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Old 8th March 2005, 12:41 AM   #1
okawa is offline okawa  China
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Default phase consideration in audio signal amplification

hello guys,
the analog amplifiers class A or Class B always change the original phase of the signals, because the frequency responses to different frequencies.
is this change important?
dose this change will affect the sound?
thanks!!
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Old 8th March 2005, 06:54 AM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
most amplifiers maintain the phase on the output to match the input.
A generic amp follows as example.
The LTP inverts the phase.
The VAS inverts the phase back to original.
The emitter follower maintains the phase.
Time delay through the stages about one microsecond (varies about 10 to 1 depending on topology and components) gradually increases the phase error at the output with increasing frequency.
Eventually at very high frequency the phase has been delayed so long relative to one cycle that the signal and output are out of phase. Before this happens the designer must ensure that gain is less than 1 and with a margin of safety- the phase margin and gain margin are a measure of this. Driving non resistive loads upsets your margins and must be taken into account at the design and testing.
For good sound most will try to ensure minimum phase errors throughout the whole audio band.
Is this what you require?
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Old 8th March 2005, 09:24 AM   #3
okawa is offline okawa  China
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you mean all the filters in the amplifier consist an all pass filter with a constant phase shift.
thank you.
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Old 8th March 2005, 01:03 PM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
No i am not referring to an all-pass filter or any filter.
The time delay is NOT equivalent to constant phase shift.
Time delay is = increasing phase shift with increasing frequency.
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