Quote:
Originally Posted by anuragn  @roc:
I think what you are trying to prove is that as we approach the rated power output, THD also increases proportionately...and hence, <0.1% at 1W & 1KHz just looks good on paper but actually at high volumes, THD would be of the order of 10%.
But I beg to differ: I was gong thru' the specs of one STK-4192 IC (rated 50W min at 20Hz-20KHz with 0.4% THD, it's used in my Yamaha Stereo Amp). To my utter surprise, I found that THD is actually higher at lower power output, then reduces to a min and then, increases drastically beyond the rated output. Considering that the receivers/ amps we are discussing have discrete output stages, so I can hazard a guess that the behaviour should not be worse than that of IC based amps.
So my point is that THD at rated output should not be much different than that given at 1W output...i.e. it can never be near 10%  After all we are talking about Onkyo and not some Aiwa/ Philips/ Sony mini compos. |
The valley sort of graph is common to all solid state amps, whether chip amps or discrete ones. The lower end receivers are chip amps and don't have discrete output stages... atleast the absolute low end onkyos and the yamahas. I have way higher respect for Marantz and Denon than either Onkyo or Yamaha's low end stuff cos they actually don't use chip amps at all.
At 1W output, its obvious that distortion levels will be below 0.1%. Its only at higher power ranges that distortion increases. Its easy to explain why - the distortion parameters simply follow the transfer characteristics of the transistorized components. My main gripe is not the distortion at 1W but rather the fact that none of these low end HT amps with humongous claimed figures actually manage to do those without significant distortion or clipping. Infact many might overload and shut down if pushed to those limits.
All I'm trying to say is take these ratings with a pinch of salt and let one's ears decide which amp is better.
Compare that to a high quality stereo amp and the tables turn. These are able to do way better than what they are rated at. For example a McCormack DNA 225 which is rated at 225W @8 ohm manages 260 odd watt when measured at 1% distortion (considered as clipping by stereophile) across the entire spectrum. See for yourself
Stereophile: McCormack DNA-225 power amplifier