crochambeau wrote:Vactrols are also quite distant from being a linear system.
As Pladask said, the signal path in these is analog. It's little different than FET switching, I believe level adjustments are accomplished via PWM while switching on & off at a supersonic speed.
Functionally speaking, the biggest difference between digital pots and vactrols is that vactorls are a two leg component, whereas potentiometers are three. So if you're hoping to do anything more complex than a variable resistance/rheostat you'll need to stack them - which will really illustrate that fact that they are not linear in response to control signal (and are slow getting there).
Of course, if all you're after is volume control you can toss VCAs into the mix as potential candidates as well, but if you need a wiper equivalent to your circuit, digital pots will probably prevail over vactrols (presuming you can drive them on the logic side of things).
Yeah not wanting a rheostat is the biggest thing driving me away from vactrols. The volume was just a quick circuit to test I could get the things working and see if there was any noticeable steps or noise. So far I can't tell the difference.
Gone Fission wrote:The voltage limitations are what stops me when I look at digital potentiometers, but I'm usually looking for tube circuits. They're bound to improve as ROHS won't tolerate Vactrols or photoresistors because of the Cadmium.
I found some with large voltage tolerance, but the number of taps really drops.
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