[R-390] 600-ohm phones?

[2002tii]

Tim wrote:

>What 600-ohm headphones are out there? I've got a number of older 
>military radios that evidently were built to drive 600 ohm phones. 
>Some sort-of drive 8-ohm modern phones but have some problems with 
>level or matching or something.

I am not aware of any commonly-available phones that have impedances 
as low as 8 ohms.  Most are in the 200-350 ohm range.  Of course, if 
you drive both channels of 200-350 ohm stereo phones in parallel, the 
load would be 100-175 ohms.  The lowest impedance phones I know of 
currently are some new Denon phones at 25 ohms (AH-D2000 and 
AH-D5000).  Koss has (or had) some 60 ohm phones.

A small filament transformer, say 20-24 volt secondary (for 120 volt 
primary), with the radio hooked to the primary and the phones to the 
secondary, works great.  That is more step-down than you need for 
200-400 ohm phones -- a 50 or even 75 volt secondary would be 
sufficient, if you have a problem with low output from a 24 volt 
secondary.  This works for speakers, too -- and it even tests way, 
way better than your boatanchors sound.  Before I went exclusively to 
line level outputs feeding a preamp, I used a homemade speaker with 
an 8 ohm driver and a 15 volt power transformer to listen to my 600 ohm radios.

For that matter, I have had good success using the two, 300 ohm 
elements of my Sennheiser HD-650s in parallel (150 ohm load) directly 
from the 600 ohm speaker output of boatanchors.  Not that most folks 
would buy the 650s to listen to boatanchors, but I have them around....

Best regards,

Don