<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"></head><body dir="auto"><div dir="auto">Scott is talking about maximum power transfer. A voltage source V with series source resistance RS is connected to load RL. If RL is open, there is no load current. If the load is a short, there is no load voltage. In either case no power on the load, it takes both current and voltage.</div><div dir="auto">So somewhere between zero and open there is a resistance for peak power transfer. It happen to be the peak of a parabola curve at RS=RL.</div><div dir="auto">I do agree that peak power transfer is not the only consideration, and different tradeoff is in order.</div><div dir="auto"><br></div><div dir="auto">Dan Lavry</div><div dir="auto"><br></div><div dir="auto"><br></div><div dir="auto"><br></div><div id="composer_signature" dir="auto"><div style="font-size:85%;color:#575757" dir="auto">Sent from Samsung Galaxy smartphone.</div></div><div dir="auto"><br></div><div><br></div><div align="left" dir="auto" style="font-size:100%;color:#000000"><div>-------- Original message --------</div><div>From: Bill Whitlock via ProAudio <proaudio@bach.pgm.com> </div><div>Date: 6/12/21 3:12 PM (GMT-08:00) </div><div>To: proaudio@bach.pgm.com, chris@chriscaudle.org, 6807.chris@pop.powweb.com </div><div>Subject: Re: [ProAudio] Microphones question </div><div><br></div></div>
<div style="color:black;font: 12pt Arial, Helvetica, sans-serif;">Where does that come from? The lowest noise at the output of an amplifier results from the source impedance being equal to or less than the "optimum" for a particular amplifier - where e-noise and I-noise are equal contributors to total noise. This is determined by the first-stage device and its operating point. The amplifier's input impedance is irrelevant. For example, a transistor with a collector current of 1 mA may have equal e and i noise with a 500 Ω source impedance, but the input impedance of the stage could be 100 kΩ! In most amplifiers, an intentional resistor is added only to lower input impedance for mic loading purposes
<div><br>
</div>
<div>See Motchenbacher & Fitchen, "Low Noise Electronic System Design" page 62 and others.</div>
<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 (in part)-----<br>
From: Scott Dorsey via ProAudio <proaudio@bach.pgm.com><br>
To: proaudio@bach.pgm.com; chris@chriscaudle.org; 6807.chris@pop.powweb.com<br>
Sent: Sat, Jun 12, 2021 2:42 pm<br>
Subject: Re: [ProAudio] Microphones question<br>
<snip><br>
<div dir="ltr"><br clear="none">In a perfect world the lowest noise would be when the input impedance of the<br clear="none">preamp matches the output impedance of the microphone, ....</div>
<div dir="ltr"><br clear="none">--scott
<div id="yqtfd96189" class="yqt3928987288"><br clear="none"><br clear="none">_______________________________________________<br clear="none">ProAudio mailing list<br clear="none"><a href="mailto:ProAudio@bach.pgm.com" shape="rect">ProAudio@bach.pgm.com</a><br clear="none"><a href="http://bach.pgm.com/mailman/listinfo/proaudio" shape="rect">http://bach.pgm.com/mailman/listinfo/proaudio</a><br clear="none"></div>
</div>
</font></div>
</div>
</div>
</body></html>