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Resistor setup for integrated amp & headphones?
Resistor setup for integrated amp & headphones?
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Old 17th November 2008, 06:31 AM   #1
Eclair is offline Eclair  United States
diyAudio Member
Join Date: Aug 2007
Default Resistor setup for integrated amp & headphones?

I'm a novice and was wondering if someone could help me out a little bit. I've got a SE pentode tube integrated amp (12AX7 feeding a EL84 per channel) that outputs 5 watts (8 ohms and 16 ohms outputs) per channel. I'm thinking of setting up some resistors on the outputs so I can use my headphones with the amp. The headphones have impedances of 32 ohms and 50 ohms. I'm not exactly sure how to calculate what resistors I need and the best way to set them up. Are there any drawbacks (other than not being able to use much of the volume pot at all) to using the resistors? Or is there a better option? Thanks for the help everyone!
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Old 21st November 2008, 12:28 AM   #2
Robert McLean is offline Robert McLean  Canada
diyAudio Member
Join Date: May 2005
Location: Stittsville, Ontario, Canada
A bit of algebra and ohms law and some equations could be written out, but so much depends on how sensitive your ears are, the sensitivity of your headphones ( nver mind their impedance) , how loud you like your music etc, So I wouldnt bother calculating resistors.

You want to present to your amp about the same impedance as it would see if it were connected to your headphones.

So just get a 50 ohm 10 watt resistor, and a 1K or maybe 10K pot. Connect the pot in series with your headphone socket. Put the 50 ohm resistor in parallel with the total series connection of headphone and pot. In other words you have 50 ohms in parallel with 1032 or 1050 ohms depending on which phones you use. Which is near enough 50 ohms total seen by the amp.

Set your amps volume pot to where you like it for normal listening with speakers. Adjust the 1K or 10K pot to get the volume you like from the headphones. If you like you can measure the pot resistance and replace with a resistor. If you dont have pots then just try a few resistors say 100 ohm to 50K to see what works best.

This way you will be able to use just as much of your amps volume control range as you want.
Robert McLean
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