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

[magnified]

Not an electronics genius here, but would it be ok to put a 10k Alps motorized K fader in the place of your 1k fader?

Thanks!

-Joshua

 

[kante1603]

 

[jsteiger]

Not an electronics genius here, but would it be ok to put a 10k Alps motorized K fader in the place of your 1k fader?

Thanks!

-Joshua

Yes it should work ok

 

[magnified]

Sweeet thanks!

 

[XAXAU]

Not an electronics genius here, but would it be ok to put a 10k Alps motorized K fader in the place of your 1k fader?

Thanks!

-Joshua

Yes it should work ok

Will it perform the same as a 1K? Is it just about impedance matching?

Also no electronic genius here!

 

[Humner]

Hi Jeff,

How many of the axial Vishay capacitors should I order with my ACABO PCB?

 

[jsteiger]

Hi Jeff,

How many of the axial Vishay capacitors should I order with my ACABO PCB?

Four of the 470uF's

 

[Humner]

Thank Jeff, I put my order through.

Excited to start playing around with one of these.

 

[darnell]

Hey again,

Got my summing mixer put together, just now hooking up to my lynx out.  I'm wiring stuff up right now and wondering if there may be something that needs addressing. 

So, i've been doing some comparative listening between opamps and seem to be finding that no matter what combo i use, there is a slight high freq roll off going on when i send out a stereo drum track to ch 1/2 on my summing.  Send levels are matched and there isn't anything weird happening aside from cymbal "shimmer" really not being there.  I've been sending a drum bus out Lynx 1/2 and back in to my lynx 1/2 input, which sounds almost exactly the same, and then out Lynx 1/2 to the summing input 1/2 into a 47k resistor on the +side through ch1/2 and out the main outs to the lynx.  I have gar2520 on the ACA board and hardy 990's on channel 1/2 on the main 4ch input board.  In order to have an unbalanced input to my input board, the - on my send from the patchbay to the summing mixer is floated at the db25 on my summing mixer (so basically, i am not attaching anything to the - pin on my db25 that goes to the 2x4 channel inverting ACA input boards.)

I haven't connected any grounds to chassis or tied xlr/db25 to ground and putting a cover on the case def cuts down on noise, but doesn't really help with the high freq loss.  I have Cinemag Cmoq2s outputs on the booster out, and Jeffs 2623-4 PCB transformers on the ACA side. 

Is this an impedance issue? Or do I need to start grounding things and see what works? Or does this summing mixer just inherently roll highs off.  This is my first crack at assembly without some sort of build thread, so please let me know if i missed something obvious.  I can post my comparative audio files and pics if you guys need them.

d.

 

[jsteiger]

The typical feedback cap in this circuit has a HF rolloff set so its down appx .5dB @ 20k so nothing you would really hear IMHO. I think you should connect your grounds before looking elsewhere.

You might wanna try connecting the - output to ground on the outputs of whatever is feeding the bus R's.

 

[darnell]

What kind of grounding should i be using?

I'm assuming that on the ACA main board, I would tie a star point from where it is labeled "ground" to chassis ground.  That will ground all connections on that board and all boards jumpered off the power "links", correct?  By doing that, i get continuity to chassis from the "ground" point on the ACA board, from pin 1 on both xlr outs and from the db25 ground and - side of the input which are tied together. 

With this setup, it still has a slight rolloff.  In comparison, I can send the same output from the lynx to an old studiomaster board and back into the lynx.  While there is a slightly different color coming back it, the highs stay intact.

I have also tried bypassing the 2x4 ch input boards and just plugging straight from db25 input to the ACA summing section.  Still a little dull.  Would the Cinemags on the output make that big of a difference, of is it probably something else?

d.

 

[darnell]

Jeff,

I tied ground and - together on the db25.  High Freq is restored!!!!  Thanks for the help.

D.

 

[jsteiger]

Jeff,

I tied ground and - together on the db25.  High Freq is restored!!!!  Thanks for the help.

D.

Great, I actually went back to edit my last reply to make that more clear but didn't have the chance to tell you. Glad you got it going!

 

[Potato Cakes]

Jeff,

I have been looking for a simple, elegant way to sum four channels for live monitors and I think I believe I can do it with this board, but wanted to double check my thinking before I began. I'm looking to sum four channels, a left and right (stereo) and two mono sources, (artist vocal and instrument). Can I do this passively and then use the booster side of the 2-ACA or do I need to run each source into your 4 channel inverting summing PCB and then the booster? At some point I would have to "Y" the mono sources to both the left and right sides. Everything is going to go in a single rack space chassis that will be just a power button and XLR in and out. No switches, knobs, or faders as the mixing levels will be performed by whatever is feeding the summing PCB. I'm trying to figure the best way to do this while taking into consideration all the relevant audio jargon.

Also, I would like to build an 8 or 16 channel version for my studio later this year. I'd love to hear what the difference would be of a real API summing mixer over my SPL Mixdream XP. I have bunch of op amps I've built that I need to do something with.

Thanks!

Paul

 

[jsteiger]

Paul, you would not need the INV PCB for this, just the 2-ACA-Bo.

Are the device that will be feeding the inputs balanced or unbalanced?

 

[jsteiger]

Actually Paul, if you don't need the insert point or master fader, you could do this by only populating 2 channels of the INV-ACA board. In addition you would need 2 off board output transformers.

 

[Potato Cakes]

Jeff,

It would be balanced. The Left and Right would be coming from a console and the mono channels from some sort of channel strip. It would be feeding an wireless in ear monitor transmitter and also return back to the console for the monitor engineer to cue it.

I'll order the parts next week. This is very exciting!

Thanks!

Paul

 

[Eliani]

I've been reading this thread for the last few days and still only made it through half of it. I just couldn't hold myself any longer so I thought I get a head-start, post my current questions and read the rest of the thread later today. If I happen to grasp what I need to do before anyone willingly answers my questions I'll take the hit and die a graceful death!! As a reference to what else I'm doing to my console here's my thread: Another TAC Scorpion overhaul, where I've used 2520 based differential line-drivers to replace the original pre-amps.

To implement the 2-aca-bo in my little scorpion I consulted with Mitsos, as he installed one in his TAC Scorpion too. I got this little hookup circuit from him. This image represents the S4000 master mix-bus and fader booster. This seems right to me besides he doesn't use the balancing and inverting 2623-4 output I guess, for this wiring schematics uses the original insert-point. I rather use the 2-ACA-Bo as designed and do as little damage to the original circuit. I Rather leave it as is so I can easily revert the output stages to the original.

• Remove C23/C24 (point 1), this is where I could take the signal to the ACA. This point would be right after all channels bus resistors with a value of 10k each. I get this step, rather obvious.
• Remove C27/C28 (point 2), and return the signal coming from the ACA. This step seems a bit strange because the signal returning from the ACA is a differential/inverted line from the 2623-4 transformer, or did Mitsos skip this transformer?
• Remove R54/R55 (point 3), where we pick up the signal coming from the fader and send it back to the booster.
• Remove C33/C34 (point 4), this is where we can inject the signal coming from the booster back into the original circuit.

The S1000 input channels have 10k summing resistors and from what I've read in this thread I would get away with replacing Rf with 6.2k and Cf with 150pF. Although I did not check this myself, maybe it's better to do so and at least understand what I'm about to do. There's a link to a resistor calculator somewhere in the first few pages, but that doesn't lead me anywhere...

I would be rather pleased with anyone confirming or helping me with errors on this attack-plan...

EDIT:
So to calculate Rf (feedback resistor) I would need to multiply the desired gain with the value of the summing resistors? Then how do I know what Gain value I need to bring the summing amplifier towards -.5dB?

Original setup: Rf=28k, Rs=47k Gain=Rf/Rs=0.59
Scorpion setup: Rf=?, Rs=10k Gain=0.59 Rf=Gain * Rs=5.96k
With a 6.81k (That's what I've got for now) I get a 0.68 gain (is this -0.68dB?)
I've left the 47pF in there for now, but still looking for the right way to calculate it's value...

So I've got it working so far, with a slightly off gain setting, no calculation for the feedback capacitor, and not so logarithmic behaving fader... But at least I don't have to die that graceful death just yet!

 

[jonbstevens]

Thanks Jeff for this great project. Last week I finished installing the 2-ACA-bo in place of the master section in my Soundcraft 200b -- everything works and sounds great, the only change I made was the feedback resistors and capacitors as the Soundcraft uses 22k summing resistors. 

Not content to stop there I'd like to replace the mixers 4 buses with 2-ACA-bo boards but i'm a little unsure of how to connect the ACA-bo which replaces the bus into the ACA-bo on the master fader.  I like the idea of having some extra gain on the bus outputs to drive the input of the Master ACA even harder, so I'm wondering if it's wise to take the booster output on the BUS ACA-bo and run those through 22k summing resistors into the master ACA-bo? Or am I better off using the -6db Booster output from the BUS ACA-bo and feeding that into the master ACA-bo via summing resistors?

Any advice would be greatly appreciated. Thanks!

 

[Potato Cakes]

Jeff,

So I've finally  acquired all the parts I need to build a simple summing mixer with the INV ACA minus a case and some VU meters (I read on the Interwebs that it had to have meters or it wasn't cool). But before I fire up the iron I wanted to see if there was a simpler way to do what I wanted to accomplish before I cast myself headlong into this project. As stated in my previous post, I'm building a box that allows me to mix a vocal from a channel strip with a stereo mix from a monitor console, allowing me to keep the vocal chain purely in the analog domain (minus the RF transmission) minimizing any latency with in ear monitors that creates a disconnect between a singer's vocal and their chest resonance. In the past I would just use a separate mixer, but that is always way over kill since I just need something that does four inputs maximum.

I was going to take the vocal signal and "Y" it to a pair of the INV ACA channels and then add the left and right signals from the monitor console (minus vocal) to their respective sides of that same pair. But I'm afraid that the split vocal signal would actually tie the LR channels of the ACA together and effectively give me two mono summed outputs. So where I've landed is to split the vocal to channels 1 and 3, the LR mix to 2 and 4, then use the JP points to merge 1 with 2 and 3 with 4. Obviously this means building the entire INV ACA board, which I don't mind doing, but my limited knowledge is preventing me with coming and understanding a simpler way to accomplish my goals. I just want to make sure that whatever I do the output is a stereo mix with vocal down the
center.

Also, since all the lines going in are balanced, would it be best to use a transformer to do the unbalancing or just tie the "-" with the ground and that be good enough.

Lastly, if I use capacitors with higher voltage ratings than what is on the BOM, could I run this at 24V? The op amps I have picked out for this can handle as high as +/-25V.

I'll post pics when done.

You and your products are super mega awesome. I'll have you a minimum of one beer next time both of us are in Nashville.

Thanks!

Paul