1 V per octave Tube VCO

[Magnus Danielson]

From: René Schmitz <uzs159 at uni-bonn.de>
Subject: Re: 1 V per octave Tube VCO
Date: Thu, 28 Dec 2000 01:08:28 +0100

> Hi Magnus, and list!

Hi René,

> Not that an all tube setup is impossible, but I think the sonic improvement
> is rather low, plus even the simplest two transistor bipolar expo would
> perhaps easily outperform this circuit in stability and tuning accuracy.

Well, while that is true, I just look on it as a engineering
challenge.

> The tube expo is drifting along already, and using 1-2 tubes for a feedback
> amp won't help on the stability either, considering the (comparatively)
> small open loop gain that they will permit. Even if you trim your circuits
> offsets, it will still drift with varying heater current (think of line
> voltage variations for example). 

Hmm... heater current needs stabilisation. Sounds like a transistor
job for my ears... oups... sorry! ;)

> My personal opinion is that the control section can make good use of the
> precision of semiconductor opamps, while the audio section takes advantage
> of the sonic characteristics of tubes. 

Good point.

> But, I don't wan't to discourage you or anyone, to lay his hands on these
> circuits and to squeeze more performance out of them. 

Right. I think this tube-expo thing is an interesting challenge. I
where under the impression that one could not do exponential
behaviours in tubes and here you tag along say "Oh, BTW here is my
tube-expo". I then naturally felt that one possibly should attempt to
do it all the way so to speak.

I am not good with tubes, but willing to learn, and as such I find
these exercises interesting to learn more about tube properties...

Cheers,
Magnus