Moog Prototypes:

There are some great photos of Moogs prototypes up on the Moog Website - I am linking to the theremin related ones below, but the site is really worth a visit IMO, as other synth prototypes are shown.

The pictures below are of the EW-Pro .. There is also a small picture of a 91 series board on the site, but it wont paste here for some reason.

Very interesting indeed! The pictures of the synthesizers prototypes are more impressive. I always wondered how they go from the prototype to the production models. I hope they kept good drawings up to date while experimenting.

I kinda want to build one!

Thanks Fred! 

The shallow depth of field is rather artistic, but for us engineers I wish they'd opted for more clarity in the photos.

Weird, but I don't see any variable inductors in the pitch circuitry.  Maybe they're too tiny, or in the blurrier part of the photo towards the back?

I wonder what those big transistor looking things are, particularly that one with the heatsink on it?  Is the heatsink to keep the thing from burning up, or perhaps an attempt at thermal drift stabilization?

"I wonder what those big transistor looking things are, particularly that one with the heatsink on it?  Is the heatsink to keep the thing from burning up, or perhaps an attempt at thermal drift stabilization?" - Dewster

I dont know! ;-) .. I have only had extremely brief encounters with the E-Pro, and a load of high resolution photos sent to me by a TW member, to whom I am extremely grateful!

I have a load of photos of both the Pro and E-Vox  on my Element-14 site.. Here is a picture of a real pitch section of the EWP board - Big power transistors!

and the Evox, big transistor with heatsink:

[Picture wont paste here.. http://www.element14.com/community/docs/DOC-25323/l/ethervox--8-circuit-boardjpg

"I kinda want to build one!" Chobbs

Charlie, its actually EASY! .. I have a PSoC which does the job of the whole logic-level section (mixer, register switching) and adds a ramp waveform output (the EW only produces XOR generated triangle waveform AFAIK).. All you need is variable and reference oscillator signals at 5V logic level, and a few extra logic components and comparator if you waveforms other than just triangle (as in, ramp and pulse with variable % width)..

The PSoC is one of the many diversions I got into, almost complete (as in, I prove the concept by prototyping, but in the process I get "new" ideas so go off chasing these - the designs get better and better - but nothing ever gets completed! :-().. I also got diverted looking at implementing it all in the new PSoCs - these would allow everything beyond the oscillators to be done on-chip - all the analogue audio processing, the volume circuitry and VCA, and the pitch to voltage converter - and the PSoC 4 is much lower cost than the less powerful PSoC I have used which are quite limited (the PSoC 4 can implement a true 4Q analogue multiplier, and has exceptionally low noise analogue blocks - I could implement sine generation and mixing with it, and was hoping to synthesise the Lev mixer in it.... But I found a better way - ;-)

However, my circumstances are forcing me to dig up this stuff with a view to making some money - I have been thinking about selling programmed / configured PSoC's and modules - about £35 for a 28 pin DIL IC which I think does everything and more that the E-Pro logic does - you just add a front-end and a audio section (waveshaping and VCA - I suspect from what Thierry has said, that a EW audio circuit - the LM13700 onwards - will give a close aproximation to a E-Pro's sound.... I dont really like the E-Pro sound, so never really looked at this much - I much prefer to take the ramp, pulse and triangle waves my PSoC generates and feed these to my sound processor ..

If there is real interest, I could probably have the ICs available in a few weeks.

Please though, everyone - Realise that this only takes care of the register switching and audio generation (mixer) - Using this IC will NOT make an E-Pro! it will simplify making one - But the critical front end on the E-Pro with its exceptional linearity YOU need to develop.... Its a BIT easier to get linearity with a register switching theremin because one can cover the range requirements in several steps - but the linearity will still be dependant on the front-end.

Fred.

"I kinda want to build one!" Chobbs

I do not intend to go into any more detail regarding 'cloning' an E-Pro here - but apart from the PSoC I mentioned in my last post, one can, I believe, get the same results from a reasonably simple circuit.. My PSoC integrates most of what is in the following articles into a single IC - but these articles give the required data..

One does not even need the PLL's - They just make the quality of the output audio much better (one uses a front-end with good linearity but limited span - something like a RCA clone front end - and cranks this frequency up using PLLs .. Then devide this down to select the register ... You end up with higher frequencies in the mixed waveform, and this equates to better resolution and its easier to filter the HF) - But I believe the E-Pro simply takes the reference and variable oscillators into the register deviders.

(my) Register switching mechanism - I do not know how close or otherwise this is to how the E-Pro does it.

(my) Enhanced source waveshaping

Fred.