Russian Valve Emulation Circuit (simple)

[raulduke]

Found this on my perusing of the webs at lunch:


Here is the website (and interesting article):
http://www.diale.org/tube_emulation.html

Anyone seen or heard of this circuit before?

It looks interesting (read comparisons with ROG Fetzer), and look easy enough to breadboard up.

[Ettore_M]

Nice find! That sounds cool! I'll just wait to see what you, designer-guys, come up with! 

Hector

[culturejam]

Haven't seen that before, but the diode in series between the input and base of the tranny reminds me of this:

[RobA]

Am I missing something? It looks to me like it's pretty much a wave shaper that depends on the amplitude of the input to get the output waveform. It would need to be embedded in some gain sections to do anything with the normal voltage levels from a pickup.

I simulated it in LTSpice and I had to put some pretty big gain on a pregain stage to get it to do anything with guitar pickup input voltage levels. Then the output curve is still pretty much a static response that depends heavily on the input voltage and very much on the output load.

It reminds me of doing static wave shaping in digital. The problem there is that this doesn't lend itself very well to any kind of natural tubelike response. Maybe this could be made to work well, but I think it would take a ton of signal conditioning before and after to get any sort of natural response. 

[gordo]

Way to kill my buzz Rob...

[raulduke]

Yeah I noticed the low output voltage vs input.

Thanks for taking the time to have a look into it.

If it is just a static waveshaper then maybe not so exciting 

Oh well eh... I might still breadboard it up and have a look.

[midwayfair]

Am I missing something? It looks to me like it's pretty much a wave shaper that depends on the amplitude of the input to get the output waveform. It would need to be embedded in some gain sections to do anything with the normal voltage levels from a pickup.

I simulated it in LTSpice and I had to put some pretty big gain on a pregain stage to get it to do anything with guitar pickup input voltage levels. Then the output curve is still pretty much a static response that depends heavily on the input voltage and very much on the output load.

It reminds me of doing static wave shaping in digital. The problem there is that this doesn't lend itself very well to any kind of natural tubelike response. Maybe this could be made to work well, but I think it would take a ton of signal conditioning before and after to get any sort of natural response.

What Rob said.

This is a source follower; you won't clip any part of the the wave at all unless your signal exceeds 0.6V. When it does, the diode conducts and half of the wave ends up in the buffer. Some portion of that is clipped and goes directly to the emitter if the signal is (again) big enough.

Some portion of the entire original wave, and the other half of it, go right to the buffer, so one half of the wave is never buffered.

I believe you will create crossover distortion with this as well, but I'm not entirely certain. It will definitely create a situation where the wave is soft clipped asymmetrically, but only under very limited circumstances (like in almost everything using diodes for clipping), and you'll need multiple gain stages before it and a buffer after it. That's a lot of work and components for what is, in the end, still asymmetric diode clipping.