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In Reply to: RE: Recent and future amplifier measurements posted by MarkJohns on November 09, 2015 at 07:59:37
The flaw is particularly obvious with class D amplifiers which are actually Pulse Width Modulation amplifiers, not digital amplifiers. The output has a series inductor to suppress high frequency noise. How that operates depends entirely on the load especially if it is reactive. It is therefore impossible to generalize how such an amplifier will sound with a given speaker system unless you know the X and R value of the series inductor, the complex impedance of the speaker system, the complex impedance of the speaker wire, and how to perform the network calculations. The YG Sonja 1.1 shows how drastically wide the range could be. Some speaker wires are so reactive they've been known to blow up amplifiers by simply creating a tank circuit at ultrasonic frequencies, a load amplifiers are not designed to handle.
Follow Ups:
performance is load independent?
try it! you know you want to!
Old news to anyone who has read ANY lab test data on these amps.
Check out the datasheet for the B&O ASP modules. While not 'latest', do show this effect in spades.
Too much is never enough
Oh, so now an audiophile is extolling the virtues of negative feedback. What a laugh. Negative feedback is supposed to be audiophile poison. Now suddenly it's the medicine that cures all ills. Well, which is it?
then have a listen. Then get back to use with an educated opinion...
try it! you know you want to!
Someone who can QUOTE Bruno about NFB should chime in. I think it boils down to a 'little' being no good, but a LOT being OK. I heard the amount of 60db bandied about but could be mistook.
Too much is never enough
Well .... listen some more and give us your "feedback " ......, :)
Go Rossi ......
I owned a 'd' amp for several years. The PSAudio GCC250 'integrated'. It was a fine piece and needed ONLY to have a stuck switch (button) freed and deoxit'ed.
But, it also did something to the HIGHS with my panels. I don't know the nature of the reaction but it was LONG TERM unsatisfying. This after MUCH adjustment to panel location. And I MEAN much. toe? Tweeter I/O? Flip 'em front to back? Spacing? All messed with and setups lasted anywhere from 2 minutes to 3 or 4 months.
I believe I gave 'd' a fair shot.
Where I LEFT them, which sounded best, also seemed pretty close (within cm) of the best place when I went to a Pair-O-Parasound.
Thus the need to move toward a line level crossover!
Too much is never enough
I don't know the nature of the reaction but it was LONG TERM unsatisfying.
Agreed. Clear and bright, but unnatural.
nt
try it! you know you want to!
Please, Kur, go find a review with Measured Data.
Frequency Response FALLS more quickly with lower impedance loads on amps with the output Zobel.
This falling response ALSO induces Phase Problems which MAY be audible.
Too much is never enough
Where? Oh, you mean out past 30KHz?
try it! you know you want to!
To also cherry pick the data, the ASP 500 module, the 'big guy' in the series was down 1/2db or so at 20khz. This produces notable phase shift in the audio band. And, if it matters, really odd looking 10khz square wave response.
I'm not going to try to find the measured data. You can find it if you are really interested.
Too much is never enough
hard to prove it's audibility at high frequencies where moving your head a few centimeters produced much more phase shift.
"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius
I stated that the ncore uses post filter feedback and thus the frequency response was load independent. The graph I posted shows that....Half dB down at 20KHz might bother the dog but I can't hear it and I doubt anyone reading this can either...
try it! you know you want to!
If you bothered to READ my post, I stipulated the B&O ASP module.
Sure, other 'd' designs, notably the ncore have skipped the output filtration.
And it's not the amount 'down' that counts, but rather the phase shift this induces. I believe this was what caused problems with my panels. There was something just not right about the highs.
Too much is never enough
If you had bothered to read my post, you might have noticed it was a reply concerning class d amps in general that contain the output filter in the feedback loop. Ncore doesn't "skip" output filtration, it's in the feedback loop, same as with Icepower, by the way....though they take feedback both pre and post output filter.
try it! you know you want to!
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