[Elecraft] K3S audio board for K3 upgrade?

[Jim Brown]

On Mon,3/21/2016 12:46 PM, Jim Bolit wrote:
> The TS-480 just sounds better to these ears.
>
> Oh, and it is magic........

Look at the RX current drain on both radios. A K3 comes in at about 1A, 
1.1A with the new KXV3B preamp or the old PR6 installed. This is the 
result of Wayne's philosophy of optimizing for portable/battery 
operation, and it leaves the speaker output stage a bit low on current 
for those who want/need it loud.

And it's more than frequency response. There's analog distortion, both 
in the electronics and the loudspeaker. And there are distortions 
associated with A/D and D/A conversions, and the number of bits used.

Early production K3s (2008-9) had the design error of placing 600 ohm 
resistance between the line output stage and the transformer, which 
caused the transformer to produce distortion, even at pretty low signal 
levels. Pro audio circuits have not used 600 ohm inputs and outputs for 
at least 40 years, but too many manufacturers of ham gear (and even 
broadcast transmitters) never got the memo. Pro output stages are about 
100 ohms, that value chosen to prevent instability when the stage drives 
the capacitance of a long line, and pro inputs are around 10K (so that 
the output stage driving doesn't have to provide current.

73, Jim K9YC