Stay on Target....

Well more work on the Bergfotron VCO but during lunch while day dreaming did experiment with a phase modulation option for a sawtooth oscillator... seems quite simple so not really sure why people haven't provided this before... probably sounds a sub-optimal?

Bergo Waves

Well the waveshapers are starting to work! Sawtooth, Sine, Square & Triangle all look good. The Double Frequency Sawtooth is a bit munted but I may have a wrong component in there... Have to check tomorrow. Was a bit surprised that all the waveforms are +ve rather than around ground when i realized that the voltage controlled wave selection won't work with a -ve signal... Got to drill a couple of missed holes with the dremel and with some luck should be able to try out the wood wind shaper tomorrow!

The Bergo Awakens!

I have been building the Bergfotron Advanced VCO for a very long time. I am pretty sure that I started this at least four years ago and it has lain dormant and unloved in the large box of Forbin possible modules. Recently I decided that it was a badge of honor to actually get this beast to life. Any self respecting Synth DIYer would rise to the challenge that Jörgen had thrown down. Well here we are -- we have the VCO core actually doing something. There has been a fair carnage in the component count that have visited this board and a lot of head scratching. There are a few wires that seem to be missing from the overlay drawing (the -1V to the CMOS switch) and a track missing (the -ve supply stops after the ferrite bead) but for sheer mid boggling options stuffed onto one board this is pretty much the pinnacle of design and you would have to take your hat of to Jörgen to have achieved that on a single sided board! Anyway I will keep trundling along as I want to get the wood-wind waveshapers to go! I have no idea how I am going to get all this onto a Forbin front panel but wait and see... hopefully not too long!

Drilling ahead...

While eating my sandwiches at lunch time I drew up a PCB for a popular VCF. The only real difference is that it DOSEN'T use CA3280's as I am not paying 20 Euro + some exorbitant shipping for them... I have substituted some LM13700's instead as they are cheaper and less likely to be counterfeit...

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...