torsdag den 22. maj 2014

Aristoteles Logic Synth Update #1: MIXER

Oh what a spring it's been! I was bedridden for about a month which really zapped all my creativity and I've slowly recovered now to bring back my mind on what is the icing on my cake of life: electronic gadgeting.

So just around New Years Eve I posted a picture of my newly assembled modular synth casing - no intestines yet though! But just before my bed claimed me for a minor lifetime, I was able to finish up the first and central part of the system: the 8-channel mixer with simple BP/LP filters + power supply.

Here's a demonstration of what I am talking about:

So the idea is that you have 8 channels in the mixer which are summed together after they've passed the filter circuit and the respective volume knob. When using stackable banana-jacks one might ask why bother with a multi-channel mixer; why not just stack 'em on top of each other and using passive resistor/diode mixing?
The problem for me was that mixing with just resistors would cause each output from every oscillator to drop in voltage and maybe cause instability with edge-detection in the chips they would enter - and diodes make distinctive modulation when used for summing. Which is why every output enters a diode, so it's still possible to mix signals together in a single mixer channel if one is running low on free channels. Other than that, diodes make sure that no cross-talk occurs if stacked for multiple operations.

Some pics:

The power supply was super simple, just a power switch and momentary N/C button to switch on  and off and discharge the 470uF cap to get the power starve effect. Starving only affects the CMOS-chips used for sound generation, the mixer circuit isn't affacted by the variable supply voltage.
I will discuss the other modules in future entries and here's some schemes for the willing.