[sdiy] Newbie alert :-)

[john mahoney]

(Here I go again using "Reply All." ;-)


> I don't think I'll ask anybody to open his source if he hasn't got
the idea
> himself.

Point taken.


> You're right. In the "iterative and incremental" world (and
"test-driven
> development", you try to get something simple done that will fulfil
exactly
> the minimum requirements, which for an oscillator is to oscillate
:-)

There's little need to argue this, but I think there's a little more
to it. There are many oscillator designs that won't get you
anywhere -- the "dead ends" to which I was referring. You can make a
basic oscillator from 2 gates (NAND or NOR), an R, and a C, but it
will never grow up to be a VCO. Very simple circuits like this in the
"Forrest Mims Engineer's Notebook" book, which is still in print (a
similar book was formerly sold by Radio Shack), and I'd bet that most
Americans on SDIY own at least one of Mims's books.


> > 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.
>
> Hmm. This strikes me as a result of design (for example, using
certain
> opamps?) rather than an external requirement.

These conventions have developed for various reasons, and I can't say
why. We tend to honor these conventions so that our DIY gear will
interface properly with existing, commercial gear. There's little
reason not to do so unless you have a specific goal such as building a
low voltage synth.

Most modular synths run on +/- 12 or 15 volts. Here's a handy
reference, by the way:
http://www.modularsynth.com/chart.html


> > VCOs tend to have exponential response (1V per octave),
>
> This is also a result of design (or, a "second-order requirement"),
although
> it of course makes a lot of sense in a musical context.

It's another almost universal convention. There are exceptions, such
as [old] EML synths which use 1.2V/oct, IIRC. (You will find people
here using "IIRC" a lot, which -- IIRC -- means "if I remember
correctly.")


> Wow, how are temperature-controlled VCOs useful for making music?
> Auto-compensating for temperature drift? Or have you made a typo? I
am
> genuinely confused.

Bad typo! :-) I meant what you wrote: Auto-compensating for
temperature drift.


> > 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.
>
> Well, I'm not sure about the "demographics" of the sdiy group. Am I
the only
> beginner around? Because to someone like me, just getting a sound of
a few
> connected components is a success.

You are definitely *not* the only beginner. I consider myself to be a
beginner in terms of experience, and maybe reaching the intermediate
level of knowledge. I read and talk more than I solder! ;-) As one of
the newer guys here, I try to "run interference" for the experts by
answering what I can and leaving the hard stuff for them.

Anyway, keep in mind that the focus of this group is electronic
musical instruments, with all the assumptions and conventions which
that implies. The group is very receptive to new ideas, too, so don't
let me paint the wrong impression.


[giant snip]
I understand what you are saying. I don't have all the answers, and
I'm out of time right now anyway. All I'll add is that you'll find the
SDIY group to be very helpful. You'll get where you want to go, I'm
sure.


> Thanks very much, this was exactly the kind of answer I was looking
for.

Quite welcome!
--
john