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DPDT switch to disconnect headphones on power down?
DPDT switch to disconnect headphones on power down?
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Old 14th September 2011, 05:28 PM   #1
nereis is offline nereis
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Default DPDT switch to disconnect headphones on power down?

I have this idea about using a DPDT break-before-make toggle, not sure how well it would work... I don't think I've seen this done anywhere.

Since headphones return at the TRS jack with a common ground, would it be beneficial to connect the common pin to a DPDT power switch so that when the amp powers off, the headphones are then seen as open circuit and any imbalance in the power rail / output cap discharge would have no effect on the phones, while also eliminating the power-down pop? This would however do nothing for power up pop though..

The switch should have sufficient current handling and be low resistance, I suppose this is not an issue with headphones. If the power switch needs to disconnect 2 rails then a 3PDT switch may be employed.
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Old 14th September 2011, 06:08 PM   #2
simon7000 is offline simon7000  United States
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No, The leakage current from the AC power circuit would leak into the headphone circuit. Headphone jacks normally have current limiting resistors to prevent any damge due to transients.
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Old 14th September 2011, 06:15 PM   #3
nereis is offline nereis
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As regard to AC, this wouldn't be an issue if the power switch is cutting DC then?
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Old 14th September 2011, 06:40 PM   #4
simon7000 is offline simon7000  United States
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Less than 24 volts DC would be okay.
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Old 14th September 2011, 06:49 PM   #5
nereis is offline nereis
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That's rather interesting... if the DC supply is sufficiently clean there would be little alternating field within the switch to induce audible current on a nearby switch.

Are you suggesting that having 24VDC+ close by might induce DC offset?
I find this a bit challenging to think of considering how low impedance loads headphones tend to be, but what do I know...
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Old 14th September 2011, 08:10 PM   #6
simon7000 is offline simon7000  United States
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24 Volts is the limit set by safety codes.
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Old 14th September 2011, 08:31 PM   #7
nereis is offline nereis
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Thanks for clearing that up!

http://www.nkkswitches.com/pdf/MtogglesBushing.pdf
The switch in question is rated for 30VDC, but I guess it's better to not run it to its rating.
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