Help with modifying a Circuit (Fostex MN-50)

[Kizzer]

I bought two FOSTEX MMN-50 mixers for building in a 1U rack.
my plan was to get rit of the mic and instrument inputs and only use the line input..like you do.
but I tested the compressor carefully and you will get a lot more extra squashing and (nice) dirty sounds
when using the mic/instr input.
My suggestion is (and that's what I'm gonna do): keep the mic, instr and line input and use a switch to have a choice of input gain/attenuation.
the tape inputs with the sliders can be omitted.

Good plan! Should be easy enough to add in the mic section on a dpdt.

 

[Kizzer]

I tried out the microphone input and it sounded good, so I knocked up a little board which works with my original layout. I also knocked up an all in one version.

 

[Bo Deadly]

If you took the time to learn how to use KiCad and submit gebers to OSHPark, I think you would find that tool chain to be much easier and produces a much better and more reliable result.

At least eventually you will. Of course the first few boards will have mistakes but you can almost always hack around them for one-off builds.

 

[bowanderror]

Unconnected is the only way to bias the Fet. Built and works great.

Thanks for posting these layouts, I'm just finishing up building the line-level version. At what voltage did you bias the FET?

 

[Marssound]

Thanks for posting these layouts, I'm just finishing up building the line-level version. At what voltage did you bias the FET?

I am gonna use the FET trimmer as an extra control for more or less dirt in the sound but what I read on internet: trimmer at 11 o'clock is factory setting. I don't know about the voltage., don't know about how to measure it to but will be easy to do , I think?

 

[Kizzer]

I used the trimmers to balance both sides. While sending a drum loop through both sides I noticed a slight difference between how dirty one side could get to the other and so trimmed that one back till they both ran identically.

 

[Marssound]

my version will be something like this:
stereo 19 inch rack. both channels has :
input (line, mic, mic2) rotary switch
gain
release
bias

I will only use it for parallel smash compression (mostly drums). I don't really need the attack function. but maybe I will add it later.