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Class A formula

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Posted on January 19, 2015 at 14:24:30
onemug
Audiophile

Posts: 1276
Location: So. California
Joined: April 19, 2003
 For someone who knows the formula, can you compute for me...

How many watts of Class A would an AB amp have if it had an idling current of 70 mA?

I'm thinking it wouldn't even be 1 watt. Just curious.

 

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RE: Class A formula, posted on January 19, 2015 at 17:00:12
Caucasian Blackplate
Industry Professional

Posts: 8313
Location: Seattle
Joined: June 18, 2004
 It's really not that simple.

Is this a solid state amp, or a tube amp?

Your answer is likely to be very correct for the average solid state amp, but way off for the average tube amp.

 

RE: Class A formula, posted on January 19, 2015 at 23:29:30
djk
Manufacturer

Posts: 6135
Joined: June 17, 2000
 "idle current need be only one half the peak output current, "

So, 70mA idle will support 140Ma Peak, or 100mA RMS.

W=(I^2)R, so it would be 80mW into 8Ω, half that at 4Ω.



 

My bad..., posted on January 20, 2015 at 08:32:57
onemug
Audiophile

Posts: 1276
Location: So. California
Joined: April 19, 2003
 It's a solid state amp.

 

RE: Class A formula, posted on January 20, 2015 at 08:42:27
onemug
Audiophile

Posts: 1276
Location: So. California
Joined: April 19, 2003
 I forgot to note that my inquiry was for a solid state AB amp if that changes things.

>>>"W=(I^2)R, so it would be 80mW into 8Ω, half that at 4Ω."<<<

So less than a tenth of a watt "in" Class A?

 

Yup!, posted on January 20, 2015 at 10:10:48
Ralph
Manufacturer

Posts: 4774
Location: Minnesota
Joined: April 24, 2002
 Its class B if it cuts off at zero volts. Generally though such amps would have high distortion, so for all practical purposes almost any conventional solid state amp is class AB unless specifically built to be class A.

'Enriched' class A (like class A to 2, 10 or whatever) is still class AB.

 

RE: Yup!, posted on January 20, 2015 at 11:12:28
onemug
Audiophile

Posts: 1276
Location: So. California
Joined: April 19, 2003
 Thanks Ralph...for everything :-)

 

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