db gain vs input sensitivity

[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

 

[scottjoplin]

Jands - Sensitivity, Gain, Power, Volume - Different Words For The Same Thing?

 

[scott wurcer]

Efficiency and sensitivity conversion - loudspeaker percent and dB per watt and meter loudspeaker efficiency versus sensitivity vs speaker sensitivity 1 watt = 2,83 volt box chart - sengpielaudio Sengpiel Berlin

 

[rayma]

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.

 

[JMFahey]

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.

 

[georgehifi]

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

 

[andyr]

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

 

[scottjoplin]

Or you hand him a fishing rod instead of a fish

 

[DF96]

Surely on this forum it should be the parts for him to make his own fishing rod?

 

[AndrewT]

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.

 

[VinDiesel]

helpful... but if i'm given an amplifier schematic on the web or on this forum ..just the schematic with no specs is there any way to know it's gain in order to calculate the input sensitivity....

 

[scottjoplin]

If by no specs you mean no component values then no

 

[VinDiesel]

no..the component value are known .. by specs i mean it's gain and input sensitivity...

 

[scottjoplin]

Gotcha. Then yes the gain can be calculated. It would depend upon the circuit topology. For example for an amplifier using negative feedback the gain is set by the negative feedback potential divider network

 

[DF96]

If it is a conventional circuit, acting like the non-inverting opamp configuration, then you can work out the gain from the feedback components. You can estimate the power output from the supply rail voltage.

 

[VinDiesel]

scottjoplin,DF96
is there any link or document that i can view to got it ...

 

[scottjoplin]

This might be a good place for you to start. Elliott Sound Products - Audio Power Amplifier Design Guidelines It's difficult to know what to recommend without knowing more about what you do and don't know. But I hope this is helpful and there is a lot more information on ESP pages for all levels