modifying amp for use with headphones

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Disabled Account
Joined 2013
Hi!
I need some help. I bought a diy e188cc tube preamp/ lm1875 chipamp hybrid some time ago and I`m very pleased with it.
However, I`m looking to move to a headphone system and the amp is made for use with speakers only.
I really love the sound it has and thought I`d just pop some resistors on the speaker out and plug in the headphones.
I`d love to use amtrans resistors but they come in 2W max.

Are the 2W enough? The lm1875 are around 20W per channel.
Also the tube preamp has (a lot of) noise - can it hurt the headphones?
I was thinking on borrowing Audeze LCD3 just to hear how it sounds and I really really really don`t want them to blow up :)

Thank you :D
 
Hi,

The IEC standard for a headphone output is 120 ohms.

To do that you only need two 120R resistors in the plus.

It gives a broad compatibility, e.g. 600R phones will
receive near full voltage, but limit current due to
the total 720R load. low impedance like 8R will
only receive limited voltage, 1/16 of output.

However due to modern portable devices many
headphones are not now optimised for 120R.

It gets complicated, but if you want lower output
impedance you need a L-pad arrangement. 33R
in series and 3.0R parallel will give a low output
impedance suitable for many modern headphones
around 32R, but would be a disaster for old 600R
headphones.

rgds, sreten.
 
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Disabled Account
Joined 2013
Abraxalito, sounds great, but to be prefectly honest, I`m not comfortable with building a step-down transformer. I don`t even know what a step-down transformer is.
Sreten, thanks a lot for the info, I think I`ll do them all and hear what`s best - various loads on plusses from 120R to 1k, and I`ll try the 33R / 3R combo.
Again, just to be clear, I need to put a 33R on the plus and after that connect the plus and minus with a 3R
Thank you all for the help :)
 
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