[Elecraft] LINE OUT output too low?

[Jim Brown]

On Tue, 16 Dec 2008 13:16:28 -0800, Lyle Johnson wrote:

>On my K3, with the AFMODKT changes in place on the KIO3 board, and 
>driving an open circuit, I get up to 600 mV p-p of audio output if LINE 
>OUT is set to 100 while listening to a moderately strong signal with 
AGC 
>activated.  This of course depends on the signal strength, AGC settings 
>and so forth.

>A typical output level is less, since the LINE OUT is normally set much 
>lower than 100.

Consumer line level ins and outs are designed to handle levels 
corresonding to a sine wave of at least 1V. 1.4v peak, 2.8v p-p. 600mV 
p-p is 13 dB below that. So yes, I agree with the guy who says that the 
Line Out level is pretty low. Sorta like a hot mic level. :) 

Now, audio is dynamic, and except for CW, is almost never a sine wave. 
Rather, it's dynamic, with its level varying widely depending on 
program. The RMS value of unprocessed (no compression or limiting) 
speech and music is typically 14 dB below the peak level. But think of 
it this way -- the audio circuitry has to be able to handle ALL the 
voltage in the audio stream, including all the noise and QRM, and most 
of that noise is very "spiky" -- that is, their peaks are often 20-30 dB 
hotter than their average value, and those peaks can clip and create 
distortion long before the signal distorts, making the audio a real 
mess. Bottom line -- an audio output stage for a communications RX needs 
a lot of headroom. 

73,

Jim K9YC