Stereo to mono summing adapter question

whoaru99

Epic Member
I'm going to experiment with building a speaker level to line level stereo to mono converter.

The speaker level to line level part will be a pair of (roughly) 10:1 voltage dividers, then will be something along this line (courtesy Rane) to take that stereo line level down to mono. But, I don't understand why the 20k resistor. Why is that used?

StereoToMonoSumming.JPG

The complete apparatus I have drawn up like this -

R5, R6, and R7 I put in per the stereo to mono summing adapter shown above. R8 represents the amplifier input.

SpeakerToLineToMono.JPG
 
Last edited:
I'm going to experiment with building a speaker level to line level stereo to mono converter.

The speaker level to line level part will be a pair of (roughly) 10:1 voltage dividers, then will be something along this line (courtesy Rane) to take that stereo line level down to mono. But, I don't understand why the 20k resistor. Why is that used?


View attachment 1143509

That's not a speaker-level to line-level setup. It's line-level summing.
You would use it after you knock the speaker-level down to line-level
 
That's not a speaker-level to line-level setup. It's line-level summing.
You would use it after you knock the speaker-level down to line-level

I understand, I've added the whole shebang schematic but I really only had a question about the summing part.
 
I understand, I've added the whole shebang schematic but I really only had a question about the summing part.

OK. Your whole thought didn't make it through my melon the first time around.
I believe that extra resistor is to aid with impedance matching.
 
I can tell you exactly why the 20k resistor is there, as Dennis Bohn (one of the former owners) was one of my bosses when I worked at Rane. It is only necessary "to assure summing when both signals are identical". This question came up all the time and I fielded many tech inquiries about the resistor in question. Network will sum without it, but having the additional R in place guarantees mixing of the inputs under all conditions. FYI: I worked at Rane over 23 years in service and support departments, so any technical inquiries regarding the brand are welcome. So far as the 10:1 attenuator ahead of the summing network, it should function adequately.
 
The 20k resistor (it used to be a 10k resistor from Rane notes) is to lower the signal attenuation (loss). This circuit will give only a 0.2dB loss. It's intended to combine two line level outputs safely into one. I use it and it works great.
 
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