[Elecraft] [K3] AGC-OFF

[Eric Scace K3NA]

    Another factor at play is the sensitivity/efficiency of the headset.  For a 
given power level, different headsets will deliver different sound levels to the 
ear.

    In the case of my in-ear monitors, I found a significant amount of 
attenuation of the K3's headphone output was needed to:
    1)  Suppress the low-level broadband hiss of the K3's audio output amplifier 
to a level where I could not hear it.
    2)  Keep the maximum output level of the K3 (the point where the AF limiter 
kicks in) just below the "ouch" level for my ears.

    A different set of headphones required much less attenuation (5-10 dB) to 
meet (2) above and the hiss couldn't be heard even without the attenuator.

    A less efficient set of headphones might cause the operator to think the AF 
limiter was kicking in at way too low a level.  In this case, that pair of 
headphones might need a bit of audio amplification between the K3 and the earpiece.

    Regarding Barry's note about long-term comfort:  custom-fitted earpieces for 
in ear monitors worked for me... but this is a more costly solution (but bought 
only once - hi!).  I can wear the in ear monitors for 48 hours without even 
thinking about it.  I could never do that with ordinary headphones.  But 
everyone is different!

    In ear monitors that do not use custom-fitted ear pieces (i.e., use the 
rubbery or foam ear plugs) exert some pressure on the sides of the ear canal and 
can be annoying after 6-8 hours... at least for me.

— Eric K3NA

p.s.:  The contesting wiki has the information to which Barry referred:
<http://wiki.contesting.com/index.php/Setting_receiver_gain_controls>

on 2011 Jun 22 07:03 Barry N1EU said the following:
> Dave Hachadorian wrote:
>> There are two major problems with turning off the K3's AGC:
>>
>> 1.  There is very little dynamic headroom until the AF Limiter
>> causes severe distortion on even a moderately loud signal, even
>> if the AF Limiter setting is max.
>>
> That's not necessarily true, although probably true with most headphones on
> the market.  Assuming non-impaired hearing, the effective dynamic range will
> be highly dependent on your baseline (ambient) noise level and subsequent
> gain settings.  That's why K3NA strongly emphasized the need for high
> isolation headphone schemes in his original treatise on AGC-less contesting.
> The higher the isolation, the greater the ability to hear low audio levels,
> the lower the needed gain setting, and the greater the dynamic range before
> onset of distortion/clipping/painfully Loud levels.  With the highest
> isolation schemes, distortion/clipping rarely occurs while the weakest
> signals are still rendered audible.  I know that in-ear type phones ("ear
> buds") can be very successful in this regard, but long term comfort is
> suspect.  Every over-the-ear headphone I've tried so far that was touted as
> "high" or "extreme" isolation didn't quite deliver the degree of isolation
> that was hoped for, and weren't any better than my Sennheiser HD-280.  I'm
> still searching for more isolation without compromising comfort.
>
> 73, Barry N1EU