Bandwidth question?

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!

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.

No one brought "harmonics" into this debate?

Ralph,
I clearly understand the statement about our ears ability, but what about speakers? Where can you place them in discussed equation? Are they identical to our ears?

Orpheus10. That's all part of this. Sine waves don't really tell you much about the bandwidth of an amp or preamp since all your getting is the fundamental frequency without the harmonics. I tend to look at square waves. That tells me a lot about the amp or preamp I'm looking at. The reason is, a 1Khz square wave shows you not only the fundamental, but the harmonics as well. A perfect 1Khz square will tell me that this piece of gear is flat from 100Hz to 10Khz or ten times the fundamental frequency in both directions. It can also shed some light on the interesting things some manufacturers do with their output coupling transformers to make it seem like the transformer has more high frequency bandwidth then it really has. So for example for perfect 20kHZ square waves, an amp or preamp needs to have a bandwidth out to 200Khz. Sad thing is, it really won't tell you how the gear under test is going to sound. For that you need the best test instrument in the world, your ears.