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In Reply to: Need help understanding/comparing Amps specs (Gain) posted by SteveLim on March 3, 2007 at 05:56:46:
Here you are...Slew Rate: This is a term used to describe how quickly the output of an amplifier can track its input. Slew Rate is measured in volts per microsecond and the higher the value, the better the Slew Rate.
Gain: This is a ratio between the magnitude of an amplifier's output to the magnitude of a (usually specified) input. As a ratio, gain would normally not have a unit applied, but a unit was created specifically for use in measuring "Loss" (over telephone lines) and was adopted for "Gain" and is the "bel", although the fractional unit of one-tenth (or Decibel = dB) is most commonly used.
This ratio (and therefore, "gain") can be measured in terms of three main determinants that should not be mixed:
1) Voltage
2) Power
3) CurrentIt is also important to understand that the Decibel is a logarithmic unit and not a linear unit, so the formula for calculating "Gain" would be:
Gain = Log (Output / Input)
So, Power Gain = Log (Output power / Input Power) - etc...
Having said all that, I would personally only use specifications for initial elimination and use my ears for any final selection - it is, after all, how a system sounds that really counts and not how it measures.
Follow Ups:
Great! Thanks for the explanation.
Think i follow your explanation, but looking at the specs stated, i am not sure what they are saying. I am not sure if can direct compare because the units given are different, one states 23dBW and other 29dB , and also seems some link to input sensitivity??Ultimately what i wish to know is, for the amps stated in my post, does the prospective amp that i am considering have a higher gain than my current amp ?
Please enlighten which of the 2 amps has higher gain ?
...nor tell him how to do it correctly.Steve, the gain of an amplifier is usually calculated using only the input and output Voltages. This is actually a misuse of deciBel, which is a ratio of 2 POWER, not Voltage, amounts, but it's easy to do, and, more importantly, it works.
First the output voltages.
A. 200 Watts into 8 Ohms is 40 Volts (using the formula V(squared)/R. The ratio of Voltages is then 40/1.68, and 10 times the base-10 Log of that is 24.8, so this amp has 24.8dB of Voltage gain into 8 Ohms.B. 300 Watts into 8 Ohms is 49.0 Volts. The ratio of Voltages is then 49/1.8, and 10 times the base-10 Log of that is 25.8, so this amp has 25.8dB of Voltage gain into 8 Ohms.
So the prospective amp has 1dB more gain than your amp, which you may not even notice if your volume control is continuous and not stepped. BUT...it's going the wrong way if I understand you correctly...that you want to be able to use the volume control at higher rotational positions. Yes?
PS. I use an Excel spreadsheet to calc the Log numbers. You too can. :-)
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Tin-eared audiofool and obsessed landscape fotografer.
http://community.webshots.com/user/jeffreybehr
Thanks. Very much clearer now about the gain differeces.Yes, i will be giving it an audition before i buy it.
Just that before i buy , i wanted to make sure the gain of the new amp isn't higher than the current amp. So i won't end up not able to use the amp with my preamp, and end up changing even more things. Thanks again. :-)
... and I was concerned that too much emphasis was being placed on the gain and not enough on how the two amps sounded. I've met too many people that have fallen into that trap and regretted it.So, if one believes that someone plans to jump off a cliff, is it wrong to point out a bench to sit on some 50 yards from the cliff-edge and better to explain to them how to jump off?
:-)
Thanks too Devil for your help and advise regards taking care of the sound quality by listening to it.
Yes, i have every intention to audition it.
Just wanted to make sure the gain compatibility was not worse off than my current amp , so that i don't end up cannot use it my my preamp and current setup. :-)
And of course gain has nothing to do with sonic quality, but we're not that far yet.
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Tin-eared audiofool and obsessed landscape fotografer.
http://community.webshots.com/user/jeffreybehr
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