[sdiy] Buchla Lowpass Gate Switch

[Peter Grenader]

I might add that I didn't use single vac's on the rev Bs I've made, but
opted for the same single 3/2 dual element used in the rev c.  I did this
for cost reason's only.  As far as the performance, the sonic characteristic
of the two, the only differences I can hear is slightly less gain in
amplitude operation and a bit more resonance in lowpass mode, which I assume
comes from the  properties of the FET.

In any event, the rev B's FET allowed for the additional bleed-killing
inverted feedback I added, I haven't been able to do this with the rev c.

- P



Peter Grenader wrote:

> Mark-
> 
> I used a straight double on-off-on on my rev B's and I've got combo in the
> center. I'll be happy to post an mp3 to illustrate this!
> 
> Have a look as the schematic- the top half of the switch puts 15K across the
> output of the second vactrol element, killing the filter.  The Rev C does
> the same thing, but does so with only 10k. The bottom half of the rev B
> switch increases the cap value, (.0047), just as C does. The additional
> third switch element in the rev C adds 15k to the input signal's amplifier,
> increasing it's gain.  Granted, the rev B doesn't do this, but this addition
> does not effect the mode switching, it just ups to output of amplify-only
> operation. This is why I didn't see that an on-on-on was required and as it
> turns out, it seems to work fine without one.
> 
> - P
> 
> 
> 
>> it actually doesn't save anything because the switch the rev B used is a
>> On-On-On switch, which is even more rare and pricey than the 3PDT one!
>> The reason i modded the rev C was because of price. I wanted a cheap and
>> simple solution. Also the wiring is easier than using multiple pole
>> switches. Fewer wires, smaller switches that can be closer together,
>> easier to get, cost less. Seems like an obvious choice to me, but I
>> guess not for everyone...
>> 
>> mark
>