We have a winner!

Well I found at Hobby King (a Hong Kong retailer specialized in RC, Radio Control toys) a 800 mAh NiMH AAA for 0.80 USD (a low self discharge type even!) This makes a NiMH setup affordable: for 24$ I bought 30 AAA's to build two 18V packs. They will feed the two voltage regulators giving internal  ±16V.

Back to the drawing board

Well, je n'avais pas encore quitté la planche à dessin!

Researching DC-DC chips I learned that 85% efficiency is really hard to obtain: you have to optimize components (inductance, condensators, etc..). As low as 60% is not uncommon... (watch EEVblog #110 @30min)

This is not acceptable for a portable solution: carrying a bulky battery pack mainly to heat your case?

So I won't finally use a DC-DC converter for main voltage (we'll see for phantom): I'll stack LiPo or LiFe cells to go up to the ~16V dual voltage rail and regulate it off the Mackie board with a zener + emitter follower  regulator (as this one ?).

Power struggle

Sure the cheapest and simplest way to power the 402 is with disposable AA batteries: 16$ each shot of 12 hours. But after two or three iterations, rechargeable batteries are more economical and eco-friendly.

The toughest choice is between NiMH and LiFePO4. They both cost around 4-5 $ for each hour of autonomy. Prioritizing economy, I'd go with the 6.6V LFP pack with DC-DC converters.

Numbers

The design so far: one 26$ 4.5Ah 2S2P LiFePo4 Pack (6.6V OCV, 6.2V under load, delivering 28 Whr for 5 hr autonomy) and

three MC34063A used as step-up DC-DC converters and inverter:

• 6.2V -> + 17V@120mA
• 6.2V -> - 17V@120mA
• 6.2V -> + 48V

New Logo

Heavy

I plan to use Ponoko to build a new case too... this one is way too heavy.

Watts and why an inverter is not considered

• The wall adaptor itself is heating: 4.1W
• The two linear voltage regulators dissipate 2.1W (2 x 9V drop out @120mA )
• the mixer board finally uses 3.8W

So the board uses less than 40% of the total power.