Conclusion:

Due to the house move, this project was built without the full resources of the workshop and the hi-fi, but despite this, I was pleased with the design and construction. I'll only be able to make a full assessment of the absolute sound quality and perhaps improve things once I've got my reference ATC's out of storage...

As a finished product, this amplifier is seriously cute, and has elicited lots of positive reaction from friends and colleagues. The design details, including the hiding of the connectors and the use of birch ply make for an interesting look.

The LM4780 runs slightly warmer than the LM3875 because it has a higher bias in the output stage. Some people report that the LM4780 runs very hot, but the problem isn't as bad as you might think. If you have a hot-running parallel design, study the datasheet and ask yourself if you really can omit everything - minimalism is good, but within limits!

The quiescent current is around 50mA per channel - compared to around 17mA for the LM3875. With 30V supply rails, this translates to 6 watts of heat with no signal - the case runs at around 12-15 degrees C above ambient under no-signal conditions. I quite like this heat - it reminds me of my old Musical Fidelity A1... Fortunately, because music has a high PMR (peak to mean ratio), moderate use doesn't raise the temperature much - the large amount of aluminum present in the chassis helps here as it causes a decent amount of thermal inertia. The overhanging top panel also helps, despite only being 1mm thick - what matters for heatsinking is surface area, and although it isn't optimally aligned for good convection, you can feel a healthy current of warm air rising from under the rear of the panel. The thermal sensor will mute the amplifier well before the chip has reached unsafe limits, ensuring reliable long-term operation...