DS> Amplifier Gain - Amplifier spec sheets usually list a "gain" or
 DS> "voltage gain" specification. Gain is usually expressed in decibles
 DS> (such as +32db) or as a multiplier (such as 40 times). Given an
 DS> amplifier with a gain of 32db or 40X, this means that the amplifier
 DS> signal is amplified by 32db or multiplied by a factor of 40.
 MI> I find myself questioning Patrick Price's qualifications to write such a 
So do I, but not for that reason.  
 MI> piece.  For one thing, it SOUNDS like he's saying 32dB 
 MI> = a power of 40... which it doesn't.  The "decibel" 
 MI> scale is logarithmic and does not denote any specific 
 MI> units, but rather a ratio or relationship.  A 3dB 
 MI> Decibels are additive -- in fact, increasing a signal 
 MI> 30dB is the equivalent of increasing the signal by a 
 MI> factor of 1000.  A 33dB boost would be a gain of 2000.
That would be a POWER ratio of 2000, with 32 dB being approximately 1600, 
which happens to be 40 squared.  40 as a voltage ratio does match 32 dB 
closely, but would require that input and output Z be constant.  The author 
is playing fast and loose with typical measurement sloppiness playing to 
readers who are likely to be confused and not question such details.  
1 volt in with a voltage amplification factor of 40 would yield 200 W into 8 
ohms, a reasonable example.  
Attempting to relate a voltage input level to amp full output, or amp 
specific output, is a perpetual industry debate.  Since we're usually talking 
bridging inputs, and outputs with various nominal ratings from 2-16 ohms, and 
actual loads that vary from 1-5 through 5-50 ohms or more widely, the entire 
concept of dB cannot be applied literally to audio power amp I/O comparisons, 
as it might be to 600 ohm audio line amps or 50 ohm RF amps.  
The author's use of dB is somewhat akin to the industry bastardization 
sometimes called dBu, dB "unreferenced".  
Terry
--- Maximus 2.01wb
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