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Rotel RB 1092

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Steve Zodiac

Established Member
From what I've read Rotel make some very good amps, but I can't see how it can output 1000 watts when it's maximum power consumption is only 600watts!
 

Steve Zodiac

Established Member
Would someone at Rotel have sussed this out? Any electronics engineers here?
I don't think you need to be any sort of Engineer for this really PPPPPP. Have you ever heard of any electrical appliance where you can put in a certain amount of electrical power in and get more out? I haven't. If there was such a thing it would answer the worlds energy problems!

There will only be losses, or at best, the same power out as in....and then it would have to be 100% efficient. That, I think, is pretty much out of the question. :)
 

miceri

Established Member
Why would you want a pair? It is a 2 channel amp, so either it is for hifi, or fo bi-amping.

Buying 2(2x500), what would you do with that?

//Dazed & Confused (not that difficult really...)
 

Graham_E

Established Member
lol, i do belive that 60 watts 240v ac is more than 600watts at the voltage that speakers run at.

Rotel would never claim something that isn't true, all you guys are doing is proving your own lack of understanding on how amps /speakers work.
 

Steve Zodiac

Established Member
lol, i do belive that 60 watts 240v ac is more than 600watts at the voltage that speakers run at.
You believe incorrectly then if you're talking about power.
Rotel would never claim something that isn't true, all you guys are doing is proving your own lack of understanding on how amps /speakers work.
Rotel wouldn't be the first amplifier or receiver company to state specs that don't add up....and rather than needing to know exactly how amplifiers and speakers work, it's more a case of knowing what an electrical watt is.
 

HiFiRuss71

Distinguished Member
From what I've read Rotel make some very good amps, but I can't see how it can output 1000 watts when it's maximum power consumption is only 600watts!
All amplifiers apparently put out more power than they draw, because they draw enough power to keep their internal power supply topped up. The power supply reservoir is a pile of capacitors that can dump the power very quickly. Quicker than it arrived in fact.

For instance:

Note that it can supply a peak current of 40A whilst 13A is the highest rated fuse you could put in the plug.

Also note that maximum power consumption is 600W. 1W=1Vx1A so 600w/230v=2.61A. Flat out, it draws only 2.16A.

This reservoir of power has to be built up, which is part of the reason why you have a lengthy pause after you turn your power amp/receiver on. It quite literally has to charge up. This reservoir is also the reason why older amps could often continue outputting sound after you'd turned them off at the wall.

Russell
 

Reel To Reel

Established Member
Why would you want a pair? It is a 2 channel amp, so either it is for hifi, or fo bi-amping.

Buying 2(2x500), what would you do with that?

//Dazed & Confused (not that difficult really...)


Bi-amping centre + FL & FR.
 

Qublai

Established Member
Sound watts per channel is completly different to watts power comsumption.

So a power amp might consume say 300watts of power, but output say 500watts per channel into 8 ohms and possibly double this into a 4 ohm load.
 

Steve Zodiac

Established Member
All amplifiers apparently put out more power than they draw, because they draw enough power to keep their internal power supply topped up. The power supply reservoir is a pile of capacitors that can dump the power very quickly. Quicker than it arrived in fact.

For instance:

Note that it can supply a peak current of 40A whilst 13A is the highest rated fuse you could put in the plug.

Also note that maximum power consumption is 600W. 1W=1Vx1A so 600w/230v=2.61A. Flat out, it draws only 2.16A.

This reservoir of power has to be built up, which is part of the reason why you have a lengthy pause after you turn your power amp/receiver on. It quite literally has to charge up. This reservoir is also the reason why older amps could often continue outputting sound after you'd turned them off at the wall.

Russell
I do understand Russell what you're saying about the reservoir of power in the capacitors, that's why manufacturers often quote the capacity of the capacitors and the peak current that an amplifier can produce.

The current an amplifier draws from the mains supply....well yes, that's simply ohms law, and the current output to the speakers is covered by the same thing.

What I'm getting at is that a correctly specified amplifier should be quoted as continuous RMS power with all channels driven together (and often stated as over a certain frequency range, eg 20Hz-20kHz). The total power an amplifier will draw from the mains should be greater than the sum of all the channels maximum continuous power output figures.

The Rotel specification quotes 2 x 500 watts at 8 ohm or 1000 watts at 4 ohms. In that case, being an efficient class D design probably having an efficiency in the high nineties, it should have a maximum power draw from the mains of just over 1000 watts if supplying 1000 watts continuous RMS to the load.

It has to be one of two things:

1) Rotel made a mistake in their specification (unlikely).

2) The 1000 watts output quoted is a PEAK figure rather than continuous RMS. Not what I'd expect from a quality amplifier manufacturer.
 

Steve Zodiac

Established Member
Sound watts per channel is completly different to watts power comsumption.
A watt is a rate of energy (one joule per second). An amplifier cannot create energy.

So a power amp might consume say 300watts of power, but output say 500watts per channel into 8 ohms and possibly double this into a 4 ohm load.
Only relatively briefly from the storage in the capacitors, rather than continuously. :)
 

HiFiRuss71

Distinguished Member
I think you're quite right about the peak figuers. The webpage for the 1092 states no references for the powers quoted. Being a Rotel I'd still expect it to be plenty powerful. That it can virtually double its 8ohm figuer into 4ohms, hints that this true whatever the absolute figuers may be.

Russell
 

Steve Zodiac

Established Member
....Being a Rotel I'd still expect it to be plenty powerful.That it can virtually double its 8ohm figuer into 4ohms, hints that this true whatever the absolute figuers may be.
A fair point and that is certainly some indication of a good design. It's just a pity Rotel don't quote continuous RMS figures which would have some real meaning, instead of using what would appear to be peak wattage figures.

Anyway, I'm sure this Rotel amp would be very good, but just not as powerful as it may first appear in Rotel's specification (which is pretty much what I said in my original reply). :)
 
J

jackal

Guest
I'd always thought that you have to be careful with class D amp 'power' figures anyway, as their ability to provide continuous peak current was very limited.
 

dingwall

Banned
There is no voodoo magic here:

The specifications clearly state FTC for the power rating. This means continuous power, all channels driven, at the bandwidth, load, and THD specified (in this case 20hz-20khz, 8 ohms, <0.03%THD).

Power consumption, by FTC and EIA standards, refers to the long-term consumption while outputting 1/8th of the power rating. Due to the very high peak-to-average ratio of musical content, this represents the output at which a typical amplifier occasionally clips on transients. (Good amps don't, hence the resurgence and importance of additional specifications based on concepts of dynamic/peak power...at least from a few manufacturers). Consumption can also be stated at a specified output (eg idle, 1/3 power, full power, specific power).

The signal voltage even at a massive 600W into 8 ohms is only 70V, so an amplifier can in theory output many multiples of the fuse current rating without using power reserves. However in practice to achieve high power, you do need the big transformers and capacitors to supply the current needed. (Current delivery is difficult and a limiting factor linked to dynamic power. You can say that continuous power rating alone does not predict or correlate with transient/shortbust power, but the peak current does. Impedance dips in the speaker load also need less voltage and more current at the same power. Hence the importance given to this specification...at least from a few manufacturers.)

I think Rotel are owed an apology!

PS The side points about amplifier workings are just based on my very limited and very possibly incorrect understanding!
 

Steve Zodiac

Established Member
Firstly, let me just say I've nothing against Rotel whatsoever, I just find their specification misleading compared to those of some other manufacturers.

The specifications clearly state FTC for the power rating. This means continuous power, all channels driven, at the bandwidth, load, and THD specified (in this case 20hz-20khz, 8 ohms, <0.03%THD).
Ok, FTC (Federal Trade Commission) was something I wasn't familiar with. For the benefit of anyone else who may be interested and didn't already know: it is an independent agency of the US Government for the protection of consumers.

According to the relevant section (432.3 for power amplifier output claims):
(e) Rated power shall be obtainable at all frequencies within the rated power band without exceeding the rated maximum percentage of total harmonic distortion after input signals at said frequencies have been continuously applied at full rated power for not less than five (5) minutes at the amplifier's auxiliary input, or if not provided, at the phono input.

In Rotel's specification it does not actually state a "rated power band". Neither is there any frequency range next to the power figures. It does state a frequency response (10 - 40 kHz ±3dB), but this is definitely not the same thing as a "power band" or "power frequency response". That wasn't my original point though.


Power consumption, by FTC and EIA standards, refers to the long-term consumption while outputting 1/8th of the power rating. Due to the very high peak-to-average ratio of musical content, this represents the output at which a typical amplifier occasionally clips on transients. (Good amps don't, hence the resurgence and importance of additional specifications based on concepts of dynamic/peak power...at least from a few manufacturers). Consumption can also be stated at a specified output (eg idle, 1/3 power, full power, specific power).
Where in this Rotel specification for power consumption does it state FTC or EIA standards? It doesn't!

Quite often two power levels are stated for electrical equipment and sometimes they use three. If three are stated they are usually for stand-by, idling and the maximum power (or current) the equipment could possibly draw from the supply. This maximum figure is required fo electrical safety and supply considerations. Are you suggesting dingwall that the 600 watt power consumption figure quoted in this specification is not the maximum power this amplifier can draw from the supply?


The signal voltage even at a massive 600W into 8 ohms is only 70V, so an amplifier can in theory output many multiples of the fuse current rating without using power reserves. However in practice to achieve high power, you do need the big transformers and capacitors to supply the current needed. (Current delivery is difficult and a limiting factor linked to dynamic power. You can say that continuous power rating alone does not predict or correlate with transient/shortbust power, but the peak current does. Impedance dips in the speaker load also need less voltage and more current at the same power. Hence the importance given to this specification...at least from a few manufacturers.)
On any amplifier high continuous power output relies on a large transformer and the maximum current output (peak power output) relies on the size of the output capacitors. With regard to "an amplifier can in theory output many multiples of the fuse current rating without using power reserves" yes, a great many amplifiers can output more current than the fuse current rating, but that's nothing to do with my original concern with the specification. What I'm saying is that you cannot input a certain maximum power (watts) and get a continuous power out to the speakers which is a higher figure than the maximum power consumption figure.

If this 600 watt power consumption figure is not a maximum figure then I don't know what use it is. If it is a maximum power consumption figure then this amplifier cannot output a continuous 1000watts.


I think Rotel are owed an apology!
Not yet, I still think Rotel's specifications are misleading!
 
W

wookie

Guest
The Rotel RB1091 & 1092 both use the B&O icepower 1000ASP Module.
1000W into 4Ohms and a 40A peak current.
stable down to 1 Ohm.

Music is not continuous pink noise, its transient.
The Icepower topology is analogue PWM and does work well with extremely high dynamic power, for "transient" material.

BelCanto re1000 uses exactly the same modules and they sound real nice.

The attached should satisfy all interest on the amps.

http://www.6moons.com/industryfeatures/icepower/icepower.html

http://www.icepower.bang-olufsen.com/sw2049.asp

www.acoustic-reality.com/articles/eng_asp.pdf

P.s. I use 4 x Belcanto Ref1000's :D & PPP, Trust me on this one!
 

dingwall

Banned
Steve,

The FTC and its power rating standards should be well known to anyone who knows about or wants to begin to understand amplifier specifications.

The facts you claim about the missing or unclear specs are completely wrong. Perhaps you want to read them again - I don't want to have to cut and paste them to embarrass you!

I've said what the power consumption refers to, and why it is useful, best representative of safe use, and the industry standard. A consumption rating which does not specify an output power should be taken as conforming to this standard, other ratings should specify the output. Power consumptions at these other outputs are indeed useful also - I'd be shocked if the maximum power consumption was not at least on the back of the amplifier.

The specs are honest, clear and straightforward to clueless consumers and experts alike. If they don't add up, I'm sorry but its because you are attempting sums beyond your capability.
 

Reel To Reel

Established Member
I am thinking of buying a pair of these - anyone here have any experience of them, or suggest suitable alternatives for the same sort of price.

UK retail is £1,595


My interest in Rotel's is picqued. Interested also that no-one has mentioned alternatives at the price/performance level.

I have been considering Bryston -great quality in a traditional design, but very expensive in the UK.

Are the new ICE amplifiers the new kids in town?
 

Steve Zodiac

Established Member
The FTC and its power rating standards should be well known to anyone who knows about or wants to begin to understand amplifier specifications.
dingwall, I am English and live in the UK. You're right, I'm not familiar with guidelines laid down by the US Government for protection of US consumers. I am no electronics expert, but I do understand clear amplifier specifications. I still feel Rotel's specifications are not as good as they could be with regard to power consumption and power output. That said, as I mentioned before, I'm sure it would be a very good amplifier.

The facts you claim about the missing or unclear specs are completely wrong. Perhaps you want to read them again - I don't want to have to cut and paste them to embarrass you!
My facts are completely wrong! Ok!! If I am wrong about anything and someone corrects me then I will happily say thank you. I think my initial comment about power in and out was very straight forward. You certainly haven't answered my concern, you have merely skated around it whilst at the same time making some assumptions that are clearly incorrect. You stated the power output is 20Hz - 20kHz. Where did that come from? This isn't stated in the specification and it would also appear to be incorrect according to wookie's second link. Power output quoted there is at 1 kHz.

I've said what the power consumption refers to, and why it is useful, best representative of safe use, and the industry standard. A consumption rating which does not specify an output power should be taken as conforming to this standard, other ratings should specify the output. Power consumptions at these other outputs are indeed useful also - I'd be shocked if the maximum power consumption was not at least on the back of the amplifier.
You said the power consumption figures were to FTC and EIA standards. It didn't state that in the specification. Why should you assume that something conforms to a certain standard if it's not stated as doing so? It seems a bit much that the consumer would have to buy a piece of electrical equipment, then look on the rear panel to find a maximum power consumption figure! It would be much easier to state this information in the website specification.

The specs are honest, clear and straightforward to clueless consumers and experts alike. If they don't add up, I'm sorry but its because you are attempting sums beyond your capability.
You say you don't want to embarrass me but you appear happy to insult me! I know my capabilities. The problems here with some of the specification figures can be understood by any literate person with basic electrical knowledge. I can read and my electrical/electronic knowledge does go a little beyond basic.


Let's just say dingwall that you appear to think that I'm not overly bright, and I think you state things that aren't accurate whilst skating around the issue by typing superfluous information!

Happy Christmas.


 
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