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<p>Thanks, Bill. I've cc'ed your comment to the Pro Audio list.</p>
<p>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. <br>
</p>
<p>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. <br>
</p>
<p>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.</p>
<p><br>
</p>
<p>And who uses VU meters anymore? I have a couple of outboard
vintage pieces of gear with real VUs incorporated!<br>
</p>
<p><br>
</p>
<p>Best wishes,</p>
<p><br>
</p>
<p><br>
</p>
<p>Bob<br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 1/28/21 1:12 PM, Bill Whitlock
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:585915434.784420.1611857579748@mail.yahoo.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div style="color:black;font: 12pt Arial, Helvetica, sans-serif;">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!
<div><br>
</div>
<div>Bill Whitlock</div>
<div>Whitlock Consulting</div>
<div>Ventura, CA</div>
<div>Office (805) 755-5018</div>
<div><a class="moz-txt-link-abbreviated" href="mailto:engineer_bill@verizon.net">engineer_bill@verizon.net</a><br>
<br>
<br>
<div
style="font-family:arial,helvetica;font-size:10pt;color:black">-----Original
Message-----<br>
From: Bob Katz via ProAudio <a class="moz-txt-link-rfc2396E" href="mailto:proaudio@bach.pgm.com"><proaudio@bach.pgm.com></a><br>
To: <a class="moz-txt-link-abbreviated" href="mailto:proaudio@bach.pgm.com">proaudio@bach.pgm.com</a> <a class="moz-txt-link-rfc2396E" href="mailto:proaudio@bach.pgm.com"><proaudio@bach.pgm.com></a><br>
Sent: Thu, Jan 28, 2021 9:26 am<br>
Subject: [ProAudio] VU meter permitted overdrive with a sine
wave...<br>
<br>
<div id="yiv8180782943">
<div>
<div>This list has been remarkably silent, but I am very
grateful that it's around when I have a question to
ask AUDIO EXPERTS.</div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div><br>
</div>
<div>Thanks and happy New Year!</div>
<div><br>
</div>
<div><br>
</div>
<div>Bob<br>
</div>
<div class="yiv8180782943moz-signature">-- <br>
<pre><font face="3D"Courier"">
If you want good sound on your album, come to
Bob Katz 407-831-0233 DIGITAL DOMAIN MASTERING STUDIO
Author: <b>Mastering Audio</b>
<a rel="nofollow noopener noreferrer" target="_blank" href="https://www.digido.com/" moz-do-not-send="true">Digital Domain Website</a>
No trees were killed in the sending of this message. However a large number
of electrons were terribly inconvenienced.</font>
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</blockquote>
<div class="moz-signature">-- <br>
<pre><font class="3D""" face="3D"Courier"">
If you want good sound on your album, come to
Bob Katz 407-831-0233 DIGITAL DOMAIN MASTERING STUDIO
Author: <b>Mastering Audio</b>
<a href="https://www.digido.com/">Digital Domain Website</a>
No trees were killed in the sending of this message. However a large number
of electrons were terribly inconvenienced.</font>
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