Is there a formula to convert v/mV to dB?

[Category 5]

Trying to find the dB equivalent of 200 v/mV

It is the open loop gain of the 2520 op-amp, but I can;t relate to v/mV!

Thanks!
Shane

 

[volki]

why don't you check this META for basic understanding:

http://www.groupdiy.com/index.php?topic=2423

dB is always a relative expression, so you need a basic voltage to relate your voltage to. in pro audio you use "dBu", with the basic voltage being .775v.

the formula is 20*log(X/.775v), where X is the voltage to be expressed in dB.

HTH

 

[alk509]

[quote author="Category 5"]It is the open loop gain of the 2520 op-amp[/quote]

200V/mV = 200V at the output for every mV at the input.

20*lg(200/.001) = 106dB

Peace,
Al.

 

[Category 5]

Thanks guys!

Shane

 

[PRR]

> I can't relate to v/mV

A different way to express gain, in a way that once was practical. 1mV at the input makes 200V at the output. Gain is then 200V/1mV= 200,000:1. Saying 50V/mV actually made sense in vacuum tube op-amps, and the custom persisted until sand-state opamps grew to absurd gain.

BUT: what use is knowing that? Because this is surely a DC gain. That is (marginally) useful in low-speed DC analog computers. And it has "Wow!" factor. But knowing a little about opamps, I expect that gain starts to fall by 100Hz, and may be less than 20V/mV or 20,000:1 in the middle of the audio band, less than 1V/mV or 1,000:1 in the top of the audio band.

In audio, Gain Bandwidth Product is important, DC gain normally is of little or no interest for the usual opamp designs and compensations.