Conrad Johnson MF-2550
At conrad-johnson we have a simple formula for achieving highly accurate, highly musical amplifiers:
• straight-forward, simple circuits designed for linear operation without excessive loop inverting feedback
• exceptional component parts selected for their ability to provide uncolored accuracy in music reproduction
Straightforward circuits provide simpler, more direct signal paths and require fewer component parts to implement. This is desirable because all component parts fall short of ideal and impose limits to transparency. Fewer parts means less of the unavoidable coloration that is imposed by each part, even the best available.
Fewer parts means that the budget can be concentrated to obtain the often costly best available parts especially for key circuit applications.
The design of limited feedback circuit demands discipline from the circuit designer in developing a circuit in which each stage functions linearly without requiring external correction from a feedback loop.
In the MF2550, high voltage FETS permit highly linear operation of the critical first voltage gain stage, while bi-polar transistors are used to configure an output stage with low output impedance to deliver maximum current to reactive speaker loads.
Linear operation of the audio circuit requires a power supply designed to maintain absolutely fixed operating voltages while meeting current demands that fluctuate rapidly with the music itself. This imposes on the power supply similar design and component choice requirements as on the audio circuit itself. The MF2550 features discrete dc regulators to power the critical voltage gain stage. The power supplies and grounds for the input and output stages are run by separate power transformer windings to isolate the input stage from the effects of the substantial current flows required in the output stage.
Circuit design is a combination of science and art. At every step consideration must be given to how a circuit will be implemented. The realized performance will depend critically on the selected component parts. Conrad-Johnson products are known for unmatched quality of parts with custom-made film capacitors and precision metal film and metal foil resistors. We even use large 30 micro-Farad polypropylene capacitors for critical circuit applications where other designs commonly use non-polar electrolytic capacitors, the factor of 1000 reduction in dielectric absorption of polypropylene resulting in a cleaner sound. The power supply electrolytic capacitors are bypassed with high quality polypropylene film capacitors that provide a small but quicker responding current reservoir. The upgraded MF2550SE takes the musical experience one step further by upgrading 16 capacitors to CJD Teflon hybrid capacitors and a couple of dozen resistors to precision metal foil types.
Our obsession with parts quality extends to the connections within the circuit itself. Power supply, signal and ground traces and wiring are parts of the circuit with limitations and shortcomings that must be accounted for. To enable the output stage to deliver substantial bursts of current, the MF2550 layout provides storage capacitors close to each output device. The internal power supply connections and ground returns between the main supply and these local storage depots are accomplished with heavy, audiophile grade multi-stranded wire in order to minimize the impedance of these longer runs.
Thoughtful engineering, specification of high quality component parts, and painstaking care in production make the MF2550 an exceptional audio amplifier. We invite you to arrange an audition with your conrad-johnson dealer to confirm for yourself its extraordinary musical performance.
Power:250 watts per channel from 20 Hz to 20 KHz at no more than 1.0 % THD or IMD, both channels driven into 8 ohms.
Sensitivity: 2.0 Volts rms to rated power
Frequency Response (at 10 watts): 20 Hz to 20 kHz, +/- .1 dB
Hum and Noise: 100 dB below rated power
Input Impedance: 100 kOhms
Dimensions: 16.25D x 19W x 6.125H inches
Weight: 26 kg