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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]

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]

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]

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.

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]

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.

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.

[John Roberts {JR}]

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.

The resistor to ground is to bleed off any leakage current to prevent pops when plugging in.

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.

It depends on the performance level (price) of the mixer. Big dog consoles will actively sum the two channels together with an op amp summer and then drive the output with low source impedance (the same or another op amp). Inside a very low cost mixer the mono output could be as simple as two passive resistors multed together. I have done it both ways depending on the target customer.

JR 

Thank you,
Garry
[email protected]

[Matthew Knischewsky]

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]

I have built the circuits from Rane Note 109 into all kinds of handy summing adapters. With some care the resistors will fit inside of a Neutrik XLR or TRS connector shell. Yes there are some commercial products but nothing beats the economy of a few 1% resistors to get the job done. Yes there can be a bit of drop in level, as Ivan mentioned " Just turn it up a little".

[Mike Caldwell]

I have built the circuits from Rane Note 109 into all kinds of handy summing adapters. With some care the resistors will fit inside of a Neutrik XLR or TRS connector shell. Yes there are some commercial products but nothing beats the economy of a few 1% resistors to get the job done. Yes there can be a bit of drop in level, as Ivan mentioned " Just turn it up a little".

All of them I've built have had the resistors in the XLR connectors.

[Frank Koenig]

All of them I've built have had the resistors in the XLR connectors.

Me too. Use somewhat thinner cable so that two fit through the strain relief on the male XLR and you get a nice, simple, rugged Y-cord with no unnecessary boxes, controls, or extra strain reliefs to break. Label it clearly and you’re good to go. --Frank

[Garry Drummond]

Good evening and thanks to all for the replies. John Roberts actually answered my question. I have built several of these circuits but only used the series resistors and not the shunt resistor and never had any problems. I am getting ready to build another for another project and reviewed the RANE article and also a similar article on the QSC website with circuit attached below to remind myself of the correct value resistors. This is what prompted the question.

Thanks again,
Garry

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