Cortex M4

New project! yep another one... Looking at building a Digital VCO, there are a couple of options here; Texas Instruments, Atmel & STMicroelectronics. I am also getting a different TI part that has the the Cortex M4F core which has floating point! Pros & Cons? Well the Atmel board has 1Mbyte of external RAM, which will be really good for my wavetable VCO. The ST chip can boot along at 168MHz. The TI one I am probably the most familiar with... There are other options out there as well, the Frescale parts (was Motorola) have a more accurate ADC but it is still really only about 14 bits really (the trouble with having sensitive analog parts on a digital substrate), the NXP parts are also quite neat in that they can come with multiple cores so one core can be monitoring the ADC values whilst the main core can be doing the calculations... What I hope to end up with is a couple of different VCO's. The wavetable one that gets the samples from an SD Card. A DX Voice one that uses FM and looks like a single voice of my DX7 but the frequency is 1V/octave. A harmonic oscillator that looks a bit like a cross between a Farlight Page 5 and a Buchla 148 Harmonic Oscillator, well at least Mark Verbos's take on it here. I would also like to do another Buchla favorite, the 259, with the whole gamut of dual modulation of phase, frequency, amplitude and timbre... All I need is a little more time...

CPLD says No...

Been making a Divider circuit, it is sort of an enhanced MOTM 120/CGS UNI01/Polyfusion Divider. It all went a bit wrong though when the stupid printer made the transfer about 8% smaller... I rather rashly tried to keep going, with some persuasion I had got all the DIL parts in but it was a bridge too far to get the VQ44 package to work reliably. The JTAG programmer did see it but that was about as far as it was going to go... While doing it all I thought of a much easier way than using a CPLD anyway... so i will just jury rig that onto the board to see... the new idea also dispenses with quite a lot of other cruft on the board as well...

Sockets + Knobs

Got a parcel from  Tayda and it arrived pretty quickly and the bits are certainly cheap. I now keep thinking of extra things I should have put on the order! Anyway hopefully this will make a few panels to sort of get things rattling along. Tried getting a few knobs and the chicken heads are pretty good -- a little smaller than the ones I have used in the past but quite nice. The Davis 1900 clones I am less enthusiastic about; I cannot get the grub screw to grip on the flat of a shaft OR the normal outside...

921B Mk II

Well having another hack at the Moog 921B. Here we have the Mk I looking on as the MkII gets drilled and it knows that all the expensive parts are about to be removed... The buggered up transistor array layout fix, like a beacon, knows that it's days are numbered... I am planning to make a complete Moog 15 in Euro and this is really the last bit that I need to make sure works properly as a true build before we embark upon that...

Long Time Comming...

On a bit of a whim I built this VCO. I think I have the full house of Thomas Henry VCO's now! This is the last of XR, VCO1, 21C (or LM), X-4046 & the 555. Thomas has always been amazingly adept at getting various VCO devices to perform for a synth environment. This is the 8038 VCO that is from his VCO Cookbook. I bought the chip about 4 years ago but the book has only recently became available again. This is the layout from Fonik's web site but I only built one channel. It roared into life immediately but I think it will need more tweeking as the sinewave is a bit skewed...

Climbing the Ladder

Put togther another variation on the Moog VCF ladder design. I had some spare LM394 matched transistors to use on ALL the pairs for this one... Haven't quite got around to firing this up yet but pretty close...

Entwicklung Bau VCF

Taken a bit of a break from the Bergfotron VCO and whipped up a few boards last week. I know... what about the panels... This is quite an intersting VCF uses a different sort of OTA, the LT1228 from Linear Technology. It was designed by Stephan Winter for (I think) his final year project. The entire synthesizer is written up here. I was only really intersted in the VCF as it is quite different. The layout was quite pleasing as only one link! The tempco design is also quite intersting as it uses a realtively easy to get part and a couple of tricks to get it to 3300ppm/C. I don't usually bother with temperature compensating VCF's but I may try in this case just to so how well it works. The LT1228 seems to have really quite good specifications -- I did a bit of a comparison with the LM13700 today and I notice that quite a few parameters are missing from the LM13700 datasheet compared with the LT1228 which suggests that they probably aren't to special... The LT1228 is fairly expensive though... but not as much as a CA3280!