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Hi,

My name is Pawel and I am new on the forum. I will be building Millet MAX amplifier, but first I would like to discuss few things.

My project will be based on custom made PCB which will fit into case I own. The case is quite small and there is no space to fit 4 radiators for DB power transistors, but the whole case is made of aluminum with good heat dissipation abilities. In that point, two options came into my mind:

1. Build Millet MAX based on original DB design with 4 power transistors per channel. My concerns of this option is that transistors may overheat (I read somewhere on forum that temperature may rise above 70 Celcius deg.), but advantage is that I should find some space for slim but tall (up to 3cm) heatsinks.

2. Build regular Millet MAX with power transistors mounted to aluminum case. In this option I am worried that case may go hot and it will have affect on transistors bias settings. Also note that the voltage regulator will be mounted to the case and will be generating additional heat.

Please advise which option is better. I will be grateful for any comment or suggestion.

This may be the better option. The original Millett Hybrid used a diamond buffer with paralleled output transistors in each channel, for a total of 8 power transistors. You can go as low as about 20-30ma per transistor. That's low enough that the transistors themselves can reject the heat without need of heat sinks. Here's how the original diamond buffers for the Millett Hybrid did it:
http://diamondstar.de/dDB_overview.html
There is also a thread about the diamond buffers in the Millett Hybrid section that may give you more info. You'll have to run extra power resistors for each paralleled complementary pair, but it's a tried and true arrangement and should work well.
In the second case, this would be hard to do unless you lengthened the leads on all of the transistors and the voltage regulator. This would probably affect their operation in other ways besides heat - oscillation, perhps. I'd go with option #1.

After considering pros and cons for both options I will definitely go with #1. Original dDB project will give me more free space in the case, and what’s more important, PCB track routing will me much simpler and cleaner (two layers with top layer filled with ground plane).

Yesterday I receive parts from Beezar.com store. After finding some free time I will try to fit all components onto PCB.

Pawel