LFOstortion

From the vendor

LFOstortion

Dec 4, 2022 2 min read

Just as I was finishing working on the Enveloping Timbre, I realized I could try different kinds of control voltages, such as a LFO to control gain and treble. I'll keep this one brief and defer most of the details to that page, where everything has been explained already.

The signal path is unchanged, while the control signal for the two BJTs is now a triangle oscillator using the LM358. It might look a bit strange, but basically R1 and R2 make up a separate voltage reference that gets contaminated both by the "Rate" attenuator and C3, while the main one stays clean, but is still good enough for its purpose.

The aforementioned capacitor was the best way I found to suppress the popping caused by the sharp transitions in both the pulse and the triangle output, which otherwise contaminated the signal, especially with high gain and fast rate.

The attenuator on the triangle output shifts it down in average level and amplitude toward BJT-compatible voltages: you could trim R12, but I found the humble 15k value to be very close to ideal already.

How does it sound like? Unsurprisingly, a lot like tremolo, which is the main issue I've faced in the past when toying with this idea with a friend. I know he will very happy anyway with this best attempt so far. To be fair, unlike a tremolo this assures minimum unity gain from the first stage, which can be further tweaked by the "Ratio" control to be a modulation of clipping more than amplitude. And also there's the synchronous action of the treble control modulation, which is quite unique to this circuit.

You can check out for yourselves: