[Elecraft] Headphone output levels on the K2?

[David Woolley]

Steve Kallal wrote:
> I have a requirement that my rigs have relatively high audio output wo/
> distortion from the headphone jack. I have a moderate hearing loss, about 45
> db down especially in the speech region. The audiologists calls that

I've had that sort of loss in one ear since childhood and some in the 
other, and I did get prescribed an aid as a child, although I haven't 
been very good at using it.

> 
> I think the best thing about a kit like the K2 is that adding a small audio
> stage internally before the headphone jack doesn't ruin the rig. But I would
> hope that won't be necessary.

As others have said, you could also reduce the series resistors on the 
headphone output, although you might need to modify the shunt capacitors 
as well; I'm not sure of the function of these (could be audio low pass, 
or could be RF pickup blocking).

You won't get 45dB of gain without transformer coupling, as I don't 
think there is enough power supply voltage for that.

Also, noise cancelling headphones normally have an amplifier, so, in 
cancelling mode, increase the wanted as well as suppressing unwanted 
sound.  Mine are vulnerable to GSM mobile phone signals, so might have 
RF pickup problems.  (My interest in Elecraft is to try getting back 
into amateur radio, so I haven't used them near amateur transmissions, yet.)

> Also I don't wear my hearing aids with headphones because of feeback. I went
> with behind the ear hearing aids. Maybe a heaphones with larger deeper cups
> would help.

Most hearing aids, including state supplied ones, in the UK, have a "T" 
setting, which uses an induction loop pickup, rather than a microphone. 
  You can use this with headphones with reasonable field leakage, or 
special, silent, ones.  I don't know how sensitive they are to RF pickup.

For some, you can get "shoes" that allow them to be connected to normal 
domestic audio equipment.  I'm not sure if these couple acoustically, or 
whether they match a connector on the aid.

Theoretically, you could also get headphones with hearing aid type ear 
moulds.  In the past, when hearing aids had output transducers that 
clipped directly onto the earmould, the clip was the same as used in 
professional head sets.  Nowadays, they couple acoustically, with a 
plastic tube, so there might not be direct compatibility.
> 
> I welcome comments from those who are familiar with the headphone output

Unfortunately, I've not built it far enough to hear more than sidetone yet.


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David Woolley
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