4-8 ohm,watt,distortion

[gasolin]

One thing i always have wondered about is that an amp can play louder in 4 ohm without distortion compared to 8 ohm

The cambridge audio cxa 60 has 60 watt rms in 8 ohm and trying to play louder then 60 watt in 8 ohm theres distortion

Why can't it play more then 60 watt in 8 ohm before theres distortion, in 4 ohm it has more then 60 watt (90watt) pr channel before it distorts

What makes it distort above 60 watt in 8 ohm when it doesn't in 4 ohm,it's not reaching the power supply's limited in 8 ohm (since it's louder in 4 ohm).

 

[lindsayt]

Think of it this way. The electricity, the electrons that you're listening to from an amplifier come from the power supply. Which come from the mains. You're not listening to any of the electricity that comes from the source.

The transistors or valves in your amplifier act as a very fast acting tap to turn on or off the electricity from your power supply.

For the power supply the electricity comes in as c240 volts AC. The amount of current that comes in depends upon how much current is sucked in, which depends on the resistance that your mains lead sees when it comes into your amplifier's power supply.

AC is no good for your transistors or valves. They want DC from the power supply. Also, when the valves are fully open, there's a limit to how much electricity they can pass before the heat would burn them out.

So the 240 volts mains AC input is passed through a transformer to step it down to a lower AC voltage. This is then passed through a set of diodes so that the AC is converted to non steady DC voltage. This non steady DC votage is passed through capacitors to smooth it out to make it a steadier DC voltage. IE the mains supply and the power supply inside the amp is all about supply a steady voltage. It is not about supplying a steady current.

This DC voltage will be connected to our "taps", the valves or transistors that turn on and off the power that is passed to the output.

As the major limitation is the DC voltage suppled on the rails to the transistors (as this is related directly to the mains voltage which is a fixed value). If the "taps" are so wide open that they are asking for more voltage than what is available on the rails the amplifier is going to hit its' maximum. IE it's not going to supply any more voltage. IE it's gonna clip.

If the output of the amplifier is connected to lower impedance speakers, they will suck more current. Which up to a certain point, the power supply will be happy to provide. In the real world there are limitations to how much current the mains transformer / diodes / capacitors can pass as the load impedance reduces. That's why amplifiers that can supply large amounts of power and can supply double the power to 4 ohms that they do to 8 ohms (give or take a little bit) tend to have huge mains transformers and huge capacitance in their power supplies.

 

[gasolin]

So if the amp is not overloaded and you could have the same speakers with only 1 difference 4 and 8 ohm

Will the sound quality be better in 4 or 8 ohm or the same?

If the amp is not overladed is there a difference in sound quality between 4 and 8 ohm?

If the load in 4 and 8 ohm is the same will the amp distort at the same setting of the volume with the only difference being watt,currency, so if the amp distorts a 12.o cloack with 1 khz test tone in 8 ohm it will also do that in 4 ohm?

 

[Vladimir]

So if the amp is not overloaded and you could have the same speakers with only 1 difference 4 and 8 ohm

Will the sound quality be better in 4 or 8 ohm or the same?

If the amp is not overladed is there a difference in sound quality between 4 and 8 ohm?

Nope.

12.o cloack with 1 khz test tone in 8 ohm it will also do that in 4 ohm?

It certanly will. If the power supply can't handle the lighter load of 8 ohms at a given loudness, it will do worse in 4 ohms for the same loudness. Smaller impedance is always more current draw and tough job for the power supply. Impedance bellow 1 ohm is effectively like a shourt circuit. 0 ohms is when you short the speaker terminals together. Most amps blow up and the really big amps start welding metal. Electric welders are essentially big amplifiers that don't blow up when you short them out.

 

[Vladimir]

> How to use a Multimeter for beginners

 

[Al ears]

> How to use a Multimeter for beginners

First, hunt down the fabled multimeter.......

 

[Andrewjvt]

Think of it this way. The electricity, the electrons that you're listening to from an amplifier come from the power supply. Which come from the mains. You're not listening to any of the electricity that comes from the source.

The transistors or valves in your amplifier act as a very fast acting tap to turn on or off the electricity from your power supply.

For the power supply the electricity comes in as c240 volts AC. The amount of current that comes in depends upon how much current is sucked in, which depends on the resistance that your mains lead sees when it comes into your amplifier's power supply.

AC is no good for your transistors or valves. They want DC from the power supply. Also, when the valves are fully open, there's a limit to how much electricity they can pass before the heat would burn them out.

So the 240 volts mains AC input is passed through a transformer to step it down to a lower AC voltage. This is then passed through a set of diodes so that the AC is converted to non steady DC voltage. This non steady DC votage is passed through capacitors to smooth it out to make it a steadier DC voltage. IE the mains supply and the power supply inside the amp is all about supply a steady voltage. It is not about supplying a steady current.

This DC voltage will be connected to our "taps", the valves or transistors that turn on and off the power that is passed to the output.

 As the major limitation is the DC voltage suppled on the rails to the transistors (as this is related directly to the mains voltage which is a fixed value). If the "taps" are so wide open that they are asking for more voltage than what is available on the rails the amplifier is going to hit its' maximum. IE it's not going to supply any more voltage. IE it's gonna clip.

If the output of the amplifier is connected to lower impedance speakers, they will suck more current. Which up to a certain point, the power supply will be happy to provide. In the real world there are limitations to how much current the mains transformer / diodes / capacitors can pass as the load impedance reduces. That's why amplifiers that can supply large amounts of power and can supply double the power to 4 ohms that they do to 8 ohms (give or take a little bit) tend to have huge mains transformers and huge capacitance in their power supplies.

This is text book stuff and very well written

While I am also a technical person and know my way around my old fluke, i could not even begin to do a write up like that. Very clear and easy to understand. Its one thing knowing what you are talking about but to make the time and effort for us all to read. Where do you guys find the inspiration? Thanks for the effort youve put in. More like text book. It just goes to show how important a well designed amp with a robust power supply is.

And that goes to vlads write up also.

 

[NS496]

Think of it this way. The electricity, the electrons that you're listening to from an amplifier come from the power supply. Which come from the mains. You're not listening to any of the electricity that comes from the source.

The transistors or valves in your amplifier act as a very fast acting tap to turn on or off the electricity from your power supply.

For the power supply the electricity comes in as c240 volts AC. The amount of current that comes in depends upon how much current is sucked in, which depends on the resistance that your mains lead sees when it comes into your amplifier's power supply.

AC is no good for your transistors or valves. They want DC from the power supply. Also, when the valves are fully open, there's a limit to how much electricity they can pass before the heat would burn them out.

So the 240 volts mains AC input is passed through a transformer to step it down to a lower AC voltage. This is then passed through a set of diodes so that the AC is converted to non steady DC voltage. This non steady DC votage is passed through capacitors to smooth it out to make it a steadier DC voltage. IE the mains supply and the power supply inside the amp is all about supply a steady voltage. It is not about supplying a steady current.

This DC voltage will be connected to our "taps", the valves or transistors that turn on and off the power that is passed to the output.

As the major limitation is the DC voltage suppled on the rails to the transistors (as this is related directly to the mains voltage which is a fixed value). If the "taps" are so wide open that they are asking for more voltage than what is available on the rails the amplifier is going to hit its' maximum. IE it's not going to supply any more voltage. IE it's gonna clip.

If the output of the amplifier is connected to lower impedance speakers, they will suck more current. Which up to a certain point, the power supply will be happy to provide. In the real world there are limitations to how much current the mains transformer / diodes / capacitors can pass as the load impedance reduces. That's why amplifiers that can supply large amounts of power and can supply double the power to 4 ohms that they do to 8 ohms (give or take a little bit) tend to have huge mains transformers and huge capacitance in their power supplies.

Brilliant! Thanks for taking the time!

 

[Vladimir]

Good explanation by lindsayt. To answer gasolin in brief

, in 4 ohm loads more current is drawn and the PSU becomes the limitation.

Let's say you are playing a 1kHz test tone. The amp tries to maintain a constant voltage assigned by you via the volume controls of say 20V. At 8 ohms, the current draw will be 2.5A and speakers will draw power of 50W (Ohm's Law). 20V/8Ω=2.5A

Now if you attach a 4 ohm speaker, to maintain the same loudness of 20V, the current must increase to 5A. 20V/4Ω=5A. The system wont be louder in that 4 ohms speaker. It will use twice the current to remain as loud as the 8 ohms speaker and thus draw twice the power - 100W. (P=VA, 100W=20V*5A)

The problem begins if the power supply can't provide those 5A because the bridge rectifier, caps and transformer are not optimized for such current draw. The capacitors are limited to a certain amount of energy (joules) they can hold and the diodes and transformer are limited at the speed they can recharge them as joules get sucked by the speakers in lower impedances. In such scenario of say only 4.23A delivered by the PSU, by Ohm's Law the voltage must go down since the speaker impedance (resistance) is constant. 4.23A*4Ω=16.92V. When voltage sags, this is the amplifier clipping. Most amplifiers these days can survive 4 ohms loads to a certain point of loudness demand, but if the speaker dip lower at certain frequencies, say in 2 ohms, things get very bad for the amp.

For this example I used a 1kHz test tone. When music is playing, the voltage is constantly changing but that still means Ohm's Law applies at all points in time. This can get a bit confusing when I say amplifier's job is to maintain constant voltage. This part was a bit of a head scratcher for me to understand when I was reading up on how amplifiers work. I find it easier to explain using a steady single frequency test tone.

As music changes with quieter and louder parts, different amounts of voltage and current are going from the amplifier to the speakers. And the speakers also have continuously changing impedance depending on frequency as music is playing. Certain music requests gobs of current only for a brief period of time (transient peak), so the PSU has time to recharge the caps before the next transient comes and draws more current. But with music like EDM and some hiphop tracks the long bass passages draw a lot of current for longer periods than for example jazz. If the PSU doesn't have lots of caps and big diodes following a big transformer to charge them up, the voltage will sag, amplifier will clip. And when amplifiers clip, the speaker vice coils don't go their usual fast back and forward in the magnet gap which makes them cool efficiently. During clipping longer periods of time are spent stuck in a position at one end of the magnet gap and this accumulates heat, which burns the hair thin voice coils, especially on tweeters.

Which leads us to the conclusion that small amps are bigger speaker killers than large amps. More clipping = more burned voice coils.