[sdiy] SVF problems

[Magnus Danielson]

From: "Stephen Begin" <trypannon at hotmail.com>
Subject: [sdiy] SVF problems
Date: Fri, 2 May 2003 13:21:25 -0400

> 
> I'm trying to put together this little circuit from Magnus's page
> 
> http://home.swipnet.se/cfmd/synths/schematics/svf1.pdf
> 
> and I've tried twice on breadboard, and both times i end up with a signal
> that is so distorted it's hard to tell if the filters are even working, and
> for about 9/10th of the range of the pots, i get no signal at all.
> 
> I'm really not very experienced here so i'm wondering if maybe there is
> something that is assumed in this schematic that i don't know
> of...basically, I got the pinouts for the two chips, and made the
> appropriate connections (or tried).

OK, you should be aware that almost anything on that page is more or less
_untested_ as it is. It's there to show the principles and you may have to
tweak thing to make it work as you want. See it as samples from the scratchpad.

So, the errors in any particular schematic may range from approx 0 to just
immensly wrong (as the VC-ADSR which is just a cute idea to ponder over).

> Are there supposed to be power supply bypass caps or anything like that?

You should almost always have that.

> Also, forgive me for even asking, but does the p1a and p1b mean it's a dual
> pot?

Yes, that's exactly the intent.

I have had something similar operating on a breadboard but it got pulled into
pieces many many years ago. It's really the ASM-1 VCF schematic reduced to the
non-CV case. Any misstakes in the transformation is due to human error (HI!
That's me! ;O) and component values is so roughfly between thumb and index
finger that I'm not sure they are not on the same hand, or even if any of my
hands is involved. So, (and I've longed to say this) your milage may vary (so,
done that ;O).

Cheers,
Magnus