Questions on definitions

Dear Dr. Jon Wong,

What are the different between active and passive Pre-Amp, and are there interchnageable?

What are the differnt in Amp with Class "A", "AB", & "B" and presently in the market how many class does it have and how to distinghish the class when we purchase?

Is it true that by changeing new tube for tube Amp ti is as good as new and how long to burn in for new tube?How good is recordable CD compare to normal CD?

Casrol

Hello Casrol,

For active pre-amp, there is circuits which amplifies the signal. The active pre-amp has better drive capability. However, for passive pre-amp, usually it is an attenuator. It does not provide gain and the drive capability is poorer.

In short, Class A means the output devices in the amplifier are biased to conduct current all the time, regardless whether the amplifier is playing music. Class B means the current in the devices conducts only when the amplifier is playing the music. Class AB means the devices are biased such that it only conducts a portion of the current at standing, and when the music is loud it will leave class A and become class B. Class A has low efficiency but very good sound. Class AB is a compromise.

Most of the amplifiers in the market are class AB type. You can’t really find class B type as they are used for PA usually. For class A type, the manufacturer usually will mention in their technical specifications.

Tubes have limited life span. If they sound muffled, start to give distortions or unusal sound, then it is time to change them. When you have new tubes installed, the amp will sound as good as new, provided the capacitors and other parts are all still in working conditions.

Certain CD players cannot play CDR well because of different reflective index!

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