[sdiy] smoothing out PWM CV

[Derek Holzer]

Dear list,

I've been using an Arduino to generate 0 to +5V control voltage for my 
modular, and I'm wondering what is the best way to filter out the PWM 
noise and get a stable DC voltage. The default PWM frequency is 30 or 32 
KHz (reports differ...).

I've been using Harry Bissel's dual lag generator circuit to smooth it 
out so far, but I'd like to find something with passive components ideally.

I tried this out:

http://narbotic.net/?p=171

which is essentially a low pass filter with 470uF from PWMout to ground 
(I substituted 2 x 220uF in parallel) and 100R from PWMout to CVout, but 
I still heard some "aliasing" frequencies when I tested it with a sine 
wave oscillator. Any suggestions?

best!
Derek

-- 
derek holzer ::: http://www.umatic.nl ::: http://blog.myspace.com/macumbista
---Oblique Strategy # 60:
"Don't be afraid of things because they're easy to do"