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Saturday, June 5, 2010

More Progress

Wow, a late night. The ENVDL boards came yesterday so I'm hoping to find time to stuff one and try it out. I also spent a lot of time updating some schematics/PCBs. It turns out the resonance and output of the Synthasystem VCF is different than the Synthacon, or even Nyle's 1974 paper. There are some "penciled" modifications which are a bit confusing, but I think I got it figured out.

The VCO information included an updated VCO core, 1976, which uses a different JFET and some other small differences. I re-did the VCO Function Generator based on the newer VCO MOD schematic. I think I'll build them both in prototype to see if one is any better. The nice thing about the newer one is the JFET is still in production, 2N5246, as opposed to the obsolete 2N5163. It seems to be a pretty good cross reference and I will try them in the other circuits like the sample and hold, etc. Since Nyle used them, and spec'd them, I can still keep the circuits original.

After I had looked through the schematics, it seems there are two which are missing. If Nyle doesn't have them, I can only assume I'll never have them. The missing two were the Voltage Follower, basically a lag, or portamento circuit, and the Voltage processor, a module which simply changes and recombines the phases of the input signals.

For the VFollower, I think I can just pull the portamento part out of one of the keyboard schematics. If I understand it right, it's little more than an adjustable low pass filter. The intended use was for control voltages like from the sequencer I think.

For the VProcessor, I'm sure it wasn't much more than some 741 OpAmps configured in normal and inverting stages. I think even I can design something like this. I have a pretty good feel for the general design practices Nyle used and so will use comparable resistors, etc. to put it together. I want to get some of the other modules laid out first though.

It's too bad I sent in the VCF design I had before I had laid out the Synthacon version. The VCO is fine as it uses the original Synthasystem schematic so I can test that core, etc. The sequencer, too should be fine.

I've optimized all of them since then anyway, so I will need to resubmit the lot. 

So, next up will be to build an ENVDL type 1 and 2 and try them out. Continue to capture the schematics, and layout PCBs.

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