I figured it out

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I figured it out

Posted by Alan A (A) on July 15, 2012 at 11:29:49

In Reply to: Basic Amplifier Question: Gain vs. Watts posted by Alan A on July 13, 2012 at 19:23:10:

Thanks to all who replied. Everyone who answered was correct, and the replies helped me to understand what was confusing me. Here's how I understand it:

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.
( That's really what I wasn't understanding ) That's why the Bryston, which offers a choice of input sensitivities, puts out 23 db with a 2 volt input and 29 dB with one volt input. The output dB ( or voltage, or watts, however we express it ) is the same. It's either 2 volts plus 23 dB or 1 volt plus 29 dB, because by doubling the voltage we are increasing the dB by 6. ( Of course, dB are dimensionless, and are just an expression of ratios )

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.

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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

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)

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