Tube Amps / Music Electronics
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|previous: Jack I'm planning on reworking and expan... -- 9/27/1997 6:07 PM||View Thread|
|9/28/1997 8:51 PM|
|R.G.||Re: LAMBDA diode...what is it?|
That sounds a lot like what Russell O. Hamm did for the ground work for his 1972 paper "Tubes Vs. Transistors - Is There An Audible Difference?", except he threw in opamps and tubes as well.
For bipolars, the exact circuit you use them in makes a difference in the spectrum of harmonics you get back, and as you can see from comparing the spectrum from an overdriven Stabilized Bias CE stage to that of a Voltage Feedback stage as used in a Fuzz Face. I'm certain that it's the same for
fets as well.
If you're into measuring harmonic spectra, you might want to look at using interated stages, where you can get a good handle on the biggest possible clipped output, amplify up to that, and then attenuate between stages so that no stage is ever overdriven by more than Xdb, where you set X by the amount of attenuation. This would allow you to build up distortion and sustain gradually over a number of stages, and since no one stage is ever overdriven harshly, and you retain as much as possible of the character of the device doing the clipping. You select the rough amount of distortion by switch selecting at one point in a number of stages that you just leave running, and fine tune it with the initial gain at the input.
This gave really good results with CMOS inverter gain stages, and probably would with any device where the design was done well. An interesting variant might use one of the unbuffered multiinput gates to allow the second input to be used with a DC level on it for modulating the distortion, or cross-modulating it with another signal.
I'm about six years behind in writing down distortion methods, let alone breadboarding them.