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Posted by jeffreybehr (A) on July 15, 2012 at 15:32:22

In Reply to: I figured it out posted by Alan A on July 15, 2012 at 11:29:49:

Alan: "The short answer to my question is that the gain specification is simply being expressed as a dB gain based NOT on just the dB increase the amp is putting out, but rather, based on the TOTAL of the input voltage PLUS the output dB."

Nope. 'Gain' is the increase in ONLY VOLTAGE; that measurement and concept has NOTHING to do with power. An amp that outputs 10 Volts (AC; RMS) into an 8-Ohm load when driven by 1VAC(RMS) has a VOLTAGE gain of 20dB*. More typical is that an amp will output 20 Volts from 1VAC in; that Voltage gain is 26dB.

Alan: "Similarly, to use the Theta amps as an example, as the Watts went up, they were also raising the input sensitivity, so that the same 26 dB gain they were listing needs to be *Added* to the (increasing ) voltage of the input sensitiviy. That's where those extra watts were going. The reasons for the manufacturer raising the input sensitivity is not clear to me, but at least partly it has to do with keeping the system quiet, as I understand it, but I suppose there are other reasons as well.

"In answer to roscoeiii below, I'm not sure why manufacturers talk about watts rather than dB, (other than tradition, and because adding 100 watts is more impressive than adding 3db to a 100 watt amp) but perhaps my problem in adding voltage to dB gain is one reason. Perhaps it's easier to go from watts to db than to convert volts to dB and add."

Nope again. Voltage and Voltage gain by themselves have nothing to with power. Power obviously is a product of Voltage into a load--hence current flow--but Voltage gain has only to do with the fixed amount of amplification a circuit is built to produce. An amp built with 20dB of Voltage gain will always increase the Voltage by 10...until it reaches its maximum power; it then starts clipping its output waveform with further increases in input Voltage.

* A deciBel is an expressions of the ratio of two POWERS, not Voltages. When we all misuse dB as a ratio of two Voltages, it's more accurate to use the term 'Voltage gain' in dB. BTW a deciBel is 10 times a Bel, that being the base-10 log of the ratio of two power amounts.

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Follow Ups Full Thread

Topic - Basic Amplifier Question: Gain vs. Watts - Alan A 19:23:10 07/13/12 (12)

I figured it out - Alan A 11:29:49 07/15/12 (3)

You've got some of it right. - jeffreybehr 15:32:22 07/15/12 (2)

RE: You've got some of it right. - Alan A 17:18:05 07/15/12 (1)

RE: You've got some of it right. - Palustris 09:47:28 07/16/12 (0)

RE: Basic Amplifier Question: Gain vs. Watts - roscoeiii 10:07:15 07/15/12 (1)

RE: Basic Amplifier Question: Gain vs. Watts - mls-stl 11:07:53 07/15/12 (0)

RE: Basic Amplifier Question: Gain vs. Watts - mls-stl 07:44:01 07/14/12 (4)

RE: Basic Amplifier Question: Gain vs. Watts - Alan A 20:42:14 07/14/12 (2)

RE: Basic Amplifier Question: Gain vs. Watts - AbeCollins 10:11:15 07/15/12 (0)

RE: Basic Amplifier Question: Gain vs. Watts - mls-stl 06:20:49 07/15/12 (0)

Excellent and practical explanation !! -nt - AbeCollins 19:51:11 07/14/12 (0)

Depends on hwo the gain spec is specified. Sometimes it's how many mV in to get 1 watt into an 8 ohm resistoo - Timbo in Oz 20:37:02 07/13/12 (0)

Follow Ups

You've got some of it right. - jeffreybehr 15:32:22 07/15/12 (2)

RE: You've got some of it right. - Alan A 17:18:05 07/15/12 (1)

RE: You've got some of it right. - Palustris 09:47:28 07/16/12 (0)

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