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Old 19th July 2014, 08:26 AM   #1
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Default Input device protection

So, I'm in the the process of building some of the DIY amps on this site, so far it going great, one finished, one in progress. When I am testing the amp modules I use either my CD-player, cellphone or laptop - but I am worried if something goes wrong/shorts in the amp-module that excessive current/voltage is going directly to my input device, and most likely destroying the input device.

My question is: Is there some way of protecting the input device (circuit, some kind of fuse, isolation transformer etc. ) ?

This will only be in the testing phase - so no special requirements for audio quality.
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Old 19th July 2014, 08:35 AM   #2
Mooly is online now Mooly  United Kingdom
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That is an unlikely scenario for any typical amplifier unless you yourself shorted (say) the supply voltage directly to the input.

If that's a possibility then the best protection is a series resistor at the input, and diode (zener) clamping on the source component side of things. You should also add a non polarised coupling cap of voltage rating equal or higher than either rail.
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Old 19th July 2014, 09:55 AM   #3
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If you are worried, you can use a pair of BZY88C5V1 zener diodes wired in series (anode to anode) and connect one cathode to ground and the other cathode to the input socket. That will clamp the maximum input voltage to about 6Volts peak to peak.
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Old 19th July 2014, 10:44 AM   #4
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Quote:
Originally Posted by JonSnell Electronic View Post
If you are worried, you can use a pair of BZY88C5V1 zener diodes wired in series (anode to anode) and connect one cathode to ground and the other cathode to the input socket. That will clamp the maximum input voltage to about 6Volts peak to peak.
I wouldn't count on it Jon
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Old 19th July 2014, 07:26 PM   #5
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To do clamping you need both a clamp and a series impedance. Zeners provide the clamp. Where is the series impedance?
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Old 21st July 2014, 04:25 AM   #6
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Use a coupling capacitor (if missing) at the initial testing. Remove it after everything is fine.

Gajanan Phadte
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Old 27th July 2014, 08:12 PM   #7
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Thanks guys, that helped a lot. I think I will go with the resistor in series with a cap, though I could also just no nothing, cause I certainly do not plan to short it by myself on purpose.

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That is an unlikely scenario
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