Modular synth madness

Latest idea.

Build standalone mixer using Bourns PTL series light up slide potentiometers, TL072 op amps and a homemade 12v power supply. All fairly easy stuff, I can find a nice Hammond enclosure, the sloped type with sides. 16 channels, so that's four TL072's - the difficult bit is cutting slots in metal for the slide pots. I can incorporate some two channel VU meters and a line level output module or two. 

Actually, I could even build a valve preamp stage into it as well. Although that's quite power hungry and the voltage regulators I'd be using in the power supply would need big heatsinks, at least. But. All do-able. 

Or I could buy a mixer, but that's hardly the point. ;-)

Thanks, mate. Well, I feel I must. ;-)

For my next trick, I've got some Chinese two column VU meters. LED jobs, really simple circuit. Now, I can pay £60 a pop to someone in Switzerland who sells these mounted into a panel with a few jacks, or I can get out a pillar drill, coping saw and get a handful of jacks and a connector out and make these into modules myself, therefore saving a small fortune and spending a day swearing in the garage in a cloud of tobacco smoke. 

I choose the latter. ;-)

PS Yes, it sounds astonishing. ;-)

The shame is that it won't ever be played live, due to the complexity of it, and also, I'm very unlikely to release any more commercial music. It's really just a fantastic studio instrument for my own amusement. Oh yes, there's going to be a liquid light show in the studio in the form of an oil wheel projector or two. Freak out, baby. ;-)

Calibration time. This is where it gets a little complicated. 

For 8 of the 10 oscillators in the main cabinet, there's quite a lengthy and technical procedure to make them play properly. There are six trim pots here by the red voltage probe. The oscillator cores produce a triangle wave. Using an oscilloscope, you adjust the trimpot to get a good looking triangle wave. You then use another trimpot to set up the square wave duty cycle.

(That's just one oscillator in the photo - the other modules are a filter, amplifier, envelope generators and a low frequency oscillator all commoned onto one panel. All you can see is about 4% of the total electronics in the synth.)

Next step is to adjust the output voltage of the internal temperature control to 0.63v, which I'm doing here. Oscillators drift due to temperature - they have to have temperature control to keep them in pitch. Talking of pitch, another trim pot sets the initial pitch and the remaining two are used to set up the octave scaling and "high end trim", which is the time consuming part. Due to some internal tolerances, I've got to desolder the scaling trim pots and replace them with higher value ones to get enough range to do the adjustments. At the moment, it's not scaling enough and notes go flat as you switch octaves.

So that'll be the oscillators done shortly. The next step is to adjust trim on various filters and amplifiers, envelope generators and a few other modules to get the right kind of response. This varies according to taste, sort of, but lots of fun with an oscilloscope, screwdriver and volt meter ahead. 

Davesax1965 wrote: I think I actually DO need a new hobby. ;-)

A very basic first test of the system. Some oscillator scaling (tuning over an octave) issues. Two of eight sequencers being used in the sequencer cabinet (via six oscillators). Two oscillators (out of eight) being used in the main cabinet. 

Back in a few months.... ;-)

Is that a bread-toaster on the second row right lower cabinet ?

Totally unnecessary sunglasses shot. 

Go on, then, I'll solder up bigger 5U format systems, instead of 3U. ;-)