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Bandwidth question?

I am interested in the qualitative difference in sound betw amplifiers that have -3db roll off at 100khz vs -3db at 300khz. Thru the amps I have tried, I suspect increased bandwidth has more openness and transparency and hence a better sense of space sharing. At the same time, it is easier to screw up the sound due to noise (from components/AC/RF) or improper cartridge loading. I am not very certain of the correlation and interested in what you guys think?

In reviewing the measurement sections of stereophile, many amps with -3db at 100khz demonstrate subtle rounding of the edges when reproducing 10khz square waves. I don't listen to square wave so I don't know what that translate into.

I realize that some amps (Spectral or Soulutions) has very high bandwidth (MegaHz) to implement negative feedabck. I am not refering to that.
128x128glai
glai's avatar
glai OP
446 posts
 
Many thanks for all the responses. To be specific, I am not interested in debating the human hearing bandwidth. Mine is 25hz to 17khz.

I am interested in the how the ultrasonic bandwidth impacts the reproduction of audible frequencies. Many responses have pointed out phase issues, noises (or ultrasonic noise modifying how a component behaves in the audible freqs.)These are very helpful to me. I also realize that bandwidth for amp is dependent on load and output.

Ralph,

Why 10 times the audbile bandwidth is neccessary. A lot of amps are -3db at 100khz. This means faithful playback up to only 10khz, if you are correct.
kijanki's avatar
kijanki
4,428 posts
 
"Why 10 times the audbile bandwidth is neccessary" - Because of phase shift. Rule of thumb says that phase shift at 1/10 of -3dB cutoff frequency is about 5 deg and that might be significant for proper summing of harmonics.
atmasphere's avatar
atmasphere
11,793 posts
 
Glai, there you have it. Our ears are not so sensitive to phase shift at a single frequency, but when a band of frequencies is involved its another matter entirely!
hifigeek1
770 posts
 
I have never been a big fan on Mhz frequency response especially in an amplifier. Having a bandwidth that high can cause major problems including parasitic oscillation, rf interference etc. This can cause the top end to sound hard, grainy, and strident. This is especially true if the amp uses global feedback. To answer Kijanki, ten times the bandwidth is just a rule of thumb but it is something I like to see especially in a preamp. Personally I find -3dB down @ 200Khz to be sufficient. Also, when talking about amplifiers there are differences in specs. between power bandwidth and small signal bandwidth. By the way, most transformer coupled amplifiers are not capable of ultra wide bandwidth frequency responses.
orpheus10
8,668 posts
 
No one brought "harmonics" into this debate?
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