[ProAudio] VU meter permitted overdrive with a sine wave...

Crispin HT crispin at crookwood.com
Thu Jan 28 10:47:46 PST 2021

The Sifams we use are a taut band design – a rectangular wire takes the current in and out of the coil, suspended in a magnet.

The torsion on the wire counters the electric force to make the meter stop at the desired level.


When you overload it, the meter needle stops the coil from rotating anymore, and as you pass more current through it, the coil will start to move away from the centre of the magnet, stretching the taut wire, and potentially grounding the coil on the magnet.


My guess is you can put a lot more than +6 into it without damage for a period of time, a bit like heatsinking on a semi, high overload for a short time, low overload for a long time.


I’m guessing + 12VU should be OK for a longish period ( 4 x voltage, 16 x power), but YMMV


Kind Regards

Crispin Herrod-Taylor
Managing Director, Crookwood
 <http://www.crookwood.com/> www.crookwood.com  

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From: ProAudio <proaudio-bounces at bach.pgm.com> On Behalf Of Bob Katz via ProAudio
Sent: 28 January 2021 17:27
To: proaudio at bach.pgm.com
Subject: [ProAudio] VU meter permitted overdrive with a sine wave...


This list has been remarkably silent, but I am very grateful that it's around when I have a question to ask AUDIO EXPERTS.


Who here knows the acceptable rating of a standard mechanical VU meter above 0 VU with a sine wave?  If I recall correctly, they are designed to accept as high as +6 VU or even higher. For example, when doing testing of a tape recorder for headroom. It's still ideal to shut off the meter, but in some cases that's not possible.



Thanks and happy New Year!





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