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Old 28th December 2010, 10:48 AM   #1
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Default Isolate the audio input

It is possible to use an optocoupler to isolate the audio input? Does anyone have any idea how to do this?

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Old 28th December 2010, 05:36 PM   #2
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The easy way is to use a line trafo.
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Old 28th December 2010, 05:55 PM   #3
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Trafo no good, optocoupler is more professional
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Old 28th December 2010, 06:00 PM   #4
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Hogwash. Both are equally good from an engineering PoW. Line trafos would be my preferred choice any day though.
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Old 28th December 2010, 06:41 PM   #5
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Optocouplers are not linear and require biasing for AC (music) signals, so the answer is basically no.
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Old 28th December 2010, 07:09 PM   #6
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I agree that an appropriate input transformer is the way to go ... not exactly cheap for the good ones but for example I was looking at a Jensen that was flat (less than +0/-0.2 dB deviation) from 5 to 40K and perfect for line level. $70 a channel, though. You may well be able to get away with less, depends entirely on the application.

Optocouplers are used in digital (toslink) inputs ... they don't have a stellar reputation even in that application although there are also those that argue they're fine and the Golden Eared are full of it, but they do eliminate any possibility of ground loop hum entering the input, which is certainly possible with S/PDIF coax or AES/EBU.

Is that the goal? I would go with transformers for analog inputs if that's the case. Considering that you probably can't listen to any non-live performance, let alone any except a completely un-amplified live performance, anywhere on the planet, without having some transformers in the signal path, I can't see what could be more professional; it's what the pros use every day.
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Old 28th December 2010, 11:14 PM   #7
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Is this ClassD of fredos. I don't have amplifier of fredos but using the audio input isolator appears to be very good. It also has some examples of isolator circuit using optocoupler.
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File Type: jpg IsoladorAudioOpto.jpg (113.6 KB, 128 views)
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Old 29th December 2010, 12:42 AM   #8
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Quote:
Originally Posted by lindomar View Post
It is possible to use an optocoupler to isolate the audio input? Does anyone have any idea how to do this?

Thanks.
Why would you want to isolate the input ?
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Old 29th December 2010, 12:49 AM   #9
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To eliminate noise in audio.
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Old 29th December 2010, 06:03 AM   #10
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Using any kind of input isolation will actually add noise since both line trafos and optocouplers are non-linear. The only advantage is that you eliminate the risk of a ground loop and incorrect connections.

It's most often used in pro audio because pro audio engineers knows that sound engineers are complete morons that will sometimes connect an XLR output from one amp to the XLR input of another amp. But the easy way to avoid damage is to just add a clamp on the input.
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