This power amplifier was part of a complete ROTEL stereo system, it can be used as a stand alone power amplifier (there is NO preamp at all)
OR
you might like to partner it with the matching RC-990BX Control amplifier. Even better run two of these RB-990BX power amplifiers from the RC-990BX and you have an excellent bi-amp system to impress both your ears and your guests!
I also have the matching AM-FM Tuner and CD Player (Limited Edition) but they will be advertised once I have double checked everything.
ROTEL Stereo Power Amplifier
Made In Japan
Model: RB-990BX
Released to market in the early 1990's
Two source line level inputs
Both inputs gold plated RCA sockets
Speaker outputs are screw down OR banana plug type fitting
Dimensions: 440mm wide x 365mm deep x 120mm height
Weight: 15.5Kg (!)
MANUFACTURERS STATED SPECIFICATIONS:
Power Output 200W per channel RMS into an 8 Ohm load
Acceptable speaker impedance load range 4 ~ 16 Ohms
Total Harmonic Distortion (at full continuous power output) no more than 0.03%
Intermodulation Distortion (at full continuous power output) no more than 0.02%
Damping Factor (20Hz ~ 20KHz into 8 Ohms): 1000
Input Sensitivity/Impedance: 1V/33K Ohm
Frequency Response: 4Hz ~ 100KHz (!!!) at =/- .5dB points (extraordinary)
Signal To Noise: 120dB
These are the manufacturer claimed figures, and very impressive they are indeed but I am unable to confirm these figures because my test equipment has all found new owners.
How Rotel achieved these design measurements is detailed below...
COSMETIC CONDITION:
Very good case, front panel, rear panel, underneath and top side. This means NO dents, ALMOST NO scratches or discolouration. I say almost no scratches because the usual culprit is the top of the case with heavy equipment such as this amplifier, this unit has one small (light) diagonal scratch (about 2cm long) at the rear left hand corner and tiny little "doodly" scratches on the right side near the front - the latter seem to have been caused by the feet of equipment sitting on top at one time.
NO buttons missing! There are barely any!
NO wear to any of the labelling
It is so true to describe this as a big black beast ... it is very black and foreboding looking with just a single red "eye" glowing (Power On) and it is a beast due to the weight - my arms are now much longer after carrying this out of my storage units.
GENERAL DISCUSSION/HISTORY/TESTING:
This Rotel control amplifier (along with the other Rotel components I have/am advertising) cost our business a fortune way back in the late 1990's but it was necessary for our "hi-end" clients with "hi-end" ears that flapped in the air due to the high level sound pressure waves assaulting their ears!
It never missed a beat, just sitting on the "Hi Fi shelf" waiting to bring pleasure to our discerning client's ears.
My professional background is technical and yes, I like to look inside our equipment and observe "how things were put together and designed"
First thing you notice is the weight, this is one very heavy amplifier - I have rack mount 1000W PA amps that weigh less than this one!
Put it on your shelf and then leave it alone - it is not to be messed with because it is quite an effort to move.
All steel case, tough as nails and considering the power requirements of this amplifier, it's really not that surprising. Central to the internals is the MASSIVE toroidal transformer sitting right in the centre of the case. I would believe this transformer is very conservatively rated for the power needs of this amplifier. I ran this power amplifier for many days continuously (to check it out after being in storage) and that transformer barely gets warm! Even at continuous high output levels.
Inside (like all Rotel equipment) it is SO SYMMETRICAL!! The layout was designed by a person or team with a very logical, organised methodology, not like some other consumer equipment that is quite frankly a tangled mess inside. Try working on the old NAD integrated amplifiers and you will know what I mean!
But not only is it laid out so symmetrically, it actually makes sense!
The heaviest component is the power toroid and being located in the centre, the whole amplifier feels balanced when you lift it up. Most other amplifiers have the power transformer sitting to the left or right side which makes the weight "lop-sided".
Behind the transformer is the very impressive collection of four chassis mount electrolytics (Rotel branded 15000uF 80V Made in UK), with copper screw terminals and a large supply rail copper plate.
On each side are the two audio power modules, completely separate units but identical in design. You can't help but notice the transistors that do all the output work, 5 complimentary sets of 2SC3856/2SA1492 - ten power transistors on each module! But I must say this channel module is beautifully laid out and looks to be easy to access if ever any service work required - nice one Rotel!
We have NEVER needed to have this amplifier serviced but nothing keeps on going forever, eventually it may need to be looked at.
Even after all these listening tests I have been doing, I have not looked at the bias voltages (detailed in the Technical Manual - available if you request it) - I have a simple philosophy, if something is working great - leave it alone!
You may notice that when looking at the "inside" photograph there is discolouration around a few components - THAT IS NOT LEAKAGE OR HEAT DAMAGE! Rotel was in the habit of applying copious amounts of a glue/resin around some of the components to keep everything "secure".
FINALLY ... let's get down to the actual functioning of the amplifier
I used my Richter bookshelf speakers (also on offer in a separate advertisement) because that's what I had to hand. Not the best choice for listening as they are rated to only 100W per channel and their bass response only goes down to 50Hz but it was sufficient for my testing of the amplifier.
All audio was fed to this amplifier via the RC-990BX Control amplifier, but it could just as well have been any other "Pre-amplifier" system
Powered up, on comes the Power On red led.
Also the Protection red led comes on for about 2 seconds before going out again, this is absolutely normal.
No horrible thumps or clicks at all from the loudspeakers, it just turns on!
So what does it sound like?
Superb in one word. So very very quiet when there is no music, at times I had to check that the amplifier was still running in between tracks when using the CD sound source, it is just so quiet when there is no music.
I cannot say that I am a true, diehard audiophile freak but I know very good audio when I hear it and this power amplifier amplifier just cruises along, I get the impression it is capable of so much more but I couldn't push it too hard due to household "peace" and the fact that my test bookshelf speakers will only safely run up to 100W each side.
Please though, don't accept my word for it, take a look around online at the discussion forums (search with Google) and you will see that "real life" users of this equipment (and the RC-990BX) love their Rotel gear and compare it very favourably to far more expensive equipment.
SPECIAL TECHNICAL NOTE:
Just one thing that many Rotel owners are not aware of.
These amplifiers are robust and usually run well within design limits BUT we noticed from past experience that if you accidentally short either speaker output cable, most likely you will "blow" one or more fuses for that channel. The fuses are slo blow types but the fuses are a first line of defense, having the fuse "blow" is a good thing for your amplifier because it means something is wrong wrong wrong!
Usually it is something simple like shorted speaker leads (easy to do, even with banana plugs)
This happened to us twice, both times caused by the shorting issue. I have indicated on one photograph where these fuses are (same location on each channel board) and the type we always used for replacement is size M205 6.3A Ceramic Slo Blow (these are commonly available e.g Jaycar Electronics)
Actually we became super-sensitive about these output issues and NEVER turned on the amplifier with no speaker connected, either. The amplifier is tough but it is also pretty sensitive to "unusual" conditions.
I guess what I am saying is, ALWAYS treat your power amplifier (Rotel or otherwise) with great respect, it might be big and brutish but at the same time, a very sensitive guy!
NEVER EVER connect your inputs and outputs while power is on, the likely hum/buzzing/noise is likely to upset something or worst still, imagine those cones in your prized (and expensive) loudspeaker system being vibrated in and out wildly! Always make sure your equipment is turned off (plugs removed from the wall or outlets) then connect all your bits and pieces, then check it all once again and finally plug in the power and turn on your equipment, component by component.
