Qualities of an Exceptional Amp

[Dan Banquer]

Damned if I know what they mean by "dynamic power". If those watts rms specs are for real I wouldn't worry about it.
d.b.

[jeffsg4mac]

So what you mean is really who knows how or what they are doing to get that number as there is no set standard? Acording to some other manufactures way it might have 300watts of dynamic power or only 30 according to someone else?

[Dan Banquer]

Dynamic power, whatever that means, is not an accepted measurement by any competent engineer that I know of. In answer to your question about standards as it applies to power amps: It depends mostly on the marketing department these days.
d.b.

[zipper]

Dan,
Would just adding more capacitance in the amp remedy the charge vs. discharge rate, or would the size of the transfrmr have to be increased proportionately?
Also, have you ever checked out odysseyaudio.com? I thinking of getting a stratos in the future but am leery of a breakin time that exceeds the 30 day return policy & the fact that,if unplugged or turned off,this thing might take a day to be ready for use again. Typical of a class A/AB amp?

[Dan Banquer]

Both the transformers and the caps. Now you need to think about your rectifier diodes and will they handle the surge currents, and that's just for the power supply. Can your output transistors handle the increase in power? are they adequately heat sinked for the increase in power? My guess is that you have a lot to think about. I don't generally comment about other manufacutrers amps as a rule and I'm not about to break that.
Dan Banquer
R.E. Designs

[Rip Van Woofer]

I agree that different amps when level matched in an ABX can sound identical. But that's not the way I listen to music. I listen over extended periods of time. I listen until I get ear fatigue. I listen until I can get all the details I can hear. I listen until a musical piece becomes nearly a part of my subconcious.

ABX testing does not preclude any of that. You may match the two amps (or whatever) at earbleed levels if you wish. You may listen to fully identified A and fully identified B for as long as you wish (minutes, hours, even days) with whatever program material you desire. All it does is "blindfold" you (figuratively) when you move the switch to "X", and ask you to identify whether X is A or B. You can listen to X as long as you wish, too. If you can't identify X correctly more than about half the time, then the existence of audible differences between A and B is most likely nil.

The ONLY thing properly done ABX testing does is to test your ability to hear a difference when you don't know which item you are hearing. In other words, it removes bias as much as it is possible to do so.

Of course, as Dan Banquer pointed out to me in a private exchange, the tester has to be honest and open about his results and data! As is the case with science in general.

[zipper]

Thanks Dan. I understand.

[av_phile]

I don't know where you guys are coming from. But dynamic power is just a consumer euphemism for a technical term called peak value that mathematically is twice the RMS value. If there is an RMS value there is a peak value. And strictly speaking technically, there is really is no such thing as RMS power. What manufacturers put in their specs, at least those who are truthful in their specs, is CONTINUOUS AVERAGE Or MINIMUM power into so and so load. There are volts in RMS and current in RMS but never Power in RMS. But I can understand that RMS power has come to be an idiomatically accepted audiophile-speak for as long as we understand each other that it is continuous average, a value derived from an equation using RMS volts.

Using voltage or current measurements, an excellent amp can have peak values exceeding twice its RMS current or voltage values across a load. But depending on design and power measurements conditions, it can be far less. An amp measured at extreme but unrealistic conditions such as those from DIN into 4 ohms at 1% THD and with just one channel driven can yield numerically fantastic figures that leave little for peak power figures to be meaningful. They are effectivaly rating their amps in peak, not continuous average. Not conservative.

Powerful amps have filter capacitors with fantastic values to take care of peak voltage requirements, say 150volts and a total capacitance starting at 46,000microfarads and some in excess of 100,000 microfarads. These storage capacitors do not charge all the time unless they fall below a certain value and will discharge FAST enough to take care of instantaneous voltage requirements. Some designs use an array of parallel capacitors with smaller capacitances on the observed behaviour that small capcitance storage devices discharge and charge FASTER than large ones. Hence, rather than use double 23,000 mF caps, some would use eight 6,800mf caps instead to achieve a much faster response to transient current peaks.

Like I said PMPO is marketing hype that have no basis in technical terms, but real dynamic power is not. But because it has become an accepted fact that musical signals are dynamic, the ability of the amp to respond to such dynamic signals instantaneously requires some peak power abilities that has come to be called dynamic power or dynamic headroom to indicate in db the gap between continuous and peak.

It is true there are nor standards for measuring peak dynamic power. This had led manufacturers to use whatever measurement conditions and standards they want to arrive at impressive numbers that are sure to attract the uninformed customer. That applies to continuous power rating as well. But just the same, there are brands that do stick to CONSERVATIVE power rating, whether peak or continuous.

Another aspect of dynamic power is the ability of the amp to respond dynamically to impedance fluctuations that can go down to 2 ohms as presented to it by the speaker's own reactive load to different frequencies. A theoreticaly good amplifer doubles its available power as the load impedance is halved. This is indicative of the ability of the amp to respond dynamically to changing impedance across the audible spectra. Again, there is nothing hype about this. This is entirely technical and a very crucial quality of amp in the real world.

A typically complete power specs such as done by musical fidelity for its A308 amplifer goes something like this:

Voltage RMS: 35 Volts 20Hz to 20 KHz
Peak: 99Volts
Power: 150 Watts per channel into 8 Ohms (21.8dBW). 300 Watts per channel into 4 Ohms.
Peak-to-peak: output current 48 Amps

They don't give dynamic headroom or state the peak power in watts but indicate a more measureable value in terms of volts and amps.

In contrast, here's a NAD power specification for its T973 seven channel power amplifier:

7 x 140W Minimum Continuous Power (8 / 4 Ohms); all channels driven simultaneously
2 x 200W Continuous Power (8 / 4 Ohms)
230W, 390W and 450W IHF Power into 8, 4 and 2 ohms, respectively

Note that in both situations, the term RMS is never used. They're some of the few manufactuers who don't need to overstate their products' specs.

[Dan Banquer]

"And strictly speaking technically, there is really is no such thing as RMS power. "
The above defys logic and standard engineering principles relating to power.

I'm still waiting for the consumer rhetoric to stop and still waiting for you to monitor the voltage peaks into your speaker with a scope.
d.b.

[jeffsg4mac]

Dan, If I were to measure the voltage peaks with a scope, what might I expect from the average 100-watt amp? Or say my Denon 2803 rated at 90-watts. I am intrigued.