[sdiy] Buchla 257 is an extremely strange circuit

[mark verbos]

The PWM solution is very linear and repeatable. It's no so bad, I use  
a SPDT switch instead of 2 SPST switches. That doesn't help too much,  
but it's something.

Mark





On Dec 16, 2009, at 3:09 AM, Aaron Lanterman wrote:

> On Dec 16, 2009, at 2:50 AM, Derek Holzer wrote:
>
>> my apologies of this thread is dead and buried, but I'm interested  
>> in analog computer functions and ways of "interpolating" or cross- 
>> fading between them, or between the input signal and the processed  
>> signal. This PWM AM sounds rather complicated to implement, would  
>> there be a simpler VCA-based solution? Something like the Serge  
>> sound processing module with it's voltage controlled cross fader?  
>> or am I missing something important in the concept of a CV  
>> crossfader/interpolator?
>
> Yeah, the PWM AM approach is really complicated... Buchla puts a  
> boatload of filtering on the output. ("Switched capacitor" filters  
> work along the same lines.)
>
> I imagine a VCA type solution would be easier in many respects.
>
> My gut is that the PWM AM would be rather precise in the sense of DC  
> offsets compared to VCAs... maybe.
>
> - Aaron
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