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Old 28th July 2004, 05:32 AM   #1
arnoldc is offline arnoldc  Philippines
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Default Creating a headphone amp out of existing 2A3 amp

hi guys,

what will it take to add headphone capability to a 2A3 SET amp? Is it going to be another transformer?

any information on how to do so will be much appreciated as usual.

cheers!
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Old 28th July 2004, 09:21 AM   #2
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Default Adding Headphones

You can just place a series resistor across the output of the amp to each earpiece.If you start at 470 ohms for the series resistor you can get the general idea. I am asuming these are the 200-600 ohm variety. If you are using the amplifier on low impeadance headphones then the resistor is even more important as you don't want to drive 2-4 watts directly into your ears.
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Old 28th July 2004, 02:20 PM   #3
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Duh, or just don't run the thing at 2W. (Like it has the voltage output to do that into >50 ohms anyway.) They make these wonderful devices known as volume controls...

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Old 29th July 2004, 12:08 AM   #4
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ok, guys so i'll start with the resistor values recommended.

probably a switch too for amp/headamp operation.

cheers!
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Old 29th July 2004, 08:50 AM   #5
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follow up question -

shouldn't i be concerned about the "load" the OPT will see? that will be the series resistor + the headphone impedance, right?

that's far off from the 8 ohm load it normally sees as the speaker.
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Old 29th July 2004, 08:59 AM   #6
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"shouldn't i be concerned about the "load" the OPT will see?"

Right you are. I'd put an 8 ohm resistor across the output of each amp.
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Old 29th July 2004, 03:10 PM   #7
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Not necessary unless it has NFB and is prone to instability. A higher load will produce greater linearity in the triode, not like you'll notice a darned bit of distortion at .01% of maximum power output.

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Old 30th July 2004, 12:10 AM   #8
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no NFB guys

it's a JE Labs 2A3 using MagneQuest DS-025 OPT

so, as a safety precaution, shall i put the 8 ohm resistor across?
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Old 30th July 2004, 01:06 AM   #9
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Hi,

Quote:
so, as a safety precaution, shall i put the 8 ohm resistor across?
There really is no need for it but you can try it for yourself.

Cheers,
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Old 30th July 2004, 02:53 AM   #10
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thanks guys
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