Here is a easy-to-do mod to improve tx audio dramatically!
In addition to my mod from 17-12-2002 here´s the ultimate way to improve tx audio
Problem: tx audio sounds muffled and is not loud enough. Reason is too less mic amplification and therefore too less average fm deviation and too much low pass effect in the mic amp stages.
Background: The mic signal is amplified, then af-clipped and sent through a low-pass filter (all in op-amp IC3 on logic board). The af-clipped signal is then applied to the D/A converter (IC 5 on main board), where the deviation is set depending on wide or narrow operation. There is no way of alignment provided by Icom.
Modification:
- Locate IC 3 and nearby C79, C50 and R103 on the pictures of the logic board and the board layout.
- Replace C79 (220p) with 68p and C50 (220p) with 150p
- Replace R 103 (150k) with 330k
- That´s all!
- Effect is much more average deviation without changing max. deviation and a better frequency range.
  
Click to enlarge the picture.
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