[sdiy] HELP! How can this possibly work? Buchla Music Easel env generator?

[mark verbos]

On Jan 12, 2011, at 2:05 PM, Dave Leith wrote:

> The circuit diagram is on Magnus's site here
> http://rubidium.dyndns.org/~magnus/synths/companies/buchla/Buchla_2080_3_200.jpg
> 
> The question is about the pulse input <6>. If the puse comes thru
> a120K resistor to point <6> then the circuit is supposed to sustain as
> long as the pulse is high. Once the pulse goes to 0 volts then the
> decay begins.
> 
> In the other mode (transient) the pulse goes thru a 390K resistor to
> point <6> then the envelope generator is supposed to be in transient
> mode where the envelope is triggered and should go thru it's cycle
> independent of the pulse going low.
> 
> IC4 where the pulse is conditioned appears to be a comparator that has
> 2 states hi or low. This is the part that is the mystery to me. How
> are the two envelope generator states created from this.
> 
> Envelope generator operation is also explained here.
> (http://rubidium.dyndns.org/~magnus/synths/companies/buchla/PaMtEO_16.gif)
> 
> Front panel wiring to the envelope generator is here.
> (http://rubidium.dyndns.org/~magnus/synths/companies/buchla/Buchla_2080_13B_200.jpg)
> 
> Thanks for any help that can be offered
> 
> Dave

Dave,

Buchla pulses are made up of a short, tall spike followed by a sustained, lower gate. In the early days, they were 15 volts and 7.5 volts, later they were switched to 10 volts and 5 volts. If you are cloning this circuit and expect to get the two modes from a normal gate, you will have to send the gate through a cap to get transient mode.

Mark