[Boatanchors] Headphone Impedance Matching

[Richard Knoppow]

-----Original Message-----
>From: "David C. Hallam" <dhallam at knology.net>
>Sent: Dec 4, 2013 9:33 AM
>To: Boatanchors at mailman.qth.net
>Subject: [Boatanchors] Headphone Impedance Matching
>
>I picked up a Lincoln headset/boom mike set a few days ago.  The box is 
>marked Telex but there is a Lincoln sticker and part number on one end 
>of the box.  I found this set listed in a 1968 Allied Radio catalog with 
>the specs.  The microphone is a high impedance ceramic element and the 
>headphones are 2000 ohm impedance.  The high impedance microphone is OK, 
>but what would be the best way to match the 2000 ohm to my 75S-3, or do 
>I even have to worry about it?  I have some 8 to 600 ohm matching 
>transformers, but nothing to match to 2000 ohm.
>
>David
>KW4DH
>
     High impedance phones will work fine even if the phone output is at speaker impedance.  The mis-match will lower the level from the phones but remember the phones are right against your ears and would be very loud if matched. BTW it is common for the "impedance" given for headphones to be the DC resistance, the actual impedance is usually very much higher typically about five to seven times. Check the resistance of the phones to see what it is.  If the _impedance_ is actually 2K the DC resistance will be about 400 ohms.