[live sound] putting Audacity between the mics and mixer

[steve]

My boss built his own "transformer isolated splitters" (that is what you need to Google) many years ago and we still use them for on-stage monitor mixing.

An easy (and much cheaper) method is to use an Op-amp buffer circuit (Op-amp follower).
Using an Op-amp follower circuit with an input from the insert connector on the mixer would be something like this:

drawing.png (2.47 KiB) Viewed 876 times

[J,R,D, Ltd]

As it has 6 AUX outs and 2 (usable for your case) groups you could use these as 8 pass-thrus but would lose them for other uses. You can build your own isolated Ys

The 6 AUX outs are actually four + two because the two (5 and 6) are switched between being AUX out and Effect on a per channel basis. Why would only 2 of the 4 groups be usable for my case?

Do you have a schematic for an Isolated Y?

I actually drew a schematic for an idea I had using the Insert I/O Jacks

in re. 4 + 2 that is why I said you would lose them for other uses--they are either AUX or Effects--so not more reverb on the vocals! As for the Groups, as per the manual the assign buttons are ganged 1/2 & 3/4 and (as opposed to the norm) are not split by the pan--so pressing 1/2 assigns to both 1 & 2 (I may have mis-read the manual).

Maybe you didn't scroll down to the bottom of page 12 where it says:

Code: Select all

9	PAN Control (Monaural Channels)
	 BAL Control (Stereo Channels)
The PAN control adjusts the signal’s pan positioning into the
Group 1-2 bus pair, into the Group 3-4 bus pair, and into the
Stereo bus’s L and R lines.
The BAL control knob sets the balance between left and right
channels. Signals into the L input (odd channel) feed to the
Group 1 and Group 3 buses and to the L line of the Stereo bus.
Signals into the R input (even channel) feed to the Group 2 and
Group 4 buses and to the R line of the Stereo bus.

I haven't had need to use the groups much yet.

My boss built his own "transformer isolated splitters" (that is what you need to Google) many years ago and we still use them for on-stage monitor mixing. He also just bought a second set but time is money and he's getting well up into his 70's now and probably has less fund soldering than mixing!

Cool sounds like a great guy.

As for your schematic, in the 60's I built huge computers for universities using nand gates, clock chips, diode arrays etc.; we silk screened our own boards and had a soldering wave tank; but...I think I was in the 60's as I do not recall them! I have a lot of hard won experience as a sound tech but my ET days are more than 50 years ago. I will have to pass!

That's understandable

My boss built his own "transformer isolated splitters" (that is what you need to Google) many years ago and we still use them for on-stage monitor mixing.

An easy (and much cheaper) method is to use an Op-amp buffer circuit (Op-amp follower).
Using an Op-amp follower circuit with an input from the insert connector on the mixer would be something like this:

drawing.png

So what is the point of the OP-amp buffer here? It makes sure the input on the recording device does not get over driven?

[Edgar]

Maybe you didn't scroll down to the bottom of page 12 where it says:

Yep, did not get to the fine print; balance and pan--it really is a full featured board!
[-ed]and priced right, too $1250!

[steve]

So what is the point of the OP-amp buffer here? It makes sure the input on the recording device does not get over driven?

The input impedance of the Op-amp buffer is very high, so effectively what the mixer sees is the Insert Send directly connected to the Insert Return, which is virtually the same as not having anything plugged into the Insert socket.
The output of the Op-amp "follows" the signal on its non-inverting input, but is isolated from it. This can then be fed into any input load, up to the drive capability of the Op-amp.

For a practical circuit you would probably want DC blocking capacitors on the input and output of the Op-amp, which would then allow a simple single rail supply to be used to power the Op-amp and a 2 resistor divider to determine "0 V" (for simplicity it could be battery powered).