Adding sends to mixer

[fragletrollet]

Hello!

I`m building a DR-2402, a 24 channel API based mixer with THAT 1646 driven direct outs that I want to use for aux sends.

I want to have 4 aux sends from each channel. Bear with me and my noobness, but afaik just splitting the signal would have an effect on the impedance from the 1646, maybe changing it to out of it`s " impedance operating range" (?), so I guess I would need what is called a "buffering" circuit to "separate" the circuits. This can be done with op-amps?

So I guess I could use something like the CAPI 2S-LA if wanting to keep with the API style. Could I then just split the signal coming out of the first section of the pcb, the splits going to each its potentiometer and to it`s respective aux output?
Then just skip the second section?


Thanks for all help and all the best!

 

[ruffrecords]

If you could post a schematic it would make it easier to advise you.

Cheers

Ian

 

[fragletrollet]

Hey Ian, thanks for chiming in. Not much of a schematic, here is a block diagram of what I have in mind. I would repeat this for 8-16 channels, depending on how many sends I`ll end up needing. Hope it`s helpful...?

 

[ruffrecords]

I am a little confused. Are you saying you want four aux send outputs per channel? For 24 channels that's a total of 96 outputs - or do you really want four aux buses?

Cheers

Ian

 

[fragletrollet]

Yeah sorry `bout that. What I really want is 4 aux busses. Probably for 8 channels (not for all 24).

This is basically a way to have echo/delay sends for 8 channels on the dr 2402 (to 4 different mono input echo units)

 

[ruffrecords]

OK, that makes sense. So you need four more buses. As they are intended for echo/delay you probably want them post fader. Without a schematic it is hard to tell if there is an amplifier after the fader but one would hope there is. If there is then that is the place to drive your AUX send pots  from. You then need four bus amps (probably virtual earth) to mix then together and the outputs of these are you four AUX sends.

To be honest I cannot understand why the creator of this project has not published a schematic because it makes it extremely hard to help you in any detail.

Cheers

Ian

 

[fragletrollet]

I believe the direct outs on the DR2402 are pre-fader, each driven from a THAT 1646 line driver. In my mind, I would want them prefader anyways, so I can control the sends i have in mind  (mults of the direct outs) separately from the level on the  mixer. So my question is about a separate box from the dr2402, that basically splits the d/o signal into 4 separate aux (busses) controlled from this separate box. Am I making sense?

 

[ruffrecords]

I believe the direct outs on the DR2402 are pre-fader, each driven from a THAT 1646 line driver. In my mind, I would want them prefader anyways, so I can control the sends i have in mind  (mults of the direct outs) separately from the level on the  mixer. So my question is about a separate box from the dr2402, that basically splits the d/o signal into 4 separate aux (busses) controlled from this separate box. Am I making sense?

Yes and no. If the direct outs are pre-fader and you want pre-fade AUXes then that is the place to connect them too. It would not be too hard to design a separate box with 8 inputs and 4 AUX sends per input and 4  buses and outputs. YOu just need a buffer amp per channel, 4 pots and four bus amps.

What puzzles me is why you want pre-fade AUXes for echo/delay - and you are not alone, a lot of people  seem to want that these days. Maybe I am just old fashioned, but in my day, echo/delay sends were all post fader so that when you pull down the fader the FX are turned down/off at the same time. Pre-fade UAXes were used almost exclusively for foldback.

Cheers

ian

 

[fragletrollet]

Thanks Ian. Reason I want pre fade auxe`s is because I want to occasionally send signal to these delay/reverb units, in dub style fashion when I just want to occasionally feed a space-echo for example.  Setting up feedback through the mixer/aux sends unit to an echo unit, back into the mixer sent out to the aux send unit back into the mixer again... creating glorius feedback  8)

 

[ruffrecords]

Thanks Ian. Reason I want pre fade auxe`s is because I want to occasionally send signal to these delay/reverb units, in dub style fashion when I just want to occasionally feed a space-echo for example.  Setting up feedback through the mixer/aux sends unit to an echo unit, back into the mixer sent out to the aux send unit back into the mixer again... creating glorious feedback  8)

OK, that makes sense, but do you really need all the AUXes to be pre-fade all the time for just the occasional space echo?

Back in the 60 when I was in my teens, my first decent tape recorder was a half track stereo Brenell MKV. As well as input level controls it also had output level controls. My first mos was to disconnect the output controls so the output level was fixed. I then reconnected the output level controls so they fed back some of the output back to the input and created built in echo. You could get some incredibly long echoes with that.

Cheers

Ian

 

[fragletrollet]

Yup, and i dont want to mod the dr2402, just add this extra box (that would be a separate  unit connected to the dr2402 through db25 cables)


Yeah,  my studio is craving an r2r

 

[ruffrecords]

Yup, and i dont want to mod the dr2402, just add this extra box (that would be a separate  unit connected to the dr2402 through db25 cables)


Yeah,  my studio is craving an r2r

OK, in that case, go pre-fader from the direct outs and make yourself a separate box with a simple four bus mixer.

I still have several reel to reels. I made some great on location recording with a little Fostex R8 - 8 tracks on quarter in tape which I still have. Some people say it is c..p but it sounded good to the clients. I also used to have a TEAC 4 track but I sold it - wish now I had not. I still have a couple of Revox 2 tracks and a Ferrograph.

Cheers

ian

 

[Rocinante]

The 'send and blend' from serpent audio could be the what you are looking for.  Kind of an 'aux' box for parallel processing

 

[fragletrollet]

The send'n'blend looks nice, but a pity using only half of the circuitry? (only send)

I was wondering if I could use the 4ch inv ACA from CAPI for this. See attached pic.
I would repeat the input x8, so each input has 4 pots sending the respective input to either of the 4 buses. Makes sense...?

 

[ruffrecords]

The ACA is nothing more than a regular virtual earth amplifier with a fancy name. You can definitely use its as a VE bus amp for the four aux send buses.  If you want a master send then you could add a 1K pot to the output provided the chosen DOA can drive a 1K  load.

Cheers

Ian

 

[qmp audio]

There was talk of the creater of this project creating a send-box addon.  Not sure if that was finished on or not:
https://www.facebook.com/plugins/post.php?href=https%3A%2F%2Fwww.facebook.com%2FDIY.Racked%2Fposts%2F388920514565987&width=500

 

[fragletrollet]

Ah cool! I`ll do some investigating :=)

 

[fragletrollet]

Ok, just had a go at drawing my first schematic 

Would this work?

 

[ruffrecords]

Not sure what R1 is for. You need to add resistors in series with the slider of each of the four AUX send pots. The pots at the output of the ACA would probably be better if they were 1K.

Cheers

Ian

 

[fragletrollet]

R1 is the 47k bus resistor from here:

http://www.capi-gear.com/catalog/images/gallery/PCBs/inverting_ACA/Block-diagram.pdf

Slider=wiper? So the 47k bus resistor should be between the wiper and aca input?

Pots:
10k (log?) ok for ACA inputs? 1k (log?) for outs?