Amp design.

[zumbo]

I have always believed an amp that resists ohm load is a better design. It delivers it's rated output no matter what the ohm load (ex: 125 x 2@8,4,2,1,0). It maintains it's distortion spec as well.

Others will argue that an amp that doubles it's power when the ohm load is halved is a better design (ex: 125 x 2@8ohm/ 250 x 2 @ 4ohm). One thing to note. An amp that doubles it's output, or tries to, doubles it's distortion as well.

I do believe that an amp that doubles, vs. an amp that doesn't (ex: 125 x 2@8ohm/ 175 x 2@4ohm), is a better design. So, this is not the question.

 

[Seth=L]

Man, I don't know. I am not to sure which way to go on this.

 

[MDS]

I voted for doubling its output when the load is halved; however, the only reason an amp appears to double its output power when the load is halved is because they rate the higher load less than what it is really capable of so that it appears to 'double down'. If the amp is capable of 150 wpc at 8 ohms and 250 wpc at 4 ohms, the 8 ohm rating will be 125 to maintain the illusion.

In order for the amp to maintain its same output regardless of load, even more rating tricks would have to be performed.

 

[PENG]

I voted for doubling its output when the load is halved; however, the only reason an amp appears to double its output power when the load is halved is because they rate the higher load less than what it is really capable of so that it appears to 'double down'. If the amp is capable of 150 wpc at 8 ohms and 250 wpc at 4 ohms, the 8 ohm rating will be 125 to maintain the illusion.

In order for the amp to maintain its same output regardless of load, even more rating tricks would have to be performed.

I think you are right for most amps that specify double the output at 4 ohms. True double down is theorectically almost impossible because when current is doubled, losses increase. It is easier to maintain that "illusion" you described because most people won't bother digging into the electrical theories so they will take it as real and think that the amp is truly more powerful than amps that don't seem quite (but almost) double down.

 

[highfihoney]

I have always believed an amp that resists ohm load is a better design.

I voted for the amp to hold its rating in all ohmages,im not sure labeling different designs or different class amps as one being better than the other represents my feelings on the subject but i do have preferances.

For every day hard usage i prefer the amps that hold their ratings as a standard,the biggest benifits to me have been the lowest distortion possible from the amplifier & keeping the current demands put on the amplifier as easy as possible,as im sure you know a 4 ohm setting will require the amplifier to work much harder than the demand put on the same amp from an 8 ohm or 16ohm load & an amp that is working hard will struggle to supply the power needed increasing the chance for raised levels of distortion,clipping & shorten the life span of the amp itself.

Amps that are made to hold their ratings in all ohmages are also not affected by impendance swings or dips caused by the interaction between the speaker & the amplifier.

 

[MDS]

Amps that are made to hold their ratings in all ohmages are also not affected by impendance swings or dips caused by the interaction between the speaker & the amplifier.

Except that it is not possible. See Peng's reply.

When the load is reduced, the current requirements go up and there is no way around that. In order for the amp to maintain the same power output regardless of load, either:

a). The amp purposely limits the current to bring the power down.
b). They de-rate the power ouput for higher impedance loads to match the power output at lower impedance loads.

 

[highfihoney]

In order for the amp to maintain its same output regardless of load, even more rating tricks would have to be performed.

Hi mds, I think you may have misunderstood what zumbo was asking,im sure all of us who are as far into audio as we all are here can agree that rating tricks are used to cloud the facts of why amps double down in power but that isnt what he is asking.

If im reading this correctly & i think i am zumbo is looking for opinions on amplifiers that are designed with the intention of holding their ratings weather it be wattage,distortion or current demand & that are unaffected by impendance or load.

 

[highfihoney]

Except that it is not possible. See Peng's reply.

I read all the reply's & in most standard amp designs i agree that it is not possible but zumbo is not asking about standard amp designs,this can be accomplished by keeping the load that the amplifier see's as a constant.

If the load the amp is being asked to handle is kept at a constant ohmage the amp is not affected by the variables that you & peng outlined in your responses.

 

[Seth=L]

Question-

If a very well constructed amp that was designed to drive speakers with 4 ohm loads or less would it halve the power if driving 8 ohm speakers? I know this is a restatement, but I am having some difficulty wrapping my mind around this.

I will use a completely hypothetical amplifier (but I will use a brand name to illustrate what grade I am discussing)

Say you have a Bryston that will output 200 watts RMS @ 4ohms (20hz-20khz 0.05 THD) both channels driven. What would be it's power rating @ 8 ohms?

From what I understand many cheaper amplifiers, like ones found in receivers have big problems with lower resistance loads. They have tests that illustrate that many times the receiver's amplifiers don't come anywhere close to double the wattage with 4 ohms instead of 8 ohms. Could it be that those amps just run out of juice? I also had an understanding that if an amplifier is given demands it will try to meet them, (unless it receives interference from a protection circuit forcing it to shut down) but without those limitations wouldn't the power supply try attempt to give power that it can't and eventually short out?

Sorry for all the questions, but this is interesting.

 

[u2generator]

I am no authority on this, but it makes sense the amp would produce more output at a smaller load (8 versus 4 ohms). It also makes sense purely from Ohm's Law the difference couldn't be double, just from the heat load (more current=greater heat loss).


FWIW,

TW

 

[dave1490]

I have always believed an amp that resists ohm load is a better design. It delivers it's rated output no matter what the ohm load (ex: 125 x 2@8,4,2,1,0). It maintains it's distortion spec as well.

Others will argue that an amp that doubles it's power when the ohm load is halved is a better design (ex: 125 x 2@8ohm/ 250 x 2 @ 4ohm). One thing to note. An amp that doubles it's output, or tries to, doubles it's distortion as well.

I do believe that an amp that doubles, vs. an amp that doesn't (ex: 125 x 2@8ohm/ 175 x 2@4ohm), is a better design. So, this is not the question.

take this to the exstreem,an amp that drives shorts and opens. oh ya@8ohms

 

[highfihoney]

Sorry for all the questions, but this is interesting.

Rated specs can be confusing,i dont know how to use the multiple quote in a single response function so im gonna have to respond 1 at a time to keep it straight,maybe a more experienced member will pm me & help me learn how to use the quotes better.

The questions you raised regarding recievers & amps abilities to produce wattages in the lower ohmages are directly related to the power supply & capacitence inside the recievers amp section, low ohm loads require more power no matter how you slice it.

A speaker rated at 8 ohms is using 1 watt @ 1 meter to produce its spec while a 4 ohm speaker is using 2.8 volts @ 1 meter to produce its spec,the 2.8 volt load that the amplifier is seeing translates into 2 watts,the voltage needed to produce these ratings is increased as the ohmages go down which is where cheaper amps & recievers get into trouble because their transformers cant deliever the power needed & their capacitors dont have the ability to store the power needed.Larger transformers & caps are needed to produce the current needed for low ohm loads & with more current comes more heat,alot more heat, so larger & more efficient heat sinks are needed to dispurse the heat.

Amplifier ratings at low ohm's directly reflect the amps build regarding transformers & capacitors,necessity dictates that an amp designed to handle low ohms will have much larger capacitors & transformers than an amp that is designed to run higher ohmages,this is where the old "weight" arguement comes into play,heavier amps have larger transformers,caps & heat sinks.

An example of how an amp designed to run all ohmages would look something like this(in theory).

8 ohms = 100 wpc.

4 ohms = 200 wpc.

2 ohms = 400 wpc.

1 ohms = 800 wpc.

Once again as we go down in ohmage the amp requires more voltage & capacitence,lets say you try to run a 1 ohm load from an amp rated at no lower than 8 ohms,the transformer will fry because it is not built to take the kind of voltage needed to run a 1 ohm load.

Being that an amps ability to run low ohm loads directly reflects its transformers & capacitors manufacturers like to do goofy stuff,this is what peng & mds are talking about,in reality not many amps truly double down in wattage the lower they go so the manufacturer resorts to under rating the higher load loads in order to make it look like the have designed the perfect amplifier,using the same example as above the same amplifiers real world power output would look something like this.

8 ohms = 150 wpc.

4 ohms = 230 wpc.

2 ohms = 410 wpc.

1 ohms = 760 wpc.

What zumbo is asking in his question is what are the benifits from running amplifiers that are designed with all of these variables in mind & are made to stay at a constant wattage no matter the load.

 

[Seth=L]

Amplifier ratings at low ohm's directly reflect the amps build regarding transformers & capacitors,necessity dictates that an amp designed to handle low ohms will have much larger capacitors & transformers than an amp that is designed to run higher ohmages,this is where the old "weight" arguement comes into play,heavier amps have larger transformers,caps & heat sinks.

An example of how an amp designed to run all ohmages would look something like this(in theory).

8 ohms = 100 wpc.

4 ohms = 200 wpc.

2 ohms = 400 wpc.

1 ohms = 800 wpc.

Once again as we go down in ohmage the amp requires more voltage & capacitence,lets say you try to run a 1 ohm load from an amp rated at no lower than 8 ohms,the transformer will fry because it is not built to take the kind of voltage needed to run a 1 ohm load.

Being that an amps ability to run low ohm loads directly reflects its transformers & capacitors manufacturers like to do goofy stuff,this is what peng & mds are talking about,in reality not many amps truly double down in wattage the lower they go so the manufacturer resorts to under rating the higher load loads in order to make it look like the have designed the perfect amplifier,using the same example as above the same amplifiers real world power output would look something like this.

8 ohms = 150 wpc.

4 ohms = 230 wpc.

2 ohms = 410 wpc.

1 ohms = 760 wpc.

What zumbo is asking in his question is what are the benifits from running amplifiers that are designed with all of these variables in mind & are made to stay at a constant wattage no matter the load.

So heat is a factor, but doesn't heat cause more resistance? I sort of knew that to produce that kind of power that a larger power supply and reservoir capacitors would be needed, and of course beefier parts all around, like transistors that don't short under the load.

 

[dave1490]

Rated specs can be confusing,i dont know how to use the multiple quote in a single response function so im gonna have to respond 1 at a time to keep it straight,maybe a more experienced member will pm me & help me learn how to use the quotes better.

The questions you raised regarding recievers & amps abilities to produce wattages in the lower ohmages are directly related to the power supply & capacitence inside the recievers amp section, low ohm loads require more power no matter how you slice it.

A speaker rated at 8 ohms is using 1 watt @ 1 meter to produce its spec while a 4 ohm speaker is using 2.8 volts @ 1 meter to produce its spec,the 2.8 volt load that the amplifier is seeing translates into 2 watts,the voltage needed to produce these ratings is increased as the ohmages go down which is where cheaper amps & recievers get into trouble because their transformers cant deliever the power needed & their capacitors dont have the ability to store the power needed.Larger transformers & caps are needed to produce the current needed for low ohm loads & with more current comes more heat,alot more heat, so larger & more efficient heat sinks are needed to dispurse the heat.

Amplifier ratings at low ohm's directly reflect the amps build regarding transformers & capacitors,necessity dictates that an amp designed to handle low ohms will have much larger capacitors & transformers than an amp that is designed to run higher ohmages,this is where the old "weight" arguement comes into play,heavier amps have larger transformers,caps & heat sinks.

An example of how an amp designed to run all ohmages would look something like this(in theory).

8 ohms = 100 wpc.

4 ohms = 200 wpc.

2 ohms = 400 wpc.

1 ohms = 800 wpc.

Once again as we go down in ohmage the amp requires more voltage & capacitence,lets say you try to run a 1 ohm load from an amp rated at no lower than 8 ohms,the transformer will fry because it is not built to take the kind of voltage needed to run a 1 ohm load.

Being that an amps ability to run low ohm loads directly reflects its transformers & capacitors manufacturers like to do goofy stuff,this is what peng & mds are talking about,in reality not many amps truly double down in wattage the lower they go so the manufacturer resorts to under rating the higher load loads in order to make it look like the have designed the perfect amplifier,using the same example as above the same amplifiers real world power output would look something like this.

8 ohms = 150 wpc.

4 ohms = 230 wpc.

2 ohms = 410 wpc.

1 ohms = 760 wpc.

What zumbo is asking in his question is what are the benifits from running amplifiers that are designed with all of these variables in mind & are made to stay at a constant wattage no matter the load.

she speaks from exspirence.1 thing thouge my bryston is a 4b200 watt model {1 of the first}and bryston say,s in brighed form it,ll put out 800watts into 8ohms.this seems to be if all losses are eliminated.this is the only lie i found them to publish.

 

[yettitheman]

So heat is a factor, but doesn't heat cause more resistance?

Well, resistance will definitely cause heat. Just look at an ordinary light bulb.
As far as heat causing resistance... the absolute zero theory suggests that electrons are at a state in which the collisions between other electrons are non existant, aka; no heat generated, and that the transfer or "push" of electrons from one atom to another are perfectly elastic and 100% of the energy used to push the electron from atom to atom is perfectly elastic and efficient.

The easiest way for me to answer this question...hm.

Suppose you overclock a PC processor...
Inside the processor ^(above), you probably can see all sorts of little blocks, those of which are integrated circuits. But, however, there are millions of very small interconnects between the blocks you see and others that the picture dosen't see. Because the wires are so small and so close together, the tempature of the core comes into play. A colder core will be less likely to have instability issues because the electrons are staying in thier wire as opposed to jumping around to other interconnects. As atoms heat up, the movement of the electrons becomes faster and more instable, creating heat as well. The tendancy is for the electrons to keep spreading out, but however the confines of insulated wire prevent grounding. In a CPU, the wires are not grounded and problems can result.

So.....
Yes, you COULD say that heat causes resistance because it wants to push OUTWARDS instead of forward......

 

[Seth=L]

Well, resistance will definitely cause heat. Just look at an ordinary light bulb.
As far as heat causing resistance... the absolute zero theory suggests that electrons are at a state in which the collisions between other electrons are non existant, aka; no heat generated, and that the transfer or "push" of electrons from one atom to another are perfectly elastic and 100% of the energy used to push the electron from atom to atom is perfectly elastic and efficient.

The easiest way for me to answer this question...hm.

Suppose you overclock a PC processor...
Inside the processor ^(above), you probably can see all sorts of little blocks, those of which are integrated circuits. But, however, there are millions of very small interconnects between the blocks you see and others that the picture dosen't see. Because the wires are so small and so close together, the tempature of the core comes into play. A colder core will be less likely to have instability issues because the electrons are staying in thier wire as opposed to jumping around to other interconnects. As atoms heat up, the movement of the electrons becomes faster and more instable, creating heat as well. The tendancy is for the electrons to keep spreading out, but however the confines of insulated wire prevent grounding. In a CPU, the wires are not grounded and problems can result.

So.....
Yes, you COULD say that heat causes resistance because it wants to push OUTWARDS instead of forward......

You and your computers Alex, do you not know this is a thread about amplifiers? Just kidding

You make a valid point, but I am more interested in learning how heat can cause more resistance and reduce output power.

 

[yettitheman]

You and your computers Alex, do you not know this is a thread about amplifiers? Just kidding

You make a valid point, but I am more interested in learning how heat can cause more resistance and reduce output power.

Heat, caused by friction. Friction caused by resistance in an part, whether it be wire or component. Everything the electricity flows through will make some sort of heat and resistance value, whether readable or not.

so... resistance makes friction. More resistance makes more friction. More friction makes more heat. More heat means cooking eggs or a small fire.
Because the electrons try to push out of the wire as opposed to pushing THROUGH the wire.... less electrons flow to the speaker/amp and give you less sound quality.

Think of it as moving a desk. You push forward on a heavy desk. It has resistance. It probably pisses you off, but you notice that it takes a lot of energy.
So, you work out. You get bigger arms (or less resistance) and you push again. You laugh at the desk, barely breaking a sweat. Less heat... less energy loss, more efficient transfer of energy.

Make some eggs.

 

[zumbo]

Once again as we go down in ohmage the amp requires more voltage & capacitence,lets say you try to run a 1 ohm load from an amp rated at no lower than 8 ohms,the transformer will fry because it is not built to take the kind of voltage needed to run a 1 ohm load.

Actually, 8ohm speakers require more voltage. 4ohm speakers allow more current to flow through.

From Mcintosh website:
The Dynamic Power Manager automatically controls and optimizes the power supply’s voltage and current balance delivering higher voltage that 8 ohm speakers require, and automatically adjusting for current-hungry 4 ohm speakers.

This is not a new debate for me. Back in my car audio days, Xtant and Phoenix Gold were all the rage because of this type of design. I had brought this up here about three or four years ago, and it turned out the same. I lost. Didn't change my thinking though.

Now that I am looking for a new amp, I ran across this fact about many McIntosh amps. I have decided on the MC205 for sure.

 

[highfihoney]

Actually, 8ohm speakers require more voltage. 4ohm speakers allow more current to flow through

Damm thats what i get for being on the audioholics forums while i was in a work meeting and to think everybody in the meeting thought i was banging away pulling up numbers for them

Your right though,i transposed current for voltage in several spots,my post should have said the lower the ohmage the more current needed.

I'll see your edit & raise you an edit.

The dynamic power management circuit is pretty awesome so are the autoformer model amps.

 

[zumbo]

I carried the tricks from car audio over into home audio. When I built my system, I chose 4ohm speakers so I could get the most out of an amp. What I have learned, is while this is a good idea for subs, it may not be the best for mids and tweets. Even if an amp doesn't double it's power, it doubles it's distortion. And, while the distortion level is still below human detection, it has to play a part in SQ.

There is another problem. I believe my speakers are some of the best made (for their size). There are many other brands that I consider to have the best SQ that are rated below 8ohm.

Now I know an 8ohm speaker dips down as well. So, having an amp that has control over whatever you throw at it just seems to be it. When my 4ohm speakers dip down, there is no telling what kind of distortion my amp is sending to them. Heck, I bet a poor designed 8ohm speaker may even dip lower than mine. As the ohms go down, there is one thing for certain. The distortion goes up. But, if you have an amp that resists this behavior, that has to be heaven.