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Does the ability of an amp to drive loudspeakers to volume vary directly with its gain in dB? If not, what does the Gain specification mean?
In looking at amplifier specifications, I see that amplifier gain varies with input sensitivity as much as with watts. For example, the Bryston 2B sst 100 watt amp has switch able input sensitivity. So, at 2 volt sensitivity the output is 23 dB, and at 1 volt it’s 29 dB. So, is it the case that this amp will play 6 dB louder when set to 1 volt? If so, what is the advantage of setting it at 2 volts, assuming that one needs the extra power, and has a source that will drive the amp appropriately?
Similarly, the Theta Citadel 400 wpc amp, the Enterprise amp with 300 wpc, and the Dreadnaught with 250 wpc, all have similar gain of 25 or 26 db., due to differing sensitivities. Do they all play equally loudly? If so, why do we need the bigger amps? Yes, I see that the larger amp will do better into 2 ohms than the lower powered amps, but that can’t be the whole story. Or does the Gain specification mean something else entirely?
Thanks in advance.
Follow Ups:
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.
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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Tin-eared audiofool, former fotografer, and terrible competitive-pistol shootist.
"Everything that can be counted does not necessarily count; everything that counts cannot necessarily be counted." Albert Einstein.
Thanks for the reply. I guess I'm just going to have to read up more on the basics.
There is considerable misinformation and misunderstanding of this topic on this thread. I would suggest that you dig out your old high school physics books and review decibels.
Alternatively you can go to wikipedia.
I am not the technical guru to do it, but I'd suggest that all that is missing here is a discussion of why we need to pay attention to power (wattage) in addition to gain. There is the common confusion of power with gain. So let's complete the story and talk about why we need to consider power, and how pwer relates to gain and the volume of a stereo.
Adding that would make this already very helpful thread into a superb resource on this question.
> > why we need to consider power, and how pwer relates to
> > gain and the volume of a stereo.
Consider the two ends of the chain. You've got a speaker at one end that needs power to produce the sound you want in your room. At the other end, you've got a source that is putting out one or two volts with very little current available. In the case of a phono cartridge playing a record, reduce this to millivolts.
Now pause for a moment and consider the difference between voltage and current. When you walk across a room and build up a static charge, you get a little shock when you touch a doorknob. That may be 50,000 volts of electricity, but there's no current behind it, so while you feel the shock, it doesn't kill you. But a car battery is 12 volts but has several hundred amps of power behind it. You can place one hand on one battery terminal and the opposite hand on the other and not feel anything. The amps are there, but the voltage isn't.
However, 120 volts with 15 amps from your wall socket can easily do you in. In short, both the voltage and the amperage need to be right in order to match the job at hand.
A speaker needs both voltage and current, but the phono, CD player or other source can't provide that. A player with a maximum 2 volt output may give only a few milliamps of power. Hence an amplifier is needed. A 200 watt amplifier, at full output, will take the 2 volt, low amperage input from a player and turn it into 40 volts at 5 amps into an 8 ohm speaker.
Gain is simply an indication of how many volts input the amp needs to reach its full rated output. Some amp specification sheets do not refer to gain, but list an input "sensitivity" voltage.
There are a couple of ways to talk about gain.
One way is to consider it a measure of how much input it takes to get full output from the amp. Take your Bryston 100 watt amps, one switch setting has 23 dB gain and the other 29 dB.
In both cases, the maximum output of the amp is the same, but the higher sensitivity number -- 29 dB -- gets there "faster". It takes less input from the preamp or source to hit full power.
With your Bryston, the point of the switchable gain is to better match the amp to your preamp or source.
If your preamp has a high output voltage, you will want your amp switched to the lower gain setting. Otherwise, on the high gain setting, your volume control won't have as much range. You may find you're trying to fine-tune your volume setting using only the bottom quarter of its range.
However, if your preamp has a low output voltage, you will need a higher gain (higher sensitivity) amp. Otherwise, you may find you can't reach your maximum listening volume even with the volume knob all the way up.
So, no, a higher gain setting does not give your amp "more power". It simply allows you to better match it with your other components.
Thanks, that makes sense as far as the Bryston amp goes. But what about the Theta amps, with 400 watts, 300 watts, and 250 watts, and 100 watts, all with about 26 dB gain. True, they all have differing input sensitivities, but if I'm using a preamp to drive them, what are the advantages of the higher wattage, if they are all putting out the same 25 or 26 dB at full power? I'm sure I'm not understanding something, but what is it?
Thanks again.
"...what are the advantages of the higher wattage, if they are all putting out the same 25 or 26 dB at full power..."
You have it kind of backwards.
Don't think of it as the amps 'putting out dB's'. The amps are putting out power in Watts for a certain amount of gain in dB. dB is the spec that describes the amount of gain or amplification that the amp provides.... how much the input signal is amplified in dB.
A 100-Watt amp may have a gain of 26dB but a 600-Watt amp may also have a gain of 26dB. The 100-Watt amp puts out 100-Watts after amplifying the signal 26dB. The 600-Watt amp puts out 600-Watts after amplifying the same signal 26dB.
Your preamp puts out a small but adjustable signal. It needs to be amplified to a level sufficient enough to drive speakers. The amp amplifies the signal, and the amount of amplification is described in dB.
More power output (in Watts) can be beneficial in driving certain speakers to a certain volume level for a certain size room. And having more Watts 'than necessary' can be a good thing to handle dynamic peaks in the music without distorting. Some speakers require more power (in Watts) to push air to a certain volume level than others. And larger rooms often require more power (Watts) to fill the room with music.
> > But what about the Theta amps, with 400 watts, 300
> > watts, and 250 watts, and 100 watts, all with about
> > 26 dB gain. True, they all have differing input
> > sensitivities, but if I'm using a preamp to drive
> > them, what are the advantages of the higher wattage,
> > if they are all putting out the same 25 or 26 dB at
> > full power? I'm sure I'm not understanding something,
> > but what is it?
You're right -- you're missing something.
Look at it this way: Gain (input sensitivity) and an amp's Maximum Power Output are unrelated. They are two different things.
Gain is one measure of how much input voltage it takes to reach the maximum output of the amp. How many watts the amp outputs is irrelevant at this point.
The reason gain is an important specification is simply so you can better match your preamp or source components to your system.
Too much amp gain used with a high-output preamp will be a problem. You'll have no effective volume control range and, in some circumstances, may overload the amp's input circuit, resulting in distortion.
Too little amp gain and you may have trouble reaching full volume, particularly if you are using a passive "preamp" or directly connecting line-out source components without using a preamp.
That's the key to understanding. Wattage has nothing to do with gain. You can have an amp with 26 dB gain and 10 watts or 26 dB gain with 1,000 watts.
.
Sometimes its a MV figure for the full rated output into a resistor without giving a db figure for gain. So gain figures are not always written to the '1watt out/8ohms' standard.
And no a gain figure on its own can't tell you how much power the amp delivers or how powerful it will sound in your system.
Viz. My two rebuilt LEAK Stereo 20s were originally spec'd as 125mV!!!!! in for 16 watts into 16 or 8 ohms at 1khz off the relevant output taps, with a few watts less into 20 Hz and 20 kHz. They have at least 3db less gain than that since the rebuilds. And they still give 16watts but from 20 to 20kHz and sound a lot more powerful.
Noting that two dissimilar amps with very different power outputs can still have the same gain and will produce the same output power in watts (or volts) into the same load, when fed the same size signal in mV or V.
Mind you they may still have different slew rates, decay, distortion spectra, damping factor and tonal balance.
Note that a post in response is preferred.
Warmest
Timothy Bailey
The Skyptical Mensurer and Audio Scrounger
And gladly would he learn and gladly teach - Chaucer. ;-)!
'Still not saluting.'
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