[sdiy] Vactrols & Lopass Gates

[mark verbos]

The Buchla 292B uses a C&K 7211 On-ON-ON switch. I am sorry, but it's a 
fact. I have built them all as well. This is the switch that looks like 
a regular DPDT but in the middle position on throw of each pole is on. 
If you don't use one the Lopass gate will work, it just will not 
compensate for the level difference between modes. In the 292c Don moved 
the switched resistor to the feedback loop on the input OP-Amp so that 
closing the switch made the signal louder rather than quieter. This made 
the input op-amp's gain follow the same logic as the resistor that is 
switched in after the vactrol, making it simpler to remote control.

The reasons to build them using 4016 switches are:
1. They are cheap. Mouser lists a C&K 7211 for $7.61 and a 7303 3PDT 
swicth for $11.34

this system uses a 7103 that's $4.90 and a few other cheap parts.

2. It's easy to wire. You wire a 7.5 volt signal to all the switches on 
you panel. then 2 wires per switch for the signals.

3. It's quieter. Why should the signal go through all that wire to get 
to and from the panel, picking up RFI and noise in the process?

Mark



Peter Grenader wrote:

> 
> The 292B  doesn't use this ON ON ON  switch!  it uses a regular on off on -
> trust me on this...I've made many.  Look the schematic over, you'll see what
> he's doing here - it's just kind of hard to pull it out (Buchla schemo
> syndrome).
> 
> - P 
> 
> mark verbos wrote:
> 
> 
>>you need VTL5C3/2 thats' the dual element one Buchla used.
>>
>>as far as schematic versions go....
>>
>>292 B uses an ON-ON-ON switch that is very expensive
>>292 C uses LF13331 switch chips that are rare and expensive
>>My mod at www.simple-answer.com/DIY uses 4016 analog switches and has a
>>tested board layout available.
>>
>>no pressure. ;)
>>
>>Mark
>>
>>PS. Even Don used 4016's in the music Easel.
>>
>>
>>
>>Michael Ruberto wrote:
>>
>>>Alright I submit, I will include some lopass gates in my new synth. 1st
>>>I have some questions. There are a handful of different schematics
>>>floating around on the web, which is the best to use as my example?
>>>I have the original schematic drawn by buchla but it gives me a headache
>>>to look at. I see from the datasheets that the Vactrols all have
>>>different rise/fall times ranging from 2.5 to 4+ mSec. Does anybody know
>>>which were used on the original? Does it matter?
>>>
>>>I plan to use an analog switch and have some samples of the ADG333.
>>>http://www.analog.com/en/prod/0%2C2877%2CADG333A%2C00.html
>>>Will these work alright?
>>>
>>>Finally, any comments, advice, recommendations, on parts and
>>>construction much appreciated.
>>>
>>>Thanks
>>>M. A. Ruberto
>>>
>>>PS: Anybody have the PCB footprint for the Vactrols?
>>>
>>>
>>>
> 
> 
>