High current amplifier

[asking you]

Hi everyone,been search amplifier type a while and saw a type of amplifier is high current amplifier which can delivered about +/-70 amps like harman kardon,rotel.I now using a bose 901 and thinking to upgrade it,(bose basher stay away,sorry)is the high current amp only recommended for low ohm speaker only?or just because they can provide high current at 8ohm speaker compare to normal amplifier or at lower watt with higher ampere?
Sorry for my english.

 

[sqlsavior]

High current capability is also beneficial with reactive loads, such as speakers whose impedance varies greatly with frequency, according to what I've read.

 

[asking you]

I now been offered by a seller a harman kardon hk 6800 integrated amplifier,and now i am using a 550watt power amplifier direct from the bose 901 equalizer,but seems the bose 901 series vi,its too big for me,so i decided to looking for a int.amplifier.

 

[savatage1973]

High current amps are great for speakers that have a low impedence rating or are (as mentioned above) a highly reactive load across the frequency range. I don't know why you consider your amp "too big"--I'm of the camp that you can never have too much power--you just don't need to use it all. As long as it is clean power, it shouldn't make any difference, and offers lots of headroom to avoid clipping transients. "Most" people don't use much more than 10wpc--I tend to listen loud, but I still never get close to the limits of my 2Kwpc capabilities.

 

[asking you]

High current amps are great for speakers that have a low impedence rating or are (as mentioned above) a highly reactive load across the frequency range. I don't know why you consider your amp "too big"--I'm of the camp that you can never have too much power--you just don't need to use it all. As long as it is clean power, it shouldn't make any difference, and offers lots of headroom to avoid clipping transients. "Most" people don't use much more than 10wpc--I tend to listen loud, but I still never get close to the limits of my 2Kwpc capabilities.

So if my speaker are rated 8ohm,so i dont need to buy any high current amplifier?

 

[whoaru99]

Hi everyone,been search amplifier type a while and saw a type of amplifier is high current amplifier which can delivered about +/-70 amps like harman kardon,rotel.I now using a bose 901 and thinking to upgrade it,(bose basher stay away,sorry)is the high current amp only recommended for low ohm speaker only?or just because they can provide high current at 8ohm speaker compare to normal amplifier or at lower watt with higher ampere?
Sorry for my english.

You can't have lower watts and higher amps at any given operating point. They're defined in relationship by Ohm's law and the impedance of the load/speakers.

In other words, despite from a purely math standpoint that 1 amp times 100 volts and 100 amps times 1 volt both equal 100 watts, neither of those situations is applicable to 100 watts for an 8 ohm speaker. 100 watts for 8 ohms is roughly 28.28 volts and about 3.54 amps. You can't have more or less amps nor more or less volts and still have 100W for 8 ohms.

There are other factors such as impedance swings as others have mentioned. Some amps certainly have better capability to handle lower impedance loads. However, if your speakers don't have low impedance swings then "high current" is of limited benefit.

 

[gslikker]

Yes the HK "high current" is about "marketing current" not "electrical current"
Most of those units have a switch on the back switching to this "high current"or stating a 8 to 4 ohm switch.
Instead of "high current", they also could have stated "lower voltage".

Since (on the HK6800) this "high current" switch switches the mains input to another part of the transformer winding.

Still, it is a smart thing to do.
It is a cheap solution for getting more safe power into 4 ohms, where other same size amps of other brands just may overheat and get defective early, cranking up using 4 ohms load.

 

[whoaru99]

Yes the HK "high current" is about "marketing current" not "electrical current"
Most of those units have a switch on the back switching to this "high current"or stating a 8 to 4 ohm switch.
Instead of "high current", they also could have stated "lower voltage".

Since (on the HK6800) this "high current" switch switches the mains input to another part of the transformer winding.

Still, it is a smart thing to do.
It is a cheap solution for getting more safe power into 4 ohms, where other same size amps of other brands just may overheat and get defective early, cranking up using 4 ohms load.

There is some opinion using the 4 ohm position may actually make things worse. If the power at 4 ohms is materially limited some may try to push the amp harder because it sounds weak, increasing the propensity for clipping.

As well, in an article on Audioholics discussing such switches, was mentioned Yamaha indicates there is no less warranty on units having such a setting.

From that Audioholics article -

In speaking with Yamaha, they told me they could not confirm any failures of receivers directly attributed to running the high impedance mode with 4 ohm speakers. Their power supply / amplifier failure rate hasn't changed with the inclusion of the impedance selector switch on their A/V receivers. One has to wonder, just how much over-protection does the user need until it starts compromising real world dynamics and headroom while using the product with musical program material and not continuous test tones in a lab environment? Is it worth potentially damaging your speakers to protect your receiver? I guess that’s a philosophical question depending on which is more valuable to you.

To that last point, amp/receiver typically has thermal protection independent of any impedance switch. It will essentially protect itself by shutting down or cutting back. What protection is there for your speakers against clipping? Little really*, except your ears and hand on the volume control.

*Yes, I know there are a few exceptions such as McIntosh Power Guard. To me though, that is not license to intentionally incur clipping.

 

[savatage1973]

So if my speaker are rated 8ohm,so i dont need to buy any high current amplifier?

This is not necessarily true. Speakers are very typically a dynamic load and ohm ratings on the back or in the manual are a "composite" or "average" impedence. That doesn't mean that at certain frequencies the speaker won't represent a much lower or higher impedence than 8 ohms. Some speakers and certain manufactures are kind of known for having wide swings in the actual impedence across the frequency response range--an 8 ohm speaker may dip to 2 ohms at certain points and stress an amp. You just have to do some research.

 

[asking you]

This is not necessarily true. Speakers are very typically a dynamic load and ohm ratings on the back or in the manual are a "composite" or "average" impedence. That doesn't mean that at certain frequencies the speaker won't represent a much lower or higher impedence than 8 ohms. Some speakers and certain manufactures are kind of known for having wide swings in the actual impedence across the frequency response range--an 8 ohm speaker may dip to 2 ohms at certain points and stress an amp. You just have to do some research.

Thanks Savatage.

 

[Putterman]

This is not necessarily true. Speakers are very typically a dynamic load and ohm ratings on the back or in the manual are a "composite" or "average" impedence. That doesn't mean that at certain frequencies the speaker won't represent a much lower or higher impedence than 8 ohms. Some speakers and certain manufactures are kind of known for having wide swings in the actual impedence across the frequency response range--an 8 ohm speaker may dip to 2 ohms at certain points and stress an amp. You just have to do some research.

Most speakers makers would not rate their speakers as 8 ohms nominal with 2 ohm dips. Even Infinity with their Emit speakers rated their speakers as 4 ohm. There may be speakers which are misrated as 8 ohm when they have very low impedance values, but I would like to see some examples.

 

[JURB]

The Bose 901s, IIRC are nine, 0.9 ohm speakers in series which adds up to 8.1 ohms. They are aluminum voice coils made of rectangular wire, wound on edge. (the bigger way being radial)

But that is the impedance they are calling them. I think it might be higher. Aluminum inherently has a higher DC resistance than copper, which means more of their impedance will be made up of DC resistance rather than reactance.

I am pretty sure that the stories about them eating amplifiers, or power, or whatever, come from the equalizer boosting the low bass by like 40 dB or something like that.

 

[savatage1973]

Most speakers makers would not rate their speakers as 8 ohms nominal with 2 ohm dips. Even Infinity with their Emit speakers rated their speakers as 4 ohm. There may be speakers which are misrated as 8 ohm when they have very low impedance values, but I would like to see some examples.

Infiniity is one of the biggest "offenders"--refer to the Kappa 9 impedence curve. The speaker was rated at 6 ohms but drops below 1 ohm at two points across the frequency range, with one of those drops in the 40 Hz range, hence the reputation of "amp killer" when you have two 12" woofers per side literally sucking the life out of your amp. I own a pair of Maggie 3.6r's and they are a very static/consistent 4 ohm load, and rated as such.