Calibrating my VU meters

[dietrich10]

Try to be as simple with this as I can

Neumann lathe installed last yr and I use Coleman meters to check signals from the lathe. Last week when I was doing monthly calibration using tone record and playback set to 0VU on the lathe turntable arm showed +1 when should be 0.
Played audiotest tone software thru both converters as setup before and still showed 0 VU.

So at this point I know VU is calibrated correct or needs to be turned back 1dB.

Today buddy came over with some old HP signal generator/meter and another meter only. both units 600in/out impedence. nothing made sense-all levels all over the place.
should a 5k tone coming from this older HP unit read +4VU? Meaning a 1k or 5k tone that shows being 0 on the HP meter should read +4 VU on the coleman?

thanks
D

[David Kulka]

It sounds like you are skipping a step or two.

You can use the HP oscillator as a reference source, but you need to use an external, trusted meter to check it's output level before going any further.

So:

Patch your HP into the system and meter it with the Colemans. Also, connect the external meter to the HP output. Adjust the HP to make your external meter read +4 dbV or 1.23 volts. Don't worry about the impedance, it doesn't matter here.

Now we have established that the the HP is outputting correct reference level. Adjust the Coleman meters to read zero VU.

After the above steps are done, you can go back and trim the RIAA preamp on the lathe playback arm for zero VU at reference cutting level. But don't adjust the meters -- adjust the playback preamp.

[dietrich10]

Thanks David.

Makes sense to me.

Trying next to match both sets of converters.
Have audiotest for osx. -14 dBFS should =0 VU on the coleman?

best
D