[Elecraft] K3 Receive Audio

[Paul Christensen]

> It would be really neat if somehow Elecraft could product audiophile audio
> in the K3...

The K3 audio chipsets already offer quasi audiophile-grade performance for a 
single-supply rail device.  Taking the performance to the next level almost 
certainly requires the use of a bi-polar +/- 15 VDC supply to take advantage 
of really low noise op-amps (or discrete transistors), the ability to use DC 
servo control, and the use of a high-current temperature-compensated, 
complimentary-symmetry transistor pair at the output.  The result?  Super 
fast slew rates, ultra low noise & distortion, total elimination of audio 
coupling caps, and low damping factor -- all the elements needed for a true 
audiophile-grade amplifier.

In the alternative, one could simply purchase an audiophile-grade integrated 
amp and tap the audio at the DAC.  In the past, I've done this with '70s 
vintage Marantz and McIntosh equipment and attained excellent results.

Regarding the low-pass filter solution: I would want to critically listen to 
any active filter before permanently embedding it into a transceiver.  With 
yet another active stage of audio in the path, one problem may be cured 
while another is introduced -- like phase distortion at the knee of a sharp 
active filter.

Based on Jack Smith's data, I would be more inclined to try a simple 
6dB/octave passive circuit, using one R and one C.  At 12 kHz, the reduction 
in grunge would be between 8-10 dB and that may be just enough for other 
factors to mask the effect of the 12 kHz artifacts.

Paul, W9AC