Audio synthesis via vacuum tubes/Keyboard controller for tube synthesizer: Difference between revisions

The '''keyboard controller for tube synthesizer''' compensates for the variable response of the individual thyratron tube used in the [[Audio synthesis via vacuum tubes/Tube VCO|tube VCO]] instead of the more familiar voltage divider network .

Classic analog synthesizers commonly achieved equal tempering with one of two schemes: either a linear-response VCO (or VCOs) with a keyboard attached to a voltage divider network with exponential scaling; or, more commonly, a VCO with an exponential-to-linear voltage scaler circuit, and a keyboard with a linear divider network. Both schemes have their weaknesses. The former, when an LFO or other modulation voltage was added to the VCO input, did not offset in equal tempering. Also, the resistor divider often required unusual high-precision values. The latter scheme was easy to do, IFIf one could control the temperature drift endemic to the exponential scaler (it usually relies on base-emitter exponential response to do the conversion, which drifts a great deal with temperature). The thermistors used in early exponential scalers are now difficult to obtain.<ref name="cont">[https://web.archive.org/web/20111001170916fw_/http://cgs.synth.net/tube/controller.html Controllers] (archived) by Eric Barbour, 1997, with permission of the author - archived</ref>

The Trautonium never had this problem--it used a [[ribbon controller]], with no fixed keys. We could always do that with our tube circuits. Refer to the classic [[Electronotes|Electronotes newsletter]] for a number of suitable circuits. However, if you insist on having an equally-tempered keyboard, we must use a divider made of trimpots.<ref name="cont" />

This circuitry is intended for the more advanced builder. Because high voltages are used, a shock hazard exists. We do not recommend that the novice DIY musician try to construct this synthesizermodule. Some experience with tube electronics is highly recommended.