Tube Challenge!!

[Doug Tymofichuk]

On Sat, 20 Nov 1999 14:27:46 -0500 (EST) 
media at mail1.nai.net wrote:

> I would like to see a tube oscillator that can be used with 
> existing CV sequencers, as well as the various modulation 
> sources typically found in modular synths, to produce 
> non-standard tunings, oscillator sweeps, and portamento

Great! So would I and lots of others too, I'm sure.

> Is it possible to build a "triode ladder" filter???

Almost anything is possible, the question should be "is it 
worthwhile?". If it requires a dozen or so tubes and 
associated components, that may be too much. But for maybe 
half that amount of parts, it would probably be very 
worthwhile.
 
> Tube VCA's seem easy enough, but I think building a tube 
> ADSR to control that VCA would be next to impossible. 

Why? ADSRs are mostly just switching and charging 
capacitors. I would think that the ADSR would be an easier 
module to design, just using thyratrons. But I think that I 
could live with a solid state ADSR running a tube VCA. And 
tube VCAs are VERY easy to build.
 
> Sample and hold is another matter 
> entirely! How about a tube noise source??  

That could be fun, you could use a tube geiger counter to 
generate random noise. Sample and hold ought to be fairly 
easy with high-impedance tubes.

If you could 
> build tube VCO's, VCA's, VCF's, ADSR's, and LFO's, how 
> would you mix modulation sources??  For example, how would 
> you send a mix of LFO and keyboard voltage to control the 
> VCF??  What's the best way to sum voltages using tubes??

What's wrong with doing just like in solid state, with 
voltage dividers? Also, keep in mind that tubes with 
multiple grids can do amazing things with modulation with 
ease. There are some things that are far easier to do with 
tubes!
 
> So I'm thinking that many of the basic features found in 
> subtractive synthesizers (eg. ADSR, S&H, keyboard tracking, 
> modulation mixers) would be impossible, or impractical far 
> beyond any desire for novelty, to build with tubes.

I disagree. In fact, the biggest reason that this has not 
been done to date, IMHO, is that very few people have made 
the effort. Thousands and thousands of people have spent 
decades on solid state synthesis. Only a handful have 
spent a few years on tube synthesis. If we used one tenth 
of the time this list has spent on tempcos, for example, 
on tube design, we ought to be able to come up with some 
truly great stuff.

Actually, the more that I think about it, the more that I 
feel that we have a very unique opportunity here. We can 
spend our time refining and "improving" solid state synth 
designs, or we can instead spend time designing entirely 
new circuits, using tubes, going where no one has ever been 
before. Overall, I feel that tubes are easier to work 
with and design with, and there are a lot of unexplored 
areas to check out. And some things may not be practical 
with tubes, and that's fine, because there are going to be 
some things that we find tubes will do quite easily, that 
solid state cannot. That's where the biggest reward for all 
this comes in, when you come up with something completely 
new, that has NEVER been done before. 

What would you prefer - being responsible for a new, .001% 
more stable TC oscillator that sounds just like the last 
one, or being responsible for a totally new, unique sound, 
that's never been heard before?
----------------------
Doug Tymofichuk
dougt at cancerboard.ab.ca