Buffer PCB to upgrade console output modules

[dasnevestheo]

Hope everyone's safe !

I'm using my free time to upgrade my Saje mixing desk output modules.

I'm trying to replace a dull opamp output circuit with a pair of Neve BA283 output stage circuits but i need a buffer before it to put a fader in between.

Does anyone know where i can find pcbs/gerbers for a simple discrete transitors buffer i can use for the summing amp ?

I guess i will have to adapt it a bit so i acts as a 0db summing point for my sumbus.

Cheers !

 

[dasnevestheo]

Forgot to mention that this is the BA283 design I'll be using (thanks Peterson from DIYRE !) https://drive.google.com/drive/folders/1qCTKOM39HZmtjWrUlgHmzmzdf5wFogwI
+ a juicy pair of carnhill/marinair

I'm going discrete transistors as I've been really pleased with mixing on consoles that had such summing typology.

 

[Whoops]

Would a circuit based on the 2520 Opamp work for you application?

 

[dasnevestheo]

I guess It could  I was thinking of a single rail circuit like 0/24V neve style like the output stage, but that could be cool (and simple) to try.
In the meantime i did a little PCB based on a Douglas Self design

 

[dasnevestheo]

If it works, I might have a few spares. Prototypes ordered

 

[abbey road d enfer]

In the meantime i did a little PCB based on a Douglas Self design

R1 is a major noise contributor. You should either short it or make it considerably smaller (<200r). The SAJE uses a VE summing amp. I think the injection (bus) resistors are 10k, so the gain will be about 7dB with the proposed circuit. Usually summing amps have no gain; typical is 0-6dB attenuation. You will need to increase NFB by putting an RC circuit in parallels with R7. That should be a resistor of a few kohms in series with a 100uFcapacitor.
You'll need to adjust the value for proper level alignment.
There is a risk of the circuit oscillating when presented with the bus capacitance; you may need to put a cap (a few dozen pF) across R7. Alternatively, or complementarily, you may replace R1 with a 47-100uH inductor
Do you have a schemo of the original summing amps?

 

[dasnevestheo]

R7 is indeed  needed to be adjusted for 0dB.
SAJE Bus Resistors are 22K. It indeed looks like a VE summing amp (upper left corner of the schematics).
Will try all of your suggestions in circuit, thanks a lot !

 

[abbey road d enfer]

R7 is indeed  needed to be adjusted for 0dB.
SAJE Bus Resistors are 22K. It indeed looks like a VE summing amp (upper left corner of the schematics).
Will try all of your suggestions in circuit, thanks a lot !

Weird design! The French know nothing about pro audio.  8)
Summing amp has about 5dB gain, so I suspect the operating level is not very high (probably lossy pan-pot).
So in fact, with your proposed circuit, you'll be 5dB short on level. You could run the channels hotter or crank the output fader... What is the nominal position of the output faders, 0dB or 10-12dB in hand?

 

[dasnevestheo]

Faders fully opened are 12dB up

 

[abbey road d enfer]

OK, so compensating the lesser gain is easy.

 

[dasnevestheo]

Yep Can't wait for the boards ! Thanks a lot

 

[dasnevestheo]

And let me just add that, even designed by stupid frenchies like me, this console is really great and its many flaws (appart from that summing) are really musical  8)

 

[abbey road d enfer]

And let me just add that, even designed by stupid frenchies like me, this console is really great and its many flaws (appart from that summing) are really musical  8)

Je suis français...

 

[dasnevestheo]

Oups !

 

[Whoops]

And let me just add that, even designed by stupid frenchies like me, this console is really great and its many flaws (appart from that summing) are really musical  8)

Das Neves is a Portuguese name,
so it was the Portuguese part of you that made it being great

;D

 

[dasnevestheo]

haha true, we have NEVE in our name

 

[Whoops]

haha true, we have NEVE in our name

"From many Neves"