Stereo to Mono

[Mcentee2]

re the simple set up for summing "stereo" or two mono inputs to a single mono signal.

ref link: http://www.rane.com/note109.html


Hi

Application is just output from two different pedals (dry overdrive and a wet-only delay), and I want to combine them to a single mono out to the next pedal in the chain.

I have firstly tried the straight splicing of the signal wires but get a significant drop in output level/volume - the tone doesn't seem to roll off but hard to tell alongside the volume drop.

I've searched and got some background for this, but still not sure of the value of resistors I would be good to "start" with or what calculations are needed to define them.

So we are looking at standard lowish output impedences from the OD and Delay pedals  around 1k for the OD and 2k for the Delay,  and a high >=1m Input impedance of the next pedal.

The Rane article has 460r, and I have seen various interweb descriptions for differing applications for headphones, iPads/iPods etc etc, but nothing really that cements "good" values for guitar effects chains.

Should I be looking at <1k, 1-2k or higher ?

Without some knowledge, I will probably just try various ones, but not sure what I am trying to avoid apart from the end goal of "not reducing overall gain"

Given one of the pedals is a wet delay signal, I am looking for the overall summed output volume to be set by achieving Unity on the main OD mono signal through to the output.


EDIT: I have just tried with 560r, then 1k, then 4k series resistors on both mono signal "inputs", but the total output is still reducing in volume quite significantly and I can detect no noticeable difference between no resistors and the 4k.

I notice Jack Orman uses 47k in a similar layout so I guess I can start to go higher, I am just concerned at what effects I might begin to listen for:

http://www.muzique.com/news/passive-mixer/

[Fuzz-O-Rama]

Mcentee2,
With a passive mixer you are going to lose level. No way around it. Sometimes this is acceptable if you can make up the loss in the next devise. The resistors before the summing point are used to isolate the output electronics of the summed devises. On another note, if one pedal is reversing the polarity of the identical input signal then you will experience phase cancelation with resulting loss. How aligned the out of phase signals are will determine the amount of cancelation. Flipping the polarity in a mono pedal doesn't usually matter because what you are trying to do is very rare. Splitting the output of one devise to feed two is very normal and the phase always matches.

[Mcentee2]

 :icon_redface

Yes, I am now learning basics around passive mixing and can see you would get signal dB loss!

Actually with no in-line resistors the signal merging seems fine with no adverse affects re back-flow of current etc

Phase seems k for this application as well.

The quality of the signal is fine, just amplitude is being lost, which is no huge pain in this test phase now I now that is normal.

At least I know what to look for in an active mixer if needed.

Ta.