Mini practice amp mod!

 Here's a little practice amp that was brought to me. It's a sponge bob theme 5W Wilkinson(JHS uk) guitar combo.... When it came in, it had a simple clean/crunch channel plus a terrible overdrive... So I wanted to make something useful out of it and maybe connect it to a bigger speaker cab!
 The amp is a solid state design and the preamp shares the same topology as a simple distortion pedal: 2 opamps and a pair of clipping diodes. In order to improve the sound of the overdrive channel, I reduced the bass frequencies that entered the circuit by placing a small 10nF capacitor in series with the input jack. That gave the amp a nice marshall-ish sound with less gain, less farty bass but more character overall.
 The next step was to increase the preamp gain to get a nice overdrive sound that would clean up once the "boost" switch is disengaged. The trick was to spot the opamps, examine their topology(e.g. inverting amp) and change a few resistors that control their gain. The result was astonishing! What an overdrive! I couldn't believe that a little amp like that could produce so much gain and lead!
  The weakest link was now the on board 4" speaker... So I placed an external speaker cab jack on the back of the chassis. The stereo jack disconnects the internal speaker once an external cab (4-16ohm) is connected. So I tested the amp by connecting it to a line6 2X12 "Vintage30 cab... What a massive sound!  What a volume level! I couldn't believe it.
  So that's what you can do with a small 20$ practice amp, just connect it to a larger speaker cab and apply a few mods, it will be worth the effort(and the tiny budget)!

Mod pics: