With minor circuit changes, both the K3's speaker amplifier and line
outputs can provide lower IMD (intermodulation distortion) at higher
signal levels. We've been testing these changes for a couple of months,
and have already phased them into production.
These changes can easily be made to existing K3s. A kit of parts is
available (K3AFMDKT). All parts are leaded (not surface mount), and
full instructions are provided. See:
http://www.elecraft.com/order_form_parts.htm#K3%20Parts
Details
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SPEAKER AMP: The mod kit includes a very low-resistance RF choke for
use at RFC47 on the RF board. This improves speaker amplifier IMD by as
much as 25 dB at moderate to high AF GAIN settings by reducing the
voltage drop across RFC47 during signal peaks.
LINE OUT: The kit also includes smaller resistor values for R19 and
R20 on the KIO3 module. At present R19 and R20 are about 600 ohms,
while the replacements drop the resistance to around 50 ohms. The
smaller resistors increase the available voltage swing at the output of
the LINE OUT transformers, which improves IMD at higher signal levels.
These two changes are independent. For example, if you never use LINE
OUTs, you might want to do only the speaker amp modification.
73,
Wayne
N6KR
---
http://www.elecraft.com
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