Vu meter alternative calbration

[Nickos]

I've a pair of Sifam standard VU meter and I would like to change the calibration.
Now I use a 3k6 resistor to read 0vu with 1.734 Vac, can someone tell me the value of the resistor to read -10VU ?
Thank you very much.

 

[abbey road d enfer]

Impossible! Even with no series resistor. -10dBv is just too small to overcome the rectifiers threshold.
Generally speaking, replacing the 3.6k with another value twists the meter's linearity.
In some broadcast applications, nominal level used to be +8dBu; some manufactures just increased the value of the series resistor (check UREI 1176, they switch to 8.2k for +8 operation), but the range became inaccurate. The proper way was to use an L-pad with 4dB attenuation and 3.6k output resistance.
For -10dBv, you must have an active gain stage; always a good idea since connecting a meter directly across an output is a source of THD (and not a nice one at that).

 

[Nickos]

Ok... so sometihng like the JLM "Vu buffer kit" will do the job?

http://www.jlmaudio.com/VU%20Buffer%20Circuit.gif

It has a small calibration trim, maybe can be modified to reach -10?

 

[Holger]

Just use two off-board trimmers and a switch to use them alternatively as I did in my Stereo Pico:
http://www.picocompressorforum.com/forum/php/viewtopic.php?f=7&t=293&sid=15cd6d2c95580243756fba7f65577ad1