[sdiy] Updated Schematics of Rene/Wasp Hybrid

[harry bissell]

Aaron Lanterman wrote:
>
> 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? 
IMHO... no  I think you need some input resistor if you are going to use 
feedback like the 10K
/ diodes.  Also the TL074 non-inverting input, after the 47uF... needs a 
resistor to somewhere
(probably ground or a 1/2 V+ bias point. It cannot get input bias 
current. If this is working at all..
that 47uF MUST be leaky.

> 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?
You can 'throw' it in and it will not explode because it will never get 
enough current to
do so... you are correct. you may not guarantee the polarity as shown.  
I'd use a NP
electrolytic in this type of case. And into the non-inverting input of 
the TL074 (wrong, as above)
the input impedance will be VERY high at that point. Suppose you use a 
1M bias resistor to satisfy
the input bias current requirements... that is an RC of 47uF and 1M ... 
a very low frequency indeed.

Probably a much smaller cap would suffice... and be easier to get in a 
NP lytic or even film ???
>
> 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?
where is it ??? or is the value different ???

I don't know what they mean by 'frequency clamping' ... does that mean 
that the filter
does not tune and stays at 16KHz cutoff...

I don't see the 'sallen key' archetecture clearly here...R5 and R10 make 
these stages look more
like single pole OTA stages... with unusual feedback.

If I have some time I'll try and simulate this circuit.  Are your 
students using any simulation
programs ???  If so they can make an OTA model from discrete transistors 
by copying the
3080 schematic... but use DIODE connected transistors (b-e junction) 
that match the other transistors.
do NOT use the 'diode' model

A pair of N-mos and P-mos transistors will make a 4069 model (do not use 
a digital
model !)... add maybe 100 ohms in series with the input to simualte the 
input protection
circuit, and 15pF to the negative supply to simulate 4000 series gate 
capacitance.

See if the model matches what you are seeing.

H^) harry   (over)

>
> (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
>
>