SCF -- 1st Attempt...

Having a go at Tim Stinchcombe's Switched Capacitor Voltage Controlled Filter. I got a bit overly entusiastic and grafted Tom Henry's front end to the 4046 from his VCO into it... Not so successful, a closer look at what is happening inside the 4046 and it becomes a bit more apparent that I should have left it alone! Anyway it shouldn't be too hard to put it back to the original design...

0.2% THD

Have just made a PCB for Thomas Henry's new VCO based around a OTA & a 555 Timer. It's pretty clean layout without too many links and roared into life immediately. The only issue with the board was i forgot R46 which biases the sawtooth. As it was in the next room I did drag in this Audio Spectrum Analyzer to help adjust the Sinewave purity adjustments and got down to a pleasing 0.2% THD ~ the peak-to-peak amplitude is a bit low for the sinewave compared with the triangle/ramp/pulse so may try tweaking up the input to the OTA by changing R34? Still need to do the 1V/octave adjustment so need to look for that last 2K tempco I have somewhere...

DX7

Accidentally bought a rather sad Yamaha DX7 off e-bay as a non functioning, "for parts" unit. I don't think that there is too much wrong with it and it did come with a spare cover & LCD display. I have stripped it down and started cleaning it up. This has included sandblasting the base which looked a bit like it had been dragged down the road behind a car… I plan to get it powered-coated this week and then start to get all the bits back into it...