<div style="color:black;font: 12pt Arial, Helvetica, sans-serif;">The performance of those old transistors is based on actual measurements from the Motchenbacher & Fitchen book ca 1973 and Motchenbacher & Connelly book ca 1993 listings in their appendices. Both were capable of noise figures (noise above the thermal noise of the source resistance) when operated at appropriate collector currents. My point is that it's not difficult to make very low noise transistors, especially if it's PNP and only one is used rather than a pair. Much easier to do a single -transistor design at the secondary of a good transformer, of course.
<div><br>
</div>
<div>Bill Whitlock<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 <proaudio@bach.pgm.com><br>
To: proaudio@bach.pgm.com<br>
Sent: Sun, Jun 13, 2021 7:36 pm<br>
Subject: Re: [ProAudio] Microphones question<br>
<br>
<div id="yiv9029501521">
<div>
<div>I am surprise that you say 2N4403 has 1nV/sqrtHz. Are you sure?
The data sheet says nothing like that. I looked up the 2N4124, it
has some plots of noise figure vs freq for 200Ohm, and also noise
figure vs resistance. The noise figure is in dB, and the 2N4124 is
better, but the noise figure with a given source resistance
combines the impact of noise current and noise voltage. Not easy
to separate it.</div>
<div>I don't view the LM394 as today's transistor. Match pair is
better then singles, but I cant find it at major distributors. It
seems like history to me. I guess there is no point to claim that
it can be done much better. I would have to actually do it. I know
it can be improved a lot, but I will stick to my area -
conversion. <br clear="none">
</div>
<div>I think that experience is very valuable. I have some. But there
is new stuff all the time...</div>
<div>Regards</div>
<div>Dan Lavry<br clear="none">
</div>
<div><br clear="none">
</div>
<div class="yiv9029501521yqt9018291010" id="yiv9029501521yqt38111">
<div class="yiv9029501521moz-cite-prefix">On 6/13/2021 6:41 PM, Bill Whitlock via
ProAudio wrote:<br clear="none">
</div>
<blockquote type="cite">
</blockquote></div>
</div>
<div class="yiv9029501521yqt9018291010" id="yiv9029501521yqt78656">
<div>
<div style="color:black;font:12pt Arial, Helvetica, sans-serif;">At
the risk of belaboring the point, extremely low-noise mic
preamps were built using quality PNP bipolar transistors such as
the 2N4403 or 2N4124, both having e-noise of 1 nV per root Hz
across the audio band and corresponding i-noise making their
optimum source impedance around 200 Ω to 800Ω. Today's
transistors, even including the LM394 (50 NPN transistors
connected as one) won't do any better. Granted, if your design
world is ICs or FETs, they've gotten way better. But mic
preamps, built with today's "state-of-the-art" transistors and
"gee-whiz" circuit topologies are insignificantly quieter than a
good one built 50 years ago. I submit that a single low-noise
PNP transistor is the "state-of-the-art" input device (PNP
devices are inherently quieter). While differential pairs and
op-amps make circuit design simpler (you don't have to deal with
those pesky h-parameters for one), simply using a differential
pair increases noise over that of a single device. I'm often
dismayed by today's convenience-driven "cut and paste" circuit
designers.
<div><br clear="none">
</div>
<div>But I do agree that, if one is to accurately predict noise
performance of any given mic and preamp, both the reactance
and resistance of the mic are necessary.</div>
<div><br clear="none">
</div>
<div>Bill Whitlock<br clear="none">
<br clear="none">
<br clear="none">
<div style="font-family:arial, helvetica;font-size:10pt;color:black;"><font size="2">-----Original Message-----<br clear="none">
From: Dan Lavry via ProAudio <a shape="rect" class="yiv9029501521moz-txt-link-rfc2396E" ymailto="mailto:proaudio@bach.pgm.com" href="mailto:proaudio@bach.pgm.com" target="_blank" rel="noreferrer noopener"><proaudio@bach.pgm.com></a><br clear="none">
To: <a shape="rect" class="yiv9029501521moz-txt-link-abbreviated" ymailto="mailto:proaudio@bach.pgm.com" href="mailto:proaudio@bach.pgm.com" target="_blank" rel="noreferrer noopener">proaudio@bach.pgm.com</a><br clear="none">
Sent: Sun, Jun 13, 2021 5:33 pm<br clear="none">
Subject: Re: [ProAudio] Microphones question<br clear="none">
<br clear="none">
</font>
<div id="yiv9029501521">
<div>
<div>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.</div>
<div>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 clear="none">
</div>
<div>Regards</div>
<div>Dan Lavry<br clear="none">
</div>
<blockquote type="cite"> </blockquote>
</div>
<div>
<div class="yiv9029501521yqt6273669420" id="yiv9029501521yqt68077">
<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 clear="none">
</div>
<div>Bill Whitlock</div>
<div>AES Life Fellow<br clear="none">
<br clear="none">
<br clear="none">
<div style="font-family:arial, helvetica;font-size:10pt;color:black;"><font size="2">-----Original Message-----<br clear="none">
From: Dan Lavry via ProAudio <a shape="rect" class="yiv9029501521moz-txt-link-rfc2396E" ymailto="mailto:proaudio@bach.pgm.com" href="mailto:proaudio@bach.pgm.com" target="_blank" rel="noreferrer noopener"><proaudio@bach.pgm.com></a><br clear="none">
To: <a shape="rect" class="yiv9029501521moz-txt-link-abbreviated" ymailto="mailto:proaudio@bach.pgm.com" href="mailto:proaudio@bach.pgm.com" target="_blank" rel="noreferrer noopener">proaudio@bach.pgm.com</a><br clear="none">
Sent: Sun, Jun 13, 2021 2:25 pm<br clear="none">
Subject: Re: [ProAudio] Microphones question<br clear="none">
<br clear="none">
</font>
<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="yiv9029501521yqt4701292098" id="yiv9029501521yqtfd89738"><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" target="_blank" rel="noreferrer noopener">ProAudio@bach.pgm.com</a><br clear="none">
>> <a shape="rect" href="http://bach.pgm.com/mailman/listinfo/proaudio" target="_blank" rel="noreferrer noopener">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" rel="noreferrer noopener">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" target="_blank" rel="noreferrer noopener">ProAudio@bach.pgm.com</a><br clear="none">
<a shape="rect" href="http://bach.pgm.com/mailman/listinfo/proaudio" target="_blank" rel="noreferrer noopener">http://bach.pgm.com/mailman/listinfo/proaudio</a><br clear="none">
</div>
</div>
</div>
</div>
</div>
</div>
<br clear="none">
<fieldset class="yiv9029501521mimeAttachmentHeader"></fieldset>
<pre class="yiv9029501521moz-quote-pre">_______________________________________________
ProAudio mailing list
<a shape="rect" class="yiv9029501521moz-txt-link-abbreviated" ymailto="mailto:ProAudio@bach.pgm.com" href="mailto:ProAudio@bach.pgm.com" target="_blank" rel="noreferrer noopener">ProAudio@bach.pgm.com</a>
<a shape="rect" class="yiv9029501521moz-txt-link-freetext" href="http://bach.pgm.com/mailman/listinfo/proaudio" target="_blank" rel="noreferrer noopener">http://bach.pgm.com/mailman/listinfo/proaudio</a>
</pre>
<div id="yiv9029501521DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2">
<br clear="none">
<br clear="none">
<hr style="border:none;color:#909090;background-color:#B0B0B0;min-height:1px;width:99%;">
<table style="border-collapse:collapse;border:none;"><tbody><tr><td colspan="1" rowspan="1" style="border:none;padding:0px 15px 0px 8px;"> <a shape="rect" href="https://www.avast.com/antivirus" target="_blank" rel="noreferrer noopener"> <img src="https://static.avast.com/emails/avast-mail-stamp.png" alt="Avast logo" border="0"> </a> </td><td colspan="1" rowspan="1">
<div style="color:#3d4d5a;font-size:12pt;">
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" rel="noreferrer noopener">www.avast.com</a>
</div>
</td></tr></tbody></table>
<br clear="none">
<a shape="rect" href="https://mail.aol.com/webmail-std/en-us/suite#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2" target="_blank" rel="noreferrer noopener"> </a></div>
</div>
</div>
<div class="yiv9029501521yqt6273669420" id="yiv9029501521yqt12636">_______________________________________________<br clear="none">
ProAudio mailing list<br clear="none">
<a shape="rect" ymailto="mailto:ProAudio@bach.pgm.com" href="mailto:ProAudio@bach.pgm.com" target="_blank" rel="noreferrer noopener">ProAudio@bach.pgm.com</a><br clear="none">
<a shape="rect" href="http://bach.pgm.com/mailman/listinfo/proaudio" target="_blank" rel="noreferrer noopener">http://bach.pgm.com/mailman/listinfo/proaudio</a><br clear="none">
</div>
</div>
</div>
</div>
<br clear="none">
<fieldset class="yiv9029501521mimeAttachmentHeader"></fieldset>
<pre class="yiv9029501521moz-quote-pre">_______________________________________________
ProAudio mailing list
<a shape="rect" class="yiv9029501521moz-txt-link-abbreviated" ymailto="mailto:ProAudio@bach.pgm.com" href="mailto:ProAudio@bach.pgm.com" target="_blank" rel="noreferrer noopener">ProAudio@bach.pgm.com</a>
<a shape="rect" class="yiv9029501521moz-txt-link-freetext" href="http://bach.pgm.com/mailman/listinfo/proaudio" target="_blank" rel="noreferrer noopener">http://bach.pgm.com/mailman/listinfo/proaudio</a>
</pre>
</div>
</div>
</div>
<div class="yqt9018291010" id="yqt86972">_______________________________________________<br clear="none">ProAudio mailing list<br clear="none"><a shape="rect" ymailto="mailto:ProAudio@bach.pgm.com" href="mailto:ProAudio@bach.pgm.com" target="_blank" rel="noreferrer noopener">ProAudio@bach.pgm.com</a><br clear="none"><a shape="rect" href="http://bach.pgm.com/mailman/listinfo/proaudio" target="_blank" rel="noreferrer noopener">http://bach.pgm.com/mailman/listinfo/proaudio</a><br clear="none"></div>
</font></div>
</div>
</div>