[sdiy] VCO reference voltages

[cheater cheater]

David,
> PSU load is largely fixed
> unless modules are added or removed from the cabinet

But what about transient loads that other modules can create? Say,
other VCOs which are not nicely decoupled...

> the rail voltages should remain fixed to
> within 1 or 2 mV during actual operation.

Out of curiosity (pedantry?), where are you getting this figure from?

> It is only when modules are added
> that the rail voltages may change measurably, and only then when the PSU is
> at or near its drive capacity.

You are here assuming a perfectly, or even properly, working
PSU/synth. It might be a deadly mistake ;-) But then you can ask
yourself how far do you want to go to correct the problems of someone
connecting a toaster to the same voltage rails as your VCO.

Either way: at A5 this voltage difference on the exp input is a
difference of frequency of over 1 Hz in comparison to an instrument
which doesn't experience this. I'm just putting this into musical
wording - I believe this is much better than many VCOs

Good (and important) point with the knob range though. I wonder if
there is some tricky/smart way to use voltage references and still
maintain full range. I'm thinking of using a range switch rather than
knob, then you don't need a continuous transfer, that might make it
simpler to implement a technique based on voltage references..

What range are you thinking of for your coarse tuning potentiometer?
Full range? Or just, say, +/- 6 semitones?

If full range - are there many practical applications of such a huge
range? I'm not saying there aren't, just wondering. The only thing for
which I really use full range knobs on VCO frequency is adding a
little audio-rate AM to the patch and changing the general setting
from the LFO area to the audio-rate area while modulating the AM
depth, for musical expression. This gives an effect similar to what
happens when the player of a string instrument pulls up a string to
change the speed of beat between his note and another instrument on
the same note.

Another thing is when I'm using sync, but I don't use such big
adjustments often. Sadly the coarse tuning knob is one mostly unused
by me, because most of the time I touch it I end up with result that
is way over the top. This got me quite interested, what other
situations are there where you can make use of such big range for
musical expression that will be nicely graded, rather tearing my ears
out?

On Fri, Apr 16, 2010 at 19:21, Ian Fritz <ijfritz at comcast.net> wrote:
> That's 800 ppm/K.  I try to get under 100 ppm/K drift with my VCOs. Of
> course, I've just learned today that all my VCOs are crap, so what do I
> know?

Who told you that? :^) I understand 'die meisten' means the same thing
in German as 'the most' in English, but maybe your translator slipped
up and wrote 'alle' in the subtitles ;-) clearly a case of 'lost in
translation'..

Aaron,
>> Most commercial *and* diy VCOs are crap.
>
> That is a rather strong statement.
>
> How would you quantify it?

I used quite a few :^)

Seriously - how many people active in this field do you think are
truly masters of their art? Not all - so what's the percentage? Out of
all VCOs that you can get out there, how many of them were made by
those few select people? I would probably end up calling a guitar not
made by someone who has mastered the basics of luthiery *crap*.. at
most mediocre. If I made a guitar right now it would certainly be
crap. The requirement of knowing what you're doing when making musical
instruments should go for synths too, in my opinion, but unfortunately
practical experience says it doesn't and people build and buy terrible
little monsters anyway.

Bear in mind I wasn't voicing an opinion about the designs of anyone
in this thread. I hadn't used your or Ian's VCOs, for one thing, and
the fact that both of you contribute so much information here is good
reason to believe you two's designs are, in fact, much better than
'crap' :) Either way no reason to feel hurt for anyone here.

Cheers,
D.