Using a low voltage supply in a class B amplifier

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Summary:: How the value of input signal affects the value of power supply for an amplifier circuit.

Hi, friends,
I have two queries.

I read somewhere that
1. In class B mode higher plate efficiency (tube amp) permits the use of smaller power supplies....and
2.For low level signals a low voltage supply is used, but as the signal level increases, so a high voltage supply is utilised.

Q1. what will happen when I drive a higher load (eg. 2 ohm), instead of a moderate one. Does the lower power supply able to provide higher voltage & current requirement of higher load? If not then why low power supply is recommended as a good design alternative.?

Q2 .what relation exist between the input signal and the value of power supply.?

Thanks!
Are you talking about tube amplifier like guitar amp or hifi power amp type?

1) No, just because you are running class B with very low bias current does NOT mean you can use smaller supply. It depends on what power output you want. class A, Class AB or Class B has no baring on the size of the power supply, it's the required output power that govern that. Sure, if you don't put any signal, yes, your class B can use smaller supply, BUT as soon as you put in some signal, the amp will clip at much lower power.

2) Yes, generally there is this relation, the higher the power of the amp, the higher the voltage you need. BUT it's not absolute, for tube amp, it depends on the current capability of the tube, the output transformer turn ratio. For transistor amps, yes, there is a direct relation of supply voltage to the power output.

Q1, for tube amp, you need to match the output transformer tap to the load impedance, You don't get higher or lower power with 2ohm or 8ohm load, it's about matching. don't look at that other parameters. Tube amps are more complicated in calculation as you have transformer taping.

You have to put the schematic, give more information. I design tube guitar amps and SS hifi power amps. I need much more information to help you.
 

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