<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
</head>
<body>
<p>I agree that "basic principles" stay the same. But I think that a
lot has changed. In 1971, I met sales reps from semiconductor,
resistor, name it companies, and they left behind tons of data
books and specs. Today, I can get a data sheet (internet) in
seconds or a minute... The materials are better, the process is
tighter, the test equipment is better and more affordable. I keep
reading everyday, articles and about product introductions. One
can wait for technology to advance, and it has since 1971. We can
get better results as technology moves forward.</p>
<p>But yes, I would agree that the basic principles of networks,
components, theorems and circuits are the same. I know that, I am
a circuit designer... <br>
</p>
<p>Regards</p>
<p>Dan Lavry<br>
</p>
<blockquote type="cite"
cite="mid:705351072.97452.1623623617793@mail.yahoo.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div style="color:black;font: 12pt Arial, Helvetica, sans-serif;">This
is all well-known and much written about - and well explored
territory - and was when I got into pro audio in 1971 at
Quad-Eight, and at Jensen dug even deeper to understand how
input transformers can greatly benefit noise performance of
vacuum tubes, for example. Nothing has really changed ...
<div><br>
</div>
<div>Bill Whitlock</div>
<div>AES Life Fellow<br>
<br>
<br>
<div
style="font-family:arial,helvetica;font-size:10pt;color:black"><font
size="2">-----Original Message-----<br>
From: Dan Lavry 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><br>
Sent: Sun, Jun 13, 2021 2:25 pm<br>
Subject: Re: [ProAudio] Microphones question<br>
<br>
<div dir="ltr">I guess I should be more precise:<br
clear="none">
<br clear="none">
1. Measure noise voltage with a short (with gain).<br
clear="none">
<br clear="none">
2. Measure with 100K (with gain), remove (compute) the
resistor noise <br clear="none">
and noise voltage, leaves i*R where i is noise current.<br
clear="none">
<br clear="none">
Clearly the sums and differences are not add linearly,
you do sqrt of <br clear="none">
the "sum or difference" square...<br clear="none">
<br clear="none">
That would yield noise voltage and noise current of the
micpre, and <br clear="none">
leaves the mics out of it.<br clear="none">
<br clear="none">
Regards<br clear="none">
<br clear="none">
Dan Lavry<br clear="none">
<br clear="none">
<div class="yqt4701292098" id="yqtfd89738"><br
clear="none">
On 6/13/2021 1:00 PM, Dan Lavry via ProAudio wrote:<br
clear="none">
> Hi again,<br clear="none">
><br clear="none">
> Let me get away from sales and what people say,
and back to the <br clear="none">
> technical stuff:<br clear="none">
><br clear="none">
> Some here suggested to look at the mic output
impedance to tell us <br clear="none">
> about noise. That is only true for the mic pre
noise current <br clear="none">
> component. And in most real world cases, that is
the smallest <br clear="none">
> component. I think there is some confusion
regarding the noise <br clear="none">
> generated by the mic pre, it does not directly
relates to output <br clear="none">
> impedance. Say some noise is due to a PNP
transistor, how does that <br clear="none">
> relates to some output inductor? The combined
causes of noise in a <br clear="none">
> analog circuit is complex, circuit dependent and
component dependent. <br clear="none">
> The question is how to model it.<br clear="none">
><br clear="none">
> I would start by using 100KOhm (not 150 Ohm),
with gain it is enough <br clear="none">
> noise to be measured well. That noise (divide by
gain) is due to <br clear="none">
> current noise (the voltage component is
negligable). Now I will go <br clear="none">
> back to a short and measure the noise voltage of
the mic pre (of <br clear="none">
> course gain is needed). Now you have in and en
(noise current and <br clear="none">
> noise voltage).<br clear="none">
><br clear="none">
> That is what I want to know. I agree, it is
difficult to translate to <br clear="none">
> the consumer. I am not going to insist on much.
Just turned 76, got my <br clear="none">
> own problems. fs=24KHz would work fine. Youtube
can have a narrow <br clear="none">
> bandwidth for the old, you add lossless
compression and a 4KHz <br clear="none">
> wireless connection to the hearing aid...<br
clear="none">
><br clear="none">
> Dan Lavry<br clear="none">
><br clear="none">
><br clear="none">
> On 6/13/2021 5:06 AM, Scott Dorsey via ProAudio
wrote:<br clear="none">
>>> Scott Dorsey writes=20<br clear="none">
>>>> In a perfect world the lowest noise
would be when the input <br clear="none">
>>>> impedance =<br clear="none">
>>> of the<br clear="none">
>>>> preamp matches the output impedance
of the microphone, ....<br clear="none">
>>> Um, no. Your perfect world would need to
redefine a lot of other =<br clear="none">
>>> parameters for that to be so. A typical
emitter-follower microphone =<br clear="none">
>>> output may have an output impedance of
100 ohms but if you load it <br clear="none">
>>> with =<br clear="none">
>>> that value the distortion will be
significant, the output level <br clear="none">
>>> severely =<br clear="none">
>>> limited. Noise performance depends as
Bill mentioned on the operating =<br clear="none">
>>> point where current and voltage noise of
the input stage is optimal <br clear="none">
>>> for =<br clear="none">
>>> the source impedance of the microphone.
This is why IEC 60268-4 <br clear="none">
>>> requires =<br clear="none">
>>> specification of both output impedance
and minimum load impedance, <br clear="none">
>>> which =<br clear="none">
>>> is typically 10-20x the output
impedance.=20<br clear="none">
>> This is all true, unfortunately. It is far
from a perfect world.<br clear="none">
>><br clear="none">
>> I'm waiting for a noiseless transformer that
gives me free voltage <br clear="none">
>> gain and<br clear="none">
>> I'm not expecting to see one any time soon.
But once I get one I'll be<br clear="none">
>> able to get the largest possible signal into
an input in order to <br clear="none">
>> swamp the<br clear="none">
>> noise.<br clear="none">
>><br clear="none">
>> I'll point out that specifying minimum load
impedance is sufficient for<br clear="none">
>> a condenser microphone but that a dyanmic
microphone should also be <br clear="none">
>> specified<br clear="none">
>> for maximum load impedance. In some cases
with weak coupling where the<br clear="none">
>> electrical load does not make a large
proportion of the total damping <br clear="none">
>> that<br clear="none">
>> maximum might be infinite, but not all
microphones are like that.<br clear="none">
>><br clear="none">
>>> Dan is pointing out that one needs to
know the output impedance of <br clear="none">
>>> the =<br clear="none">
>>> microphone to design an optimal preamp
input stage, and this <br clear="none">
>>> information =<br clear="none">
>>> is seldom supplied. There are preamp
designs that don=E2=80=99t play =<br clear="none">
>>> well with very low output impedance mics,
for instance, because of <br clear="none">
>>> their =<br clear="none">
>>> negative feedback structure (applying NFB
to the input stage in <br clear="none">
>>> parallel =<br clear="none">
>>> with the input signal.) There are many
mics that don=E2=80=99t do <br clear="none">
>>> well =<br clear="none">
>>> when loaded with anything less than about
1500 ohms, and if you <br clear="none">
>>> parallel =<br clear="none">
>>> a few consoles at a venue without
considering this, performance may <br clear="none">
>>> be =<br clear="none">
>>> impacted. Performance may also be
different depending on impedance <br clear="none">
>>> from =<br clear="none">
>>> each side of the input to ground, which
may be related to the =<br clear="none">
>>> differential output impedance, or not.=20<br
clear="none">
>> This is all true, and it's why some preamps
perform better with some<br clear="none">
>> microphones while other preamps perform
better with other microphones.<br clear="none">
>><br clear="none">
>> But nobody sells an "optimized for condenser
microphones" or "optimized<br clear="none">
>> for moving coil dynamic microphones" preamp
although there are a <br clear="none">
>> couple of<br clear="none">
>> "optimized for ribbon microphones" preamps
out there.<br clear="none">
>> --scott<br clear="none">
>>
_______________________________________________<br
clear="none">
>> ProAudio mailing list<br clear="none">
>> <a shape="rect"
ymailto="mailto:ProAudio@bach.pgm.com"
href="mailto:ProAudio@bach.pgm.com"
moz-do-not-send="true">ProAudio@bach.pgm.com</a><br
clear="none">
>> <a shape="rect"
href="http://bach.pgm.com/mailman/listinfo/proaudio"
target="_blank" moz-do-not-send="true">http://bach.pgm.com/mailman/listinfo/proaudio</a><br
clear="none">
>><br clear="none">
><br clear="none">
<br clear="none">
-- <br clear="none">
This email has been checked for viruses by Avast
antivirus software.<br clear="none">
<a shape="rect" href="https://www.avast.com/antivirus"
target="_blank" moz-do-not-send="true">https://www.avast.com/antivirus</a><br
clear="none">
<br clear="none">
_______________________________________________<br
clear="none">
ProAudio mailing list<br clear="none">
<a shape="rect" ymailto="mailto:ProAudio@bach.pgm.com"
href="mailto:ProAudio@bach.pgm.com"
moz-do-not-send="true">ProAudio@bach.pgm.com</a><br
clear="none">
<a shape="rect"
href="http://bach.pgm.com/mailman/listinfo/proaudio"
target="_blank" moz-do-not-send="true">http://bach.pgm.com/mailman/listinfo/proaudio</a><br
clear="none">
</div>
</div>
</font></div>
</div>
</div>
<br>
<fieldset class="mimeAttachmentHeader"></fieldset>
<pre class="moz-quote-pre" wrap="">_______________________________________________
ProAudio mailing list
<a class="moz-txt-link-abbreviated" href="mailto:ProAudio@bach.pgm.com">ProAudio@bach.pgm.com</a>
<a class="moz-txt-link-freetext" href="http://bach.pgm.com/mailman/listinfo/proaudio">http://bach.pgm.com/mailman/listinfo/proaudio</a>
</pre>
</blockquote>
<div id="DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2">
<br /><br />
<hr style='border:none; color:#909090; background-color:#B0B0B0; height: 1px; width: 99%;' />
<table style='border-collapse:collapse;border:none;'>
<tr>
<td style='border:none;padding:0px 15px 0px 8px'>
<a href="https://www.avast.com/antivirus">
<img border=0 src="https://static.avast.com/emails/avast-mail-stamp.png" alt="Avast logo" />
</a>
</td>
<td>
<p style='color:#3d4d5a; font-family:"Calibri","Verdana","Arial","Helvetica"; font-size:12pt;'>
This email has been checked for viruses by Avast antivirus software.
<br><a href="https://www.avast.com/antivirus">www.avast.com</a>
</p>
</td>
</tr>
</table>
<br />
<a href="#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2" width="1" height="1"> </a></div></body>
</html>