Resistor value passive sum mixer with transformers

[Buffalo Tom]

Hi. I have two stand alone Lehle 1:1 isolation transformers on my left and right outputs in a pedalboard interface I'm building. I want to sum these two signals to a mono jack using switched jacks on left and right outs. How do I know what resistor values to use when summing after the transformer? I have tried 100k ohm but it sounded no good. I assume I need to know the output impedance of the Lehle transformer? Can you find the output impedance here? http://v3.lehle.com/_data/products/P-Split%20II/Manual/Lehle-P-Split-II-EN.pdf The interface outputs is the last thing on the pedalboard before the amps. Anyone got suggestions for resistor value? Thanks!

[bool]

I would try with 10kOhm. And then going progressively to lower values, all the time cautiously checking out for the L-R channel bleed-through. So a bit of trial-and-error ...

Simplified; try using the lowest value resistors that don't cause significant cross-channel bleed-through.

[Buffalo Tom]

Thanks! will try 10kOhm

[anotherjim]

If the secondaries areotherwise completely isolated, you can just wire them in series I'd have thought. Maybe parallel too. If there is a common signal in the 2 outputs, be careful of phasing issues so you aren't adding opposite polarity signal in the blend . Of course, the transformers can correct that if needed.

[Buffalo Tom]

If the secondaries areotherwise completely isolated, you can just wire them in series I'd have thought. Maybe parallel too. If there is a common signal in the 2 outputs, be careful of phasing issues so you aren't adding opposite polarity signal in the blend . Of course, the transformers can correct that if needed.

Thanks! Sounds very interesting! The two LTHZ transformer Im using has following:

Green = Ground (sleeve)
Pink = Primary + in phase (tip)
Blue = Primary - out of phase (ring)
Black = Secondary + in phase (tip)
Red = Secondary - out of phase (ring)

So at the moment I have left+right IN jacks and left+right OUT jacks. The two transformers are wired TRS from primary to secondary. My output jacks are switched so I wanna go from there to a dedicated MONO jack that sums left+right outs. So like you said maybe I don't need resistors at all? I like that! But Im trying to understand how to wire the secondaries from the two transformers in series??

[anotherjim]

I was thinking (vaguely) that switched sockets would be useful. Paramount would be if you expect the merged output to function at the same time as the separate outs? I was thinking something like the common arrangement of separate L & R outs, but if you only use one in particular, then that one outputs L & R merged to mono.

[bool]

If secondaries are ---completelly--- electrically separated (ie. "floating"), then and only then you can switch them in series (!!) for "mono" output - without any resistors!

Do NOT wire them in parallel --ever-- without series resistors!