Penfold modules up and running!

[Josh Brandt]

In a mad frenzy of drilling and soldering, I finished my dual VCO
and dual VCF boards from the Penfold book. (I had 4x6 copper-clad boards,
which were wide enough to put two complete circuits on each board.)

The finished modules were mounted in a PAiA fracrack cage. The dual VCO took
up two spaces, and the dual VCF took up three. (I really need to get smaller
jacks... That's what most of the width is.) Since I'm using switching jacks,
I also half-normalled them together, so I can control both VCO's or both
VCF's from one CV input and run an audio signal through both filters in
series if I like.

Here's the quick review, in the format I had suggested before. Predictably
enough, I will be archiving this post and any others people post with
similar reviews on my web page for future reference. (For ratings: 1==good
and 5==bad.)

VCO:

Cost: 1. Super-cheap. There isn't more than $20.00 worth of parts here,
including panel controls, PCB, wire, and IC sockets. 

Performance: 4. It isn't awfully stable, and doesn't track very well.
Sometimes it gets lost and will play a semitone or so off from the note you
_wanted_ to play. Turning portmento on seemed to help this. (This could also
be a weakness in the keyboard I'm using...)

Sound: 2. Hm, not bad. It has square and triangle outputs. I set it up so I can
crossfade between them, which works nicely. It's not a wildly flexible
sound, but with two of them together and slightly detuned, it does sound
pretty nice. 8)

Complexity: 2. Slightly more complicated than a single op-amp LFO (which is
my basis for complexity of 1, here), but not much. It took an hour or three
to build up, including drilling the board. 

Tutorial Value: 1. Not _quite_ a treatise on electronics, but the book seems
pretty useful to me, and there are lots of notes on what is going on with
the circuit. It's not _too_ complicated, and shouldn't be too daunting for a
novice to sit down and lay out pretty quickly. I used the PCB layouts and
etched my own boards, because I wanted to see if I could. I certainly
learned a lot from doing that. (i.e. how easy it is. 8) 

Overall impression: I'm glad I made it. It works pretty well, and tracks the
202's sequencer pretty well. Not a bad little synth, and it's easy enough to
wire up and go with it.

VCF (12db/Oct):

Cost: 1. Also super-cheap. Slightly more expensive than the VCO, but not by
much. 

Performance: 4. Tracks okay. Doesn't really oscillate, and it sounds like it
overdrives and starts clipping and sounding all nasty very easily if you
aren't careful. Subsituting out better op-amps might help this, but I
haven't tried yet. 

Sound: 4. I'm not _horribly_ impressed by this. The resonance gets
really odd-sounding at high values-- don't expect a nice hollow-sounding
Roland-type filter from this one. Two of them in series isn't bad. 

Complexity: 2. Slightly more complicated than the VCO, but not much.
There's almost nothing to this one, either. 

Tutorial value: 2. Not as much information, but it isn't bad. It's still a
good novice-level project (or something for someone who wants to build
something quickly.)

Overall impression: I'm glad I made this-- it's interesting to play with,
anyway, and it certainly doesn't sound like anything else out there... 
For future modules, I may set up the front panel differently.



Tonight: The Voltage-Controller Panner. 

Josh
hoping he'll start a trend of people posting these sorts of things...