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@mcreyn - "George, still waiting for you to demonstrate how an amp putting out 200 watts at 2 ohms is flowing more current than one putting out 400 watts at 2 ohms." I'm pretty sure this is George's point. This is from the Pass Labs website - https://www.passlabs.com/press/power-supplies-commentary-consumers: "If the stereo amplifier is rated 200 watts per channel pure Class A, it will draw about 1000 watts all the time, meaning that about 3000 watts of power transformer is called for, no less." Also from the same article on Switching Power Supplies: "This can be a deep subject, but suffice it to say that I believe that some of the same caveats apply to switching supplies as linear regulators. Again, they should be rated far beyond the nominal current requirements of the amplifier circuit, particularly as the switchers I have seen usually degrade badly beyond their ratings. Also, it helps if the power supply capacitors before and after the switcher are very substantial. This is typically not the case, since one of the primary motivations to use switchers is to save money." And here's an example from Stereophile for the Mytek Brooklyn Class-D amp that viper6 owns: Defining clipping as when the THD+noise in the output reaches 1%, Mytek specifies the Brooklyn Amp as clipping at 250Wpc into 8 ohms (24dBW), at 300Wpc into 4 ohms (21.7dBW), and at 400Wpc into 2 ohms (20dBW). I measured clipping powers of 245W into 8 ohms (23.9dBW, fig.4) and 315Wpc into 4 ohms (22dBW, fig.5), both with both channels driven. However, when I tried to measure the clipping power into 2 ohms, the Mytek went into protection mode at 310W (18.9dBW), with any further increase in the input voltage not resulting in a higher output power - https://www.stereophile.com/content/mytek-brooklyn-amp-power-amplifier-measurements I believe all George is saying is that regardless of manufactures specs, it's probably in the best interest of a potential buyer for any amp to have measurements done independently to support the specs. It seems to be more often than not that when Stereophile measures Class-D amps, there's a comment about careful matching to low impedance speakers. |
golfnutz, Thanks for quoting Stereophile on my Mytek Brooklyn amp. George would say it is a mediocre amp because it doesn't increase its output capability much as the impedance is lowered. SO WHAT? It is a budget amp which happens to have accurate/neutral sound within its power limitations. It sounds much more accurate/neutral than the pure class A Levinson ML2 which was a perfect voltage source with hefty power supply. We are here to find amps that reveal more music, not to debate specs. The latter is for academic societies. Specs are useful to rule out very low powered amps for very inefficient speakers, for example. |
M.S Electrical Engineering, University of Southern California (2017)Here is more of the text George didn't include which precedes the above text by Jacob VonWagoner: BJT's can give you a lot higher gain. Just take a bunch of components and compare them, and you'll find the BJT's give you better gain characteristics and therefore require fewer gain stages.The words 'gain', 'linearity' and 'bias voltage' tell you that this has nothing to do with class D amplifiers which do not operate their output devices in the linear region. Instead class D amps go from Off to On and spend as little time in the middle (linear region) as possible. This is the reason they are so efficient. Obviously while all this stuff is correct with regards to conventional amplifiers it has nothing to do whatsoever with class D amps. George's remonstrations notwithstanding. |
- 420 posts total