[Elecraft] Possible K2 sidetone mod

[Bill Noyce]

"dw" wrote:
> I noticed in the schematic that the side-tone output(U10B pre-amp) looks to
> be connected as a secondary input to AF-amp(U9 LM380).
> This makes me assume that side-tone volume is not fixed, but instead
> changes along with, and is a percentage of AF volume.

No, the side-tone volume is adjustable independent of the AF gain setting.
The AF gain pot is between the product detector and the LM380.
Sidetone volume is set through the menu, and is controlled via pin 1
of the DAC (U8) on the control board.
Sidetone enters the LM380 without going through the AF gain pot.
The LM380 output then goes directly to the headphones or speaker (see
sheet 1 of the RF board schematic).

    -- Bill, AB1AV
(Proud parent of a week-old K2, #6636)