[Elecraft] Optimizing K3 Mini Speaker Gain with RemoteRig

[Paul Christensen]

> "Note that the default RemoteRig setting in the control RRC gives a loud 
CW sidetone. This can be easily lowered by going into the keyer settings 
and change "side tone -db" to another number."

As discussed in my post, a change in RRC sidetone level also affects
sidetone level in the headphones.  Reducing the sidetone level alone can
create an imbalance between speaker and headphone audio -- enough to be an
annoyance for me.  In my case, if I reduce RRC CW sidetone level to
eliminate speaker blasting, the sidetone level in headphones is too low.
Moreover, reducing RRC CODEC gain to avoid speaker blasting results in
digital artifacts in some sensitive headphones.  

This may not bother others -- and RRC menu changes may be an acceptable
compromise to some users.  But the resistor change significantly optimizes
and rebalances level between the two output stages when using the K3 Mini
with the RemoteRig RRC.  The end result is a rebalancing of receive audio
and sidetone level between speaker and headphones with no addition of
digital noise or other artifacts.  

Paul, W9AC 


-----Original Message-----
From: Paul Christensen [mailto:w9ac at arrl.net] 
Sent: Sunday, January 17, 2016 11:10 AM
To: 'elecraft at mailman.qth.net' <elecraft at mailman.qth.net>
Subject: Optimizing K3 Mini Speaker Gain with RemoteRig

Since last May, I've been using a K3 Mini with RemoteRig.  Apart from one
anomaly, operating the K3 Mini has been a great experience.  However, when
using RemoteRig, K3 mini speaker audio is extremely loud and the CW
side-tone is even louder.  However, receive audio and side-tone level in
headphones is excellent.  If one tries to reduce CODEC gain in the
RemoteRig, then headphone audio suffers and low-level digital artifacts
start becoming detectable.  

The fix inside the K3 Mini involves replacement of two (2) "603" size SMT
resistors at R39 and R40.  The stock values are 15K.  I changed these to
100K.  This results in a computed gain close to zero (Av = 1) for the
speaker amp and allows it to be used as a current driver for the speakers.
After the modification, speaker audio approximates headphone level without
excessively loud receive audio and side-tone.  This change may affect
operation of the K3 Mini when a RemoteRig is not used in some applications.
However, probably most K3 Mini owners use theirs with a RemoteRig.

Suggestion to Elecraft:  if there was a design reason for so much speaker
gain, consider placing 0.100" headers on a future PCB revision to allow
jumper selection of either the 15K resistors or 100K.  

Many thanks for a great product.

Paul, W9AC