Jfet VCA

Build
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What would be the most efficient resonator for the purpose?

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It donā€™t mean a thing if it aint got that PENG! Seriously, I would probably use the built-in filter with resonance or a bi-quad with feedback. The built-in rings nicely and is pretty efficient. Be careful! The built in will happily go into self oscillation. Best to keep the resonance a bit below 1. Remember that the resonant frequency wonā€™t be quite the same as the cutoff frequency.

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I noticed that the clip is asymmetric. That implies that the clip is occurring after the JFET. Since the JFET is already attenuating one side of the waveform, a symmetrical clip will chop off one side before the other. Itā€™s not clear from the traces whether there is also a DC offset on the signal going into the clip, but I think probably not. You should be able to vary the gain (multiply) of the output of the FET stage and feed it into a clipping function. clamp() will give you a hard clip.

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I just had a thought. I wonder if the dirt control is a feedback loop. Maybe back to the gate or possibly the drain. That could explain the resonance at high dirt levels. Certainly an area for exploration. I think I still need to build a new model with the signal on the drain. It will necessarily be a VCA rather than just a waveshaper since varying the bias will change the gain. Since the JFET has two distinct areas of operation I may need to use two equations. I downloaded the spec sheet for the JFET used in the Gristleizer so Iā€™d have some parameters to work with.

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That would definitely be something to mess with!

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Playing video games with my sons in the AM maybe in the afternoon if I feel up to it. BTW David is now the proud owner of a MiniBrute 2. $500 at Guitar Center.

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Ahh, the modern family. :slight_smile:

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Good way to spend some time together with us scattered all over.

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dirt%20oscilloscope

TG-4 proto.audulus (43.4 KB)

Ok, I whipped something up!

I combined both spline and the uJFET models and added a enveloped sine wave that is threshold triggered. I am reasonably satisfied with the results.

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Glad to see youā€™re having some success. I worked on the JFET model today and Iā€™m doing something wrong. When itā€™s connected, it goes into oscillation for some reason. I think I have the formulas correct, but Iā€™m obviously missing something. Probably a simple error, but I canā€™t see it at the moment. The voltage at the drain is dependent on the current through the FET, but the current is dependent on the voltage at the drain. Itā€™s not a linear relationship (hence the distortion).
I havenā€™t given up but I need to rethink my approach.

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I like the thought process! Does the oscillation sound interesting? Iā€™d be curious to check out the patch regardless for potential glitch sound use.

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Unfortunately it oscillates from + to - infinity (well overflow anyway). Probably not a useful signal. Iā€™m sure itā€™s the result of a logical error on my part.

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Thought I was over my bug. Yesterday I felt fine if maybe a bit sore, but today the chills are back. Off to the doc in the AM. David posted his first efforts with the MiniBrute on SoundCloud. I know theyā€™re probably a bit lame by your standards but I know heā€™d like a listen

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Feel well soon, friend.

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It occurs to me that the technique I used for making the glitch could be used for making a sub harmonic generator.

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