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

[Bob Katz]

Thanks, Bill. I've cc'ed your comment to the Pro Audio list.

Not all VUs to my experience incorporate the 3.9k internally. The oldest 
Weston meters required you to add an external resistor. I can't remember 
if the Sifams incorporate the resistor internally or not.

As a matter of fact, depending on the source impedance, you might want 
to be anal about it and decide to use a slightly smaller resistor if the 
source impedance is fairly high, as would have been the case in 
transformer coupled, older vintage gear, where a 3.6k plus the 300 ohm 
source impedance would have been a better match.

But I quibble in today's world, you would use a vu meter driver with 
negligibly small output impedance and admittedly a 3.9k ohm.


And who uses VU meters anymore?  I have a couple of outboard vintage 
pieces of gear with real VUs incorporated!


Best wishes,



Bob


On 1/28/21 1:12 PM, Bill Whitlock wrote:
> I'll tell you what I know about vintage VU meters: internally, there's 
> a series resistor, 3.9 kΩ usually, going to a copper-oxide rectifier 
> and then to the meter "movement" coil, which I believe has a 
> full-scale sensitivity of about 1 mA. Electrically, even if the 
> resistor is only a 1/4 watt type, an input of 31.2 Vrms or +32 dBu 
> would do no damage to the electrical parts. I doubt that any 
> mechanical damage would occur if the level slowly rose to that level 
> and remained indefinitely. But if suddenly or intermittently applied, 
> I'd expect that the "slamming" of the needle against the stops might 
> bend the needle!
>
> Bill Whitlock
> Whitlock Consulting
> Ventura, CA
> Office (805) 755-5018
> engineer_bill at verizon.net
>
>
> -----Original Message-----
> From: Bob Katz via ProAudio <proaudio at bach.pgm.com>
> To: proaudio at bach.pgm.com <proaudio at bach.pgm.com>
> Sent: Thu, Jan 28, 2021 9:26 am
> 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!
>
>
> Bob
> -- 
> If you want good sound on your album, come to Bob Katz 407-831-0233 
> DIGITAL DOMAIN MASTERING STUDIO Author: *Mastering Audio* Digital 
> Domain Website <https://www.digido.com/> No trees were killed in the 
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If you want good sound on your album, come to Bob Katz 407-831-0233 
DIGITAL DOMAIN MASTERING STUDIO Author: *Mastering Audio* Digital Domain 
Website <https://www.digido.com/> No trees were killed in the sending of 
this message. However a large number of electrons were terribly 
inconvenienced.

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