" It would be kind of neat to have that Hammond sound emanating from a Theremin " - Dewster

LOL - We think alike! ;-)

The possibilities for additive synthesis are huge - and the theremin topology is ideally suited to it, because one is playing with high frequency signals having extremely small frequency variation - for example, with a 200kHz reference, the VFO only changes by about 5kHz.. about 2.5%.. Any PLL can lock to this.. All one needs to do to produce a 2nd harmonic is to multiply both reference and VFO by 2, and heterodyne the resultant frequencies (if ref = 200k, VFO = 201k, multiplying these gives 400k and 402k, difference = 2k)

One can continue this integer multiplication up as many times as one wants, and produce harmonics this way.. This was the basis for my last prototype (in fact, one doesnt need a PLL for each harmonic - for example one can get the 5th harmonic and 10th harmonic as square waves with equal M/S ratios by multiplying the reference and VFO frequencies by 20, then deviding these down by 2 and 4, and heterodyning these devided frequencies)

But I have found a far easier way of doing the above which does not use PLL multiplication, and which produces pure sine outputs. Its just a shame in a way that these schemes only work with a heterodyning system - in order to get it to work with other signals (voltage or MIDI control for example) one needs to effectively create a voltage/MIDI controlled theremin front-end. A lot of my effort has been devoted to doing this - The market for theremins is tiny - But I think that a VCO with additive synthesis would have a much bigger market in the Synth world - Increasing the volume of units I could sell is essential to bring the price down and make the product/s viable.

"The $19 Cyclone 2 board looks like the deal to me"

Thanks for that advice - I will certainly look at that more closely.. Do you have expierience with this part, and particularly - what is its development software / environment like? I need to factor in the learning curve and any costs for software etc.. If you have any first hand expierience with this I would be most interested in your opinion.. Otherwise I will just download anything I can find and read this.

Thanks for your help!

Fred.

Ouch! - I have just downloaded the free Altera web version of their Quartus II development software.. This is heavy stuff! - Makes the Mach4 and its ispLever software look like a piece of cake by comparison!