switching power supplies in amplifiers?

Most that I have seen are transformer powered. Not that it couldn't be done with switchers but if the transformer solution is only one cent cheaper that's how it'll be done.

Regards, Joerg

Well, I can tell you there are no longer any heavy transformers driving the speakers, not unless you are shopping for tube amps.

Luhan Monat (luhanxmonat-at-yahoo^dot^com)

"Reality: what a concept!"

So those 600W stereo amplifiers, are, um, 80% transformer, then? ;)

If it's only a few cents cheaper, but 20% lighter, they could save a bundle in the shipping costs alone... ;)

Ah, I guess that's what I meant to ask. So, how are the speakers driven nowadays? Are they step-down DC-DC converters? (DC coming from a filtered bridge rectifier, connected to the mains?)

Many mfgs are pretty "creative" when it comes to power data. I have seen

200W amps that had a transformer no larger than that in grandpa's tube set, 50-70W.

With the rising oil prices that might play an increasing role. It's also size. Nowadays the macho thing isn't all the rage anymore. We bought a new set and my wife made it very clear that it should not be as large as the old Kenwood stack. It's amazing, the new stereo is barely larger than a shoebox but with the speakers that came with it the thing sounds almost as good as the old one. Plus it was a whole lot cheaper than the old one had been.

Regards, Joerg

The transformer in a 600W amp is 'quite' heavy but probably not *80%* of the weight.

SMPS PSUs are used in some amplifiers these days.

Graham

Well, you can reduce line voltage to something more reasonable (depending on your power spec) with an iron transformer or a switcher, and you can drive the speaker through a linear amplifier similar to say, this:

This circuit can be class A, B or C. The only difference is the power dissipated at idle (heatsinks, eh?), and a small "tit" of crossover distortion in class C. Just add a small filter choke on the output to clean that up. Efficiency runs from maybe 45% class A (sine wave output) to oh,

75% I think.

Or, you can use a reasonably fast PWM circuit and drive the speaker that way. Class D with stiff MOSFETs nets you 90-99% efficiency. Linearity is questionable; with a fast, stable circuit you can at least wrap it with feedback and correct it back more or less.

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

I wouldn't recommend Class C !

Modern Class D can be very good indeed btw. 0.01% THD is quite acheivable from better examples now.

Graham

Whyso? Bipolar transistors turn on pretty quickly, you can bias it within say -0.3V. A fast op-amp front end can correct that in a hundred nanoseconds. After the transient, one transistor is conducting and it's linear as any other amp is, with 60dBV NFB.

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Distortion at the zero crossing point is highly unpleasant. I'll defy you to find an output stage that responds adequately in a hundred nanoseconds too.

I have *never* seen a commercial Class C amp for audio.

Graham

Strange. I know a fellow who built his own 1kW amp and he says it's a few bits of a volt (just as I described) into class C. He says it's good at full power out to something like 300kHz, so damned if it isn't fast enough.

OBTW, any regular output stage using reasonable transistors (fT > 20MHz or so, not wimpy-ass 2955/3055 or TIPxx stuff) will certainly respond in 100ns. I'd be more concerned about the diff amp responding in under 300ns... which can certainly be done, especially with somewhat faster transistors than generic (maybe 200-500MHz fT) and careful design.

Tim

-- Deep Fryer: a very philosophical monk. Website:

Must have repaired several hundred units back in the 60's. All ran in the A-B region. Just biased to conduct slightly at zero signal to avoid the dreaded 'crossover notch'. The last place you want distortion, is near zero.

Luhan Monat (luhanxmonat-at-yahoo^dot^com)

"Reality: what a concept!"

"Tim Williams"

** Such arrangements are generally known as "zero bias, class B" - never called class C.

Many famous high powered audio amps have the output devices biased off and rely on the drive devices to "fill in" the missing bit in crossover region.

The Crown DC300A is one example.

The Quad 405 "current dumping amp" is another.

....... Phil

I don't think I was ever impressed by their home amplifiers weight, allthough it usually goes by price. Switching, probably not. Most of these cheap amp have overdriven transformers, so they skimp.

greg

Many current designs use the brute force transformer-rectifier-filter approach. However, new regulations are proposed that would require all consumer products to meet a minimum power factor requirement. This requirement would eliminate the old approach in favor of switchers with power factor correction. Also, class D amplifiers require tightly regulated supplies for the output stages, which make switchers more attractive, since linear regulators are notoriously inefficient.

"Jon"

= another publicly masturbating FUCKWIT !!!!

** There is nothing "brute force" about it.

SM is a brute force idea by definition.

** Please cite your evidence !!

I bet it does not exist.

** Jon is full of shit up to his f****ng eyeballs.

A wanker without a cause .......

** Shame about the many consumer and professional class D amps that have ordinary transformer based PSUs.

Check out the Crown K series, released nearly 10 years ago, still on sale.

Best Class D amps ever made.

** This "Jon" FUCKWIT is yet another know nothing, f****ng asshole .

Audio power amps do not have *linear* regulated PSUs .

....... Phil

In article , Pooh Bear wrote: [...]

I've both seen and heard class C audio. It was a PA system used for voice. It sounded very bad but you could understand what was said.

--
--
kensmith@rahul.net   forging knowledge

Overdriven transformers ?

Graham

Actually IEC61000-3-2 let them off the hook on account of the low contribution from such devices.

Power amplifiers don't use regulated supplies.

Graham