Hi
In discussion last night I was saying how to my ears diode cathode biasing makes the amp sound brittle. I was wondering if anyone had put a sine wave through a forward biased sic diode and measured the output to see if it introduces nonlinearity? I don’t have the scope and freq analyser to do this but my physics background really wants to do the expt ;-)
Happy Thursday y’all
In discussion last night I was saying how to my ears diode cathode biasing makes the amp sound brittle. I was wondering if anyone had put a sine wave through a forward biased sic diode and measured the output to see if it introduces nonlinearity? I don’t have the scope and freq analyser to do this but my physics background really wants to do the expt ;-)
Happy Thursday y’all
What do you mean "put a sine wave through a forward biased sic diode"? That's not the same as diode biasing.
What I mean is put a forward voltage across a diode and then add a smaller sine wave onto it and see how the diode affects the signal. Is that clearer? So have a 3v dc (diode and resistor) with a 1v sine ripple.
The shape of a diode transfer function is well known, you can simulate that setup in SPICE. I don't know what you think it will tell you about diode biasing though.
This is too explicit a subject to make any generalized conclusions. We're often discussing an operating point of the LED somewhere in or below the knee on the LED's I/V curve. Here the Goddess and the Devil dwell together in the details. In the 1mA to 4mA range slope varies a lot, but is in the single or small two digit Ohm range, so its contribution is scaled by that as a factor of other circuit resistances, the sum of whatever actual stripey resistor is in series and the reciprocal of Gm, roughly but close.
So, it's quite a non-linear part, but its distortion contribution is scaled (linearly, if I'm very much mistaken) by a ratio of its slope of a few Ohms to a circuit total of, maybe, about 1K Ohms, or a couple. Ballpark, with a headwind. A distortion generator with a 30dB disadvantage.
Actual measured data with a high mu triode (low current, at or below the knee, larger contribution because of shallower slope) at large output will naturally be different than a medium mu triode (medium current, on the higher end of the knee, smaller contribution because of steeper slope). When in doubt, add bias.
I guess this is a carryover from jhs' recent thread, which was a carryover from stephe's thread. The beat goes on.
All good fortune,
Chris
So, it's quite a non-linear part, but its distortion contribution is scaled (linearly, if I'm very much mistaken) by a ratio of its slope of a few Ohms to a circuit total of, maybe, about 1K Ohms, or a couple. Ballpark, with a headwind. A distortion generator with a 30dB disadvantage.
Actual measured data with a high mu triode (low current, at or below the knee, larger contribution because of shallower slope) at large output will naturally be different than a medium mu triode (medium current, on the higher end of the knee, smaller contribution because of steeper slope). When in doubt, add bias.
I guess this is a carryover from jhs' recent thread, which was a carryover from stephe's thread. The beat goes on.
All good fortune,
Chris
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