headphones/line level on speaker output |
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amlu
Young Croc Joined: 30 November 2009 Location: london Status: Offline Points: 740 |
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Posted: 25 June 2018 at 8:47pm |
Hiya
how would you do about hooking up pair of headphones or a preamplifier into speaker output? for monitoring and experimentation purposes. got some class d modules in here and they dont like oscilloscopes, no common ground between power and speakers. and too much messing around. i would like to hook the amp to pair of 8ohms dummy load and listen whats up in my headphones... amps in question are sure electronics, wattage 50-500? chinese watts. thats what i want to check. pair audio transformers? plus a wire wound pots may do the job? or some other solutions? thanks, adam. |
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I-shen Soundboy
Registered User Joined: 21 December 2016 Location: Big Smoke Status: Offline Points: 375 |
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Koss electrostatic headphones?
Designed to run straight off the speaker terminals of the amplifier, and they need a pretty beefy amplifier too. Only problem is finding some cheap, but they've been making them for fifty years, so plenty about.
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Earplug
Old Croc Joined: 03 January 2012 Location: Europe Status: Offline Points: 7216 |
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Just use a dropper resister of around 500 ohm, 1W or 2W in series with the headphones. A wirewound pot in there is also a good idea in order to compensate for the different impedences you get with headphones.
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Earplugs Are For Wimps!
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APW
Young Croc Joined: 13 November 2012 Location: Kent, UK Status: Offline Points: 1174 |
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Hold on to your horses..... It’s a class d amp and possibly running as a full bridge, and as such its outputs will be ‘plus’ and ‘minus’ as opposed to ‘plus’ and 0V (ground) for a non-bridged amp, if this is the case you will have to transformer couple the headphones/amp as the speaker outputs on the amp won’t be referenced to 0V (ground) and will probably have a DC offset that’s about half the amps supply rail, however the outputs won’t have a dc offset relative to each other. |
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Earplug
Old Croc Joined: 03 January 2012 Location: Europe Status: Offline Points: 7216 |
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Yes, but as long as you don´t earth reference anything off the amp - ie as would happen with an oscilloscope, you´ll be ok. |
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Earplugs Are For Wimps!
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APW
Young Croc Joined: 13 November 2012 Location: Kent, UK Status: Offline Points: 1174 |
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Amlu wants to connect a pair dummy loads and then monitor/listen to the amps output on headphones, headphones have a common 0V connection for both left and right channels, how the hell do you get a common '0V' for the headphones without a pair of transformers? Of course it’s possible to monitor one channel at a time using just a dropper resistor but not both without transformers due to the shared '0V' connection on the headphones. |
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Earplug
Old Croc Joined: 03 January 2012 Location: Europe Status: Offline Points: 7216 |
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Ok - I saw 'Class D modules' and assumed mono. For monitoring that could be better anyway. Or have a switch to change over from one channel to the other. Easy then to compare the output of the modules as both ears would be getting the same signal. |
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Earplugs Are For Wimps!
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