svart-hvitt
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@John_Siau , any plans for a more powerful amp, say 1kW, 2kW or more?
We could do more with respect to measurements. Question is whether we confuse the readers and overwhelm them with information. For example, some reviewers use square wave and show those waveforms. The ones that don't know what they are doing use fast rise-time square wave which cannot happen in our audio-band music.
With respect to difficult loads, we could add reactive ones. I tried to build one but faced resistance on them being too difficult than typical speaker loads. At the end of the day, they just lower the impedance of the load at higher frequencies.
Note that sine waves are more difficult load for the amp than music. They have every low crest factor, pushing the amp to deliver more power than music would. So our simplistic test here is actually more extreme than the real application. The capacitors in the power supply for example work a lot more effectively with ups and downs of music than sine wave we use for measurements.
Sure, amps with similar architecture and good measured performance can be indistinguishable.
I am also searching for the reason for observed differences, as others have stated, in so many words.
The systems are described here:
https://www.audioholics.com/amplifier-reviews/ati-at4002
Game Room: Revel M20's, Oppo UDP-205, Oppo HA-1 (Preamp) sourced my Roon (network)
Living Room: Revel Salon2's, Oppo UPD-205 Emotiva XMC-1 (Stereo Reference mode) sourced by Roon (USB-DAC)
My systems have changed as of late:
In the game room, the switch between the AHB2 and AT522NC in less-than 20 seconds.
- Sold the HA-1 for the game room. Going Oppo UHD Direct (thanks to Roon)
- Added an LA-4 for a two channel mode: Oppo UDP-205 -> LA4 -> Salon2's.
Directly comparing these amps in my systems, I find it unremarkable that completely different architectures (which also measure differently) sound differently.
Are you in the Boston area? If so, perhaps I could demonstrate.
- Rich
In terms of audio memory, 20 seconds is likely too long a period of time. Never mind that appears from your description that this is a sighted comparison. In order to make the best determination the switch should be immediate and the comparison should be blind to remove bias.
Correct. In Harman speaker testing, the shuffling time of speakers is about 4 to 5 seconds and I found that excruciatingly long even though speakers have a strong sonic signatures.In terms of audio memory, 20 seconds is likely too long a period of time.
Knowing how unreliable the human hearing sense is listening is not a good bet. Connect the amplifier to the speaker and repeat all measurements done previously with a resistive dummy load makes much more sense. Just make sure that the speaker is not driven with too much power.Speakers are not a passive load. They generate its own voltage which then feeds back the amplifier. Amplifier then tries to damp these parasite signals the best way it can - but it's never perfect and various amplifiers do this with various success. Measurements being done with passive resistance don't cover what will happen with real speakers. Does it generate additional distortion, this feedback from speakers? Why, of course it does - there's a parasite signal that should not be there at all in an ideal case - which never happens in reality. [..]
All in all, one who looks in whole complexity of amplifiers, understands that set of measurements performed simply cannot seriously cover all what it takes to make a correct, objective evaluation of the amplifier. The only proper way to assess the amplifier is to actually connect it to the speakers you want to pair it with...and listen to it. [..]
With respect to difficult loads, we could add reactive ones. I tried to build one but faced resistance on them being too difficult than typical speaker loads. At the end of the day, they just lower the impedance of the load at higher frequencies.
Knowing how unreliable the human hearing sense is listening is not a good bet. Connect the amplifier to the speaker and repeat all measurements done previously with a resistive dummy load makes much more sense. Just make sure that the speaker is not driven with too much power.
It would be interesting to connect the AP both to the output of the amp and the input of the speaker and compare the data depending on the cable.
I am well aware of that. It is a low power load though and is only used for frequency response tests. Is that that useful?Ken Kantor's load is fair and accurately represents tweeter inductance though of an older variety before shorting rings:
https://www.stereophile.com/reference/60/index.html
Here is an Audioholics article that may be of interest to some:
https://www.audioholics.com/audio-amplifier/audio-amplifiers-sound
I don't suppose that most speaker have LPF on the tweeters, does this matter?
I am well aware of that. It is a low power load though and is only used for frequency response tests. Is that that useful?
Class D proponents of course say no, it doesn't matter.
I've yet to investigate these, but I wonder, can the constant presence of the switching frequency:
- lead to heating of the tweeter coil?
Voice coil inductance is your friend here. And it takes a LOT of current to demagnetize things.
I've inadvertently significantly reduced the B of a neo magnet in a tweeter used in an initial proto speaker design, driving it with excess power (loud but not ridiculous levels in a large room) from a high wattage class d amp.
Wow, how much power did it take to do that?
Knowing how unreliable the human hearing sense is listening is not a good bet. Connect the amplifier to the speaker and repeat all measurements done previously with a resistive dummy load makes much more sense. Just make sure that the speaker is not driven with too much power.
It would be interesting to connect the AP both to the output of the amp and the input of the speaker and compare the data depending on the cable.