[sdiy] PAIA for Appreciation of Heathkits?

[Dave Manley]

Andre Majorel wrote:
> On 2006-09-12 08:39 -0700, Dave Manley wrote:
>> Andre Majorel wrote:
>>> On 2006-09-11 22:27 -0700, Dave Manley wrote:
>>>
>>>> [...] the [PAiA] 2720 series modules: [...] the specs for the
>>>> low pass filter are given: "Cut-Off Freq: 50 Hz,  Roll Off Rate:
>>>> 0 to 12 db/octave".
>>> How do you do VC slope ? Cross-fade between wet and dry ?
>>>
>> Here's the circuit in all its glory:
>>
>> http://www.freeinfosociety.com/electronics/schemview.php?id=390
> 
> Thanks. I don't see any crossfade. Looks like... a pi RC filter
> referenced to the CV ??
> 
The 'crossfade' is based on the diode resistance which decreases
as the control voltage increases.  At 0 CV the capacitors are 
essentially out of the circuit.

I ran spice on the circuit, you can see the results here:

http://www.sonic.net/~dlmanley/paia_2720_lp_ac.jpg

The AC response is plotted stepping the control voltage from 0->5V in 1 
volt increments.  It's not a very exciting filter for a synth, eh?


-Dave