gain calculations - diyAudio
 gain calculations
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 11th May 2004, 05:27 PM #1 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?
 11th May 2004, 06:04 PM #2 diyAudio Member RIP   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 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 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 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 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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