[sdiy] non-mechanical switching solutions

[Richie Burnett]

> Build four filters, one with each capacitance range, and pick whichever 
> output you want to use.  If you use surface-mount parts the whole thing 
> will still be smaller than the original.

Maybe you only need to build four of the actual transistor ladder part... 
If you can find a way to turn off the common-mode current that flows down 
the ladder (and sets the filter's cutoff frequency) then the transistors in 
this ladder are essentially open-circuit anyway.  So maybe there is some way 
to capitalise on this feature of the transistor/diode ladder filter, by 
paralleling up multiple filter "cores", but only activating one of these 
ladders at a time, whilst keeping the other ladders "switched off" by 
programming their operating currents to zero?  Just a thought.

-Richie,


-----Original Message----- 
From: Mattias Rickardsson
Sent: Tuesday, June 28, 2016 10:49 PM
To: Gordon JC Pearce
Cc: synthdiy diy
Subject: Re: [sdiy] non-mechanical switching solutions



I've had similar construction dilemmas and sadly/intriguingly this might be 
the best solution so far:


Den 27 juni 2016 4:49 em skrev "Gordonjcp" <gordonjcp at gjcp.net>:
>
> Your nine pole rotary switch is by far the most expensive component. 
> Opamps are cheap, discrete trannies are cheap, passives are hell of a 
> cheap.
>
> Build four filters, one with each capacitance range, and pick whichever 
> output you want to use.  If you use surface-mount parts the whole thing 
> will still be smaller than the original.


:-)

/mr






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