All My Circuits

Homemade audio doodads.  Note:  I am NOT an electronics engineer, so you don't need to tell me how haphazard these things are .. and if you try to discuss tech theory with me, I probably won't understand it.

The clear plastic jar with jacks all over it is the passive mixer I built this weekend, based roughly on a mixer schematic from the book _Handmade Electronic Music_ by Nicolas Collins.  It has no volume pots because most of my devices have volume controls of their own already; I just needed a way to blend them all down to one (or two) output channels.  Ins are on the side, outs are on the top.  All channels are mono.  Each channel has a mini jack and a 1/4" jack because some my synth devices only have mini connections.  Plugging into the 1/4 jack will disable the mini jack on that channel.  All six inputs are mixed by default to output A.  Plugging into output B will split inputs 1-3 to A, and inputs 4-6 to B.  I have verified with a meter that signals pass through this contraption as intended, but have not yet sound-tested it.

The "Dirty Attenuator" is the only one with a hand-made custom enclosure - in this case, a handsome wooden box.  It's basically a passive volume control with a bypass switch I salvaged from an old washing machine.  The switch acts as a cheap hand-operated signal gate.  I built this because chopping an audio signal with a Morse key made my recording devices freak out (it was literally opening and closing the input circuit, roughly equivalent to rapidly plugging and unplugging a jack) so I needed a way to do a signal interrupt without breaking the circuit.  This thing sort of works, but turning the trim to zero shorts the signal to ground and disables the bypass switch, so you get silence no matter what you do.  I added a resistor between the pot and the ground line, but that didn't seem to make any difference.  Best I could come up with was to add a diode just before the output, selectable via the "DIRT" switch, which cuts signal strength in half and gives it a sort of gritty, static-y sound.  It can get the attenuated signal low enough, compared to the bypass signal, that it will disappear in the mix as long as there's other noise to cover it.

The Tone box is exactly what you'd think it is:  A passive tone control, which I needed after installing piezo discs in a ukulele and discovering that the output signal was much too bright.  The enclosure was one I found somewhere, originally wired to split an RCA jack to two 1/4 mono jacks.  There was just enough space to install my tone pot in the center hole where the RCA was, so I did it.  This was by far the easiest one to assemble.  Most of it was already done for me.

The Kentmere film box with three jacks labeled "I C O" (Input, Carrier, Output) is a passive ring modulator.  To be honest, I did not design this circuit.  It came as a cheap kit from Synthrotek:  Four diodes, three jacks, and a little tiny circuit board all in a plastic baggie.  I soldered it together and installed it in this box, as it was the only container I had on hand at the time.  I planned to use this, along with an untuned radio, as a "static-izer" effect - but, although I did test it & verified that it works (almost two years ago now), I have never recorded anything with it.