Amp modelling

[suryabeep]

Hi everyone,
This may be a noob question, but here goes: How can I 'convert' an amp schematic with tubes to something with transistors? What are those 'amp-modelling pedals' out there (like the Wampler black 65 and stuff)?
Thanks!

[R.G.]

The short answer is that you probably can't.  Think about it - if someone could do this, it would already be done, given the decades that Very Smart People have been trying to get tube sound out of non-tube electronics. If they had been successful, tube amps would no longer exist, except as curiousities.

There are two big classes of "tube amp" emulators, analog and digital. You're asking about analog means, I think. In terms of analog "tube amp modelling", there are several sub-classes. It has become popular in this forum and others like it to simply sub in a JFET for a tube, tinker with the bias, and as the British and Australians say, Bob's your uncle. The problem is that JFETs are not tubes, they only bias in a similar way. They do not clip or amplify like triodes. These "drop in a JFET" emulations do preserve the filtering aspects of the amps they try to emulate, and in many cases this is kind of reminiscent enough of the amp's sound that the builder is convinced that it's PERFECT!!! in every way. The problem is that the person who is doing this doesn't have a real amp like that to compare to, nor, even worse, the speakers and cabs that the real amp has. Speakers and cabinets can have a huge effect on the tone of an amp.

The digital emulators try to use active filtering and parametric signal shaping to copy the actual clipping of tubes and the filtering "voice" of the amp, and some of them even try to fake the response of a speaker and cabinet. Some of these are pretty good now, after nearly 30 years of trying. But DIY DSP on this scale is not easy. You have to be well versed in DSP learning to do useful work. Then you have to have good DSP hardware, usually more than you'll get in an FV1. We know that because of the "existence theorm" above: if it could be done, and many people have been trying to do it (they have) and it's not yet here, it's going to be difficult to do. If it was easy, someone would already have done it. Not that it's impossible, just difficult. I'm guessing it's going to need a much fancier, speedier, more capable DSP.

I have not looked at the Wampler Whatever, but I have looked at the insides of several other "amp modellers" and the analog ones all tend to be as described above - some king of clipping that's not too far from a tube, maybe, then filtering to make the clipped sound at least have a similar voice.