2. amps-preamps
  3. 156758-132585

What am I missing? Pre/power gain and input sensitivity.

I’ve read a few posts about power amps with lower gain needing a pre with additional gain, but no one seems to mention input sensitivity in those conversations. If my source outputs 2V and my power amp input sensitivity is only 1.2V then whether the power amp gain is 16dB or 26dB my pre amp is attenuating the signal and the amount of gain on the pre doesn’t matter at all. With a given set of speakers, to get the same SPL with 2 different amps they should just need to output the same voltage, regardless of how they get there.

Am I missing something?

cat_doorman

Showing 2 responses by erik_squires

erik_squires
16,853 posts
 
Remember that preamps tend to have fixed gain stages internally.
erik_squires
16,853 posts
 
See, here’s the thing about the internet: zero editorial standards

Some people need to prove this every day.

Think of gain as a voltage multiplier. 26 dB of amp gain ~ 20x the input voltage.

16 dB ~ 6x the input voltage.

Of course, every device has a fixed output voltage, set by the voltage rails of the power supply. This is one of the amp watt limits.

To drive an amplifier with 16 dB gain to the same level, you must provide 20/6 more volts, or 3.33 x the voltage.

This will require your pre to put out more voltage than normal, and also more noise.

Another way to think about this is that 1 Watt into 8 Ohms is 2.83 Volts.

At 26 dB, the input required is 0.141 Volts to create a 1 watt signal.

At 16 dB the input required is 0.47 Volts to create a 1 watt signal.

Best,
E



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