2BJTE - 2 BJT triode emulator

[DDD]

I think it's better to compare "full versions" of the scaled up circuit with the initial one. Also, special attention to the intermodulation products is to be the most important.

[Quackzed]

maybee stick a cap in parallel with r2- say 5uf, see if theres a way to clip the lower frequencies equally. lower the input cap a bit maybee as well?

[DDD]

It seems R2 may be omitted at all (?)

[tca]

Hi again,
I should first confess that I'm a bit confused about all the facts, and not only that, about what really means to make a triode emulator. Let us consider again Jack's muffer  (amplifiers of the bigmuff). The graphs shows what happens to when one varies the input voltage from 10mV to 50mV for different values of the emitter resistance (150, 100 and 50 Ohm):



"Almost" every one would say that the figures show a "typical" triode response under overdrive and in some way mimics the behavior of a triode, even the non overdrive behavior part, compressing the positive half of the wave and stretching the negative part.

Given that, what's missing, if anything, about this form of emulation? The frequency response? The transients when one strikes a guitar string?

Cheers.

EDIT:

Or even if one adds the diodes in the feedback path (emitter resistance = 150Ohm).

[aroneous]

Hi tca,

I think that there is more to tube emulation then just the way that the device distorts under a voltage range, you also have to look at the way that the device distorts in response to current as well.

A transistor responds to current to control how hard it turns on (current controlled) where a FET responds only to the voltage (due to the high impedance of the input). Since a pickup coil of a guitar is a current source, the response of a transistor and a FET will be vary different.

What is the current you are using for your source? What happens to your model if you vary the current.


Aaron

[tca]

a pickup coil of a guitar is a current source, the response of a transistor and a FET will be vary different.

Agreed.

Actually the pickup coil of a guitar is neither a current source or voltage source, to my view. It has a non-zero internal resistance, has some of the inductors properties and  capacitors  characteristics. I'm not saying that these circuits are tubes, I say that they emulate some properties of a triode. The same could be said about any triode tube. A given triode tube emulates some other triode?!?!

One could make a list of BJT and FET circuits that would behave like a triode under some regime, and trust me I've tested a few, and they all sound like some kind of a triode.

Cheers.

EDIT:

P.S.

Probably you all been there on this tone quest!

[Renegadrian]

Hi,
    I would like to share with you my latest experiment. It is a two transistor "booster" that has a triode type behavior. Here is the schematic

Actually I did the same with FETs, starting from the valvewizard article about cathode follower and bootstrapping. Here's the schem I successfully used for my build.