[Elecraft] BHI HP-200 and other headphones

[Paul Christensen]

> I don't know about the big Icoms or their new 7600 and would be interested 
> to hear from anybody who has one.

The Icom '7700 and '7800 are nearly hiss-free at the minimum AF setting.  My 
K3 is totally silent using Sony MDR-7506 and Bose Tri-Port headphones.

There's generally only one time when I hear hiss from my K3 -- and that's 
right after a F/W flash.  I have now become accustomed to turning power off 
after the flash is complete, then wait > 5 seconds and re-start.  If I do 
not wait ~ 5 seconds, I oftentimes hear slight latent hiss.  But it's cured 
100% by this off-on sequence.

The rig tried here with the highest latent AF hiss was the TS-950.  In fact, 
the hiss level was so high that VS designed a special relay "cut off" 
circuit to kill the hiss (and all audio) when the AF control is turned full 
CCW.

On the TS-950, the hiss comes into play when the AF control is just slightly 
advanced.  IOW, at full CCW, a relay opens up the headphone line.  And when 
the AF control is advanced, the relay closes and the hiss becomes apparent. 
That's the first attempt I've seen by a manufacturer to mask a design 
problem by using a relay as an audio 'knife switch."

Anyone owning a TS-950 can try this test without wearing headphones:  Turn 
the AF control CCW and repeatedly advance and retard the control slightly. 
Hear that relaying clicking inside the cabinet?  That relay's sole purpose 
is to mask hiss.

Paul, W9AC