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When does power output @ 2Ω become important?

davidro

davidro

Lunatic Member
G'day all

As I'm on the search for cheap affordable power amp for my AR-3a I notice a lot of amps don't bother specifying the output at 2Ω at all. Well you'd be lucky if they tell you what the output is for 4Ω actually.

If they don't specify the output at 4Ω that is it safe to assume those amps aren't designed to run 4Ω speakers like my AR-3a?

I'm actually somewhat surprised to find out specs of my modest NAD 3120 clearly state what its dynamic output at not only 4Ω (55W) but also 2Ω (70W) as well. Man that's one capable little amp.
 
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Yes, if 4Ω rating is not stated, assume that it is not designed for it, with some exceptions...
2Ω specs are good for even more challenging speakers, some of which like to approach a dead short.
 
Theoretically, a zero ohm load, would allow the maximum current to flow, the closer to zero you get, the sound will be exact.

Is all based on old cars that needed 4 speakers (4 ohms) but so long as the amp has a consistent load,, it should affect the signal the same while playing all forms of music though it.

2 ohms will allow a snappier AND smooth Baas sound, but amps puke out and make it worse then 4 or 8 ohm loads.
 
I am also on a quest to power my AR3's and found that more than a few folks recommend the AudioSource Amp One/A. They seem to be very affordable and sound good with these speakers.
:dunno:
 
It becomes important when your speakers ask for it and whether or not your amp can deliver it then. Some of course can, most cant do it very well if at all.

I would recommend the Sunfire 300 X 2 stable to 1 ohm @ 2400 WPC and can be had for less than 1k used.



REGARDS JIM
 
The abiltiy to deliver power into a low resistance is only important of the speakers have a low impedance. Hardly any speaker has a constant resistance, with most commercial designs it varies with the frequency between some 4 and 12 Ohms. However, there are speakers that are notorious for their impedance curve: for instance the Apogee Scintilla (constant 1 Ohm) or the Infinity Kappa 9, which drops below 1 Ohm in extended mode. Most amps will try to deliver into such a small load, but might encounter one of the following problems: the output transistors may overheat and/or blow up, the power supply is not able to deliver the current needed or the protection circuit of the amp may cut in.

There are not many amps capable of delivering lots of power below 2 Ohms, but good examples are the older Krells, Thresholds, H2O, Plinius and indeed some Adcoms. I don't know the Sunfire mentioned by Jim, but if it really delivers that kind of power, that's impressive.
 
Here is a quick breakdown of the specs for the Sunfire 300 X 2.

Sunfire Solid State Power Amplifier - Class AB, 300 watts/ch into 8 Ohms, 600 watts/ch into 4 Ohms, 1200 watts/ch into 2 Ohms, 2400 watts/ch into 1 Ohm (all values rms), frequency response 1 Hz - 80 kHz, balanced and unbalanced inputs, input impedance 470 kOhm, output impedance 0.01 Ohm (voltage source), 1 Ohm (current source), size 6"H x 19"W x 15"D, weight 43 pounds. $2,175. Sunfire Corporation, 5210 Bickford Avenue, Snohomish, Washington 98290, (206) 335-4748

I used this amp on a pair of 4 ohm nominal speakers Polk SDA SRS for quite some time and I could never get it to even get warm to the touch let alone hot no matter what volume or music played.

REGARDS JIM





REGARDS JIM

.
 
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The Sansui AU-11000 is one of very few vintage amplifiers (that I know of) that will tolerate 2Ω loads.
 
Indeed, not many amps are rated to 2Ω, but, thankfully, not many speakers are either.

More popularly, some integrated amps, power amps, and, even some receivers are rated dynamically into 2Ω; that is, they can play into that sort of load for a (very) short time, at or near max power output. This is usually enough to allow them to play with the sort low-impedance speakers that might be nominally rated as a 4Ω load, but might dip well below that at certain frequencies. Such an amp should work with 95% or more of the speakers out there, save for the sorts mentioned above, which might hit even well below 2Ω.
 
Just ask my Philips or BGW power amps how important it is, when my stats dropped below 2 ohms.

Oh that's right you can't. They are both dead.
 
I run the ribbons in my Magnapan IIIa's with an Acurus A200 with no heat build up at all. It is rated at 350 WRMS per channel @ 4 ohms and smooth as silk on the ribbons.
Regards,
Jim
 
davidro said:
As I'm on the search for cheap affordable power amp for my AR-3a
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Hi David, I've found a lowly priced Nikko Alpha 2 power amp (dual mono!) a few years ago and use it since then with my AR-3s. They shine with that amp! (120 wpc). My bedroom system stabilized after that addition since then. How is the Nikko market locally? Generally speaking, Nikkos are not so well-known and therefore priced below similar amps of other Japanese brands.
 
Just because a manufacturer publishes a 2 ohm specification, it doesn't make the amp reliable into 2 ohms. Some amps that don't publish a 2 ohm spec are just as capable.

If you want 2 ohm reliable drive capability, you're better off with an amp that is purposely designed to see 2 ohm loads all day long. That's a professional market device. Those types of amps are qualified using 2 ohm loads.

Any amp can be connected to a 2 ohm load. It will play.

Transistors are good at having a high voltage across them OR a high current through them, but not at the same time. High power requires both.

The typical approach, to enhance reliability, is to have a high rail voltage and lot's of output transistors so that the current can be divided.

Another approach is what Bob Carver did on the Sunfire, where he has something like a Class-D power amp in the supply that supplies just enough voltage to contain the signal. This way the voltage across the output devices is kept low, so large currents can pass though the output devices.

Another approach is to use stacked supplies like Soundcraftsmen's Class-H amplifier.

The lower the speaker impedance is, the higher the dissipation on the output devices for a given output voltage. Make sure there's adequate cooling capabilities through forced air or large heatsinks.

MOSFET's tend to have some built in protection as they become more resistive as they become warmer. The down side is, you lose output as they become hot.

I recommend not going solely by manufacturers brochures. They all have marketing people. Some of the marketing teams are better than others. Out of the amps I've heard mentioned, I think the Sunfire could be the most reliable based on topology. A place I used to work at had two Sunfire Theater Grand's and they were fine and never gave any trouble. They were driving some 4 ohm B&W's and some 4 ohm (I think) M&K's. Other than that, Crown or QSC would be good choices, IMO.
 
guiller said:
Hi David, I've found a lowly priced Nikko Alpha 2 power amp (dual mono!) a few years ago and use it since then with my AR-3s. They shine with that amp! (120 wpc). My bedroom system stabilized after that addition since then. How is the Nikko market locally? Generally speaking, Nikkos are not so well-known and therefore priced below similar amps of other Japanese brands.
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Unfortunately Nikko gears aren't often seen here. I've never seen a Nikko power amp particularly. I once had my eyes on a Yamaha MX-2 in Melbourne but it was quickly taken by someone local there.

Jon_Logan said:
A place I used to work at had two Sunfire Theater Grand's and they were fine and never gave any trouble. They were driving some 4 ohm B&W's and some 4 ohm (I think) M&K's. Other than that, Crown or QSC would be good choices, IMO.
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Sunfire amps are non-existent here. Those Crown and QSC, they're PA amps right? Are they suitable for Hifi uses? How about fan noise etc?
 
A lot of PA amp do have fans. The fan circuits on some are quite sophisticated nowadays, where they adjust the fan depending on heating. The turbulence sound from the fan blades is only noisy at full speed. At lower rpm's they're virtually silent.

So that's the tradeoff, for lower impedance loads you're going to have more heat generated in the output stage. To combat the heat, you'll need heatsink real estate or some better way to get the heat away from the output devices. Be it fans, heat exchanger, or whatever.

The Sunfire works (is relaible into low impedances) because the supply has low voltages across the transistors. That's another way to get your reliability is to choose a lower powered amp, say 20~30W, that happens to have a lot of heatsink area. With the lower power comes lower rail voltages. Dissipation is reduced for a given output voltage, as well as a lowered voltage across the output devices.

If you want a lot more output capability into lower impedances, that's going to move you into the larger, potentially more noisy (fan), power amp.

You also might consider something in a Class-D (Switchmode) amp. They utilize a different output stage design that allows high power and cooler operation than linear amplifiers. I've heard some and to my ear, they sound pretty damned good.
 
Unfortunately the choice isn't very broad where I live. I haven't seen any affordable pre-made Class-D amps with high output specs yet here.

What do you think about this amp called Alto Macro830? That's a PA amp and the catch phrases are like 'High fidelity and low noise', 'S/N Ratio: 100dB'. Can be had relatively cheaply. Those QSC and Crowns go for high prices here...
 
I can't comment on the Alto Macro830. I don't know anything about it.

In general, though, PA amplifiers can be used in the home to good effect. I've been involved in several high end installations where there was an equipment closet and often times there were professional PA amplifiers doing all of the heavy lifting.

Class-D amplifiers have come a long way from where they started at. I'd definitely keep those on the possible choices list.
 
Jon_Logan said:
Just because a manufacturer publishes a 2 ohm specification, it doesn't make the amp reliable into 2 ohms. Some amps that don't publish a 2 ohm spec are just as capable.
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Please bear in mind that the OP specifically asked about the AR-3A speakers. Unless I am mistaken, they are not the most difficult loads to most amps (the rated impedance is 4 ohms), I mean, perhaps what you mentioned would be more than enough, probably good even for some far more difficult loads. As I've mentioned, in my concrete experience of several years, the AR's just behave nicely with non high current amps, like the Nikko Alpha 2, provided they have enough power (I would use 100+ wpc). Perhaps somebody could bring in a plot of the actual impedance versus frequency for the AR-3As. Or perhaps the OP could ask in the Speakers forum, given that it is for these speakers that the question was raised.

PS: this is the basic data sheet for the AR-3As : http://audio-database.com/AR/amp_speaker/ar-3a-e.html
 
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