[Elecraft] k2 audio power

[Jim Brown]

On Mon, 14 Jun 2004 9:20:37 -0400, edfinn1 at verizon.net wrote:

>When we used a second op for logging and "Y'ed" the headphones it was definitely at full throttle. 

The audio system in a K2 is entirely adequate for serious contesting. 

I suspect you have made a poor choice of headphones. I own several good pairs
of headphones, and all produce plenty of level when used with the K2. What
you are looking for is a good combination of relatively high voltage
sensitivity and moderate load impedance (100-250 ohms). It also helps if both
sets of headphones are similar in this regard.  

The K2 headphone output has resistors in series to limit the output level. If
you hang a low impedance load on it, you lose a lot of level. Many cheap
consumer headphones are on the order of 8-20 ohms, and that is most likely
your problem. 

The headphones I own and have used with the K2 are:  

Etymotic Research ER4S and ER4P -- these are tiny in-ear earphones, super for
lightweight portable operation, and have the additional advantage of
excellent isolation from outside noise. The ER4S's are 100 ohms, 108 dBSPL
for 1 volt input; the ER4P's are 27 ohms, 108 dBSPL for 0.25 volts. These are
precision professional units and aren't cheap, but the company makes a lower
cost version (about $100 list) that should be fine for ham radio.  Shure also
makes a product like this for the in-ear monitors that they sell to
musicians. 

Sony MDR-7506 and MDR-V6 -- these are standard, large, closed headphones with
nice soft cushions, work for for long operating sessions.  These sell in the
$100 range.  Sony, being Sony, doesn't put impedance and sensitivity specs on
the data sheets that I have, but I suspect they are in the same range as the
ER4S's. 

Technics RP-HT220 -- similar to the Sony units, not as nice, no longer made.

All combinations of two pairs of these headphones are plenty loud enough when
both are plugged into the K2 at the same time.   

AKG and Sennheiser also make good headphones of this type.  When translating
sensitivity specs, remember that dB is 20 log (V2/V1) and 10 log (P2/P1).  So
the ER4S and ER4P have the same power sensitivity. 

Jim Brown  K9YC
Audio Systems Group, Inc.
Chicago
http://audiosystemsgroup.com