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

[ask]

That's good

...I wouldn't terminate the unused side of a power amp !!

 

[mylesgm]

So Thinking about building a stand alone simple line summing box.  Like the idea of doing api way and I'm wondering about balanced inouts prior to the 47k resistors.  So I've got a pile of astor/awa 1:1 line transformers and was going to do 16 inputs via transformers then on to the 47k resistors and the rest of the circuit.  Will this be suitable and could I add a pot before the 47k for attentuation?  Also, how could I add multiple outs to the master out?  I would like to return 2 channels to the daw and a 2 channel split to go to the studio monitor selector.

thoughts?

 

[jsteiger]

So Thinking about building a stand alone simple line summing box.  Like the idea of doing api way and I'm wondering about balanced inouts prior to the 47k resistors.  So I've got a pile of astor/awa 1:1 line transformers and was going to do 16 inputs via transformers then on to the 47k resistors and the rest of the circuit.  Will this be suitable and could I add a pot before the 47k for attentuation?  Also, how could I add multiple outs to the master out?  I would like to return 2 channels to the daw and a 2 channel split to go to the studio monitor selector.

thoughts?

The 1:1 transformers and the level pot before the 47K buss resistors would be a fine idea. Check out this link for something similar. For multiple outputs, I have the boards set up with a 2nd output already via a simple mult. You could easily add a 3rd if you wanted with no real change.

Best, Jeff

 

[conleycd]

Jeff's summing amp is definitely on my list of DIY projects to do.  I have to finish my other commitments first but I've been planning this one for a while.

I'm planning a bit of weird box.  Essentially, it is combining amplifier (2 actually) with some main mix sends and returns for parallel processing, some VU monitoring/metering, maybe some patchable stereo spreaders.... blah, blah... the list grows - hopefully to eliminate the size or need for a console (so I have to slim down a little!).

My thought is to actually use Joe Malone (JLMaudio)'s JLM99vs.  Joe makes great stuff, I'm also a sucker marketing so when I hear "Neve on steroids" I'm lost in potential mix ecstasy.  That along with the idea of running 34v +/- for huge headroom is kinda hot too.

Anyway... I've been thinking back and forth between iron or opamp for the polarity reversal coming out of the combining amplifier (my box will actually have 2 stereo combining amplifiers).  The first one can remain unbalanced but really needs to be proper polarity.  The price is about the same either way.  Ed's transformers or a nice DOA (mind you it is just at unity - so no real thrill) is around $30. 

Any thoughts opamp for polarity or transformer?

CC

 

[martthie_08]

OK, I've been meaning to do this for a long time, but I've finally managed to get a frequency plot of my modified studer and the measurements pretty much go hand in hand with my subjective observations. Please note that I have changed the resistance and capacitance for adaptation to my specific console.

The Studer summing on mixbus 3-4 is the orange graph and the api summing on mixbus 1-2 is the blue graph, recorded through the same converter. Both the level drop (1dB) and the limited HF response tell me that something still needs tweaking. I have come to like the overall sound of the API summing and although the vertical dimension are pretty extreme on the above image, it would still be nice to get a tad more high end out of it. I might try a smaller cap in the summing amp, but maybe the problem is in the 2520 opamps not being fully happy at -/- 15V

Anyways, if anyone else would like to see a diagram of their main bus frequency response (preferably with the 2-ACA-Bo), rum this sine sweep through your console (watch your ears!), send me an email of the recording and I'll post a chart.

cheers, Marten

 

[jsteiger]

Very interesting Marten. Do you have a comparison of maybe the channel direct out as well? It would be fun to see if the input channels stay more flat near 20k or if the slight roll off is all from the summing stage.

 

[martthie_08]

yes, here is the channel direct out response in green, the level is a bit different, I am on a different mix right now  8)

the high end frequency response of the direct out is very close to that of the studer summing section (aside of the global difference in audio level).

side note: I wish my "speakers in the room" response would like any of those charts  

 

[conleycd]

Hmmm... you would expect the high to be a little more level.  I think 2520s love 15v +/-.  This should really affect primarily your headroom.

Are you using a capacitor on the way into the mix bus?  What is it's value?  I don't fully understand why your direct channel looks the same way too.  What's creating a low pass perhaps unexpectedly.

Cables with roll off?  I dunno?

CC

 

[jsteiger]

Is the API plot of both stages or just the first ACA stage? The customary API gain structure is -2db after the ACA with 12 db of gain in hand at the 2 mix fader then +4db of course after the 325 booster section.

I remember you modified the feedback R and C to match with your buss R's??

 

[martthie_08]

Hmmm... you would expect the high to be a little more level

well, yeah measurements are often a bit off at the extremes of the measurement, but it is the relative graph between studer summing / studer direct out and the api summing that shows a qualitative difference. I should repeat the measurements at 96KHz or 192KHz, hadn't really thought of that as I always record at 44.1KHz.

s the API plot of both stages or just the first ACA stage?

both stages - I will repeat the measurement and check levels taking the signal at the inserts before the 10K Alps pot that sits in front of the 325 booster stage.

I remember you modified the feedback R and C to match with your buss R's??

yes I'm using a 470pf cap with a 3K3 resistor and I have a feeling the problem lies there. Maybe I will replace the 3K3 resistor with a 5k pot to fine tune the gain and then recalculate the capacitance needed.

 

[plumsolly]

I graphed the frequency response of the 2-ACA-equipped 2-buss in my Auditronics 110 console along with a direct out for comparison:

The blue is the 2-buss out (post 2-buss fader) and the red is the direct out (pre channel fader and bypassed eq section: it would have made more sense to measure the direct out after the channel fader and eq but I didn't, so oh well) at first glance it looks pretty poor, but the resolution on the y-axis is .2db, which I did to be consistent with Marten's graph. The response of both of my outputs is flat +/- 1.5db. Marten's is flat +/- .5db. Also, the 2-buss out on my console is very very close to the direct out. The difference between the direct out and 2-buss on my console is pretty similar to the difference between the direct out and the 2-buss on Marten's console, which would suggest that your cap and resistor modifications on the aca board are providing a similar result to using the stock values and 47k buss resistors - which is what are in my console. Anyways, I am plenty satisfied with the response of mine ... Best, Ben

 

[RyanC]

Hi Jeff-

So I'm looking to price this out for a larger matrix mixer, what would be the pot/fader values (pan and level)?  And are there any specific parts you would recommend?  I'm looking at a 34x20 matrix mixer, with stereo buss assign, pan and level (probably on a pot to save space) on each mono input.  Does panning require extra buffer circuitry, or just a linear pot?

Also, on the matrix mixer, I wont need a meter or an insert point (would just insert post mixer) so is the 325 half necessary if the -2dB level is not a problem for me?  The output of the ACA half of the card is balanced right?

If it helps, I'm looking to use the matrix mixer half during tracking for cue sends, routing and printing of parrallel fx chains etc, and then at mix time have DACS->OBFX->VCA auto/recall-> API Matrix->OBFX-> DAW with all 10 stereo stems back to daw.  And then print all the stems, so only the relevant stem would need to be recalled.  Just throwing that out there to see if anyone has any ideas.  Thanks

 

[jsteiger]

Hi Jeff-

So I'm looking to price this out for a larger matrix mixer, what would be the pot/fader values (pan and level)?  And are there any specific parts you would recommend?  I'm looking at a 34x20 matrix mixer, with stereo buss assign, pan and level (probably on a pot to save space) on each mono input.  Does panning require extra buffer circuitry, or just a linear pot?

Ryan, to answer the above would be a text book worth of data! That is more about "input channels" than the ACA part of the console. This build is more about what comes after the input channel, the ACA. I would recommend many searches here and also picking up the book "The Handbook for Sound Engineers". I also remember John Roberts posting a link here to a rather large and great article he had written on console design and architecture. This will also be helpful.

Also, on the matrix mixer, I wont need a meter or an insert point (would just insert post mixer) so is the 325 half necessary if the -2dB level is not a problem for me?  The output of the ACA half of the card is balanced right?

Yes the ACA output is transformer balanced with 2623-4's. The polarity is properly inverted with the primaries of the 2623-4. The booster or 325 part of the circuit is not 100% necessary.

Cheers! Jeff

 

[RyanC]

I was afraid of that. . . time to hit the books.  Thanks jeff.

 

[PATAPETER]

Dear jeff: I'm new in this forum . I want to tell you that I love What you are doing  at classicAPI. I have an API 2488 from 1972 ,If you need any schematics just ask for it, With 528 modules and 550 A eq's . And my question is , my console doesn't have any cards like your's ( 312 or 325 ), I want to know if the summing stage is like yours with almost a 325 cards after de st fader , Because i see the st and busses aca , but dont see the oder stage.
I'm trying to built a mini console with a replica of the 528 modules without the cue sends and aux send,only the line/mic and the 1 and 2 buttons for the low filters , and the pan and st / busses assign . Then I will need you ACA bo cards and transformes , i already have scott's sl 2520 vintage and some vintage 2520 originals.
Best Regards
Pedro Pearson.

 

[jsteiger]

Dear jeff: I'm new in this forum . I want to tell you that I love What you are doing  at classicAPI. I have an API 2488 from 1972 ,If you need any schematics just ask for it, With 528 modules and 550 A eq's . And my question is , my console doesn't have any cards like your's ( 312 or 325 ), I want to know if the summing stage is like yours with almost a 325 cards after de st fader , Because i see the st and busses aca , but dont see the oder stage.
I'm trying to built a mini console with a replica of the 528 modules without the cue sends and aux send,only the line/mic and the 1 and 2 buttons for the low filters , and the pan and st / busses assign . Then I will need you ACA bo cards and transformes , i already have scott's sl 2520 vintage and some vintage 2520 originals.
Best Regards
Pedro Pearson.

Hi Pedro,

Great console you have there. From what I have seen, the 2488's did not have the 300 series card cage. Our friend Dennis in Sweden has confirmed this a few times with the various 2488's he has owned or does own now. What they did was use the 4 channel ACA boards for multiple purposes. Some are populated as the ACA circuit and some are populated exactly the same as the 325 card booster circuit. The only difference is the output transformer on yours is probably a 2623-4 instead of the 2503 found on the 325. Quite interesting how they did this. I don't know why exactly. Space in the console frame maybe?

It's kind of like the input channel PCB's. The boards that are used for your 528 modules are the same exact boards that are used for my 536 modules, which are the same as used for the 544 modules found in the 1604's. They would just populate the boards a little differently and use different faceplates and switch caps. Kind of genius I think.

BTW, my board does not have the 312 cards. My pres are on the 536 input modules just like yours.

I am planning on a 500 sized modular desk that uses the vintage API input channel. I have the modules layed out already. If you search for "500 modular console" you should find the thread here in the Lab.

Cheers!
Jeff

 

[PATAPETER]

here the picture, API TRANSFORMERS SPEC.

 

[PATAPETER]

my post didn't show up.... Don't know why .
But jeff : I was saying that the aca boosters only have the 2623. the 2503 are inside the 528 modules 2 of them , 1 is for the insert going to the patchbay and the other is the multi out channel going to pachtbay too. The directs out of the modules are aca booster cards in the back of the console y think every output is going thru those cards.Also de submasters too.
So i found that the 2623 and the 2503 are pretty much the same, the 2503 has another secondary than the 2623. So the sound will be pretty much the same.In my other post is the picture .
I will build my small api 16x8x2 summing with mic/pre like the 2488 , but without first the cue sends and aux send , may be i'll add that later.
First i want to sum .
Do you have any ideas on cloning the 550A EQ ? I think the difficult part is getting a replica for the caps keys . Any ideas on that ?
I think Api is using a different thing on the 550B, but i didn't see one of them.
Thanks for every thing Jeff. I love to have someone to chat about my API.
Best Regards.
Pedro.

 

[jsteiger]

...the 2503 are inside the 528 modules 2 of them...

Pedro, are you sure about this? My input channels have 2623-1's on them. I don't see how 2503's would fit on the boards. They would not fit between the DPDT Schadow switches and the channel peak circuit. I have 2 544 channels here from a friend's 1604. One module has a single 2623-1 (no direct out) and the other channel has 2 of the 2157's. They are also the smaller transformers with 2 secondaries. I would not be surprised if maybe your modules were custom? I know API did a lot of custom work back then. Almost all of their consoles were different in some way or another.

Do you have any ideas on cloning the 550A EQ ?...

No, on this one I don't. It will take a bigger man than me to tackle the 500a. I think maybe Peter Purpose could do it for sure.  :-* ;D Common Peter. I double dog dare you! 

Cheers, Jeff

 

[PATAPETER]

JEFF : DID YOU SAW THE OTHER POST WITH THE PICTURE THAT HAS THE SPEC FOR THE API TRANSFORMERS ? THERE YOU CAN SEE THAT THOSE XFORMERS ARE THE SAME....I WILL PULL OUT A MODULE TO SEE WHAT I'VE TOLD YOU BEFORE.
BUT I'M ALMOST SHURE ABOUT THAT. I WILL TAKE SOME PICTURES.
AN ABOUT THE 550A WHEN YOU SELECT A FREQUENCY THE ROTARY SWITCH SELECT A DIFERENT CAPACITOR SO THAT IS WHAT THE ROTARY SWITCH DOES. IF SOMEBODY HAS AN 550B ,COULD YOU OPEN AND TAKE SOME PICTURES OF IT?
THANKS. REGARDS.

PS: I 'VE POSTED MY OPINION ABOUT THE MODULAR CONSOLE 500 SERIES.

PEDRO.