Trainwreck amp in a pedal?

[thorpy6]

i haven't tried any of the runoffgroove AIABs, or any clones of commercail types, but i did my own exploration into this AIAB idea back in 05. 'decade'
it has a JFET feeding a Ge trans, a dumble-inspired tone stack and a 3rd FET tage. the trimmers on the FETs allowed tuning to emulate preamp and power amp distortion, the Ge gave a round tubey flavor ( and player dynamics) that FETs alone couldn't match IMO.

Looks really nice,
If the dynamics are so difficult to emulate, why don't more pedals utilise the opto-fet like in the bixonic expandora? I've only seen this in this pedal and it seems a really neat way to ensure picking strength etc are taking into account to give a good distortion characteristic.

[joegagan]

good point. i recall seeing threads about the expandora a long time ago, but i have not seen a schematic.

not familar wth opto-fets either, they sound like they would be good to explore.

[midwayfair]

If the dynamics are so difficult to emulate, why don't more pedals utilise the opto-fet like in the bixonic expandora? I've only seen this in this pedal and it seems a really neat way to ensure picking strength etc are taking into account to give a good distortion characteristic.

The opto-FET idea is cool, but there are other ways to emulate the picking dynamics of a vacuum tube. FETs are very good at it (slightly better than BJTs), and they've been used as solid state tube emulators for decades. Diodes aren't as good at it, but mostly because the methods of using diodes as clippers involves sticking them in a place where they fall after a boosted signal that gets well above their clipping threshold. They would still clean up like an amp with picking dynamics if the size of the signal through them were adjusted with a series resistor (that's what's in Joe's circuit, and I did something very similar in my Fallstaff booster to mimic the breakup characteristics of a Rangemaster's transistor). There are things like the knee of the distortion to take into account (germanium generally sounds like it has a softer knee than silicon). An asymmetric arrangement of diodes will get closer.

But this is all still working with solid state technology, which will ALWAYS be a little different from tube distortion in some manner. However, JustNick has done some fun blind tests to see if people can tell the difference between tube and solid state distortion. You can see where that's going ...

You might want to check out Samhay's decompression overdrive on DIYSB and Mictestester "Secret Sauce" on freestompboxes. Both utilize a somewhat unique method of compression on the diodes to mimic amp sag, which is one of the important parts of the "feel" of a tube amp.

[thorpy6]

i am going to go back to this one after ive done a bit of research, there are so many options. but it strikes me that you could get a pedal that could emulate the  full tube compliment.

whether or not this is any use to the effect pedal world is debatable but imagine a pedal with either opto-fet or a well designed diode clipping section to represent the preamp and fets to represent the power tubes.

a true amp in a box?

[ch1naski]

Preamp emulation is one thing, but I have my doubts that power tube saturation can ever be accurately emulated. Seems to me that it's kind of a combination of what's feeding those tubes, how hot they're burning, and finally the transformer. There are a lot of interdependent factors when you get to that section of an amp sound.

Not that I don't want to see it attempted. It would be great, and the Trainwreck amps are a perfect aiming point for a project like this.


Ultimately, this is how new breakthroughs begin, right?
 "Can it be done?"

And then someone figures out a way.

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