Headphone Choice for Paramounts?

[casanis]

The resistor - 120 ohms, 150 ohms, or whatever - won't make a lot of difference with the 300 ohm 650s. The resistor is mostly effective for low-impedance phones (like 40 ohm Grados). If you need to attenuate the headphone signal, it's better to make up an L-pad - two resistors per channel. That way you can retain a lower output impedance too.

What values to start toying with?

I've taken a look online to find an L-pad calculator:

http://www.sengpielaudio.com/calculator-Lpad.htm

Thoughts on where to begin?

[Grainger49]

Since my high frequencies are rolled off I am ordering some non-inductive Mills resistors to pad the super tweeters I have on my Orcas. 

Any inductive resistor will not only block highs but also mess with the phase of them.  Many film (metal or carbon) resistors have a spiral trim and are somewhat inductive.  The Mils resistors are perfect for me.

[Paul Birkeland]

Thoughts on where to begin?

You could try a variable L-pad. 

[Paul Joppa]

...Thoughts on where to begin?

First determine what your requirements are. Any attenuator will reduce the peak signal level available, as well as the noise - you want a balance between those factors.

Radio Shack still lists a 25-ohm rheostat, which you can wire up as a potentiometer to feed the headphones. When you find the setting that works best, you can measure the resistances to determine the attenuation you want - or just keep the rheostat, it's wirewound and should sound decent.

BTW, very few resistors of any type or value have enough inductance to affect the treble. But it's difficult to find specifications for resistor inductance, making this hard to evaluate.

[casanis]

Update:

The HD650's sound VERY NICE with the Paramounts/Foreplay III combination.

Incredibly low noise floor / hum...almost non-existent.

I ended up installing a toggle switch on each Paramount to select between speaker o/p and the cans (hardwired). No longer required to unplug bananas for speakers to switch to late night headphone listening. ...I also put the 150ohm resistors in line, which took just enough "hotness" off the cans.

New ear foams and blue dragon cabling on the way for the 650's.

Thanks all for the input.