... | ... | @@ -13,7 +13,7 @@ Vactrols allow us to control a resistance with a voltage fairly easily. So if we |
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<img src="/uploads/2ba93135b4e99c2d71a4fd98cd420d66/RC_LP.png" width="33%" height="auto" />
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we could easily replace the Resistor R with a vactrol – this would result in a lowpass filter whose Cutoff Frequency could be set with an external voltage. One could use a control signal or a simple voltage divider (potentiometer) or both at the same time! And this method can be applied to nearly every circuit that uses resistance as some sort of variable. You could also take a old toy piano and strategically replace resistors with vactrols to allow circuitbending with a modular.
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Vactrols are not fast. This means if you want to change the LDR's resistance with a high speed the resistance will not change instantly but will rise with a certain rate, and once the LED is switched off it will fall with a certain rate. While this can be a problem for fast switching signal stuff, it can be quite usefull for musical purposes, because the resulting sound can be quite musical. A famous use of vactrols is in so called [Low Pass Gates](LPG) (LPG) – a combination of a Lowpass filter and a Gate/VCA. If you trigger the Vactrol with a short pulse and it is the right vactrol with the right time response, the input sound gets it's timbre changed in way similar to that of a bongo drum (example: [youtube: buchla bongos on acid](https://youtu.be/XmgoCD4NgUk?t=35)).
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Vactrols are not fast. This means if you want to change the LDR's resistance with a high speed the resistance will not change instantly but will rise with a certain rate, and once the LED is switched off it will fall with a certain rate. While this can be a problem for fast switching signal stuff, it can be quite useful for musical purposes, because the resulting sound can be quite musical. A famous use of vactrols is in so called [Low Pass Gates](LPG) (LPG) – a combination of a Lowpass filter and a Gate/VCA. If you trigger the Vactrol with a short pulse and it is the right vactrol with the right time response, the input sound gets it's timbre changed in way similar to that of a bongo drum (example: [youtube: buchla bongos on acid](https://youtu.be/XmgoCD4NgUk?t=35)).
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## What types of vactrols are there?
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Typically vactrols are quite expensive, that why building them yourself is probably a good idea. The classical vactrol used in most older synthesizers come from the VTL5C series with a price per piece between 6 and 15 Euros, you could get them for example [at Thonk.co.uk](https://www.thonk.co.uk/shop/vactrols-vtl5c/).
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