Power Amplifiers

Rotel RMB-1575 Five-Channel Class D Power Amplifier

ARTICLE INDEX

Rotel RMB-1575

Introduction

Class D switching amplifiers are more and more common. Manufactures have made great strides in overcoming the high-frequency shortcomings found in the early models. Rotel in particular has been involved with this technology for a few years, with a significant portion of their line-up now using this.

Many manufactures of Class D amplifiers are using the well-known IcePower modules created by Bang & Olufson. These modules come in different flavors, powered modules (ASP series) of 250 500 and 1000watts and passive ones (A series) also at 250 500 and 1000watts. There are also three other series of modules supplied by B&O that exceed the scope of this review. Using these modules allow manufactures to build high-quality amplifiers without investing a ton of money and time into R&D.

Specifications

  • Design: Class D (Switching)
  • Power Output: 250 Watts RMS x 5 into 8 Ohms, 500 Watts RMS x 5 into 4 Ohms
  • Dimensions: 2.9" H x 17.1" W x 15" D
  • Weight: 15 Pounds
  • 12 Volt Trigger
  • MSRP: $2,799 USA
  • Rotel

Design

The Rotel RMB-1575 is the multi-channel powerhouse of the Rotel's 15series that utilize both the ASP and A modules to create a powerful amplifier. By using two of the powered (ASP) modules for the front LT/RT Rotel then powers three additional passive (A) modules for the C/SL/SR channels. This sharing of power supplies could potentially decrease the available power to all channels, yet Rotel claims that the RMB-1575 is able to deliver 250watts a channel, with all channels driven (20-20 kHz, 0.03% THD, 8 ohms). This is an impressive amount of power for such a relatively small amplifier.


Setup:

Rotel RMB-1575

Using a Denon 4308ci as a processor I fed the five single-ended outputs into the RMB-1575. Source came from an Oppo 981HD DVD player. Speakers consisted of 2 Raw Acoustics OB3 open baffle speakers (in the front), 2 Raw Acoustics OB2 open baffle speakers (on the sides) and a Paradigm CC170 center speaker. To put this amplifier through its paces I used Pink Floyd's Dark Side of the Moon (SACD), Frank Zappa's Halloween (DVD-Audio), The Melvin's A Senile Animal (Redbook CD) and Stephen Chow's Kung Fu Hustle (SD-DVD).


In Use

Music

The power supply in any amplifier is crucial to sound quality. As this amp utilizes a shared power supply configuration I wanted to test this amp with multi-channel music to really tax the power supply. As well, Class D amplifiers in the past have been know to have some high-frequency artifacts so the extended high frequency response found in SACD and DVD-Audio discs make them perfect for testing class-d amps.

Rotel RMB-1575

For my first listening session I used the SACD version of Dark Side of the Moon. One of the finest examples of what the SACD format is capable of outside of classical music. The clocks chiming at the beginning of Time were clean, clear and showed no distortion. Next was Great Gig In The Sky – Claire Torry's vocal solo was consistently beautiful and melodic at all volumes with no noticeable distortion.

Rotel RMB-1575

My next session was with the Frank Zappa live compilation Halloween, recorded over five days in NYC around Halloween 1978. Dweezil Zappa and Joe Chiccarelli have done an admirable job recreating the live shows and the DVD-A format is ideal for Franks live music. The mix puts you right in the audience, the sound is astounding with the band up front and you are immersed in the crowd. The recording is amazingly clean for a live recording from the 70's. There is great separation of the instruments and band members. The RMB-1575 never failed to provide clean sound even at (close to) live SPL levels.

Rotel RMB-1575

One of the more dynamic and demanding discs I have, especially for high-frequencies is The Melvin's A Senile Animal. This album finds the Melvins with two drummers and is an all out percussive assault. Percussion separation is what I am listening for with this album, there are layers of heavy distorted guitar, solid bass playing and too many drums to count. With the RMB-1575 the cymbals, high-hats and gongs (yes gongs plural) never muddled together and were always crisp. Lower quality amplifiers just cannot resolve the detail present in this album when pushed too hard. The Rotel had no problem presenting all the intricacies contained within this heavy-rock tour de force. Every song was easily reproduced with no shortage of dynamics. Of course this is an easier test than the previous albums as the amplifier only had to power two channels. This album proved that this amplifiers high-frequency response is excellent.

Movies

Rotel RMB-1575

As this is a muti-channel amplifier it will see more movies than music for most people. When I really want a surround work-out I use the funny and intense Stephen Chow epic Kung Fu Hustle. There are many scenes that test the systems acoustic balance with flying axes, swift punches and unreal bass. An abundance of immersive special effects and slow motion fight scenes put you right in the middle. After the end of the movie I was unable to detect any excessive heat from the amplifier.

For Comparison

Rotel RMB-1575

I had two other amplifiers on hand to directly compare to. The internal amplifiers in my Denon 4308 receiver plus a 10series Rotel RMB-1085, review here. Compared to the Denon the Rotel was slightly better in dynamics and soundstage at moderate to loud volumes and some-what cleaner at very loud volumes with DVD playback. At softer volumes I found the Denon had more detail and was more engaging. Compared to the 10 series amp the difference was slight, with the RMB-1575 having better bass control and mid-bass clarity. Given that my speakers are relatively easy to drive I was not surprised that the difference was minimal.


Conclusions

The RMB-1575 is a great sounding amplifier that provides bottom-less power and suffers little from its high-efficiency switching design. Clearly Rotel is taking the Class D topology seriously and have made excellent use of the IcePower modules. Once again I must state that you need to hear this amp and forget the old notion that Class D is for car-audio and subwoofers. The RMB-1575 is high-quality from start to finish.