Creating a headphone amp out of existing 2A3 amp

arnoldc · 28th July 2004, 05:32 AM

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!

MIKET · 28th July 2004, 09:21 AM

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.

Sch3mat1c · 28th July 2004, 02:20 PM

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...

Tim

arnoldc · 29th July 2004, 12:08 AM

ok, guys so i'll start with the resistor values recommended.

probably a switch too for amp/headamp operation.

cheers!

arnoldc · 29th July 2004, 08:50 AM

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.

Frank Berry · 29th July 2004, 08:59 AM

"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.

Sch3mat1c · 29th July 2004, 03:10 PM

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.

Tim

arnoldc · 30th July 2004, 12:10 AM

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?

fdegrove · 30th July 2004, 01:06 AM

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,

arnoldc · 30th July 2004, 02:53 AM

thanks guys

28th July 2004, 05:32 AM	#1
arnoldc diyAudio Member Join Date: Apr 2003 Location: Makati	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!

28th July 2004, 09:21 AM	#2
MIKET diyAudio Member Join Date: Jul 2003 Location: Maine	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.

28th July 2004, 02:20 PM	#3
Sch3mat1c diyAudio Member Join Date: Jan 2003 Location: Milwaukee, WI	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... Tim __________________ Seven Transistor Labs Projects and Resources

29th July 2004, 08:59 AM	#6
Frank Berry diyAudio Member Join Date: Sep 2003 Location: Midland, Michigan	"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. __________________ Frank

29th July 2004, 03:10 PM	#7
Sch3mat1c diyAudio Member Join Date: Jan 2003 Location: Milwaukee, WI	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. Tim __________________ Seven Transistor Labs Projects and Resources


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29th July 2004, 12:08 AM	#4
arnoldc diyAudio Member Join Date: Apr 2003 Location: Makati	ok, guys so i'll start with the resistor values recommended. probably a switch too for amp/headamp operation. cheers!

29th July 2004, 08:50 AM	#5
arnoldc diyAudio Member Join Date: Apr 2003 Location: Makati	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.

30th July 2004, 12:10 AM	#8
arnoldc diyAudio Member Join Date: Apr 2003 Location: Makati	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?

30th July 2004, 02:53 AM	#10
arnoldc diyAudio Member Join Date: Apr 2003 Location: Makati	thanks guys

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