA BO. I'm hoping to do API, Jensen and Neve style summing on a 2 pole 3 way switch. I'll be making a new master front panel with the three faders and switch which will go next to the existing master section which I will still use for the Aux returns, and Bus 1-16 outs. I have questions about how to get the right impedance for the Neves, but I'll post in a different thread with those questions. I've attached a diagram of what I'm thinking. Just wanted to run it by some people to make sure that I'm on the right track. Thanks!

I am very interested in this as well!

Hi Jeff,

I really appreciate you continuing to check in on this thread. I installed the ACA buss into a 32 channel Yamaha PM2000 console. It sounds great but. . .

I'm noticing after using it for a while that I'd like more gain. I'm summing 32 (actually only loaded with 24 right now) through 33K buss resistors.

Here's your recommendation for the feedback resistors and caps for my situation, quoted from back on page 11:

"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.

Cheers, Jeff"

Anyway, I'm finding that there's a few occasions that I'm having to push my inputs too hard to get the level I want on the final 2 track. I've returned to using my console's original output busses because the increased output level allows me to have my input strips down one more click which makes the total sound a little less pinched sounding. I attached a schematic of my Yamaha PM2000 output buss for reference.

My question is this. Would changing the feedback caps/resistors be a good way to get (an estimated 3-6 dB) more gain?

Or is this the whole reason that the inverting ACA board was created in the first place? Perhaps this is what I need.

You can temporarily put a trimmer in place of the feedback R to get the level up where you want it. Pull the trimmer and measure. The feedback cap should then be adjusted for a similar rolloff as stock.

Hi Jeff and fellow members.

I have an Alice 828 mixer that I really like although I would love to implement a Discrete summing section and balanced output with transformers.

The desk has 8 channels plus 1 stereo echo return and summing is done originally with 33k resistors, then the Master has a really cool Stereo Limiter, Master fader, makeup gain with IC and unbalanced out.

Could you please help me out on how I could incorporate the 2 ACA BO circuit in this layout while maintaining the Limiter?
I would like to replace the original summing to API style and get rid of everything in the Master section with the exception of the Limiter Circuit.



here is the schematic:



thank you so much for your help and guidance.

Can I get rid of IC1 or it's part of the Limiter Circuit?

Thanks Jeff,

I used a pot for the feedback resistor to get the level where I want,  I'm getting 44.2K for the feedback resistor.  (Had a 19.6K in there prior)

I have a 68pF cap in there now, which was in conjunction with the prior 19.6K feedback resistor.

What's the feedback cap size I need for the proper roll off?

30pf should keep it in the same range which is ~120khz

Thanks Humner!

Where is the calculation you're referencing? Page 7 had a calculator from somebody named Bicycle Bob, but that link is gone.

Also, I'm guessing it's gonna be 27pF or 33pF. Haven't gone looking for caps yet though.

JW said:

Thanks Humner!

Where is the calculation you're referencing? Page 7 had a calculator from somebody named Bicycle Bob, but that link is gone.

Also, I'm guessing it's gonna be 27pF or 33pF. Haven't gone looking for caps yet though.

Click to expand...

I use this - http://www.muzique.com/schem/filter.htm

So you punch in

44000 ohms
0.00003uf (30pf)

And then it gives you the corner frequency. For some reason that calculator doesn't like determining the capacitor value, so I just get things in a ball park and go from there.

You can check the frequency with either 0.000027 uf and 0.000033 uf  to see the results from those PF caps you have access to and decide which way to go, but either will do fine.

Hello,

I'm using the CAPI ACA & Booster on my summing system. I'm having the ACA feed a patchbay and return into the Booster side, but with no master fader. I just want to be able to insert a buss compressor there. Do I have to change anything if I skip the master fader?