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yamaha high current?


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#1 of 5 Steve_Han

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Posted April 26 2003 - 02:06 AM

First question:

are yamahas considered "high current" receivers, like the way HK advertise their receivers? What about Onkyo and Denon? What would one consider is the minimal amp rating to be considered "high current"? I am talking about both lower end HTR-5550 and mid level RVX 1300.

Second Question:

I am thinking of getting a HTR 5550 for the Bedroom as a low cost solution to run 4 ohm speakers (Magnepan) since it has a switch for 4 ohm. Is this adequate? or should I get something better?

I currently have a Kenwood VR-357. On the speaker terminals it says 8 ohms speakers only. Can i safely run 4 ohms on this receiver?

As you can see i am on a budget.

#2 of 5 Chuck Kent

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Posted April 26 2003 - 02:38 AM

Steve: My advice is to take the "High Current" marketing claims with a grain of salt. There is no scientific or FTC definition for high current measurements. I have yet to read any manufacturer ads diclosing the complete test conditions that these claims are made under. The best thing to look for, if the maker rates it, is to look for long term output wattage power ratings into 4 ohms or less (hint: you won't find many.)

That said, many receiver, including your Kenwood, can run 4 ohm rated speakers. But, if they are pushed too hard or have limited air ventilation, they can have a short life due to thermal self-destruction. I run a Yamaha 5550 in a bedroom HT setup with a pair of 4 ohm Thiels connected as the mains. It works fine (and I leave it in the 8 ohm position) but I never play it near the levels I run in my living room setup. So heat buildup is not an issue. (The 4/8 ohm switch is a switch that helps these receivers pass CSA or UL heat safety ratings. The 8 ohm setting is the normal rated output. The 4 ohm setting lowers the power supply voltage and thus lowers the output by published averages of 25% or so. So when tested in the 4 ohm position, the receiver generates less heat (less power.) But under real world condiditions, this means we (the users) have a higher chance of amp clipping due to the lower power output.)

In the end, it all comes down to what you want the receiver to do. If all you want is some light background music, your old Kenwood might do the trick. But if you want to crank it up once in a while, then you going to have to buy something that can provide more power (translating to better high heat handling since higher power units will come with better cooling capability.)

#3 of 5 Shiu

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Posted April 26 2003 - 03:19 AM

I am not sure if you can define high current neither. However, many high power power amplifiers, fewer receivers (but they are there) do rate their power output at 4 ohms significantly (e.g. 2X) higher than that rated for 8 ohms. Such units are capable of delivery currents of relatively "high" magnitudes, say 20 amps and up...way up in some cases. One thing I notice, Harmon Kardon and some Denon products tend to have huge power supply transformers in their mid/high end receivers.

Those who claim 4 ohm capable, but their current output is obviously not that "high" provide a switch that Chuck talked about. In such case and despite there is a lack of definition, I would still consider it not "high current" capable, but just 4 ohm capable.

#4 of 5 Marc H

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Posted April 26 2003 - 04:48 AM

The other comments are all true in that the high current claims on receivers can be quite vague. H/K brags about their peak current ratings but they are the only receiver manufacturers that will actually specify a current rating at all.

I would categorize the Yamahas as high current though, they do show much higher peak power specs into two ohm loads in their propaganda. That does indicate a decent power supply usually.
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#5 of 5 Chu Gai

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Posted April 26 2003 - 05:33 AM

With regards to high current amplification, unfortunately, IMHO, there's no easy answer. To some extent it is a load of BS, especially the way some manufacturers play the game.
Some speakers have impedances that drop to low values at certain frequencies. Also they may have high phase angles between voltage and current. It maybe is more accurate to say that at any frequency there is a phase angle associated with the impedence. Faced with this type of situation, the amp will have to deliver more current than if the speaker behaved like an 8 ohm resistor.
We can calculate the peak current by knowing what the peak voltage is and dividing it by the impedence. Let's say your speakers bottom out at a little over 2 ohms. If you've got electrostatics its lower. Now take your run of the mill 100 watt receiver. At clipping the receiver will put out about 28 volts (rms) with 40 volts peak. So, 40/2=20 amps is the amount of current that receiver will be putting out at clipping. Now if your receiver can put out more than 20 amps it just won't clip. Some manufacturers quote values much higher for peak current. However given a particular setup, its a moot point since if your unit can deliver 25 amps and another can put out 100 amps neither one is going to be clipping.
Now if your speaker were strictly a resistive load, and using the same 100 watt receiver, we'd find that at that power, the peak current would be 5 amps at 8 ohms and 7 amps at 4 ohms. The people who market amps with high current want big numbers. Its a sales tool. So what they do is to treat the speaker as resistive and then they determine the peak current by defining it at the peak output voltage using a small-value resistor with tone bursts. Now speakers though aren't purely resistive loads, they're reactive. However if they determined the peak current using a reactive load the numbers would be smaller and not have that 'je ne sais quoi'. So here you and I sit where we're trying to figure out which is the better performing receiver or amp based on peak currents but we're faced with the fact that the values were determined resistively and our speakers behave reactively.

One other point to keep in mind is that amps can clip two different ways.

It has run out of voltage. Since the amp has two output stages, one of the stages will remain conductive and tries to keep the load under control. I'll grant you its still not a pleasant thing to hear.

It has run out of current. In this situation, the entire output stage becomes nonconducting and the load goes nuts resulting in massive oscillations with voltage swinging all over the place. This oscillation is even worse sounding than running out of voltage.

So is having adequate current capability important? Sure but you probably need far less than you think.




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