[R-390] Line Level meter

[2002tii]

Brian wrote:

>0dBm is 1.228Vrms

The de facto standard for audio dB measurements is 600 ohms (which is 
also the 390/A output impedance), or 0 dBm = 0.775 vrms.  1.228 vrms 
is +4 dBm.  +4 dBm was often used in the US as a "0 VU" reference in 
the prehistoric days, and was obtained with a meter of a specific 
resistance that reads 0 VU = 0 dBm when a sine wave was applied 
directly to the meter, and a 3900 ohm resistor in series with the 
meter (to make it a "bridging" load on the 600 ohm line).

If anyone cares, the VU meter standards are ANSI C16.5-1942 and IEC 60268-17.

Best regards,

Don