[sdiy] Newbie alert :-)

[john mahoney]

Note: a long post follows but it does contain a short answer.


> What happens if I just use the default, e. g. have you received this
> message twice? I'm pretty sure that it is a listserver setting. Was
the
> decision to make replies to-the-list conscious or accidental?

Yes, I got it twice. I used "Reply to All" and you can see the
addressing on this message. You will also receive this twice.

The reply-to topic has been discussed in the past. I think the short
answer is: "We have to live with it."


> >Ray Wilson's "Schematic Publisher" ...
> >
> Just looking at the screenshots, this seems pretty cool. Now if only
it
> were open-source. ...

You'd have to talk to Ray about that. He's great at answering e-mail
questions.


> >Ray's website has a lot of synth circuit designs...
>
> Yes, looks nice, but I'm wondering whether (watch out, more
stirring!)
> people are really reading what I'm writing. I want something simple
to
> get started! All these fascinating links I will save and look into
at a
> stage when I'm a little more advanced. But for now I just want THE
> SIMPLEST THING THAT COULD POSSIBLY WORK (tm).

I'm wondering if you are reading what people are writing in return.
<G> As far as I can tell, your question has been answered. It depends
on how you define "work." People on SDIY are building synthesizers for
musical use, so there are certain assumptions made.

Circuits that we care about are usually voltage controlled. Power
supplies are typically +/-12 or +/-15 volts, with some exceptions
(Ray's Sound Lab is +/-9V). Signals (audio and CV) are usually +/-5 or
10 volts. VCOs tend to have exponential response (1V per octave),
though you'll find linear VCOs, too. Temperature-controlled VCOs are
common, since they are more useful for making music, but you'll see
that the "tempco" stuff is optional.

Therefore, the SDIY group isn't very interested in a 555-based
oscillator with frequency controlled only by a pot, except perhaps as
a simple LFO. Besides, you can find such circuits in the "standard"
books like the CMOS Cookbook, IC Timer Cookbook, and IC Op Amp
Cookbook, as well as the simple Forrest Mimms books that Radio Shack
used to sell (in the US, anyway).

So, when you ask for a VCO, people can't help but direct you to one
that isn't a "dead end" design.

HERE IS THE SHORT ANSWER TO YOUR VCO QUESTION:
Look again at the link to Rene Schmitz that was provided by Scott
Gravenhorst:
http://www.uni-bonn.de/~uzs159/vco4069.html
It uses the cheap CD4069UB (must be the unbuffered UB version, as I
recall). You can omit the "expo current sink" stuff on the left and
you can omit the pulse/pw/pwm stuff at the bottom. This leaves you
with a sawtooth VCO that has linear CV response. By my quick count, it
uses half of a CD4069, 2 diodes, 2 caps, and 4 resistors. It doesn't
get much simpler than that! :-)

After building the linear sawtooth osc, you can add the pulse
converter part. Later, you can build the expo converter. Good enough?
Simple enough? I hope so.


Oh, you also asked about a keyboard. From what I've seen, building a
resistor ladder (matrix? whatever...) keyboard -- that is, an "old
style" CV keyboard -- is a lot of work. Once again, Ray Wilson has
done this and you can find the plans on his website. Personally, I'd
just as soon find a cheap synth with an analog output *or* use a cheap
MIDI keyboard with a MIDI-to-CV converter (the one from Paia.com is
probably the cheapest and it's not too bad).


One more thing: We tend not to reinvent the wheel, so a few websites
will be mentioned time after time on this list. That's because some
folks have done a tremendous job of finding and creating various
circuits. Oddly enough, we repeatedly use those which are the most
sensible. ;-) You don't want to bother with a circuit that relies on
hard to find parts, for example. You'll often be directed to the ASM-1
stuff (mostly at Magnus Danielson's site, which is *full* of synth
stuff) and the work/findings of guys like Gene Stopp (the ASM-1), Ian
Fritz, Rene Schmitz, Ray Wilson, Jeurgen Haible, Charlie Lamm, and
others. Harry Bissell has published a few articles, too (excellent
guide to caps, the nifty MorphLag, and a great envelope follower).
Apologies to those I've forgot to mention.
--
john