XPost: comp.sys.mac.system   
   From: burns4@nowhere.com   
      
   On 2/9/14, 6:49 PM, Salmon Egg wrote:   
   > In article , J Burns    
   > wrote:   
   >   
   >> If you need to transfer the most power, matching impedance is important.   
   >>    If the output circuit has reactive components, matching impedance is   
   >> important.   
   >>   
   >> The amplifier didn't have any capacitors or inductors in the output.   
   >> Wanting only a few milliwatts from a 50-watt amp, I wasn't worried about   
   >> power transfer.   
   >   
   > First, move responses to alt.engineering.electrical.   
   >   
   > Most, should I say all, have large negative feedback. Gain these days is   
   > cheap. Negative feedback removes distortion arising from nonlinearity of   
   > the power components in the amplifier.   
   >   
   > In particular, voltage feedback makes amplifiers look like low impedance   
   > sources. Speaker wire resistance adds to the impedance of the effective   
   > source driving the speaker. Even so, unless there are long runs of   
   > relatively small speaker wire, that increase in source impedance is   
   > small. Monster cable is an expensive and unnecessary way of minimizing   
   > the effective source impedance.   
   >   
   > Negative current feedback increases source impedance to where the   
   > amplifier becomes a constant current source. Any natural vibrations of   
   > the speaker will not be damped under those circumstances.   
   >   
   If the impedance of my phones varied from 20 to 170 ohms depending on   
   frequency, I could say a 220-ohm resistor in series had the effect of   
   negative current feedback.  With my resistor network, the amplifier saw   
   more than 20 ohms, but the phones saw 1.8 ohms, meaning 99.2% less   
   negative current feedback than from the standard resistor.   
      
   --- SoupGate-Win32 v1.05   
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