Amp gain calculation

For the life of me I can't recall how to calc this or where to find it (I've come real close though).

If I have an amp that requires a 600 mV signal for full power of 20W into 8 ohms, what is the gain (in dB).

Thanks in advance.
Hi Paul,

See my post near the end of this thread.

For the example cited in your post, the answer would be approximately 26.5 db.

Best regards,
-- Al