Unity gain mixer project -- anyone taken apart a Boss KM2?

[niftyprose]

Hi guys, I'm designing an unusual micromixer. I'll spare you all the details but the basic idea is to use a very simple unity gain mixer circuit like the Boss KM2 of yore as one link in a chain. The completed box will enable me to chain several such circuits together. I know the theory for a unity mixer is prettty easy and I'm sure I could work out a circuit from first principles. However, if anyone has hands-on with a KM2 or a decent schematic, I'd be delighted to see how Boss tackled this one. Best, NP.

[PRR]

https://desitol.exblog.jp/24192797/

[niftyprose]

Wow, thanks, that's even simpler than I thought. Got the circuit? Best, NP.

[PRR]

FWIW: it's not "unity gain", unless you turn the gain-knobs to the {UNITY} mark.

By the simplicity, it is probably a single transistor inverting amplifier. For more than a few signal paths, sanity recommends non-inverting.

The inverting mixer with over-unity internal gain is susceptible to hiss troubles.

I think in this day of 19 cent dual opamps, you can do better from a clean sheet. The woods (well, innernet) is full of mixer pages. Jack AMZ Orman, R.G. Geofex Keene, Rod ESP Elliott are some no-BS sources.

[niftyprose]

Thx guys, definitely food for thought.... NP

[2SC732GR]

the trannies are 3 2SC732GR's and 1 2SC970. google boss km2 pictures and there's a detailed facebook post
by a japanese guy that show the pcb gut shot front and backside. the first transistor pair are the 732 and 970,
second are 2 732's.

i built it on a perfboard and it turned out to be a great distortion for synths and guitars.
a bit noisy if you dime it but lovely never the less.

[2SC732GR]

2SA970, sorry, not 2SC970