Voluptron

A stack of logarithms

The transistor and diode ladder VCFs have been around almost since the dawn of the synth era, but depended on precisely matched semiconductors, temperature control, and the occasional beating. With the right kind of nonlinearity, vacuum tubes can do the same thing but without the hammer.

The Voluptron has a 4-5 octave cutoff frequency range (or more if you're willing to go beyond the bounds of 1V/oct CV). Its resonance capability extends up to self-oscillation, and at lower frequencies the audio signal can adjust the cutoff slightly — FM synthesis with a vacuum tube circuit.

Tubes supplied
6ES8 x3
Tubes compatible
6AQ8
6BK7
6BQ7
6CG7
6DJ8
6ES8 (best CV accuracy)
6FQ7
12AT7
12AU7
12AV7
12AX7
12AY7
12BH7
12DW7
Other 9-pin dual triodes may work if the pinout matches those above; please contact us.

https://www.epicycloidengr.com/products-voluptron.html