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It seems like a lot of money is spent on the power supply. Small Bluetooth speakers draw power from lithium ion batteries which are, in turn, topped up with a c

It seems like a lot of money is spent on the power supply. Small Bluetooth speakers draw power from lithium ion batteries which are, in turn, topped up with a cheap external power source. I understand that you can draw very high current from these batteries even if only briefly. Why don’t high end amps use the same trick instead of these giant toroidal coils and smoothing capacitors?

deleted 6y ago
[deleted]
pjc50 6y ago
Because then you have to charge the battery. Terminal voltage matters too; higher voltage is required to deliver more power. 3.7V into 4 ohm limits you to under a watt. So many systems have a boost converter in there too - which is a potential source of electrical noise. You could certainly have a stack of 18650 cells do the job if you want a portable boombox...
- regularfry 6y ago
  And, importantly, discharge it. Keeping a battery healthy is a moderately involved task, and the circuitry to do it is another-thing-to-go-wrong that's avoidable complexity with just about any other option. Besides which, no matter what you do the batteries will fail out within a single-digit number of years, even under low usage. It's a good option if you need portability, and pretty terrible by almost any other metric.
analog31 6y ago
A dark secret of power amp design is that the power supply is half the battle. Note that this design uses a conventional line frequency transformer rather than a switchmode power supply. Making an all-switchmode amp is actually a bit of a challenge. I've been there. My home stereo is a cheap switchmode power amp board, but the power supply is line frequency, as a concession after I discovered that powering it from a switchmode power supply makes it put out all sort of weird noises. An extremely nice product are the "IcePower" modules made by Bang and Olufsen, which incorporate both power supply and power amp into a single board. So they've worked out the bugs of making the parts play nicely together. These are now the jellybean power amps in smaller musical instrument amplifiers, of which I own a couple.
de6u99er 6y ago
I guess because batteries while being great for high current operations, are not the most environmentally friendly solution. My DIY power amp requires a +/- 20-40V power supply. That would be quite a lot of batteries. Toroidal transformers are the next best choice, since they are smaller than comparable regular transformers. Large caps are not only for smoothing but also act as power bank for instantious large current needs.

deleted 6y ago

[deleted]

pjc50 6y ago

Because then you have to charge the battery. Terminal voltage matters too; higher voltage is required to deliver more power. 3.7V into 4 ohm limits you to under a watt. So many systems have a boost converter in there too - which is a potential source of electrical noise. You could certainly have a stack of 18650 cells do the job if you want a portable boombox...

regularfry 6y ago
And, importantly, discharge it. Keeping a battery healthy is a moderately involved task, and the circuitry to do it is another-thing-to-go-wrong that's avoidable complexity with just about any other option. Besides which, no matter what you do the batteries will fail out within a single-digit number of years, even under low usage. It's a good option if you need portability, and pretty terrible by almost any other metric.

analog31 6y ago

A dark secret of power amp design is that the power supply is half the battle. Note that this design uses a conventional line frequency transformer rather than a switchmode power supply. Making an all-switchmode amp is actually a bit of a challenge. I've been there. My home stereo is a cheap switchmode power amp board, but the power supply is line frequency, as a concession after I discovered that powering it from a switchmode power supply makes it put out all sort of weird noises. An extremely nice product are the "IcePower" modules made by Bang and Olufsen, which incorporate both power supply and power amp into a single board. So they've worked out the bugs of making the parts play nicely together. These are now the jellybean power amps in smaller musical instrument amplifiers, of which I own a couple.

de6u99er 6y ago

I guess because batteries while being great for high current operations, are not the most environmentally friendly solution. My DIY power amp requires a +/- 20-40V power supply. That would be quite a lot of batteries. Toroidal transformers are the next best choice, since they are smaller than comparable regular transformers. Large caps are not only for smoothing but also act as power bank for instantious large current needs.