Systemic Development > Amplification and Preamplification

Class A/AB?

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richidoo:
What does "ultra high bias class A/AB mean?"

Parasound JC1 amps say they run at switchable 10W/25W class A before morphing magically to 400@8ohms class AB above that. What is going on with the signal and the output devices that makes them A or AB? I assume the changeover to class AB is inaudible? (except for the deafening roar of music...)
Thanks a lot!
Rich

_Scotty_:
Here are some links with explanations of amplifying classes.
http://www.pcmag.com/encyclopedia_term/0,2542,t=amplifier+classes&i=55350,00.asp
http://www.tpub.com/neets/book7/25e.htm
http://en.wikipedia.org/wiki/Electronic_amplifier#Class_B_and_AB
Scotty

steve:

--- Quote from: richidoo on November 02, 2007, 02:49:44 PM ---What does "ultra high bias class A/AB mean?"

Parasound JC1 amps say they run at switchable 10W/25W class A before morphing magically to 400@8ohms class AB above that. What is going on with the signal and the output devices that makes them A or AB? I assume the changeover to class AB is inaudible? (except for the deafening roar of music...)
Thanks a lot!
Rich



--- End quote ---

Hi Rich,

     In essence, in simplified terms, it means the output devices, transistor/tube, bias is set on each output transistor/tube so that each output transistor/tube fully conducts the entire signal until 10/25 watts output is reached. In class A below 10/25 watts output, as one device reduces plate current, the other device is increasing plate current. However, none of the devices ever fully completely turn off during the negative portion of the musical cycle.

As the output power is rises above 10/25 watts respectively, each output transistor/tube begin to shuts off over more and more of the negative portion of the musical signal. As one device turns off, the other output device (push pull application) increasingly turns on. This is a very simplified explanation. The above links provide more in depth info for those who wish to explore further.

Hope this helps.

richidoo:
Beautiful. Thanks guys!! Looking forward to getting a grip on this.

steve:
Good luck and just received the CD a few minutes ago. Thanks for your time and efforts with the details and CD.

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