[Boatanchors] Best Headphone Impedance for SX-42

[Richard Knoppow]

----- Original Message ----- 
From: "Frederick Bray" <fwbray at mminternet.com>
To: <Boatanchors at mailman.qth.net>
Sent: Sunday, July 14, 2013 7:43 PM
Subject: [Boatanchors] Best Headphone Impedance for SX-42


> What's the best impedance for a set of headphones to use 
> with an SX-42?  I looked at the manual, but I didn't 
> notice any specifications.
>
> I am thinking that it might be either 2000 or 600 ohms, 
> but I could easily be wrong.
>
> Thanks.
>
> Fred
> KE6CD

     The headphone jack is connected to a rather high 
impedance source through a 0.02uf capacitor.  It appears to 
be meant for high impedance magnetic headphones.  Typically 
the impedance of magnetic phones is about five times or more 
the DC resistance so a pair of 2K DC phones will be around 
10K to 20K. These will work fine but not be very hi-fi.  600 
ohm phones may work but may be low in volume and deficient 
in bass.  I think the phone jack was intended mainly for CW. 
Hi-fi phones can be fed from the speaker terminals in the 
back but use a pad to lower the power.  That can also help 
to provide an impedance match between the 500 ohm terminals 
and modern phones which are around 8 to 30 ohms.
     The headphone jack is driven from one plate of the 
phase splitter, the switch in the jack disconnects and 
grounds the output stage grids.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com