[sdiy] Negative resistance elements

cheater cheater cheater00social at gmail.com
Sat Apr 3 19:35:56 CEST 2021

are there any circuits other than oscillators that can use negative
resistance diodes? What about:

- filter gain elements in ladder filter: either after a transistor in
a transistor ladder, or as the diodes in a diode ladder filter
- filter gain elements in an SVF: in an svf, you have a stage made out
of an op amp with negative feedback loop through a transistor. What if
you biased the tunnel diode so it was right at the peak between
positive and negative resistance. Then, take its output, put it
through a tank envelope circuit, and feed that envelope (positive
feedback) back into the input of the diode. because the positive
feedback puts the diode in a negative resistance region, it actually
becomes negative feedback.
- filter gain elements again: instead of using negative feedback, use
positive feedback but have the diode biased like above at the positive
input into the op amp
- four quadrant gain element, as described above - if you bias the
diode towards negative resistance that gives you a flipped signal; if
you bias it towards positive resistance that gives you a non-flipped
- resonance shaper in the feedback loop of a filter. just wonder what
that would sound like, really.

On Sat, Apr 3, 2021 at 3:44 PM Mike Bryant <mbryant at futurehorizons.com> wrote:
> > Interesting question. Reminds me of UJT's. There are still a few available according to digikey. I think UJT's were used on some old organs as top octave oscillators if I remember correctly.
> And more famously as the 2N2946 oscillating element in the original Moog 901 modular oscillators.
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