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Battery PS for Class A power amp?

eastone

eastone

pfm Member
Have been reading around the Hiraga le Monstre this last week, and having also owned a battery DAC for some time, I got to wondering about this:

Is it possible to design a battery PS for a 25W Class A power amp?

My battery DAC is continuously ‘trickle-charged’ from mains and the battery itself supplies power to the DAC board.

The DAC runs happily all day and as long as it’s switched off overnight there are no issues.

Could a setup like that be scaled up? How big - physically - would it need to be?
 
Yeah it could be done. I designed such a thing years ago... for the hell of it as it were... I can see no point in battery power though. It would need to be something like the size of your M2.
 
Arkless Electronics said:
Yeah it could be done. I designed such a thing years ago... for the hell of it as it were... I can see no point in battery power though. It would need to be something like the size of your M2.
Click to expand...

That probably rules it out on WAF grounds then.

What does the battery power bring to the Le Monstre?

The rationale for the battery powered DAC makes sense to me, would you say that doesn’t translate to the needs of an amplifier? Or are you sceptical of battery power in general?
 
While battery powering a device may sometimes improve things, hum loop problems for instance, in general it would be better to use a better power supply design and connect the system correctly.

Sometimes it is suggested that batteries provide the ultimate low noise supply but actually batteries can produce a fair amount of noise.
 
would you say that doesn’t translate to the needs of an amplifier?
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An amplifier, yes, particularly a low-power amplifier. A 25W class A stereo amplifier, no. Low efficiency in class A means 100W, regardless of voltage, is required permanently just to keep the output devices functioning, and a power amp is usually more than just the output devices. 12V can only manage 18W (into 8 ohms) at absolute best. You could make it drive max. 6 ohm loads only... else you need more volts, and always plenty of current, so you might as well run it off the charger, i.e. a mains transformer, rectifier, smoothing cap, etc...
 
eastone said:
That probably rules it out on WAF grounds then.

What does the battery power bring to the Le Monstre?

The rationale for the battery powered DAC makes sense to me, would you say that doesn’t translate to the needs of an amplifier? Or are you sceptical of battery power in general?
Click to expand...

Any amplifier of any power rating can easily be powered by SLA batteries using the concept I came up with. The batteries should never need charging;)
I can think of no advantage to batteries other than where complete Galvanic isolation from the mains is required for some bizarre reason. The ONLY items of hi fi equipment that need really low noise power are phono stages, MC ones being about 10 - 20 times more sensitive still to this than MM ones. The best "Super-regulators" can beat batteries in every way other than providing 800A to a starter motor!
 
I ran a Naim preamp from lead acid batteries on the assumption it would be 'better' in some way, but it wasn't - it just sounded grainy and dull. I then developed a passionate hatred of switch mode PSUs so tried powering things like my Squeezebox Touch and RPi Streamers from lithium ion batter packs, even built timed overnight chargers and so on, but found that they didn't sound any better and when the voltages started to drop things became very odd indeed. I've now convinced myself that my current system just isn't sensitive to mains or RF interference and use whatever PSU I need.
 
Similar experience here
Decided to power my headphones amp via lithium battery to see if it made a difference over the wall wart
It didn't
Then tried an expensive linear supply instead
Big uplift in performance
 
I'll just add that there is no reason to suppose a battery supply will be anything but superb. But no more so than a good mains supply.
 
I built a huge linear PSU for my Sony Pro Walkman, a bit like a 6v HiCap - it was great, but in reality no greater than a smaller one, or the batteries. I then built a linear PSU for my Squeezebox Touch, maybe not HiCap spec, but pretty decent, and it made no discernible difference. Maybe a competent circuit design doesn't care how it's volts and amps are produced, and isn't upset by noise.
 
Something I have mentioned MANY times before and will now do so again is that many/most items have regulators built in and so the external PSU is largely irrelevant. It can be as crap as you like (within reason!) and probably won't make any difference.
This is the single most important thing to take into consideration for anyone wanting an "improved" external PSU but of course rarely gets mentioned in mags, in adverts etc as those making and advertising external supplies would obviously not want this to become "accepted wisdom"....
 
I always laugh when people swap to external linear psus to power something packed with switching regs.

Re batteries lifepo chemistry cells experience much lower voltage drop with use compared to other lithium chemistry types. I get six hours from my dac psu and it drops from 3.35v to 3.3v, a similar capacity 18650 unit dropped .2v in the same use.
 
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