Icom IC-736
Less white noise
As almost all modern rigs also IC-736 suffers from one little technical flaw. While the whole TCVR is composed from quality low-noise semiconductors, somehow nobody cares about the very last piece of the chain. That is the final AF stage. It is usually TDA2003 integrated circuit or an equivalent. The final AF amplifier is usually set to a high gain and no measure is taken to reduce the hiss it produces. As the amplifier is after the AF volume regulator this hiss goes to the speaker in full strength even if AF gain is rotated fully CCW. It is mainly disturbing when one uses a quality headphones.
The following modification reduces the white noise (hiss) higher than about 3 kHz:
Top view of the MAIN board with added parts:
The extra parts are soldered on the pins of the uPC1241H integrated circuit at the bottom side of the MAIN PCB.
The preamplifier consisting of Q49 serves as a low-pass filter as the simulation showed. It also possible to lower a bit the threshould frequency here:
