Battery power vs Linear Power Supply…
Battery is the most quiet power? Not exactly.
Battery is the low noise of power supply, right? The most common assumption is that because they are a pure DC source they must have no AC noise. In theory…
Well, we live in REAL world. So let’s find more truth about battery.
The way battery produces power
Battery produce and provide the power through a chemical reaction. Every type of battery will have a slightly different chemical mixture that is used to generate power. Lithium Ion, SLA and others amount totally 150+ types of battery. You could find a LONG list here…
http://en.wikipedia.org/wiki/List_of_battery_types
As a battery drains, the amount of chemical compound available to produce electricity reduced. That means there’s an exponential decay on the amount of power a battery can produce. So a battery at 100% will have far more capability of producing fast transients, on opposite, battery will be much LESS ideal right after it start discharging, especially below its 50% capacity.
The even worse situation is: Depending on what type of manufacturing process and what is the stage of living cycle of that battery will create quite a different result.
So that is why you could hear people say: Use NEW battery, charge them close to 100% will make the sound better… And the funny thing is: You will make the new battery wore out sooner if you charge them more frequently.
Battery noise generation
Batteries have a substantial amount of high frequency ripple. This means there is a large AC noise to the DC output voltage. Battery’s chemical reaction will generate different types and frequencies of noise. The chemical reaction changes as the battery drains. That means the spectrum of noise changes as well. As a battery drains so does the output current and the output voltage. As these elements change the voltage will become less stable and the transient response slower.
So ultimately you are creating a non-constant source that has varying spectrums of noise, that is constantly changing, and produces the exact noise we want to get rid of.
Battery vs SMPS (switched-mode power supply)
Battery’s noise generated is usually very high frequency noise up into the Mega Hz or Giga Hz ranges. This is not only more difficult to filter, but it’s the exact noise we hate the most. The noise generated may be less than the noise filtered out compared to a SMPS, but it is still generating noise that is a challenge to compensate for.
So Battery is better than SMPS, but still not the best.
Recharging the Battery
No need to say, recharging is also a problem.
Automatic detection seems a good start, but that will also invoking chargers only begin trickle charging when a battery is below a certain charge level. Introducing AC noise into the battery’s path means the system has to filter out both AC noise and battery noise BOTH.
The other possible way is: Use manual switch recharging.
It’s better for noise generation, but no so good for users like me. Well, I hate to PAUSE or CHECK if my battery is still there when I listen to my favor 1.5-hour Mahler Symphony.
Even bigger issue here: Grounding
By using a battery you are no longer connected to ground in the same way. The whole device is either isolated to earth ground or direct depend on the computer’s ground other other devices’ ground. This means that shields become a noise “cage” and in addition, you end up easily having ground loops along cables and your system must find an alternative path for ground noise.
Trust me, finding these ground loop is NOT easy.
Linear Power Supply with Super Quiet DC circuit
Unlike battery, LPS can be built to a much higher bandwidth and much stabilized voltage and current capacity. Usually, a well-designed LPS can be considerably lower noise, higher bandwidth and more powerful supply than battery.
The only two issues for LPS are: Weight and Cost.
A good LPS is heavy. Seems no quick solution for the last 30 years. More wattage you need, more heavier it is. Especially the transformers and big Caps.
A good LPS is not cheap. Seems no quick solution for the next 10 years. I hope someday someone can have a good solution.
Battery is definitely better than SMPS and not too heavy and costly.
Well designed Linear Power Supply could be even better with two issues: Weight and Cost.
Email me when Larry Ho publishes or recommends stories