V/U Meter Buffer and Calibration

[MoltenVoltage]

I have a bunch of analog VU meters scrounged from old cassette players and can't seem to find a good schematic for a buffer circuit (the GGG one that was in a previous thread is no longer available).

I was also wondering if anyone knows what the correct calibration is for -20dBu, 0dBu, and +3dBu.

I have read the standard for 0dBu is 1.23 volts, but have also read that its .78 volts.

Thanks!

[alanlan]

0VU is usually +4dBu or 1.228V rms.  

[idiot savant]

0VU is usually +4dBu or 1.228V rms.  

not always!
check out these good articles:

http://soundsofnewmexico.com/PDF_Files/dB_or_Not_dB.pdf
http://www.jlmaudio.com/AT51%20DIY%20VU.pdf

[MoltenVoltage]

0VU is usually +4dBu or 1.228V rms.  

not always!
check out these good articles:

http://soundsofnewmexico.com/PDF_Files/dB_or_Not_dB.pdf
http://www.jlmaudio.com/AT51%20DIY%20VU.pdf

Great articles, many thanks!

For those who haven't read yet, the first one explains the various calibration standards and the second one has a universal schematic with a calibration control built in.

[alanlan]

not always!

I did say usually.  I work in broadcast (mixing desk design).  The BBC uses this convention.  Several European and US broadcasters do not, which is why we offer an adjustment.  Same goes for PPM meters.

The truth is you can put it wherever you like.  It's not illegal.