db gain vs input sensitivity
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 11th March 2017, 10:20 PM #1 georgehifi   diyAudio Member     Join Date: Sep 2003 Location: Manly Australia (Jewel of the Pacific) db gain vs input sensitivity Just to prove to my friend if a power amp has 24db of gain, what is it's input voltage sensitivity for full 90w output, he's watching Cheers George __________________ Avatar : Production Lightspeed Attenuator www.lightspeedattenuator.com Last edited by georgehifi; 11th March 2017 at 10:42 PM.
 11th March 2017, 10:29 PM #2 scottjoplin   diyAudio Member     Join Date: Dec 2015 Location: Penrhyndeudraeth __________________ Woofer Assisted Wideband is the New Testament renounce the anachronistic acronym FAST
 11th March 2017, 10:53 PM #3 scott wurcer   diyAudio Member     Join Date: Jan 2004 Location: dorchester ma __________________ "The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."
rayma
diyAudio Member

Join Date: Apr 2011
Quote:
 Originally Posted by georgehifi if a power amp has 24db of gain, what is it's input voltage sensitivity for full 90w output.
90W into 8R --> VxV/8R=90 W --> V= 26.8V output voltage at 90W

Gain=24dB --> 24=20 x log(26.8/Vin) --> Vin= 1.69V input voltage for full output voltage/power

All voltages in Vrms.

Last edited by rayma; 11th March 2017 at 11:19 PM.

JMFahey
diyAudio Member

Join Date: Mar 2009
Location: Buenos Aires - Argentina
Quote:
 Originally Posted by georgehifi Just to prove to my friend if a power amp has 24db of gain, what is it's input voltage sensitivity for full 90w output, he's watching Cheers George
Incomplete question, you did not mention load impedance.
Without that, any answer is just a guess.

Unless it includes "all answers", meaning a sensitivity vs. impedance table.
__________________
Design/make/service musical stuff in Buenos Aires, Argentina, since 1969.

georgehifi
diyAudio Member

Join Date: Sep 2003
Location: Manly Australia (Jewel of the Pacific)
Quote:
 Originally Posted by JMFahey Incomplete question, you did not mention load impedance. Without that, any answer is just a guess. Unless it includes "all answers", meaning a sensitivity vs. impedance table.
90w 8ohms

Cheers George
__________________
Avatar : Production Lightspeed Attenuator
www.lightspeedattenuator.com

andyr
diyAudio Member

Join Date: Nov 2003
Location: Melbourne (Oz, not Florida!)
Quote:
 Originally Posted by JMFahey Incomplete question, you did not mention load impedance. Without that, any answer is just a guess.
Or you assume the customary 8 ohms, as Ray did.

Andy

 12th March 2017, 09:37 AM #8 scottjoplin   diyAudio Member     Join Date: Dec 2015 Location: Penrhyndeudraeth Or you hand him a fishing rod instead of a fish __________________ Woofer Assisted Wideband is the New Testament renounce the anachronistic acronym FAST
 12th March 2017, 02:32 PM #9 DF96   diyAudio Member   Join Date: May 2007 Surely on this forum it should be the parts for him to make his own fishing rod?
 13th March 2017, 10:29 AM #10 AndrewT   R.I.P.   Join Date: Jul 2004 Location: Scottish Borders Rayma guessed the speaker impedance correctly and gave the correct answer for full power sensitivity. Vmax = sqrt(max power * Speaker Impedance) = sqrt (90*8) = 26.8Vac Gain factor = invLog(dBgain / 20) = inLog(24/20) = 15.85 Sensitivity = Vmax / Gain factor = 26.8/15.85 = 1693mVac Any CDP and similar digital source will need to be attenuated to prevent the amplifier from clipping. __________________ regards Andrew T.

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