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Wondering if the rb-1080 would handle a 4 ohm speaker and what its power output would be.I looked at the specs on the rotel site and they list only for a 8 ohm load.Have been contemplating selling my carver m4.0t that is powering my polk lsi 15's up front and replacing with the rb-1080 but am concerned if it would be a step back as far as power output is concerned.
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MY RB 1080 owners manual states that speaker impedance should be 4 ohms minimum, and no power output is given. I suspect it will be in the 250 wpc range as the power supply doesn't have the capacity for much more.
Hope that helpsJerry Rappaport -
I actually have that exact question into my contact at Rotel so we'll see what they have to say on its 4 ohm ratingComment
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The 4 ohm rating is 300 watts per channel from the RB-1080, per Rotel tech support.
G.
:grab:Comment
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Anyone have any experience using this amp with 4ohm speakers?Comment
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I also emailed Rotel's tech support concerning the RB-1080 handling a 4 ohm load just last week. The response was very positive, and within the hour actually, :T ...the 1080 will handle a 4 ohm load without any problems. Tech's response was 300 w/ch in 4 ohm load.
Also if you go to Rotel's web page under support, then FAQ...you can look up your model under model-specific FAQ for more info...I looked up the RMB-1075 and it even gave the 4 ohm rating per channel. Just a heads up!
~JoeComment
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RACER4551,
I have decided to purchase this very same model...and have been doing research on different models. In speaking with 4 or 5 owners of the RB-1080 powering 4 ohm speakers, it handles the 4 ohm speakers very well. I plan to run my 4 ohm speakers with this amp as well...300 watts to my two front mains. Also, as a side note, I have heard this amp runs a bit hotter than the multi channel 1075 and 1095. Just FYI
~JoeComment
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That is interesting....I am waiting for my 1080 to come in and I will be trading in my 1075. I was told that "good amps" will nearly double power upon halving the impedence...I believe some Carver designs do this....The 1075 is 120@8ohms and 200@4ohms isnt it?
So why is 1080 at only 300@4ohm? Shouldn't it be closer to 360watts or so at least?Comment
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There's a number of factors that go into how well and amp can double the power as resistance is cut in half. The double value represents a perfect situation which never happens unless the higher values are fudged to make it look good. For example an amp might bench at 100 watts into 8 and 160 into 4 ohms but the manufacturer will state that its 75 into 100 and 160 into 4 to make it look better...or they'll use a full 20 to 20 khz test for the 8 ohm rating and a DIN rating for the 4 ohm load (which is what Rotel does for the 1075's 4 ohm rating) I'm not sure about the 300 watt rating given to the 1080 it might be a 20-20 test in which case the DIN would likely be a fair bit higher...either way its a lot of power
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The biggest factor is the capacity of the power supply, as I stated in an earlier response. The 1080s power supply transformer is capable of delivering 550va. Assuming the amp is 90 percent efficient (that's probably a gift) that means 510 watts total. As I mentioned in that same earlier response based on power supply capacity 250-wpc is probably the best one could expect to see at 4 ohms.Originally posted by Andrew PrattJerry RappaportComment
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Hi DrJRapp.
I agree that the biggest factor here is the power supply, but disagree that the PSU transformer is only capable of 550W. 550W is the 1080's average power conumption. The 1080's transformer is rated at 1.2KVA (according to a review on Rotel's website), so 300 or higher (Rotel tends to understate their power ratings) WPC into 4 ohms could easily be achieved.
-BenComment
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Thanks for the info gents...Comment
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stupid question... if resistance is lower for 4 ohms vs 8 ohms, why are 4 ohm speakers harder to drive?Comment
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Ohm's law states: V=R*I. Hence, for a given voltage, if the impedance is halved, the current must double, so for a given voltage (the result of the input signal and amplfer gain), halving the impedance results in the amplifer working twice as hard to produce the required current (twice as much).
If the amplifer cannot meet this current demand, the voltage is reduced to such a point that Ohm's law is still satisfied (and nasty things like clipping and compression happen).
-BenComment
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The resistance is lower, and more power will go to the speakers, but the amp itself doesn't know when to stop producing power. The amp will keep cranking out power untill it outputs more than the components that make up the amp can handle. After that something will fail and you get the magic smoke out the top.
Same applies to some speakers that can be considered 'hard to drive'. Take a B&W 802. 8ohm nominal. Key word is nominal, average. The 802 dips pretty close to 2ohms in the woofer range. If you have an amp that can't handle lower ohm loads it just can't produce good clean power at the lower ohm loads. With an 802 the spread that's close to 2ohms isn't wide so it won't blow an amp up, but these amps just can't produce the fullness other amps can with that speaker.
Kevin D.Comment
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Little bit OT but is there a correlation between the nominal impedence rating and the quality of the speaker? It appears that many upper brands of speakers run 6ohm or below.....I wonder why that is?Comment
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Oh..and for what it's worth, I found this tidbit of info regarding the Rotel 991 which I believe is the predecessor to the 1080...which leads me to believe that Rotel's 300watt rating is pretty conservative....
"Offering Rotel RB-991 power amp. Balanced/XLR inputs. Stereophile rated (vol 22, no. 8) at 240 wpc @ 8 ohms/416 wpc @ 4 ohms. Reviewed as an "exceptional performer...resolution of detail and overall neutrality hint at a performance level that one would expect from an amp costing two or three times as much". Rotel rating is 200/300 wpc."Comment
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I can vouch for the fact that the 991 and 993 handle 4 ohm speakers fine. I don't have a sub and get almost room shaking bass out of my little 4 ohm Dynaudio Contour monitors set to Large (have used both amps, currently using the 993), if thats any indication of the amps abilities.Comment
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I think I've got what you're asking about. I've got a 1080 with Polk LSI25's in the front and I'm very satisfied. Pre/Pro is a 1055 with one LSI/C and 4 LSI/FX's. Had everything about a year and had no problems, no regrets...bam 8)Comment
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RACER in case you are still reading....I have run my new 1080 for the past 2 weeks .....I think I am finally there. The 1080 drives the LSi 15s pretty well....SOOOO much better bass than 1075 even when passively bi-amped.... much tighter. The higher frequencies seem a bit softer than the 1075. Anyways, no prob. except I had to run a ground wire between my HK 230 and the amp to get rid of a tiny buzz. The amp runs pretty hot.....good luck.Comment
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Thnks for all the great info on my question.It sounds like the 1080 would deliver enough power output to satisfy the needs of the lsi 15's.But am still on the fence about how it would compare to the carvers output,have always been confused on how carvers amps have power ratings so high but dont weigh very much compared to other amps.Do they make their power in a different way vs rotel amps.Comment
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Carver amps
Racer,Originally posted by RACER4551
It depends on the model (and year), but generally the Carver/Sunfire amps rated > 200 watts use a class H design, which is slower in power delivery than the typical class AB design, produces more harmonic distortions, but allows for delivery of high voltages - for short periods of time (thus high power ratings). It also runs cooler so no need for heat sinks. - but do they stick in cooling fans instead 8O ?? I believe the Carver Pro series amps have cooling fans. (Fans are simply unacceptable to me :M ).
I'm not a big into amps which are inherently slow and have high harmonic distortions (what - about .5% THD?? - more than 10 times the RB1080!!!). So, Carver was not an option, and Rotel was my answer. Beauty is in the ear of the listener, so it is a matter of preference, and you will have to decide for yourself. If you are still curious about the specifics of Bob Carver's designs, here is a link to his "white paper" on amplifier design: http://www.vxm.com/21R.69.html
And here is a link to Rotels website to view their "balanced design" video.
Good luck in your decision making :wink: .
Cracking!Comment
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Thanks cracking for the links,good reading.It seems the best thing to do would be to find a 1080 to compare,but havent had any luck short of buying a new one.I wonder if i could borrow two channels from my 1095 to see if there is any difference in sound quality vs the carver.I am currently using it(1095) to power my center,side surrounds and rear surrounds.Would this give me an idea on how a rotel amp would handle the 15's?I know the 1080 would have a little better control in stereo mode vs the 1095 but should give me an idea on the sound differences and whether the differences are enough to warrant the swap from the carver.Comment
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Racer,
Tough question about the sound of the 1095 vrs. the 1080, the differences are subtle at best. It is a question that has just recently been discussed.
I got the general consensus that the sound of the two was too close to tell apart. I think the 1095 would give you a sound close enough to the 1080 to use in a comparison with the Carver. If you get the chance to do it, I'd love to hear your review.
Cracking!Comment
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I plan to try this out this week sometime as long as i dont eat to much turkey!Will let you know what i find out.Comment
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im about to upgrade to a 1080 from a carver 1.5. Sure, the carver says it is 300wpc and 1200 wpc (short term) but there is a lot of smoke and mirrors with the old carver wattage ratings. I think the whole magnetic filed power amp stuff was a bunch of baloney designed around Bob Carver trying to put huge wattage numbers on amps.
Open up your amp....then open up the rotel.
Big amps need big capacitors....period. Anything else is a compromise.Comment
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I think i have to agree with you ken,always been kinda curious on how the carvers made those big numbers.Let me know your thoughts on your swap.Comment
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Just my .02 cents, while you have the cover off of your'e carver you will notice the dark area on the circuit board around the driver stages, as well as some discolored resistors........I had a TFM15, 25, and 35X, all of wich were replaced by an RMB-1075 with no second guessing to date. I have had the 1075 for about a year and could'nt be happier.Comment
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I've owned a couple of Carver's products through the years including "The Receiver". Never been impressed. Loud, yes but inner detail, what inner detail???Jerry RappaportComment
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loud as hell.
i run a block party with my 1.5.
yep, the entire inside is black. thetransofmer looks like it was in a fire. The peopel at sunfire/carver say that is normal.Comment
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Specifically "Normal" for their design....Comment
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This will slide of topic for a moment, but, amps are designed to meet specific needs, and I get the feeling from Carver that they are to many things to, for to many people. Eric Clapton would no more dream of running his system in his den with his Marshal amps than he would take his Classe' amps up on stage (hypathetically speaking). Peavy for example makes some pretty descent pro equipment, and I would bet if you ask most of their employees if they would run their amps @ home they would tell you no. They hammer at pushing a set of 18" bass bins, various horns, but would sound terrible pushing a set of Klipsch Reference, or B&W Nautilass speakers. These are two completely different animals. As stated many times in this hobbie, the beauty is in the ears of the beholder, it's our musical tastes, our pursuit of audio nirvana, and ultimately our money, BobComment
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