[sdiy] Genital Electric P/V converter LIVES

[Cynthia Webster]

on 9/13/05 8:37 PM, harrybissell at harrybissell at prodigy.net wrote:

> Sometime in the late 70's when young Harry Bissell was realizing he
> would never be a serious keyboard player... he dreamt of controlling his
> modular from his guitar. Now if only he could afford a Gentle Electric GE-101
> Pitch to Voltage converter, he could DO that. At that time they were
> distributed by Sergeas a 'kit' (board set)... in fact the very set that I got.
 
> They were obviously intended for the Aries system originally, as they have
> the same outline and 22 pin edge connector.
> 
> It was about $800 at that time... cost more than my entire modular AND
> guitar. Glad I didn't get one then, it would not have worked well enough.
> It does not have any filtering, so octave hopping and pitch-to-glitch
> conversion is very real possibility.
> 
> It does have all the right stuff. What I came up with on my own has
> quite a lot of the same features. They use a compressor, ride the largest
> peaks on positive and negative half cycles, square that up with the equivalent
> of an RS flip-flop. They reset and sample hold a ramp (same as Roland,
> 360 systems, Etherwave/Moog P/V, and my own system)... check for valid range
> sampling) and look for subsequent samples to be within a certain range of the
> previous sample, or again inhibit the S/H.  It also features linear and log
> amplitude envelopes, gate, trigger, retrigger... all the standard features.
> 
> How it works on other instruments I have no idea ???
> 
> That about sums it up.  I always wanted that P/V converter. Now I have
> it and can understand it as well. Like a kid who wanted a mini-bike, and
> thirty years later realized
> his dream by buying a Mercedes.  Who needs a mini-bike anyway.   :^P
> 
> The original designer, Carl Fravel is still around. I gave him Cynthia's
> web address incase he wanted to release a 'Tribute' version.  He did offer
> to reveal the contents of the potted module in exchange for a non-
> disclosure agreement.  I declined because I had already RE'd the circuit...
>  and am doing P/V work of my own. Don'twant to tie my own hands.
> I'll give him some time to maybe come-out-of-the-closet and make some
> modules or kits for the diy crowd. Failing that I might do so myself.  I
> think he needs to either make some boards, or loose the design to the world.
> Just mho.  Maybe you guys should contact him and tell him to come out and
> play.  Analog synthesis LIVES.

(Right on!)  Hi Harry!

Thanks, but I actually have already contacted Mr. Fravel and found that he's
now a high power type executive in the satellite industry and has absolutely
no time for such projects.  He was nice enough, however after expressing my
desire to do a tribute recreation of his famous module, he suggested that I
contact his secretary to schedule a half-hour appointment to chat on a
future Saturday several ~weeks~ in advance.  (I refrained from suggesting
what he could go and do, but as I remember it involved a lake and a bucket).

I did get one question in, and that was if the parts in the original design
were unavailable or obsolete.  He said they were, so right then, I decided
to go a separate way, (that's when I contacted you Harry!)

Two-years ago, you and Tom, and Bob Moog were kind enough to grant me
permission to do a recreation of the EFM Board design, or to purchase
those boards directly from EFM.  Unfortunately there has been little
interest from customers about such a module, so it is on hold indefinitely.

The longer we wait however, the better DSP and exotic semiconductors
get, so ultimately, it may be the best plan after all?  LOL!

Congratulations on decoding the little beastie, and resurrecting it!

Best Wishes!


Cynthia 

http://www.cyndustries.com/





> 
> H^) harry
> 
> Tim Ressel wrote:
> 
>> Way to go Harry!  Woo Hoo!  You da man!
>> 
>> Just one thing: What the hell is a GE-101 PV
>> converter?
>> 
>> --TimR
>> 
>> --- Harry Bissell Jr <harrybissell at prodigy.net> wrote:
>> 
>>> My Gentle Electric GE-101 PV converter has come
>>> back from the grave. I bought it "as is but in good
>>> shape" from someone on AH. It was blown to kingdom
>>> come, probably from reverse voltage on the power
>>> supplies. I paid way too much for it in the
>>> condition
>>> received (but hey, it was 'as-is' right ???)
>>> 
>>> My first clues to an amateur repair attempt was that
>>> ALL THE ELECTROLYTIC caps were replaced, cheap
>>> sockets
>>> were inserted for all the opamps (also replaced).
>>> 
>>> another clue. One IC had the non inverting input
>>> drilled OFF CENTER to accomodate a guard ring
>>> (common
>>> S/H technique).  The person (dis)effecting the
>>> repair
>>> put in an IC socket with that pin 'folded under' so
>>> no
>>> connection was made. Were they going to hook it up
>>> later, or did they just bone it ???  I think (from
>>> the
>>> mass capacitor destruction) the latter...
>>> 
>>> Sad is that the potted modules (2) were blown out...
>>> the fundamental extractor AND the expo module. Even
>>> the 2K Q81 tempco was toast. All the cmos chips were
>>> trashed, as well as a large number of transistors
>>> and
>>> diodes.
>>> 
>>> Glad is that I was able to reverse engineer the
>>> modules
>>> with hammer, chisel, and propane torch.  I just
>>> found
>>> the last problem, which was a defective opamp that
>>> still worked, but maybe had an extrememly LOW input
>>> impedance due to internal damage.  Replaced it with,
>>> yup... a 741 and it started working. OK so 741's
>>> suck... but I'm fresh out of LM301s
>>> 
>>> It was a lot of pain to fix this, but I wanted it
>>> for
>>> educational purposes. If it HAD worked, would I have
>>> smashed the potted modules open ???  Probably not.
>>> How well does it work ?  I'm not sure yet, but it
>>> does
>>> the P/V thing as advertised.
>>> 
>>> Maybe when its in a box, I should send it to another
>>> Gentle Electric owner for an A/B test ???   :^P
>>> 
>>> Anyway... I just wanted everyone to know there is
>>> life-after-talking-about-your-manhood on s-diy
>>> 
>>> H^) harry
>>> 
>> 
>> 
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