20 Watt Audio Amplifier

This is a more recent project, I completed it around the end of March 2009. It is rather more polished and complete than any of my previous projects and so it shows that my level of skill has somewhat improved.

The whole idea started with an impulse buy of two LM1875 amplifiers, after doing some research online, I found some communities centred around making high performance chip amps with this part being featured as a popular design element. A lot of these improvements involved reducing the length of the signal path by using "Ugly Bug" point-to-point construction, a lot of power supply filtering tricks, such as snubber capacitors, very heavy shielding (A baking pan! Brilliant!) and diverting noise from signal ground. I used a little bit of everything, except point-to point, because it's ugly and gives me a headache, and I managed to pull it off with the reference circuit/PCB design from the data sheet!

Using small value capacitors on the rectifier bridge was really worth it, there was no output ripple from the power supply when I measured it with my trusty scope. The power transformer is double insulated and the chassis is a plastic box so no mains earth is required which also eliminates that nasty ground loop business that often adds the requirement for extra isolation circuitry.


Stacks Image 0
Stacks Image 1
Stacks Image 2