Starved Plate Tube sound

[william]

When unsing 12AX7 tubes with a starved plate do they clip the same as with high voltages?  I've been looking at the Paia Stack In a Box and am unsure.  Most of what I've heard is the IC's do the clipping and the tubes are used to soften the harshness usually presnt with opamps.  If the tubes are clipping what prevents someone from creating a multi-stage tube preamp?  Something similar to a marshall pre, but with lower voltages?

Something like:
Op-amp->V1a->V1b->V2a->V2b->Tone->Op-amp->Out.

Something like that should easily fit into a larger stompbox.

[slajeune]

Hi William,

from my understanding, the tubes clip almost the same in low voltage as they do in high voltage.  The major difference is that at low voltage, they tend to distort easier/earlier (which is a good thing if you are building a distortion pedal!).  The major difference is the headroom between a starved plate and the high voltage one.

Someone please correct me, but, from my understanding, the more headroom, the more nuances you can get in tone / distortion.

Anyways, if you want to see a fairly simple tube distortion with starved tube, go see:

http://www.geocities.com/slajeunesse/ruby_tuby.html

What you are looking for is the first part right before it gets to the LM386.

Another interesting thing that might be worth while to investigate, instead of using an opamp to drive the tube section, try using the fetzer valve circtui from runoffgroove!!!  This could prove to be a kickass combination!

Cheers,
Stephane.

[Johan]

when you lower the voltage to the point where you would consider the tube starved, you've also significantly reduce the region where the tube can work linear, often to the point where its not linear at all. this will give you a sound that is almost like a caricature of tubesound.
if you overdrive the tubestage too much it will usualy start to hardclip and sound harsh. this also happens when the tube is operating with high voltages, but much much sooner when starved. this i beleive is why many people dont like starved tubes, they simply push the tube much more than what maby they should have. I think R.G had an article on this in his tube-faq.. so to keep it sounding/ behaving like a tube operating at high voltages when using low voltages, you must be carefull not to drive the tube too much. dont send too strong signal into the tube and attenuate the signal between the tubestages...
...did that make sence?

Johan

[Paul Marossy]

I recently designed my own tube overdrive, which is kind of a hot-rodded version of a Shaka Tube. I used a JFET instead of an opamp at the front end, and then used a LM386 at the end to boost the signal. I think that the JFET sounds a little better than an opamp.

[will]

Hi,

if you overdrive the tubestage too much it will usualy start to hardclip and sound harsh. this also happens when the tube is operating with high voltages, but much much sooner when starved. this i beleive is why many people dont like starved tubes, they simply push the tube much more than what maby they should have. I think R.G had an article on this in his tube-faq.. so to keep it sounding/ behaving like a tube operating at high voltages when using low voltages, you must be carefull not to drive the tube too much. dont send too strong signal into the tube and attenuate the signal between the tubestages...
...did that make sence?

Johan

Gee, I wonder if it is as simple as over loading the grid of a tube with a signal that swings so positive that the Grid is more positive than the cathode. Then the tube essentially cuts off during the extreme swings, due to the overload. I can imagine this distortion not being pleasing to hear.  :x Whereas the tube maxed out clipping distortion at the plate sounds great.  It seems overloading the bias on a low voltage circuit will occur sooner than a high voltage circuit.  

Regards,
Will

[william]

The thought about using a jfet at the input is a good idea.  I will look into that.  I've built the Dual rectifier type circuit that Ansil adopted to Jfets but got a so so sound out of it.  http://209.240.71.22/circuit/wrecktumflinger/index.html  The distortion was brittle and needed tweaking to get more low end out of it.

But I guess my main question was if when using a voltage doubler like utilized in the Paia Stack in a Box (http://www.paia.com/siabsch.pdf) you could drive two tubes.  

I guess I got my answer here.  http://fclarke.softwareballistics.com/Distortion/siab2tube.gif.

What are the things to take into cosideration when designing a starved plate tube pedal.  How do you have to alter a design?  I'd like to adapt a slo 100 (lead) or dual rectifier (orange)type circuit.  Stick in a box like Puretube does, and call it a pedal.  I could throw a pair of 386's in there for a whopping 2 watts of output, and have a tiny 12AX7 tube amp.

Lofty goals are the best to have I always say.

P.S. I know Zvex beat me to the tiny amp, but I would have the smalled 12AX7 amp.  there it is.........

[puretube]

here`s a nice example of sticking a "Tube-Zipper" (2x 12AX7) into a different box, reduce the number of controls, throw in an EL84 to get 6W - pure-tube FX;
(HT, though...) :


the footprint of this little amp is exactly the size of Aspen Pittman`s "The Tube Amp Book" (4th ed., 1993, paperback), i.e. smaller than the E-H "diamond" boxes.

[The Tone God]

Aww thats so cute. I'm sure if you keep feeding it good tubes it will grow up to be a big amp.

Speaking of small amps I should get back to the Ruby Tuby sometime. I actually bought some 386s so I can build the whole thing now.

Andrew