Tube synth diy

On 5/18/08, sasami@... put forth:
>Interesting. Do you mind if I add this message to the VCA page as
>constructors notes?

Well, it's still a work in progress.  If you like, I can write up
something for your website after I'm finished.

I'm still trying to figure out the correct bias settings, and I am
open to suggestions.

As far as my speculation about the need for a cathode bypass cap, if
someone has one without a bypass cap they could test it by sending a
signal in the low audio range, turning up the gain pot, and checking
the cathode for an AC voltage.  If someone with a scope finds a
signal on the cathode out of phase with the input signal, then that
would demonstrate negative feedback.

Imho, determining the minimum cathode bypass cap would require
testing it as a VCA.  It seems likely that rapid changes in voltage
on the control grid (eg. an envelope with a steep attack) would cause
a sudden demand for plate current enough to deplete the cathode,
which then bounces back causing an unwanted noise.