Let's say I have a pre-amp that read volume as -dB.

I connect it to an 50W amp. Play music at -35dB and get a certain sound level. I replace the amp with a 300W amp and play music again at -35dB, is it playing at the same level? Or louder?

I know the 300W amp can play louder w/o distorting. But does it play louder at the same pre-amp volume setting? Or just let me increase the volume to higher setting w/o distortion?

I know, dumb question and I should know by now.

You can't judge anything based on the volume knob setting.
Gain may vary from machine to machine.
FWIW, every 3db is a doubling if volume.

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You can't judge anything based on the volume knob setting.

So, even w/ the same pre-amp and setting it to, say, -35dB, I can't tell what the volume level will be between a 50W amp and a 300W amp? There is no correlation at all?

Is there not any gain control on the main amps?

Without any adjustment control, I would guess that the 300 Watt amp would probably sound a lot louder (3X ?) than the 50, for the same preamp setting (given that it is audible with the 50 Watt amp).

Otherwise, where would the additional 250 Watts be going?

If the amplifier input sensitivity is set correctly, you will get 0 watts to maximum watts output of the amp when the head unit goes from 0 to maximum output. Labels don't really matter.

So the answer is yes, you will get more power output from the higher wattage amp at any given radio volume setting.

Thanks guys - makes sense but wasn't sure.

This influences what I'm looking for in an amp then.

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Labels don't really matter

Wait, what. Excuse me....

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Originally posted by smschulz:
You can't judge anything based on the volume knob setting.
Gain may vary from machine to machine.
FWIW, every 3db is a doubling if volume.

Ummm, actually, every 3 db is a doubling of amplifier output power. A 10 db increase in power is ~ a doubling of "volume"... Unless we're not referring to DBA or DBSPL.

As noted, everything is relative to a baseline...

^^^ yeah that's what I meant.

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Originally posted by stoic-one:

quote:

Originally posted by smschulz:
You can't judge anything based on the volume knob setting.
Gain may vary from machine to machine.
FWIW, every 3db is a doubling if volume.

Ummm, actually, every 3 db is a doubling of amplifier output power. A 10 db increase in power is ~ a doubling of "volume"... Unless we're not referring to DBA or DBSPL.

As noted, everything is relative to a baseline...

Stoic-one is right, 3dB is approximately a doubling of power, 10dB is increasing the power by a factor of 10 (3dB + 3dB + 3dB + 1dB ~ power * 2 * 2 * 2 * 1.25 = power * 10).

With human hearing, increasing power by a factor of 10 (10dB) is perceptually about doubling the volume. 3dB is generally accepted as about the smallest perceptible change in volume.

The way this stuff is supposed to work, everything except the amplified signal going to the speakers (interconnects from components to preamp, interconnects from preamp to amplifier(s), etc) is referenced to "line level."

There are some caveats, but let's ignore them and say "line level" means a "max volume" signal is 1V RMS.

Let's say you have a CD player going to a preamp going to an amplifier.

The CD player's signal to the preamp is supposed to be at line level - the "loudest" signal it should be able to put out is 1V RMS. We can also call this "0dB" with reference to line level - 0dB means no change in power, which means the same as line level.

Then, again hypothetically, the preamp isn't supposed to output above line level. To output the 0dB CD player signal at line level, the preamp doesn't change the power level. The volume setting on the preamp is 0dB (no change). Now the preamp is sending the 0dB CD player signal at 0dB to the amplifier.

In theory, the amplifier is supposed to output its maximum power/volume when fed a line level signal, and you can't "turn it up" past that, you can only "turn it down" from there by decreasing the signal.

If you want turn the volume down to half of maximum volume, you turn the preamp volume down to -10dB. Now the preamp's output is at -10dB from line level, and the amplifier puts out 10dB less power, which is approximately half as loud.

In practice, that's pretty much how it works big-picture, but consumer equipment generally isn't perfectly referenced to line level, some can't put out line level at all (only somewhat smaller signals), some can go well above line level, etc.

Now, on the question comparing a 50W amp and a 300W amp. The formula for decibels is 10*log10(power ratio). IN THEORY, the 300W amp should be 10*log10(300/50) ~ 8dB louder, so considerably louder but not quite twice as loud.

HOWEVER, amplifier power ratings are NOTORIOUSLY fudged and unreliable. Cheap amplifiers are typically rated for "peak power" rather than continuous or "RMS power" and the ratings are frequently laughably optimistic. You might see a cheap amp advertised as 1000 watts (because under ideal circumstances it could put out 1000 watts for a millisecond) that would struggle to put out 100 watts RMS. This is totally obvious if you look at the power consumption rating. A "1000 watt" amplifier that is rated to consume at most 200 watts of electricity from the wall outlet is OBVIOUSLY not actually putting out 1000 watts.

If you could look up the actual gain ratings of the two amps and compare them, that would be a better basis for comparison but still not perfect.

The distortion question is similarly problematic. A good 100 watt amp will put out 100 watts RMS with negligible distortion. A cheap 250 watt amp (even if the 250 watt rating is RMS) might start having noticeable distortion at 50 watts. There's no standardization of power ratings and many manufacturers just do whatever they can to slap the biggest possible number on the box.

Maladat - thanks for the overview in layman's terms. Very helpful.

^^^ yes, excellent post with a lot of good info to digest.

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Originally posted by maladat:
{snip}

In practice, that's pretty much how it works big-picture, but consumer equipment generally isn't perfectly referenced to line level, some can't put out line level at all (only somewhat smaller signals), some can go well above line level, etc.

Yes, Consumer grade equipment has pretty much settled on a lower "line level" as their standard when it comes to CD players and the like. The voltage level is less than half what the Professional Grade equipment uses, IIRC.

Thanks, Maladat. I sort of knew some of that, but didn't know a lot of it.

If you turn on the amp and the lights in the house dim, you've got it about right.