Skip to main content ↑ ↓

Notice

Please note that most of the software linked on this forum is likely to be safe to use. If you are unsure, feel free to ask in the relevant topics, or send a private message to an administrator or moderator. To help curb the problems of false positives, or in the event that you do find actual malware, you can contribute through the article linked here.
Topic: Amp power AVR vs Power amp (Read 29103 times) previous topic - next topic
0 Members and 1 Guest are viewing this topic.

Amp power AVR vs Power amp

I don't know if EE's post here, but I need your input here.

What is the purpose of big power supplies in power amps over AVRs? Some people complain that AVRs have puny power supplies that don't supply high current for speakers. Like Yamaha AVRs. Its like they push plenty of volts, but are low in current.

Can you have high power, as in wattage, but low current? The other thing is that high current can control the speaker, the bass sections easier than a low current amp?

Amp power AVR vs Power amp

Reply #1 –
If an amplifier can supply 100 Watts in to 4 or 8 Ohms, that's the important spec.    If it can't supply the voltage or current required for 100W, you're not going to get 100W into the speaker.

Some companies do "fudge" the specs a bit, and you are more likely to get honest specs from a high-end amplifier manufacturer.  (I'm not saying Yamaha specs can't be trusted...  I don't really know.)

If you see a spec that says something like "100W RMS continuous all channels driven into 8 Ohms 20Hz - 20 kHz at less than 1% distortion", you can probably believe it. 

You can't get the power (Watts) without the required voltage and current, or with a load (speakers) connected. 

Power is calculated as Voltage x Current.

Voltage, Current, and Resistance are related by Ohm's Law (Current = Voltage/Current).    So, it doesn't really make a difference if you have "extra" current available from the power supply because you are not going to get that current unless you also have the voltage, impedance (resistance), and an amplifier output stage that can handle that current.

So, if you halve the resistance by going from 8 to 4 Ohms or by connecting two 8-Ohm speakers in parallel, and if your amplifier puts-out the same voltage under either condition, you'll get twice the current and twice the power into the lower impedance load.

Amplifiers are "constant voltage" devices.  That doesn't really mean that the voltage is constant (it varies with the signal input and the gain).  It means that if you feed-in a constant test tone, the output voltage doesn't change when you connect speakers or change the speaker load.    However if it can't supply the required-calculated current, the output voltage will drop and you'll get distortion.  (Ohm's Law is always true!)  Or if you connect a 2-Ohm load, the amp could be damaged or it might safely go into thermal shutdown.

A switching power supply is more efficient and much lighter in weight than a "regular" linear power supply, and Class-D switching output stages are also more efficient than a standard Class A/B output circuit.  So, you can't always tell from the heft of the amplifier.

Amp power AVR vs Power amp

Reply #2 –
P.S. 

The power in your house is also "constant voltage".    If you live here in the U.S., you have 120VAC coming out of the wall.  A 100W light bulb draws slightly less than 1 Amp.  If you replace your standard 15 Amp circuit breaker with a 20 Amp breaker, the light bulb still draws about 1 Amp.    A lower wattage bulb as higher resistance and draws less current.  With nothing plugged-in (infinite resistance) you get no current and no power is consumed, although there is still 120V at the outlet.

If you connect a toaster and a hair dryer to the same circuit, you'll blow the breaker and suddenly there will be zero volts. 

BTW - As you can see from Ohm's Law, if you double the voltage, you also double the current.  That means doubling the voltage out of an amplifier gives you 4 times the power (with the same speakers).    Of course, the amplifier has to be re-designed to supply the increased current.

Amp power AVR vs Power amp

Reply #3 –
Quote from: DVDdoug on
P.S. 

The power in your house is also "constant voltage".    If you live here in the U.S., you have 120VAC coming out of the wall.  A 100W light bulb draws slightly less than 1 Amp.  If you replace your standard 15 Amp circuit breaker with a 20 Amp breaker, the light bulb still draws about 1 Amp.    A lower wattage bulb as higher resistance and draws less current.  With nothing plugged-in (infinite resistance) you get no current and no power is consumed, although there is still 120V at the outlet.

If you connect a toaster and a hair dryer to the same circuit, you'll blow the breaker and suddenly there will be zero volts. 

BTW - As you can see from Ohm's Law, if you double the voltage, you also double the current.  That means doubling the voltage out of an amplifier gives you 4 times the power (with the same speakers).    Of course, the amplifier has to be re-designed to supply the increased current.


Thanks for the reply! I sometimes go to S&V to look at bench test results of amplifiers and I normally look at their 2ch specifications. Sometimes I see small power amps that have large power supplies. Like they claim 50 watts, but at high current. Compared to an AVR at 50 watts, which has a shared power supply and is puny in comparison, it's not nearly as robust.

So what you are saying is that if an amp can push lots of volts that means it's also pushing lots of current to. I thought you could have an amp that pushed high volts but low current to = power. Like some amps have 100 watts, like a Sony AVR, but compared to a Pass Labs amp at 100 watts, the Sony is low current. The Pass Labs can push lots of current to a speaker.

If Ohms Law is true that means there is no such thing as high volts or high wattage and low current. So then doesn't it actually matter how much or how little you have assuming the amp isn't clipping? If its not clipping its pushing enough current into the speaker?

Amp power AVR vs Power amp

Reply #4 –
I don't know if anything has changed since, but quite some years ago US consumer protection laws defined certain specifications for home entertainment equipment. To advertise X watts from an amplifier, whether stand-alone or in something like a receiver, the equipment had to be certified as passing a 24 hour test of delivering that much RMS power continuously into a 8 ohm passive load. Therefore 100 watts advertised meant it could indeed provide around 100 watts to normal speakers.

There is also headroom, which was not a required specification. Whatever amount of power your speakers are using, on average, for playing any particular music (and in many circumstances that is unlikely to be more than a few watts), a music peak might require 2 or 3 or 4 times as much, for a short time, but very suddenly.

Suppose, for instance, that you were actually playing into a large enough space, or with inefficient enough speakers, that the average output was around 100 watts, the specified power for you amplifier. Suddenly the orchestra comes to a crescendo and your amp has to put out 250 watts, only very briefly, to properly reproduce the waveform. A high enough quality power supply, and proper amplifier design,  will allow it to do so. Some lesser piece of equipment, able to meet the 100 watts RMS spec, might fall flat at 112 watts, far short of what the source demands.

Also, even if the average power output is modest, a marginal power supply might not be able to react fast enough to prevent distortion when the demand suddenly goes up for a large factor, even if that peak demand is less than what it could deliver under less stressed conditions. 

There is also a consideration involving speakers. Some speakers, especially very low impedance speakers, might require much more from the power supply to keep the voltage up adequately. The legal specs are for 8 ohm but the manufacture of a quality amplifier is likely to provide specific values for other speaker loads.

I don't know about now, but that original legislation did not apply to automobile, and various other use, audio equipment. Automobile amplifiers typically specified the peak power potential, without telling the potential customer that the continuous power output that could be provided was generally much lower.

Amp power AVR vs Power amp

Reply #5 –
Quote from: Rich B on
Some people complain that AVRs have puny power supplies that don't supply high current for speakers.

The thing with arguments over audiogear is that they're usually biased in some way. Some people buy expensive amps because they look good (or just because they are expensive) and start preaching that anything cheaper isn't good enough. Some people believe that the use of a hand-wound toroidal core transformer delivers better sonic performance than solid-state power supplies do. Those transformers are big, heavy, energy inefficient and fairly expensive, but designing them is hard to mess up compared to switching power supplies.

Instead of embracing a well designed solid-state power supply that is energy efficient, small and lightweight, they say that it is impossible to have the switching noise not affecting the amplifier section or that the amp is underpowered because the amp is not heavy enough. Some of those people really judge amps on their weight.
Music: sounds arranged such that they construct feelings.

Amp power AVR vs Power amp

Reply #6 –
So high wattage means high current always? That's Ohms Law? So it's not possible to have high wattage = higher volts x lower current to = a given power vs another amp with higher current x lower volts = a given power?

Or is current supply don't dependent on if the amp is clipping or not? So if the amp isn't clipping then its supplying all the current that a speaker needs? Don't speakers benefit with high current from an amp at any volume level? This is a very confusing part of audio for me because I've grown up believing certain things in audio, reading magazine reviews, and audiophiles waxing lyrical over high current amps etc etc.

Amp power AVR vs Power amp

Reply #7 –
Quote from: Rich B on
So high wattage means high current always? That's Ohms Law?

No. High wattage means high current for a high impedance. That's why amps are usually supplied with various power ratings for different speaker impedances. However, when considering different amps with the same set of speakers, a certain power always translates to a certain current for a certain input.
Music: sounds arranged such that they construct feelings.

Amp power AVR vs Power amp

Reply #8 –
Quote from: ktf on
Instead of embracing a well designed solid-state power supply that is energy efficient, small and lightweight, they say that it is impossible to have the switching noise not affecting the amplifier section or that the amp is underpowered because the amp is not heavy enough. Some of those people really judge amps on their weight.


Going even further than this, (in very simple terms) class-D amplifiers are just switching power supplies with variable output frequency and high enough switching frequencies that the noise is easy to filter out.

Since almost all music these days is distributed digitally, it makes sense to stay in the digital domain all the way through the signal chain until you reach the speakers, which have to be analog for obvious reasons. I think we're going to see a move towards more and more class-D amps, even on budget-minded and mainstream hardware as the tech starts to trickle down.

Just like with tube amps versus solid state, any change will be dismissed as inferior to "the good old stuff", in this case analog amplifier tech itself as a concept.

Amp power AVR vs Power amp

Reply #9 –
Quote from: ktf on
Quote from: Rich B on
So high wattage means high current always? That's Ohms Law?


No. High wattage means high current for a high impedance. That's why amps are usually supplied with various power ratings for different speaker impedances. However, when considering different amps with the same set of speakers, a certain power always translates to a certain current for a certain input.


So a 100 watt Sony AVR and a 100 watt Pass Labs will have the Pass Labs having a much greater current delivery into low impedances due to the much larger power supply sections.

So this high current supply will always benefit the speaker? If the Sony amp was not clipping at a certain output, does that mean it was supplying all the current the speaker needed?

Amp power AVR vs Power amp

Reply #10 –
Quote from: KozmoNaut on
Since almost all music these days is distributed digitally, it makes sense to stay in the digital domain all the way through the signal chain until you reach the speakers

Maybe, but the thing is, most class-D amps are analogue as well. You could feed it directly with a pulse train, but usually that pulse train is generated by combining the (analogue) input with a sawtooth wave. That's way off-topic however.

Quote from: Rich B on
So a 100 watt Sony AVR and a 100 watt Pass Labs will have the Pass Labs having a much greater current delivery into low impedances due to the much larger power supply sections.

Not really, no. The size of a power supply does not say much about the amount of power it can safely deliver. Furthermore, it might be that the power supply is oversized and that the actual amplifier section is the bottleneck.

Quote
So this high current supply will always benefit the speaker?

No, because it might not be the weakest link in terms of power output of the system.

Quote
If the Sony amp was not clipping at a certain output, does that mean it was supplying all the current the speaker needed?

Things all interconnect. You can't talk about current while excluding impedance, voltage and power. The speaker doesn't 'need' a current, there is a current flowing because of the voltage across the voice coil and it's impedance. There is no more simplifying or breaking it down to elements here, really.
Music: sounds arranged such that they construct feelings.

Amp power AVR vs Power amp

Reply #11 –
Quote
No, because it might not be the weakest link in terms of power output of the system.


That's not what I meant. If an amp can supply high current, whether its because of the power supply or not (the Pass Labs has a huge power supply section) using the Pass Labs example, which seems overbuilt, my question is whether the high current design would benefit the speaker always. Would it, or would it not?

Quote
Things all interconnect. You can't talk about current while excluding impedance, voltage and power. The speaker doesn't 'need' a current, there is a current flowing because of the voltage across the voice coil and it's impedance. There is no more simplifying or breaking it down to elements here, really.


But if an amp is not clipping at a specific volume level then doesn't that mean its clean power output is not being exceeded at any impedance? If using Ohms Law, power = voltage x current. So what I'm saying is that for a given speaker, if the amp is not clipping the signal does that mean it is already supplying all the power the speaker needs? Or am I missing something?

Amp power AVR vs Power amp

Reply #12 –
Quote from: Rich B on
That's not what I meant. If an amp can supply high current, whether its because of the power supply or not (the Pass Labs has a huge power supply section) using the Pass Labs example, which seems overbuilt, my question is whether the high current design would benefit the speaker always. Would it, or would it not?

If you really want to know in detail, please specify what you mean by a high current design. I can only guess now. If it means what I think it means, only speakers with a impedance lower than usual (say 2 ohm) will benefit.

Quote
If using Ohms Law, power = voltage x current. [...] Or am I missing something?

Yes, you are. Ohms law isn't power = voltage x current, it says voltage = current x resistance (or impedance).
Music: sounds arranged such that they construct feelings.

Amp power AVR vs Power amp

Reply #13 –
ktf, thank you for replying. I noticed you did not answer my question concerning clipping.

My speakers are B&W CM9s and I am currently using a Onkyo NR626 receiver. Seated distance is 4 meters. Now I've been told that this receiver won't be able to drive these speakers to their full potential. People I know have recommended I go out and buy a power amp and use my AVR as a preamp. I figured it probably had to do with current delivery or lack thereof on the Onkyo.

However *I* have noticed no audible distortion at the kinds of SPL I listen to. So I assume the amp is not clipping, although I don't know what clipping would sound like. So I don't know at this point if buying a  power amp that can deliver high current into low impedances would benefit me or not, or if my amp isn't clipping that my speakers already have all the current they need. I'm trying to understand the technical aspects as best I can so I can make a better informed decision about this.

If I can save money then I'm all for it. But if I need something more robust or if my current AVR isn't driving these speakers to their full potential then I might decide to get a bigger amp. This is where I need some advice and to understand the technical aspects a bit better as it concerns impedance and current.

Amp power AVR vs Power amp

Reply #14 –
It is not high current that needs to be delivered to the speaker, it is power, which is the product of current and voltage. The speaker impedance depends on the audio frequency, not the signal level, so it is the same whether the music is loud or soft.

If adequate current cannot be supplied, the voltage falls, the power drops. If the signal rise is rapid enough, the signal may clip when it exceeds the supplied voltage. When the signal rise is not so sudden, the output may just fall off as the input signal tries to rise to heights not available to the amplifier. This later is often less noticeable.

In point of fact, in most home situations, the demands upon the power amplifier are always modest. Your AVR might not be able to supply all that the speakers can handle but you may never play your music loud enough for that to be a factor.

As I explained in my first post, the RMS power rating tells the same thing for both amplifiers. The more expensive amplifier might (might) have more headroom to provide more realistic sound on major short term audio peaks. It might have that capacity, but you might never call upon it. If you are in the habit of blasting out music at very high levels that exceed the potential of your amplifier, then, and only then, will you hear the deficiency.

Amp power AVR vs Power amp

Reply #15 –
Quote
It is not high current that needs to be delivered to the speaker, it is power, which is the product of current and voltage.


Now I'm confused. Earlier it was said that high power is high current at high impedances. Not low impedances. So now it's just power, regardless of where the source comes from. So then it doesn't matter if its a Sony AVR at 100 watts or a Halco? Power is power?

So then what is the point of dedicated power amps?

Amp power AVR vs Power amp

Reply #16 –
Once upon a time there were no receiver. A receiver is just a power amplifier and preamplifier incorporated into a tuner (or vice versa if you want to look at it that way). There are still good reasons for separate power amplifiers, where the preamp and tuner and other bits of a AVR will never be used, such as driving the speakers in a live performance situation. However, if the receiver had a large enough amplifier section to meet those demands, it would serve the function quite well.

Separate power amplifiers for a home music system are mainly a good money maker for speciality companies, a status symbol for the buyer, or a solution where the set-up doesn't involve the additional capabilities of an AVR. If you just want to play CDs, a great many CD players have a volume control. They can thus easily be the input directly to a power amplifier, and nothing more is needed. That isn't to say that a receiver would not work just as well, regardless of "wasting" it additional facilities.

Power is Voltage multiplied by current. In the case of alternating current, and especially of variable impedance, the formula is a little more involved because those factors effect either the instantaneous voltage or the current that any given voltage must provide (lower the impedance and more current is required or the voltage will drop, raise the impedance and the voltage must rise or it cannot deliver the current to that load). In general, very low impedance speakers are the most difficult to drive properly. This is where high current potential becomes most important.

In music playback, the voltage varies with the music level, the speaker impedance varies with the music frequency. The power delivered is still voltage times current but both voltage (music loudness) and impedance (music frequency) constantly vary, therefore the current demand varies, but none of the factors are independent.

Amp power AVR vs Power amp

Reply #17 –
Quote
Power is Voltage multiplied by current. In the case of alternating current, and especially of variable impedance, the formula is a little more involved because those factors effect either the instantaneous voltage or the current that any given voltage must provide (lower the impedance and more current is required or the voltage will drop, raise the impedance and the voltage must rise or it cannot deliver the current to that load). In general, very low impedance speakers are the most difficult to drive properly. This is where high current potential becomes most important.


So then it is a question of output. I assume amplifier power is measured into various impedances at full rated output. If that's true, does that mean that my AVR could supply all the current it needs into a low impedance load at some volume level? Then I don't think I would need a power amp.

For a long time I was under the assumption that high current amp designs could drive speakers better than amps that were not high current, something about the current controlling the speaker better. But an AVR can supply current into low impedance loads, just not to the same level as a bigger power amp. So then my way of thinking is that if I don't clip my AVR it should be fine.

I assumed clipping meant the receivers rated output was exceeded. So if you don't exceed the rated output then it doesn't matter how low the impedance is, the amp will be able to drive it as well as any power amp can at a given volume. Is that correct?

Amp power AVR vs Power amp

Reply #18 –
A high current means that you have a low output impedance, and yes, generally speaking a lower output impedance does lead to better performance.  Ideally you should have an output impedance about 1/8th the load impedance. 

See:  http://en.wikipedia.org/wiki/Damping_factor

Amp power AVR vs Power amp

Reply #19 –
The discussion was not about amplifier output impedance but load impedance. Many amplifiers that can deliver full power to 8 ohm speakers cannot do the same to 4 or 2 ohm speakers. Said amplifier may be capable of good performance with such a low impedance speaker under moderate demands, but does not have the capacity to deliver as much power as it is rated for (the legally defined standard is for an 8 ohm load; the manufacturer may provide stats for other loads).

While a very low amplifier output impedance may be a good thing, it is not related to power capacity. If the output stage, and its power supply, can deliver only 1 watt, it may do an excellent job at one watt into an appropriate load, but it can still deliver only one watt before the output stage voltage drops below regulated level.

Amp power AVR vs Power amp

Reply #20 –
As long as your desired output is significantly below the rated AVR amplifier output, the speakers perform the same as they would for a higher capacity amplifier. You will reach that limit faster (i.e. at a lower output level) for lower impedance speakers, but if you are not too close to that limit, you have no problems.

Amp power AVR vs Power amp

Reply #21 –
Quote
It is not high current that needs to be delivered to the speaker, it is power, which is the product of current and voltage. The speaker impedance depends on the audio frequency, not the signal level, so it is the same whether the music is loud or soft.


Could you explain what you mean by "it is the same whether the music is loud or soft"? I'm not entirely sure what you mean in your second sentence. English is not my first language, so I'm trying to understand this as best I can.

Quote from: AndyH-ha on
As long as your desired output is significantly below the rated AVR amplifier output, the speakers perform the same as they would for a higher capacity amplifier. You will reach that limit faster (i.e. at a lower output level) for lower impedance speakers, but if you are not too close to that limit, you have no problems.


Why does it need to be significantly below rated output? Isn't the rated output measured at low enough distortion? At S&V their benchmark tests rate amps full rated power at 0.1% distortion. I would have thought that was low enough.

Amp power AVR vs Power amp

Reply #22 –
Quote from: Rich B on
Could you explain what you mean by "it is the same whether the music is loud or soft"? I'm not entirely sure what you mean in your second sentence. English is not my first language, so I'm trying to understand this as best I can.


Let me try. We are talking about four different things here - power, voltage, current and impedance. They are all related. Power is what counts, and is the result of voltage multiplied by current (P = U * I), so a result of both voltage and current. Current depends on voltage and impedance (this is Ohm's Law), current is voltage divided by impedance (I = U / Z). If you combine the equations, you get P = U * I = U * (U / Z) = U²/Z - thus power depends on the square of the voltage divided by the impedance. The impedance doesn't depend on power, voltage or current, but varies with frequency in a complex way. It is usually specified as a "typical" or "average" value over the frequency range, or at some specific frequency (so typically 4 or 8 ohm).

Amp power AVR vs Power amp

Reply #23 –
Speaker impedance is not dependent on signal level.

To your other question, the concern is the amplifier's ability to handle transient peaks. THD measurements are measured using a continuous tone.

Backing up to the beginning, what prompted you to think you need a new power amp?  From reading the discussion I'm under the impression you don't need one.  Rather, it sounds like you've been sucked into the idea that you will achieve audio bliss by buying a new amp from reading things on the web by sources that are highly questionable.

Amp power AVR vs Power amp

Reply #24 –
The impedance of all speakers varies with the frequency of the signal driving them. The rated impedance is obtained by some means I no longer remember, but is probably something near the minimum impedance the amplifier will see. The impedance at any given frequency does not depend on whether you are playing the music at a high volume control setting or a low volume control setting, only upon the frequency of the signal.

As I explained in my first post, on short term music loudness peaks, the required power can be several times the average power being used. If your average power delivered is near the upper limit of the amplifier specification, there many not be enough headroom to meet those peak demands. The music output will then be distorted. This is where amplifier with excessively oversized power supplies (and plenty of filter capacitance) can make a difference. They might be able to meet the peak demand while a lesser amplifier, having the same basic specifications (e.g. 100 watts RMS) might not.

If, however, the average demand is well below the rated RMS output, there will be plenty of headroom available withing that basic spec. In other words, the less expensive amplifier may not be able to provide very much above its 100 watts RMS rating, but if your speakers are only using 12 watts RMS, there is still considerable power available for peaks before it is pushing its 103 watts limit. Running at relatively low power is the most common way for home music playing.

If you were using a single ended triode power amplifier that was only capable of producing a few watts RMS, because you love that old fashion tube distortion sound, then you might need to be concerned about power reserve. If you have a huge music room, and you love to make the walls rattle, then you need a large power amplifiers. Most people will never use anywhere near the capacity of an average AVR.