1- External speaker jack
2- More powerfull power transformer. The unrated original unit (probably 1A) was replaced by a 2A transformer.
3- Original 14W TDA2030 chipamp replaced by a 20W LM1875
4- Original distortion circuit's red LEDs replaced by 1n34A germanium diodes
5- Original OPAMPS replaced by JRC4558DD mounted on sockets for chip swapping on the go.
The Pathifinder 10 is a great little practice amplifier that you'll find to be a wolf in sheeps clothing...
The miniature stock speaker does not make justice to the circuit's capabilities and you won't help a very sincere WTF! when you first listen to this little box roar through a proper 12 inch driver. So the first and most cost effective mod is the external speaker jack socket.
Mine is wired in the usual fashion in such cases: Using a switched jack. Whenever an external speaker in connected to the jack, the onboard driver is shut off (thankfully).
As for the electronic mods the changes are somewhat less noticeable, nevertheless very rewarding:
- The 4558s rounded things of a little bit in what concearns the high frequencies;
- The distortion is smoother after the replacement of the original red leds by 1N34A germaniums in the clipping circuit;
- At max output there may be an increase in undistorted sound volume, courtesy of the higher capacity transformer and LM1875 chip in place of the original TDA2030 and tiny transformer.
Although this may be just my ears playing me I've had very good previous experiences in Hi-Fi DIY with the 1875 and the general opinion out thereregards the 1875 as a generaly "better" chip than the 2030, being more dynamically responsive
More on this work in progress later