There are many kinds of optical isolators, but the most common is the LED/photo-transistor type.
A vactrol is a combination of a light depending resistor (LDR) and light source (LED) both put into a small 100% light-proof case.
The principle of a Vactrol is very simple.
When an input current is applied to the LED, the output phototransistor turns on.
The only connection between the LED and phototransistor is through light -not electricity, thus the term optical isolator.
When an input current is applied to the LED, the output phototransistor turns on.
The only connection between the LED and phototransistor is through light -not electricity, thus the term optical isolator.
These optical isolators are primarily digital in nature with fast response times suitable for interfacing with logic gates. Rise and fall times of a few microseconds, faster for some isolators, are typical.
So together, the coupled pair act as an electrically variable potentiometer.
Since the output element of the AOI is a resistor, the voltage applied to this output resistor may be DC and/or AC and the magnitude may be as low as zero or as high as the maximum voltage rating.
Because the input will control the magnitude of a complex waveform in a proportional manner, this type of isolator can be used as an analog control element in all kind of ways in analog synthesizers.
More info on Vactrols: Doepfer Vactrol Basics page
Vactrols on Wikipedia
PDF via DatasheetCatalog.com
Interesting stuff; can you describe a few examples of how you'd use it in a specific patch?
ReplyDeleteMarc JX8P
@Marc Vactrols introduce voltage control to any function that is controlled by a fixed or variable resistor (e.g. a two-terminal normal or trimming potentiometer). Typical examples of vactol use within the A-100 are:
ReplyDeleteAttack, Decay, Release of all envelope generators (A-140, A-143-1, A-143-2)
Slew time of slew limiter (A-170)
Delay time and duration of trigger delay (A-162)
Clipping functions of the extreme filter (A-106-1)
Clock rate of digital noise (A-117)
Random rate and level of analog noise (A-118)
Frequency of Trautonium filter (A-104)
The A-101-2 Low Pass Gate module that i bought has 2 Vactrols inside, 1 for it's low-pass filter and 1 for the VCA.
An A-101-9 (Dual) Universal Vactrol Module can be used to control other modules. (after some modification of these modules)
Also see http://www.doepfer.de/A1019.htm