[sdiy] CEM3340 question

[Mike Beauchamp]

On 12/3/20 4:29 AM, Joel B wrote:
> The Behringer Neutron uses two 3340s but it has a feature that I’m not seeing in the CEM3340 data sheet - voltage controlled wave shape - you can sweep between four different shapes. It’s a little glitchy unless you modulate at a fairly low frequency. Yet when I look at what is available otherwise, especially in Eurorack format using this chip, nothing has that feature.
> 
> How did Behringer implement that?
> 
> Joel

It's weird that it's glitchy when you modulate it fast - are you able to 
make it glitch just by turning the knob really fast, or is this only 
when you patch an LFO or something to the wave shape control?

As others have posted, the analog way to do this is an "interpolating 
scanner". Don Tillman has a pretty low-parts count version of this as an 
example, but if the Neutron is glitchy I can't help wonder if maybe 
they're just digitally controlling VCA's for each waveform.

Mike