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SET Asylum Single Ended Triodes (SETs), the ultimate tube lovers dream. |
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In Reply to: phase response posted by njjohn on March 22, 2007 at 15:50:50:
maintaining accurate phase through the full range of audio frequencies from input to output. Every reactive element in the chain has the potential to "distort" phase by leading or lagging (the OP compared to input). This is true at the frequency extremes where the reactive components form a filter and the frequency response begins to fall.What I am suggesting is that if an instrument produces a fundamental of say, 1000Hz it may produce many octaves of overtones. It's relatively easy to design and build an amp that maintains phase accuracy on the 2ndH of 1KHz fundamental but less so at much higher frequencies. So in effect the 9thH may be phase shifted compared to what was input and this shift (compared to the fundamental) could IMO lead to incorrect spatial cues. Playing with phase shift is basically how pseudo surround sound works ... it tricks the ear.
NFB can exacerbate the problem. You can imagine how complex the scenario might become by feeding back phase shifted harmonics (relative to the feedback point) especially if the signal contains varying degrees of phase shift at different frequencies.
The best way of controlling the complex situation is to build a very wide band amp with zero global NFB (common wisdom). Local NFB can also be a problem but this is much easier to control through proper design.
Naz
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- What I mean is ... - Naz 16:53:36 03/22/07 (0)
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