Can gain make up for low wattage?
Subscribe to Ask Paul Ask a QuestionIf your amplifier hasn't enough wattage to power speakers properly, does it help to add preamp gain?
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If your amplifier hasn't enough wattage to power speakers properly, does it help to add preamp gain?
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Hey Paul — I have to say that I, presumably like others, do struggle with some of this stuff. And I suspect it has to do with the definitions of gain, voltage, current, and power (leaving alone impedance, as I only barely get that concept). I can absolutely see why someone might think that, if a power amp has a gain of let’s say 10, it will turn a voltage of 1 into a voltage of 10. And, therefore, if you add gain to the signal you send the power amp — let’s say the power amp is now getting a voltage of 2 — the power amp should turn that into a voltage of 20. 4 into 40, etc. So, if wattage (power) is voltage multiplied by current, and the current is staying constant in my simple hypothetical, why doesn’t a power amp deliver more power when it starts with a higher voltage? On the other hand, I can understand why a thing that delivers maximum power of X cannot be tricked into delivering more than X. But math suggests otherwise. It seems you are saying that when we leave the world of electrical-only, enter the physical world at the transducer stage, and need power to make a physical material move, there’s some kind of intervention that says “nope, your electrical/mathematical gymnastics can’t fool me.” Which sorta kinda makes sense. But only sorta kinda. Anyhoo, I know you never signed up to teach electrical engineering to, say, lawyers. But I thought maybe other subscribers might have a point of view. Thanks as always.
Now I am the one confused. You ask “why doesn’t a power amp deliver more power when it starts with a higher voltage?” and if I understand your question the answer would be that it does—if by higher voltage you’re referring to input voltage. This is because for a given gain, more input equals more output.
Or did you mean higher power supply voltage?
In any case, I think you’re on the right track.
The limitations of an amp are found in its power supply and output chain. If you keep pushing the input voltage higher, eventually an amplifier clips because it runs out of steam.
This made me think about a related problem. Maybe Paul can provide some wisdom.
Suppose a manufacturer makes a range of power amplifiers that are similar except for maximum power output. For example, suppose we have 300 W and 700 W amplifiers. Should the higher-power amplifiers have correspondingly greater gain, so that a fixed input signal drives all models to their rated power? In this example, the 700 W amplifier needs an additional 3.7 dB of gain. This makes sense if we assume the user has purchased the high power product because he/she has a larger room, or likes to listen at high level.
On the other hand, if the user of the 700 W amplifier simply wants more headroom, we would think that 300 W and 700 W amplifiers should have the same gain. This is also the case if the amplifiers are used in some more complex set-up such as with an active crossover, where the lower-power amplifier might be used with a tweeter.
Yes, this might make sense but it brings up more problems than it solves. For example, say you wanted to bi-amplify the system. You wanted the high power amp for the bass and the low power amp for the tweeter. You absolutely want them to have the same gain or the sound will be out of whack.
Maybe a better way to look at this would be the example I just used of bi-amping. Having identical gain amps but each with differing wattage abilities. We know tweeters don’t need many watts. This is because the nature of most music doesn’t have a lot of amplitude at higher frequencies: not as much air is being moved as might be the case with bass.
So, the output of the amplifier will never be pushed too hard. But bass is different. It’s often 10 or 20 times louder than the tweeter. Thus, you need more watts. Your input signal will be considerably louder in the bass regions than it will be in the treble regions.
This is why we like big power amps that provide plenty of headroom—the ability to handle with ease, as many watts as is required.
As someone who did well in college Physics but never quite grokked electromagnetism or its applied aspects, I thought the original question might really be about speaker volume. I could be wrong.
My own Schiit Freya+ runs into your Stellar 300 power amp. The Freya+ has two no-gain, no tube settings and also one tubed setting that boosts the input signal by 12 db or so. At any given volume setting on the Freya+ when I engage the tubes and their 12db of gain, the volume jumps markedly. Is that because the Stellar has the horses to sense the higher gain and multiply it? And are you saying that the higher gain input will eventually be irrelevant if the amp wattage hits its max? Like a car has the same fixed maximum speed no matter whether it starts from 0 under its own power or is pushed to 20 mph before it uses its own engine?
So if the question is whether the gain boost from the Freya+ tubes can help an otherwise low wattage power amp run a given set of speakers at a higher volume, the answer is yes, but only to a point?
By the way, I understand the Schiit 20 watt power amp runs Class A for at least the first 10 watts. Isn’t that plenty to run at least average efficiency speakers pretty handily?
The preamplifier gain can cause your amplifier to put out more watts at a lower volume setting but it cannot make your amplifier deliver more power to the speakers then your amplifier is capable of putting out. What might occur with a preamplifier with higher gain is your amp could be at full power at the 11 or 12 o’clock volume control setting which can cause the user to think the amp is only half way to it’s maximum output and that can cause the user to keep cranking the volume past the amps maximum output causing the amplifier to clip or overdrive and that can cause damage to your speakers.
Get an amp that can safely drive your speakers to their full potential instead of worrying about preamplifier gain. When I say safely I mean more clean power since too little power is what typically damages speakers, especially tweeters due to clipping the amplifier. Not to say you cannot clip a powerful amplifier especially if you have inefficient speakers but it’s less likely to occur with a more powerful amplifier.
The only time you need to worry about preamplifier output is in a phono section particularly when using a low output moving coil cartridge where you’re going to need a step up device. Most preamplifiers are active which boosts the line stage much more then you will ever need, and those that are passive usually have sufficient gain from the CD player or FM tuner to efficiently drive your amplifier to it’s maximum output.