Practical Amplifier Basics

E

ensoll

Enthusiast
I've been reading up on amplifiers and I'm a little confused on how things actually work. I currently have some decent low end speakers and am looking to upgrade to a more robust setup. My receiver right now is an Onkyo TX-SR605 and all of my speakers have an impedance of 8 ohms. Some of the speaker lines I am interested in have an impedance of 4 ohms. The TX-SR605 does not support 4 ohm speakers and it does not have pre-outs for anything but the subwoofer.

So if I were to purchase 4 ohm speakers I would need at least a new receiver if not an external amplifier. My question is at what level of speakers do you actually _need_ an external amplifier. From reading these and other forums it seems like certain brands of speakers are always paired with stand-alone amplifiers. If I were to purchase a receiver that is in the $1500 range such as an Onkyo TX-SR876 (140wx7 @ 8ohm) or a Denon AVR-2809CI (115wx7 @ 8ohm) can those actually power good mid-range speakers? This would be for a small room now (11x13x10) but the system would eventually be placed in a slightly larger room.

Do Paradigm Studio 100's or Rocket floorstanders need standalone amplification? Those are 8 ohm but the Studio 100's list their max power as 210 watts. Even for a large room or if you wanted an extremely high volume can a good $1500 receiver do the job well? For 4 ohm speakers like Triad Gold LCR's or Thiel speakers or PSB Synchrony One's can you effectively drive those with a $1500 receiver in a 5.1 setup?

I think part of my confusion is that you can get a $1500 receiver that can push 140wx7 that also handles all kind of processing and connectivity but a stand-alone amplifier that does 140wx8 and nothing else is $2400. Are stand-alone amplifiers like $50/foot speaker cable or are they actually so much better than the all in one AVR's?
 
TLS Guy

TLS Guy

Seriously, I have no life.
I've been reading up on amplifiers and I'm a little confused on how things actually work. I currently have some decent low end speakers and am looking to upgrade to a more robust setup. My receiver right now is an Onkyo TX-SR605 and all of my speakers have an impedance of 8 ohms. Some of the speaker lines I am interested in have an impedance of 4 ohms. The TX-SR605 does not support 4 ohm speakers and it does not have pre-outs for anything but the subwoofer.

So if I were to purchase 4 ohm speakers I would need at least a new receiver if not an external amplifier. My question is at what level of speakers do you actually _need_ an external amplifier. From reading these and other forums it seems like certain brands of speakers are always paired with stand-alone amplifiers. If I were to purchase a receiver that is in the $1500 range such as an Onkyo TX-SR876 (140wx7 @ 8ohm) or a Denon AVR-2809CI (115wx7 @ 8ohm) can those actually power good mid-range speakers? This would be for a small room now (11x13x10) but the system would eventually be placed in a slightly larger room.

Do Paradigm Studio 100's or Rocket floorstanders need standalone amplification? Those are 8 ohm but the Studio 100's list their max power as 210 watts. Even for a large room or if you wanted an extremely high volume can a good $1500 receiver do the job well? For 4 ohm speakers like Triad Gold LCR's or Thiel speakers or PSB Synchrony One's can you effectively drive those with a $1500 receiver in a 5.1 setup?

I think part of my confusion is that you can get a $1500 receiver that can push 140wx7 that also handles all kind of processing and connectivity but a stand-alone amplifier that does 140wx8 and nothing else is $2400. Are stand-alone amplifiers like $50/foot speaker cable or are they actually so much better than the all in one AVR's?
You have asked a complicated question which vexes everybody involved in this complex problem of the loudspeaker/amplifier interface.

There has been about as much ink spilt on these forums on this technical question than any other.

Let us start with the loudspeaker. First of all manufacturer's specifications are pretty much meaningless, and tell you just about nothing concerning the difficulty of load or otherwise to an amp.

First please understand that a speakers impedance is not constant. If the enclosure is ported there will be two sharp peaks around the tuning frequency. A sealed enclosure and a properly damped TL has one bass impedance peak. Most speakers these days have narrow fronted cabinets, which result in a first order bass roll off starting between 600 Hz and 400 Hz depending on driver size and cabinet width. Good speakers have compensation for this. This compensation always involves dropping the impedance progressively below the roll off point. Now the power divide is 400 Hz for most program material. So half the power is required below 400 Hz. However if the impedance is dropping, that doubles the power requirement below 400 Hz, so that two thirds or so of the amp power is required below 400 Hz, where the amp is seeing a progressively dropping impedance. There may be drops in impedance around crossover points also. On the whole better speakers will be effectively four ohm speakers no matter what the manufacturer says the "nominal" impedance is.

Now the problem gets more complicated than that. Loudspeakers do not present resistive loads, to amplifiers, they present inductive and reactive loads. This results in the voltage and current being out of phase to varying degrees. This results in the concept of apparent and true power. Usually the apparent power is significantly higher than the true power. The problem is that the amp has to provide the current to meet the apparent power requirement. The upshot of this is that the amplifier actually sees an impedance lower than measured.

To make matters worse amplifiers are tested and specified into resistive loads, and not the sort of loads presented by loudspeakers. In order to discern the complexity of load presented by a speaker to an amplifier, you need to see a plot of impedance with frequency. Also you need a plot of the phase angle between voltage and current with frequency for the speaker. Very, very few manufacturers release this data. They would very much prefer that no one knows.

Now let us consider the amplifier. The first thing to realize is that the voltage developed at the speaker terminals into a given load determines the current through the load and therefore the power. Now lets say we have an amp that can generate a maximum voltage swing of 40 volts. Into an eight ohm load that amp will deliver 200 watts. Voltage squared (1600) divided by resistance (8). Now if that amplifier is a good one, it will maintain 40 volts across four ohms and will deliver 400 watts. If it is a very, very good and usually expensive amplifier it will maintain 40 volts across two ohms, and deliver 800 watts. The current required is 4, 10 and 20 amps respectively.

Now lets take the usual case of a budget receiver. Usually, the maximum current available is pretty close to what is required to meet spec into 8 ohms.

So if 4 amps is the maximum current, then the power into four ohms will be 100 watts and the power into two ohms will be 50 watts. If it is a 100 watt receiver then it will deliver 50 watts into four ohms and 25 watts into two ohms.

The situation may be worse than that, as the attempt to deliver high current close or beyond its maximum power, into clipping range, may trigger the amp protection and shut it down. Frequent activations of protection circuits will greatly shorten the life of the amp or receiver.

So what do you get from this. Well amps that have power supplies and output devices big enough to deliver high currents in the 20 amp range are worth their money, and not in any way comparable to "funny" wire.

That if you limit your listening levels then you reduce current demands, and a humble amp may give you your desired results. If you want clean high power and long life from your amp, then you have to pay the piper.

One other point, a 3db increase in the sensitivity of a speaker is equivalent to doubling your amp power. However make sure the rating of the sensitivities is the same. If it is one watt one meter spec, then it is equivalent. However often sensitivity is quoted as 2,83 volts 1 meter. Now 2.83 volts is the voltage that will put one watt though an 8 ohm load. So if a speaker is four ohms it is going to take more power from the amp to produce that one watt. As I told you impedance on the whole drops in the bass frequencies, thus increasing power demand in those frequencies. So you really need to have an idea of a speakers impedance curve to get a handle on the sensitivity when the 2.83 volt 1 meter spec is used. This is just one more of many ways speaker manufacturers confuse you, and lay a trap.

The real answer to this problem, I think will be the placing of high efficiency class D amps in the speakers, one for each pass band, and using active electronic crossovers in place of passive ones. That way power can be optimally matched to load. This will prevent us from leaving an awful lot to chance like we do now
 
E

ensoll

Enthusiast
Thanks so much for the detailed reply. So for big and/or power hungry speakers you really do want a separate amplifier for optimal sound. Are some of the cheaper amps like the Emotiva XPA-5 or Rotel RB-10** models good value or do you really need to be spending more money before you reach significant diminishing returns?
 
TLS Guy

TLS Guy

Seriously, I have no life.
Thanks so much for the detailed reply. So for big and/or power hungry speakers you really do want a separate amplifier for optimal sound. Are some of the cheaper amps like the Emotiva XPA-5 or Rotel RB-10** models good value or do you really need to be spending more money before you reach significant diminishing returns?
I'm glad you found the information helpful.

Both of those companies make adequate amps. However not all of Emotiva's amps are very high current. If you are going to spend money on separate amps, then get one that at least doubles its power into four ohm loads as compared to eight. if you want quadruple power into 2 ohms, then you will HAVE to pay!

I visited Emotiva at SOTU you can read my review here.
 
C

cfrizz

Senior Audioholic
Hi Ensoll.:)

TLS gave a great technical explaination. Now I will give you an easy, plain english one.;)

All speakers benefit from more power, probably even the ones you have now.

I know my 8ohms 18 year old speakers came to life when I gave them 200wpc to chew on!

So, I always reccommend at least 200wpc for all speakers, but especially for 4ohm speakers. You will really hear a difference that power will make.

You do have the right idea with going for an Emo XPA's. You can also look at one of Outlaw Audios 5-7 channel amps, these are good bang for the buck new amps.

If you are not afraid to buy used from Audiogon, look for Sunfire, Rotel, Nad, B & K, Rotel, Parasound.

You will also have to get a new receiver with preamp outputs to hook up the amp. Get one that has all the bells & whisltes that you want it to have & preouts.

Or you can try to go straight for a prepro/amp combo.

I started out with 2 channel separates, went to a receiver to get into HT, and now have gone back to all separates for both 2 channel/HT duty.

Your choices are endless. Have fun shopping!:)
 
TLS Guy

TLS Guy

Seriously, I have no life.
Hi Ensoll.:)

TLS gave a great technical explaination. Now I will give you an easy, plain english one.;)

All speakers benefit from more power, probably even the ones you have now.

I know my 8ohms 18 year old speakers came to life when I gave them 200wpc to chew on!

So, I always reccommend at least 200wpc for all speakers, but especially for 4ohm speakers. You will really hear a difference that power will make.

You do have the right idea with going for an Emo XPA's. You can also look at one of Outlaw Audios 5-7 channel amps, these are good bang for the buck new amps.

If you are not afraid to buy used from Audiogon, look for Sunfire, Rotel, Nad, B & K, Rotel, Parasound.

You will also have to get a new receiver with preamp outputs to hook up the amp. Get one that has all the bells & whisltes that you want it to have & preouts.

Or you can try to go straight for a prepro/amp combo.

I started out with 2 channel separates, went to a receiver to get into HT, and now have gone back to all separates for both 2 channel/HT duty.

Your choices are endless. Have fun shopping!:)
That was in simple plain English. What don't you understand?
 
C

cfrizz

Senior Audioholic
:D MOST of it!!! TLS dear, when you start going into breaking down Hz, and dividing this & splitting that. or this entire paragraph!:eek:

"Now let us consider the amplifier. The first thing to realize is that the voltage developed at the speaker terminals into a given load determines the current through the load and therefore the power. Now lets say we have an amp that can generate a maximum voltage swing of 40 volts. Into an eight ohm load that amp will deliver 200 watts. Voltage squared (1600) divided by resistance (8). Now if that amplifier is a good one, it will maintain 40 volts across four ohms and will deliver 400 watts. If it is a very, very good and usually expensive amplifier it will maintain 40 volts across two ohms, and deliver 800 watts. The current required is 4, 10 and 20 amps respectively."

That right there gave me a massive headache!:eek::confused:

I didn't take any of those kinds of courses in school so it's all Greek to me!:D

That was in simple plain English. What don't you understand?
 
TLS Guy

TLS Guy

Seriously, I have no life.
:D MOST of it!!! TLS dear, when you start going into breaking down Hz, and dividing this & splitting that. or this entire paragraph!:eek:

"Now let us consider the amplifier. The first thing to realize is that the voltage developed at the speaker terminals into a given load determines the current through the load and therefore the power. Now lets say we have an amp that can generate a maximum voltage swing of 40 volts. Into an eight ohm load that amp will deliver 200 watts. Voltage squared (1600) divided by resistance (8). Now if that amplifier is a good one, it will maintain 40 volts across four ohms and will deliver 400 watts. If it is a very, very good and usually expensive amplifier it will maintain 40 volts across two ohms, and deliver 800 watts. The current required is 4, 10 and 20 amps respectively."

That right there gave me a massive headache!:eek::confused:

I didn't take any of those kinds of courses in school so it's all Greek to me!:D
I just don't understand how anyone can walk away with a high school diploma and not understand very basic physics indeed.

I'm coming to realize that a very large part of our economic disaster is a progressive failure of education. If your education is lacking in such an important area of basic knowledge then it it your responsibility to remedy it.

We are all called to life long learning. We need to recognize and admit that we have graduated a population without the educational tools to function in the current world. We need to worry about not only those in school or will be in school, but also those who have been through our educational system.

Evidence for this is all around me.

Just last Sunday, a colleague of my wife had to come around here last Sunday. She has a 2002 Chevy Trail Blazer. Sometimes it starts, sometimes it doesn't. After a boost it always starts. She was getting tired of having it boosted once or twice a week. Two shops said they truck would have to quit altogether before they could tell her what was the matter with it. She took it to a GM dealer who wanted to change the ignition switch!

I knew since it was GM and they have used poorly designed battery connectors for over thirty years that, that was the problem. And sure enough there was almost a complete ring of copper sulfate under the battery terminal on the positive connector, with only a tiny area left for the terminal to make contact with the battery. So I did an obsessional clean up job.

All of this really comes down to education. All of the mechanics involved had not even been taught to think logically at a basic level. GM engineers over generations are guilty of not being able to see what is wrong with their terminal connector design and effect a remedy.

All of these issues are multiplying at an exponential rate throughout our society.

I could go on and on about just recent issues where I have not been able to get sensible service, and the root cause is a failure of basic education among the individuals I'm dealing with.

I'm not going to dumb my posts down. They will be written in the English language, and require no greater knowledge basic physics than every high school graduate should posses. In fact I'm going to challenge members to life long education.

A post which says just buy a powerful amp and everything will be OK is not going to cut it.
 
F

fmw

Audioholic Ninja
Hi Ensoll.:)

TLS gave a great technical explaination. Now I will give you an easy, plain english one.;)

All speakers benefit from more power, probably even the ones you have now.
No, only speakers that have inadequate power for their application benefit from more. Unused power provides no benefit at all.

I know my 8ohms 18 year old speakers came to life when I gave them 200wpc to chew on!

So, I always reccommend at least 200wpc for all speakers, but especially for 4ohm speakers. You will really hear a difference that power will make.
I don't know how a speaker "comes to life." I have no idea what that means so I won't comment. My speakers, in my application would not benefit from having 200 watts per channel. In fact they don't have any use for 50 watts per channel. Most of the amplifier power I have is unused. So to recommend it as a minimum is overkill in almost all normal home audio applications.

Power and the ability to drive low impedance loads are two different issues that should not be confused with each other. Many low power amplifiers are stable with low impedance loads. Many high power amplifiers are not.
 
C

cfrizz

Senior Audioholic
Hold on now TLS, there is NO need to be insulting. I think that both of our explainations were quite good and covered all the bases.

Nor is my education lacking, I learned all of the basics that most kids that I hear today obviously paid no attention to if their speech is anything to go by.

I didn't ask you to dumb down anything, but you should also realize that people can be educated without taking a physics course. And if it is not used in whatever you do for a living are you really going to remember it?

The idea should be to spread knowledge one way or another so that everyone can understand.

And if it is required to have a physics degree in order to understand something like a stereo system then this world is in trouble!

You do it your way & I'll do it mine.
 
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highfigh

highfigh

Seriously, I have no life.
:D MOST of it!!! TLS dear, when you start going into breaking down Hz, and dividing this & splitting that. or this entire paragraph!:eek:

"Now let us consider the amplifier. The first thing to realize is that the voltage developed at the speaker terminals into a given load determines the current through the load and therefore the power. Now lets say we have an amp that can generate a maximum voltage swing of 40 volts. Into an eight ohm load that amp will deliver 200 watts. Voltage squared (1600) divided by resistance (8). Now if that amplifier is a good one, it will maintain 40 volts across four ohms and will deliver 400 watts. If it is a very, very good and usually expensive amplifier it will maintain 40 volts across two ohms, and deliver 800 watts. The current required is 4, 10 and 20 amps respectively."

That right there gave me a massive headache!:eek::confused:

I didn't take any of those kinds of courses in school so it's all Greek to me!:D
In the link, you'll find an Ohm's Law diagram and from this, you can derive power levels and other data from Voltage (E), Current (I) and Resistance (R).

http://www.the12volt.com/ohm/ohmslaw.asp
 
P

PENG

Audioholic Slumlord
.

And if it is required to have a physics degree in order to understand something like a stereo system then this world is in trouble!

You do it your way & I'll do it mine.
I think you did a great job doing it your way by sharing your own experience with the effects of amps on speakers. You did say TLS gave a great technical explanation so I am still in shock after reading TLS's response. Something must be bugging him today.:confused:

I can also tell you that his "great technical explanation" isn't totally correct anyway but is close enough for all intents and purposes.
 
highfigh

highfigh

Seriously, I have no life.
I just don't understand how anyone can walk away with a high school diploma and not understand very basic physics indeed.

I'm coming to realize that a very large part of our economic disaster is a progressive failure of education. If your education is lacking in such an important area of basic knowledge then it it your responsibility to remedy it.

We are all called to life long learning. We need to recognize and admit that we have graduated a population without the educational tools to function in the current world. We need to worry about not only those in school or will be in school, but also those who have been through our educational system.

Evidence for this is all around me.

Just last Sunday, a colleague of my wife had to come around here last Sunday. She has a 2002 Chevy Trail Blazer. Sometimes it starts, sometimes it doesn't. After a boost it always starts. She was getting tired of having it boosted once or twice a week. Two shops said they truck would have to quit altogether before they could tell her what was the matter with it. She took it to a GM dealer who wanted to change the ignition switch!

I knew since it was GM and they have used poorly designed battery connectors for over thirty years that, that was the problem. And sure enough there was almost a complete ring of copper sulfate under the battery terminal on the positive connector, with only a tiny area left for the terminal to make contact with the battery. So I did an obsessional clean up job.

All of this really comes down to education. All of the mechanics involved had not even been taught to think logically at a basic level. GM engineers over generations are guilty of not being able to see what is wrong with their terminal connector design and effect a remedy.

All of these issues are multiplying at an exponential rate throughout our society.

I could go on and on about just recent issues where I have not been able to get sensible service, and the root cause is a failure of basic education among the individuals I'm dealing with.

I'm not going to dumb my posts down. They will be written in the English language, and require no greater knowledge basic physics than every high school graduate should posses. In fact I'm going to challenge members to life long education.

A post which says just buy a powerful amp and everything will be OK is not going to cut it.
You're assuming that A) All school systems require that all students take physics, B) All students have strong math and science aptitude and C) all students care about science and math. That doesn't work, on several levels, but I do agree that there are many problems with our education system. I have read that some educators are advocating that Physics be taught before Chemistry and other sciences, basically because it governs everything. Whether this happens, it still doesn't deal with the issue of students who just don't care about these subjects. Also, less people will use this information after graduation than not. Knowing it does make a lot of things much easier to understand, though.

Regardless, not everyone is a math/science wiz and there are many reasons for this.

BTW- CuSO4 isn't from bad battery cable terminal design, although I agree that what they use is hardly adequate, it's because of exposure to H2SO4, often from the stud being tightened too much and cracking the rear of the lead insert by bottoming out. The leak may not be more than a tiny trickle, but that's all it needs to kill the cable and terminal(s). GM went to that version because it saved money and padded their profits. Just another example of bean counters making things worse, just so they could pray at the alter of the almighty bottom line.
 
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P

PENG

Audioholic Slumlord
No, only speakers that have inadequate power for their application benefit from more. Unused power provides no benefit at all.



I don't know how a speaker "comes to life." I have no idea what that means so I won't comment. My speakers, in my application would not benefit from having 200 watts per channel. In fact they don't have any use for 50 watts per channel. Most of the amplifier power I have is unused. So to recommend it as a minimum is overkill in almost all normal home audio applications.

Power and the ability to drive low impedance loads are two different issues that should not be confused with each other. Many low power amplifiers are stable with low impedance loads. Many high power amplifiers are not.
I can comment on the Studio 100 because they sounded the same to me and my friends with young ears when we A/B them with a pair of high end Anthem and a Yamah RX-V1400 a few years ago. The RX-V1400 has decent 2 channel 8/4 ohm outputs but very poor ACD outputs. We did the A/B listening tests using 2 channel CDs. That being said, there are definitely speakers that will sound much better with higher power amps or at least high power receiver such as the Onkyo 876.
 
F

fmw

Audioholic Ninja
That being said, there are definitely speakers that will sound much better with higher power amps or at least high power receiver such as the Onkyo 876.
Those would be speakers that are inefficient enough or in a venue large enough that less amplifier power will fail to drive them to the desired output without clipping. No doubt about that.

It is uncommon, however, to encounter that situation in the home audio world. Unused power is simply unused. If more power is necessary, then it is necessary, but more unused power is of no value and it is a common audiophile belief that it is of value. I was just keeping the record straight. I don't want newcomers to the hobby thinking they will benefit from amplifier power that their speakers don't use.

The reality is that the huge majority of home theater installations with the huge majority of speakers available in the industry have no use for more than 50 wpc. My point was that recommending 200 wpc as a minimum is very rarely good advice. These are just facts. Just trying to keep the record straight.
 
davidtwotrees

davidtwotrees

Audioholic General
That was a little harsh, TLS....maybe you're having a bad day, or your health is poorly....Your posts are often very technical. You might find them understandable, but not all can understand that level of techspeak. WmAx can post in this manner as well. Does that mean people who don't understand the post are "dummies" that need dumbing down of your posts? Gosh, I don't know.
I do know that people who trash other people for whatever reason rarely, if ever, come off as intelligent.
 
E

ensoll

Enthusiast
The reality is that the huge majority of home theater installations with the huge majority of speakers available in the industry have no use for more than 50 wpc.
Interesting thread and it has really helped me a lot. So an Emotiva XPA-5 (200Wx5 @ 8ohm and 350Wx5 @ 4ohm) seems like what I am looking for. A price I can live with what seems to be enough power to drive most speakers.

More of a theoretical question but assuming I had very inefficient mains (or some other reason to need more power) can you have multiple amps? Could you have the XPA-5 do the center and surrounds and then have a separate XPA-2 for the mains? Other than taking up more space are there any issues with this kind of setup?
 
C

cfrizz

Senior Audioholic
Yes you can have that combo of amps, and it will sound great! Lots of people go this route. Your choices are practically endless. Keep us posted & have fun!:)


Interesting thread and it has really helped me a lot. So an Emotiva XPA-5 (200Wx5 @ 8ohm and 350Wx5 @ 4ohm) seems like what I am looking for. A price I can live with what seems to be enough power to drive most speakers.

More of a theoretical question but assuming I had very inefficient mains (or some other reason to need more power) can you have multiple amps? Could you have the XPA-5 do the center and surrounds and then have a separate XPA-2 for the mains? Other than taking up more space are there any issues with this kind of setup?
 
C

cfrizz

Senior Audioholic
Thank you Peng I appreciate the support.:)

The world of audio is complicated enough since the advent of HT, that I think that keeping it simple will help more people enter into this enjoyable hobby.

Why do you think HTIB is so popular? But even for those of us who want to branch out & expand, some of us would still like to keep it simple.

It took me the better part of the afternoon to reset up my system once I moved to my new place. And I was exhausted by the time I finished. I felt accomplished but exhausted. And I still have yet to get my back speakers up!:eek:

I think you did a great job doing it your way by sharing your own experience with the effects of amps on speakers. You did say TLS gave a great technical explanation so I am still in shock after reading TLS's response. Something must be bugging him today.:confused:

I can also tell you that his "great technical explanation" isn't totally correct anyway but is close enough for all intents and purposes.
 
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