770 and 4 ohm loads?

I see the 770 is rated at 200 wpc with an 8 ohm load. What is its power output and compatibility with a 4 ohm load? I have a 6.1 setup now with a 1050 + SVS sub powered by a Peavey amp. If I go to a 770 later on, I would like to use the 7th channel for the SVS (which has a 4 ohm driver). My 6 speakers are 8 ohm.

Thanks... KJP

I don't think we'll know that for a while, but you might toss Outlaw an e-mail asking them, as I somehow suspect that the answer is floating around their office somewhere and Scott may have it within reach.

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Gonk

Do let us know if you find out, will you? My Axioms are 4 ohms (actually something like 5.5 ohms) and I'm curious as to how much sound will come from this thing.

I plan on using Thiel 2.3s. They drop down to 2.3 ohms. I wonder if the 770 can handle that kind of load ?

Don't most speakers drop below their "nominal" impedance at some point? I wouldn't be surprised if my Axioms are occasionally below 4 ohms.

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Matthew J. Hill
matt@idsi.net

Thiels are notorious for being hard to drive.

I've had 3.5 in the past which my Rotel 100w would NOT drive. It would shut down.

I no longer have those speakers but really love the 2.3 and don't want to encounter the same problem.

The 2.3 are rated at 4ohms but for must of the range they are around 3ohms according to a review in Stereophile.

The (minimal) specs for the 770 are now posted in the products section of the Outlaw's web site at http://www.outlawaudio.com/products/770.html#

It lists the 770 power output as 300 watts for 4 ohm speakers.

Full list follows:

Power output: 200 watts RMS x 7 (all channels driven simultaneously into 8 ohms from 20 Hz to 20 kHz with less than 0.05% total harmonic distortion). 300 watts RMS x 7 @ 4 ohms (other conditions same as above)

S/N: 119 dB

Power Bandwidth:5 Hz - over 100 kHz (+0/-3 dB)

Damping factor: 850 (10 Hz - 400 Hz)

Input sensitivity/Impedance: 1.43 volts for full output/28 k ohms

Remote Trigger voltage: 3 - 32 volts AC

Power requirements: 115 V 50-60 Hz

Power consumption: 1,800 watts (maximum)

Dimensions (W x H x D): 17.2 x 7.75 x 18 (inches)

Weight: 90 (lbs)

I currently own a Counterpoint SA220 amplifier thats rated at 220 watts @ 8 ohms, at 4 ohms it increases to over 440 watts. I have checked other amps ratings like the Sunfire amps and other high end units, it appears they also for the most part double there wattage going from 8 to 4 ohms.
Outlaws amps appear to only increase their wattage by 50% instead of doubling it according tho the specs for the 750 and now the 770. Are they just conservatively rating the units or is it an inferior design technology (I wopuld be suprised if it was the latter).
Can somebody please shed some light on this subject.

Power consumption = 1,800 watts (maximum)?

We're talking dedicated circuit here. Even then, most home wiring is maxxed at 1800 watts, so toooo much sound can trigger breakers. You should be deaf by then, so you won't hear the music stop :-)

JJ,
An efficient amp should theoretically double its output from 8 ohms to 4 ohms, as I've understood. Less efficient models will have lower output levels.
I'll try to dig up the article. Or the 770 may just be limiting the output.



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Emin

The best an amp can do is double its wattage with each halving of the load. The amplifier topology and the capacity of the transformer all work together to determine the actual wattage. From 200W into 8 ohms to 400W into 4 ohms, the current of the amp must double. Most amps are current limited as the load decreases. Most reach a point of instability as the load goes even lower (i.e. 2 or even 1 ohms). The amount of rated power at 4 ohms compared to 8 ohms gives you an idea of how much current the amp can deliver.

50% more wattage at half the load is not bad, but there are "better" amps out there. Some receivers actually decrease in wattage from 8 ohms to 4 ohms, as they are limited by current and the possibility of overheating.

If you have a low impedance speaker, you can either buy an amp that nearly doubles its power into 4 ohms or just buy an amp with lots more power than you need. That way you won't be pushing it too hard, even with a 4 ohm load.

With the 770, 300W into 4 ohms is still 300W. My amp does 125W into 8 or 200W into 4 - a little better than 50% more power into 4. I also have 4 ohm speakers. I have no problem driving them. I have driven the amp into clipping with the opening of Toy Story when the bass is really pounding and during the depth charges of U571, but never for music.

Any decent amp will drive 4 ohm rated speakers. The question is how loud do you want to be able to go. You can try the 770 and return it if it doesn't have enough volume for you. If a 200W amp doesn't cut it, then you are gonna have to pony up some serious bucks for an even bigger amp - buy the 750 for the other 5 channels and then a 250W or 300W x 2 (into 8 ohm) amp for your mains. The other option is to passively biamp you mains, which would give you higher volumes using 4 amp channels of moderate power. Are the Thiels bi-wire/amp capable Roderick?

I don't believe that Thiels are biwireable/biampable. Supposedly they sound great, when driven by a great amp and supporting electronics. They supposedly don't sound nearly as good when driven by bad amps and electronics.

I am currently using an Onkyo receiver to drive three 4 ohm Linn speakers and two 8 ohm Mirage speakers. Even though the receiver manual has a warning to not use speakers with less than 6 ohms, I've had no problems. The Onkyo, however, isn't very musical (however, I'm comparing a $600 receiver with my friend's $5000+ Proceed separates driving the same speakers). It's much better for movies than music.

I'm going to either try the Outlaw 950/770 combination or, if I don't like the Outlaw combo, buy used Proceed gear. Another option is to use a 2-channel proceed amp (for the front Linns and stereo) but then use the Outlaw 950 and maybe the 750 amp.

No the Thiels are not capable of being bi-amped......

The specs for the 770 look promising. I will give it a try....

Question? Does anyone know if the 770 is stabile into 4ohm loads. I realize it is not out yet so the answer is likely to be no. All of my speakers are 4ohm.

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Troy

The 770 isn't available yet, but Outlaw did post specs for it recently (see this link ) and they do list it as capable of 300W per channel at a 4 ohm load, so I would assume that it is stable there. If you're really not sure about the 770 being able to handle your speakers, fire an e-mail off to Outlaw -- they're good about answering questions like that.

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Gonk

HI GUYS,THE 770 SHOULD BE ABLE,IT IS ABLE TO DRIVE ANY SPEAKER OR LOAD TO 1ohm,REMEMBER 300watts AT 4ohms CONTINOUS,BUT SHOULD BE,WOULD BE ABLE TO HIT OVER 400 watts,at any given time.....eurorom.

Correct me if Im wrong but your talking about a two channel amp. When you start putting 7 amps in one box you are still limited to the 15 amp outlet on the wall. I believe if you look at even the high end multi channel amps they won't double the wattage when the load is halved. Some I have seen rate the wattage the same at 4 ohms. I belive most mfgrs. if honest would give you a rating based on a transient using energy stored in the capacitors. As far as Sunfire is concerned they use a entirely diffrent approach. Where most amps are running at full idle Carver uses a tracking down converter which allows the amp to keep the idle just above the input signal. which consumes much less power and requires minimal heat sinks. But the Sunfire amps are not as clean as conventional designs. Come to think of it if you have electric heat you could disconnect the line from it and connect it to your 770 and let this puppy heat your home theater.

You might want to see my post in the Transformer Size thread. I'm willing to bet the 770 cannot manage 300w x 7 continuous power with all 7 channels driven at once. This would require over 3000 watts of AC line draw. Of course, there aren't any other 7 channels amps I know of that can manage that feat either.

If you can run a 220 volt circuit, a big Cinepro amp will easily outpower the 770 but it's also about 3 times the price. Likewise, the Sunfire Cinema amps are more efficient so they can manage more power on a typical 120 volt circuit but they don't make a 7 channel model and some question their sound and reliability.

If all your speakers are 4 ohm models (or inefficient/difficult to drive), and you like it loud, I'd seriously consider using TWO power amps running on two dedicated AC circuits. You can only get so much power out of one 15 amp power cord.

As for the power doubling when you go from 8 ohms to 4 ohms that's usually somewhat a game of specsmanship. A perfect amplifier would indeed behave that way, but even the amps that are rated to do it, don't really test that way. An amp rated for 200w/ch at 8 ohms and 400w/ch at 4 ohms (like the Sunfire Cinema Grand) will in reality usually put out like 250 - 300w/ch into 8 ohms and say 405w/ch in 4 ohms. So while it meets the spec, it only does so because they (oddly) adjust the 8 ohm rating downward to make it appear like a "perfect" amp.

As applejelly posted, the 770 is respectable with its 50% increase into 4 ohms. The catch is, I doubt it can do it with all channels driven. But that's not really the amp's fault as much as what you get from a single 120 volt wall outlet and a shared power supply.

Power question. I just built a home theater and put a dedicated 30amp circuit in my wiring closet, with only a 20 amp plug. Is the power cord on the 770 going to limit me to 15 amps anyway? or can I substitute a nema 20amp plug... and does it matter as it's limited to 1800 watts anyhow? confused. How many amps does the 770 pull under it's maximum load.

I am guessing from the spec saying 1800 Watts that they put a transformer in there that will handle 15 amps. This would give them about 1800 watts. It would be hard to drive all 7 channels at once at maximum output using music or movies. I am guessing if you do that for sustained periods of time you are going to have a melt down or a thermal shutdown. 300 watts is a lot of power for a speaker and if you need more than 7 channels at a little under 300 watts you will definately have a hearing problem in the near future. I would also wadger a guess that while running normal music and movies the 770 would be capable of handling well over 300 watt transients , but doesn't have the caps to keep it running for sustained operation. I can't imagine the capacitance required for 1800 watts sustained! Would be some monster caps.

Does anybody know how much capicatance the 770 and 755 have per channel? IIRC, the 750 had 20,000 uF, but I haven't seen any figures listed for the newer models.

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Matthew J. Hill
matt@idsi.net

Matthew,

The new 770/750 manual says 22,600 uF I believe.