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previous: Rick Erickson I must be missing something here. W... -- 5/15/2003 6:23 PM	View Thread

Re: Opto-Coupler vs LDR

5/15/2003 9:24 PM
stephen conner	Re: Opto-Coupler vs LDR An Opto-coupler is normally taken to be an LED shining on a phototransistor. It's not so good for switching/muting audio signals because the transistor only conducts in one direction and can't take more than a few volts in reverse. The proper name for it is 'Opto-isolator'. The thing you find in SLOs, Peavey 5150s, etc, which is a LED shining on an LDR, is properly called a 'Vactrol' or something. Folk seem to refer to the whole LED/LDR assembly as a 'LDR'. To complicate the issue, you can also get opto-isolators made with an LED, a tiny solar cell, and one or two MOSFETs. These may be usable as replacements for Vactrols, although they have rather a high shunt capacitance. Steve C.

5/15/2003 9:24 PM

stephen conner
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Re: Opto-Coupler vs LDR

An Opto-coupler is normally taken to be an LED shining on a phototransistor. It's not so good for switching/muting audio signals because the transistor only conducts in one direction and can't take more than a few volts in reverse. The proper name for it is 'Opto-isolator'.

The thing you find in SLOs, Peavey 5150s, etc, which is a LED shining on an LDR, is properly called a 'Vactrol' or something. Folk seem to refer to the whole LED/LDR assembly as a 'LDR'.

To complicate the issue, you can also get opto-isolators made with an LED, a tiny solar cell, and one or two MOSFETs. These may be usable as replacements for Vactrols, although they have rather a high shunt capacitance.

Steve C.