[sdiy] Updated Schematics of Rene/Wasp Hybrid

[Aaron Lanterman]

Dear Kai Chi and Sean - this is very interesting. I'll forward to the SDIY 
list.

List folks: You can see the new schematic at

http://users.ece.gatech.edu/~lanterma/ece4803/drafts/renems20_wasp_crossbreed.bmp

or in general just http://users.ece.gatech.edu/~lanterma/ece4803/draft

Another note: I wouldn't call it an EDP Wasp modification - it's really a 
Rene MS-20, modified to use an idea from the EDP Wasp. It's closer to 
Rene's MS-20 than it is to the original EDP Wasp. Make sure you follow the 
list for feedback.

So now you get interesting effects as you change the resonance knob? If 
so, I'd say you're close to ready to commit this to 
perfboard/stripboard/veroboard/whatever.

In your final design, there's no need to bother with the bypass switch - 
we're targeting this as a synth effect module, not a guitar effects pedal 
(guitar pedals need a bypass function).

Dear listies: is the CD4069 in the feedback loop biased right? Does it 
need some kind of DC blocking cap after the TL074 or anything? Also, can 
anyone explain the "frequency clamping" behavior they're observing?

One final thing I've wondered... the 47 uF electrolytic at the output... 
how can we "know" that the voltage on one side will always be higher than 
the voltage on the other? How can we throw that in and make sure nothing 
will ever blow up?

I wonder the same thing about the Buchla 259 timbre generator:

(how weird, type "Buchla 259" into google, and my Homework #3 comes up as 
the second link...)

There's a 10 mufarad cap that looks polarized due to the "+." One side of 
the cap is at virtual ground. The other - well, how it looks like the 
voltage on the other side swings both ways - how come this doesn't blow 
up?

(I admit I'm just a DSP guy who is hacking circuits...)

- Aaron

On Fri, 28 Apr 2006 gtg067b at mail.gatech.edu wrote:

> Aaron,
>
> Here is the updated version of the schematic. We have made some adjustments to
> the following material and observed the following:
>
> * The original Cv1 & Cv2 pots were grounded at one end. Now those ends are
> connected to the -15V supply (see R16 & R18).
>
> * Originally the negative end of the electrolytic cap was connected directly to
> the output and feedback to the LED network. Since leaving it like this reduced
> the signal, we decided to route the negative end of the electro to a TL074 opamp
> in a noninverting configuration in an adjustable gain fashion with a pot as the
> gain adjuster. The output is then placed in the output of the whole circuit &
> the LED feedback network (See top right corner of schematic; Circuit components
> A2, C3, R12, & R13).
>
> * Even though the circuit made cool noises (after adding in the new opamp A2),
> when we put in a sawtooth wave 10V p-p 200 Hz - 2 kHz signal through the new
> amplifier, the output seems to get a 3V p-p at the maximum gain. While varying
> the frequency of the sawtooth, the output signal seems to clamp itself at
> approximately 16 kHz, regardless of how the frequency is changed at the input.
>
> * Both LEDs lit brightly while we were experimenting.
>
> --Kai Chi Wong