Little advice about OHM ratio please

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I am building a little rather simple passive summing mixer.
I use the retrokits pcb kit. After speaking to Gerrit from RK i was told to make it a 8x mono summing instead of stereo i should add a 10k resistor.
I saw a graphic and seems doable but not sure where to put that resistor exactly?
Or would a stepped mono attenuator that has its own 10k resistor, wired to the pcb place thats originaly intended for the stereo jack suffice?

After that stage i want to wire in a utc 500:500 ohm transformer wich lets me choose different ratios.

All the time i was thinking i should use it to „tame down“ the hot synth level and use it like 500 primary and for example 150 secondary. But i am not so sure anymore. It seems modular synths have actually a low impedance output?

Should i go like 3:1 as planned or rather 1:2?

I do want to drive the transformer (moderate) and i would like to use it in reverse to bump up my weak passive epiano a bit (wich has its own step up transformer at its out actually, so not sure if i add up impedance?)

Not too complex a project but better to have asked before i mess up:D

Sounds like a nice project… Meng Qi Please exist uses 600:60k if that helps…

Yup i hope i get high enough ratio going. I wanted vintage utc/triad iron and the high ratio mic transformers fetch heavy cash

I just dont have the slightest idea what having for example a 100 ohm coming out of the secondary side means for my audio levels and amplifier load. Just dipping around as always :smiley: