Product Concept and Description

The Cello Rhapsody amplifier contains the most recent thinking in high-powered amplifier circuitry and mechanical design from the staff of Matthew James, L.L.C. Available as either a two- or three-channel amplifier, the Rhapsody is designed to deliver in excess of 200 watts per channel into an 8-ohm load, and more than 400 watts per channel into a 4-ohm load. The Rhapsody is designed to have the lowest possible levels of distortion while under actual use, as opposed to measuring well simply on a test bench. The circuitry is designed to perform well under the complex resistive, reactive and regenerative loading which loudspeakers present to an amplifier. And again, it does so without adding additional forms of distortion before the overload threshold is reached.

Many amplifiers utilize some form of soft-clip circuitry to deal with overload. The problem is that many of these approaches introduce additional forms of distortion before the actual overload threshold is reached. Furthermore, most designs to control overload are not comprehensive in dealing with all of the situations that negatively affect an amplifier's ability to remain stable under demanding situations. They might only control voltage overload, while current and frequency overloads also have a significant impact upon the reproduced sound. The Rhapsody has been designed to control all three forms of overload under all conditions.

Considerable effort has been made to reduce low frequency errors, because most of the energy in music and film sound reproduction is present in this part of the frequency spectrum. It is crucial to maintain low intermodulation distortion of low level, high frequency information in the presence of large low- and mid-frequency signals under complex loading. In the Rhapsody, the driver and output stages are set to have the lowest distortion at small signal levels and to gradually increase with signal level. While this results in slightly higher total harmonic distortion (THD) measurements at full power levels, it conversely allows for the lowest possible distortion under actual listening conditions. Again, the requirements for accurate music and film sound reproduction have taken precedence in all design decisions.

All electrical connections for signal flow within the Rhapsody are accomplished via flat silver cables insulated with Kapton, or by heavy, solid copper buss bars. The chassis is manufactured with heavy aluminum plates on all six sides.

The input stage of the Rhapsody amplifier remains under control under any overload condition. The design tactics were chosen because they provide wide dynamic range and provide a greater measure of resistance to overload, before loss of control, than other possible choices.

The output stage of the Rhapsody employs six pairs of 250 watt, metal case, bipolar output devices per channel. The number and type of devices were chosen because they remain stable with a less complex circuit, requiring less negative feedback, and are easier to match to each other than other possible choices for this stage. The choice of devices, the location of devices on the heat sinks, and the heat sinks themselves were carefully considered to minimize the temperature variations among the output devices. The power devices are mounted with all metal hardware, compression washers and special graphite and metal composite gaskets to insure maximum thermal conductivity and full utilization of the output devices. Once again, consistent performance, stability and reliability under normal conditions of actual use were the driving factors in the design.

The location of the transformer was carefully considered relative to the other circuitry in the amplifier that can be affected by the magnetic fields that it generates. Heavy nickel plated copper buss bars have been utilized to improve grounding and power distribution within the amplifier. The signal from the amplifier's audio channels is delivered to the speaker buss bars via flat silver cables (AWG 10) insulated with Kapton. Special high temperature filter capacitors, with high current terminals are used to insure the utmost in performance. (3) Three specially designed feet, utilizing ball bearings of a similarly hardened steel and a proprietary coating, eliminate the possibility of surface-borne disruptions from affecting the performance of the circuitry.

Limited Warranty

Matthew James, L.L.C. warranties all mechanical and electrical parts of the Cello Rhapsody amplifier for (5) five years from original date of manufacture.

Specifications

Class AB2 with inverting and non-inverting polarity; balanced input, bridgeable.
Continuous Sine Wave Power rated at 200w/ch (800w/ch when bridged) into 8 ohms from 20Hz to 20kHz at maximum .25% THD.
Continuous Sine Wave Power rated at 400w/ch (1600 w/ch when bridged) into 4 ohms from 20Hz to 20kHz at maximum .5% THD.
Power consumption: 1,500 watts at full output.
IMD SMPTE: <.1%
Gain: 23dB
Dynamic Headroom: 2.5dB
Frequency Response: 20Hz to 20kHz +/-.5dB
Input Impedance: 10K ohm inverting, 10K ohm non-inverting
Noise: -100dB below full rated power. C weighted
Dimensions: W: 43cm (17.05") x H 26cm (10.148") x D 55.3cm (23.316")
Weight: (2 channel version) 105lbs; (3 channel version) 115lbs.

 

Matthew James 84 Long Hill Road Middlefield, Connecticut 06455 USA 860 349-5999   Fax 860 349-0579 Email - jimm@matthew-james.net