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Stereo to Mono summing circuit

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Garry Drummond:
Good Day All,

I have a question regarding RANE Note 109 "Why Not Wye?" regarding the stereo to mono summing circuit. Does anyone know the purpose of the 10K ~ 20K ohm shunt resistor from mono output to ground (common)?  It seems to reduce the output slightly. I want to use this circuit where I take the stereo output from a laptop computer or other typical consumer device, and convert the stereo signal to mono to feed an audio mixer where I'm only using one output to feed a mono amplifier/speaker system. I know there are other ways to do this but going this direction seems the easiest way to accomplish what I want to do.

One other question regarding this, does anyone know how audio mixers do basically the same thing when a L & R line input is sent to the "Aux Send" jack where it is combined into a mono signal? I don't have a service manual from any of the audio mixer manufacturers to find how they do this.

Thank you,
Garry
[email protected]
 



Ivan Beaver:

--- Quote from: Garry Drummond on September 03, 2022, 09:00:51 PM ---Good Day All,

I have a question regarding RANE Note 109 "Why Not Wye?" regarding the stereo to mono summing circuit. Does anyone know the purpose of the 10K ~ 20K ohm shunt resistor from mono output to ground (common)?  It seems to reduce the output slightly. I want to use this circuit where I take the stereo output from a laptop computer or other typical consumer device, and convert the stereo signal to mono to feed an audio mixer where I'm only using one output to feed a mono amplifier/speaker system. I know there are other ways to do this but going this direction seems the easiest way to accomplish what I want to do.

One other question regarding this, does anyone know how audio mixers do basically the same thing when a L & R line input is sent to the "Aux Send" jack where it is combined into a mono signal? I don't have a service manual from any of the audio mixer manufacturers to find how they do this.

Thank you,
Garry
[email protected]

--- End quote ---
You don't need a resistor to ground, but 10-20K does not hurt anything.

HOWEVER you MUST use a series resistor (or 2 for balanced) on each leg of the "summing Y" in order to keep from loading down the OPPOSITE channel, which can result in distortion, or possibly damage to the drive circuit.

Anything from 500-1K is a good starting point.

Yes, you will lose a wee tad amount of level, but most consoles have more than enough output capability.  Just turn it up a little

Robert Lunceford:

--- Quote from: Garry Drummond on September 03, 2022, 09:00:51 PM ---I want to use this circuit where I take the stereo output from a laptop computer or other typical consumer device, and convert the stereo signal to mono to feed an audio mixer where I'm only using one output to feed a mono amplifier/speaker system. I know there are other ways to do this but going this direction seems the easiest way to accomplish what I want to do.

--- End quote ---

This is what I use.
https://www.switchcraft.com/1-8-stereo-jack-to-balanced-mono-3-pin-male-xlr-with-volume-control-and-ground-lift-switch-mic-level-output-/318/

John Schalk:

--- Quote from: Garry Drummond on September 03, 2022, 09:00:51 PM ---I want to use this circuit where I take the stereo output from a laptop computer or other typical consumer device, and convert the stereo signal to mono to feed an audio mixer where I'm only using one output to feed a mono amplifier/speaker system.

--- End quote ---
This is what I use.  Not cheap, but I am very happy with it.  The XLR output is a mono sum, but it also has two 1/4" outputs for stereo.

Tim Weaver:
This is what I use. Handy if you also need a volume knob.

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