gain calculations

demons_wing · 11th May 2004, 05:27 PM

i was wondering how the gain factor of an amp is calculated...i was reading the ESP website, and rod said that for a 60W amp, the gain is about 27..how do you get this figure?

sreten · 11th May 2004, 06:04 PM

Nominal max output voltage / Nominal input voltage for max output.

sreten.

rayban68 · 11th May 2004, 06:07 PM

You would use normal op-amp gain calculations, Rf/Ri for inverting, 1+Rf/Ri

to get the gain in dB , 20Log(gain)

In the case of Rods amp ( I assume you were reffering to his P3A?)

It looks like Rf=22k and Ri = 1k which gives the voltage gain of 27dB

demons_wing · 11th May 2004, 07:00 PM

i understand the formula...its the same for inverting and non inverting op amp circuits...so am i to assume that it would be

gain = Vout(rms)/Vin(rms)

where Vin(rms) is approximately 1V (depending on desired sensitivity)?

traderbam · 11th May 2004, 09:27 PM

The AVERAGE power into a load of resistance R for a sinewave is (Vpeak)^2/(2R).
So you work out the Vpeak you need for the average power you want (sometimes average power is incorrectly refered to as "RMS power" by the way - "RMS power" doesn't exist), then divide this by the Vpeak you have available at the input and this is the voltage gain you need.

Example: You want 100W average into 8-ohms at full volume and your CD player gives 2V peak as an input. The output peak voltage needs to be at least SQRT(100*16) = 40. So the voltage gain must be at least 40/2 = 20.

A voltage gain of between 20 and 50 is usual for domestic power amps.

demons_wing · 11th May 2004, 11:33 PM

cheers mate...i really appreciate everyones help

..makes learning so much easier when you can read books and ask questions too

11th May 2004, 05:27 PM	#1
demons_wing diyAudio Member Join Date: Apr 2004 Location: BC	gain calculations i was wondering how the gain factor of an amp is calculated...i was reading the ESP website, and rod said that for a 60W amp, the gain is about 27..how do you get this figure?

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11th May 2004, 06:04 PM	#2
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Nominal max output voltage / Nominal input voltage for max output. sreten.

11th May 2004, 06:07 PM	#3
rayban68 diyAudio Member Join Date: Mar 2004 Location: Prince George, BC, Canada	You would use normal op-amp gain calculations, Rf/Ri for inverting, 1+Rf/Ri to get the gain in dB , 20Log(gain) In the case of Rods amp ( I assume you were reffering to his P3A?) It looks like Rf=22k and Ri = 1k which gives the voltage gain of 27dB

11th May 2004, 07:00 PM	#4
demons_wing diyAudio Member Join Date: Apr 2004 Location: BC	i understand the formula...its the same for inverting and non inverting op amp circuits...so am i to assume that it would be gain = Vout(rms)/Vin(rms) where Vin(rms) is approximately 1V (depending on desired sensitivity)?

11th May 2004, 09:27 PM	#5
traderbam diyAudio Member Join Date: Jan 2002 Location: Earth	The AVERAGE power into a load of resistance R for a sinewave is (Vpeak)^2/(2R). So you work out the Vpeak you need for the average power you want (sometimes average power is incorrectly refered to as "RMS power" by the way - "RMS power" doesn't exist), then divide this by the Vpeak you have available at the input and this is the voltage gain you need. Example: You want 100W average into 8-ohms at full volume and your CD player gives 2V peak as an input. The output peak voltage needs to be at least SQRT(100*16) = 40. So the voltage gain must be at least 40/2 = 20. A voltage gain of between 20 and 50 is usual for domestic power amps.

11th May 2004, 11:33 PM	#6
demons_wing diyAudio Member Join Date: Apr 2004 Location: BC	cheers mate...i really appreciate everyones help ..makes learning so much easier when you can read books and ask questions too

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