[JDUBS]

Guys

What is the easiest way to convert input sensitivity of 2.5v (to get to full power in a power amp) to gain expressed in dB?  The amp in question is a two-stage design with amplification factors of 16 and 3.5 (1st and 2nd stage, respectively).

I'm wondering how this amp would compare to an amp that has 24dB of gain.

Thanks guys.

-Jim

[Speedskater]

Let's see:
16dB has a voltage ratio of 6.310
3.5dB has a voltage ratio of 1.496
6.310 times 1.496 equals 9.440
A voltage ratio of 9.440 equals 19.5dB

Oh, the short way is 16 plus 3.5 equals 19.5

[JohnR]

For voltage, if the linear gain is X, then
 dB = 20 log X

(Where the log is base 10.)

Conversely going the other way
 X = 10 ^ (dB/20)

Also, linear gain multiplies, and dB adds. A quick to do it is to remember that a linear gain of 2 equals 6dB and a linear gain of 10 equals 20dB. Then you cheat by converting everything into multiples of 2 and 10.

So if you meant that the linear gain of the stages is 16 and 3.5, then 16 = 2x2x2x2 = 6+6+6+6dB = 24dB. A gain of 3.5 is a bit less than 2x2 = 6+6dB = 12dB, say 11dB. So the total (open loop, I presume) gain of the amp is 35dB. Feedback will lower that of course.

Input sensitivity is stated with respect to full power output... you would have to provide more information.

[JoshK]

For voltage, if the linear gain is X, then
 dB = 20 log X

(Where the log is base 10.)

Conversely going the other way
 X = 10 ^ (dB/20)

Also, linear gain multiplies, and dB adds. A quick to do it is to remember that a linear gain of 2 equals 6dB and a linear gain of 10 equals 20dB. Then you cheat by converting everything into multiples of 2 and 10.

So if you meant that the linear gain of the stages is 16 and 3.5, then 16 = 2x2x2x2 = 6+6+6+6dB = 24dB. A gain of 3.5 is a bit less than 2x2 = 6+6dB = 12dB, say 11dB. So the total (open loop, I presume) gain of the amp is 35dB. Feedback will lower that of course.

Input sensitivity is stated with respect to full power output... you would have to provide more information.

Very succinct explanation!