Fantastic new audio amp !

On a sunny day (Sat, 21 Nov 2009 09:56:56 -0000) it happened "TTman" wrote in :

Links to:

100 W *peak* power output. That would be 100 mW normal RMS?

Someth [1] Normal listening level is defined as 73dBC sound pressure level (SPL) at a distance of 1 metre, with a speaker sensitivity of 89dBC/W at 1 metre. Quiet background music, from relatively efficient speakers located only a few feet from you. -16 dBW, or only 25 milliwatts of audio delivered to the speakers.

Let's see... "up to 10 months on a set of four C batteries, playing for up to three hours per day." That's 300 days, 900 operating hours,

45 watt-hours (assuming 100% efficiency), or 15 amp-hours at 1.5 volts.

According to The Great Dubious Reference (WikiPedia) alkaline C batteries have a nominal capacity of 8530 mAh. Four of them in parallel would have about 35 amp-hours of energy, which is quite a bit more than the 15 amp-hours which would need to be delivered to the speakers. Required "battery in to audio out" electrical efficiency would be around 40%.

So, it seems to me that their claims don't necessarily violate the laws of physics... assuming high efficiency in the amp, the sound level and speaker sensitivity that they assert, and the "up to 10 months" and "up to three hours per day" boundaries. They don't seem to specify frequency response, distortion, or noise levels.

They'd need a *very* different power supply arrangement in order for the "100 watt" number they quote to be even slightly relevant and believable.

Seems as if it may be an interesting niche product.

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And also "is 20 times more efficient than competing devices, such as Class D amplifiers...". Well, that spec is obviously not measured anywhere within 13 dB of full power, since Class D amps are near 100% efficient at full power. Reading further, it seems that they do power rail switching (a la Class G) to get their claimed high efficiency at low power output. The big question is of course, "So what?".

The first product on their product listing is the AS2001 50 WPC stereo amp. Let's assume that at power levels below 1 WPC, that they have higher efficiency. However, any decent product built with this part will need a power supply capable of > 100 W, or energy storage capable of delivering ~ 100 W for some reasonable amount of time. Once you've done that, who cares whether you can save 0.5 W dissipation when you're listening really, really quietly?

be

It quotes peak output power. I switched off then. Only amateurs use peak power or fraudsters. Power is defined as average power or instantaneous.

F.

I use peak power in amp design but I kinda call it 'clip power' over here. It's the power at the peak of the signal. When clipping is audioable at the lowest common audio frequency, I call that the peak power or clip power. It can depend on load, frequency and waveform. It's also the max instantaneous power Ipeak^2*Z =Peak power.

Or perhaps your thinking peak music power... :P

In the uk, the power output is usually specified as the rms value of a continuous sine wave into a resistive load just below clip level and is usually less than instantaneous power due to power supply sag...

Anything else is a lie, though quite common in the specmanship world...

Regards,

Chris

Not that this hasn't been done to death many times, but there's no such thing as "rms power", and the "rms value of a continuous sine wave" isn't really quite explicit.enough to be useful.

AFAIK the fictitious term "rms power" means something like V^2/R, where R is the nominated load resistance, and V is the RMS voltage of a sine wave that the amp can be sustain into such a load resistance without clipping.

Cheers, Tony

as "rms

explicit.enough

Sure there is and what's not explicit enough ?. An amplifier can be seen as a voltage generator and can have it's continuous power expressed in terms of rms value.

the nominated

sustain into

Fictitious ?. Ok, here's a wiki article on it:

Even the us makers specify rms now, when in the old days, they specified peak or some variation. Jap quality hifi manufacturers always specified rms, fwir, as did uk builders.

There have to be standards. Some domestic and auto amplifiers have in the past claimed Kw, when you can tell just by looking at the size of the box that it's bs. Some strange runes and arithmetic may have got them there, but it ain't engineering.

Here, such claims go into the same bin as tinfoil hats and o2 free copper cable :-)...

Regards,

Chris

You didn't spot the bit: 'In common use, the terms "RMS power" or "watts RMS" are erroneously used to describe average power.' then? Or the references:

a.. The so called "RMS Power" a.. Meaningless RMS Power - Why there is no such thing as 'RMS watts' or 'watts RMS' and never has been

Unfortunately, the Wiki gnomes don't manage to weed out all the dross and they've left in stuff like: 'The peak power of a sine wave of RMS value X is ?2*X; ' which is wrong for the same reason.

Chris (a different one)

[snip]

I was always fond of touting my amplifier as 400W CONTINUOUS RMS, as opposed to those nutcases who spout "music power" or "peak power" ;-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
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That was a bit of an own goal, but to be honest, just searched for an article as an explanation, without reading it in full :-(.

Doesn't change the fact that rms measurement of power is just as valid and accurate for power as a true rms voltmeter is as valid as an average reading voltmeter, depending on what you are trying to measure. A true rms measurement takes into account waveform shape, whereas an average reading meter is calibrated for a given waveform shape, usually sine wave, at calibration time. It will be in error with anything else. Thus, a true rms measurement is more usefull in practice...

Regards,

Chris

Agreed. The real power, not bullshit power, tells a lot about the design. However, there is one more parameter: for how long the amp can sustain that power level undistorted.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

In my case "CONTINUOUS" meant exactly that ;-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

No it isn't. RMS is valid for voltage and current because the square is useful for calculating power. The square, thus the root of the mean square, of power is meaningless. "Average" power says it all, regardless of waveform. Any other sort of power is bogus.

Right, not '1 minute duty' like you see on some motors, but continuous,

24/7 if required and stay within spec :-)...

Regards,

Chris

Umm, isn't that what we are trying to measure ?.

Why do you think all pro audio gear is specified in terms of rms power output ?...

Regards,

Chris

No, you said that you were measuring power.

The same reason that Monster Cables are so popular; audiophoolery.

Notwithstanding the PMPO type of lies, I have seen serious audio work (new patents and technology etc.) being done to maximize the music or vocal performance from a fixed amount of power input.

It isn't! A popular manufacturer of professional audio power amplifiers is QSC and, for example, the specifications of their CX-series of PA amps

give the output powers in W ... not W RMS, just watts. However, they do use RMS, correctly, in their specification of input signal _voltages_ (sensitivity and clipping threshold).

Chris(tofire)