The Pink wires!

Actually been a fair bit of activity recently and I have also been trying to plough through the dozens of semi-complete boards that are littering the house. This being probably the most challenging build of the whole lot. This is the VCO board from the Bergofotron and it is a complete beast! It has one particular aspect that I am really interested in experimenting with so after a lapse of 3 or 4 years since i started it the wires are going on...

LFO Noise Spectra

Well a bit of a break again but we are back into about 3 old projects. I have decided not to start anything new unitl at least 5 of the old modules get finished and panelized! This is from the Forbin LFO that I started ages ago that uses a dsPIC to generate the waveforms. Along with the usual suspects, Sine, Saw, Ramp, Triangle, Pulse I have put in noise and it will be brownian noise and the frequency control will also effect it. I have done a reasonable amount of work on it and at the momement is seems to work after a fashion. I seem to have a bit of a problem with the dc offset in the noise sources causing the integrated signal to run to a rail reasonably quickly. I am looking at ways of overcoming this at the moment. The rest of it seems quite good. This is the spectra of the white noise source that drives the brownian integrator. It is based upon some code from the internet. My other noise source is based upon a shift register approach but the spectra is even less flat than this one... I think that I will have to incorporate some sort of AC coupling of the signal in a digital sort of way... basically a high pass filter.

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...

Paper Hellfire

This is a bit old but it shows the transformer...

Timber!

A very long time between drinx! Not really sure where the last year has gone but hopefully things will start to crank back into action over then next few months... This is a start... The local council verge collection yielded a new keyboard for Forbin from a Kawai MR270 electronic piano. It is rather nice as being wood, nicely balanced and weighted. The electronics is shot but an AVR doing the scanning and a MIDI feed and we are back in business with 88 keys of goodness!