|Conrad Johnson MF2500 Stereo Power Amplifier|
|Home Theater Power Amplifiers Stereo Amplifiers|
|Written by Brian Kahn|
|Sunday, 01 April 2001|
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Bill Conrad and Lew Johnson joined forces in the early 1970's to form Conrad-Johnson Design, Inc. with the goal of building high quality tubed audio preamplifiers. From the beginning Conrad Johnson was all about the sound and stayed far from the hype and flash of the high end audio industry’s hey days of that era. Conrad Johnson’s first amplifier, the MV-75 was introduced in 1978. The MV-75's success opened the doors for Conrad Johnson to become a serious contender in amplifiers as well as preamplifiers.
Conrad Johnson produced its first solid state electronics in a new line called Motif. The Motif line was soon after joined by the Sonographe line to form a respectable product offering of solid state gear, from mid-level high end and up. The company continued to develop both tube and solid state gear and has used its two and a half decades of experience to bring us its latest products, including the solid state MF2500 amplifier.
The MF2500 ($3,495) is one in a series of three MF2000 series amplifiers; the MF2250 (120 watts x 2), MF2500 240 watts x 2) and the MF5600 (120 watts x 5). The series shares its basic aesthetic and circuit designs. The MF2500 is quite beefy at 7 1/2 inch high, 19 inch wide, 16 inch deep and weighing in at 56 pounds. The thick champagne colored metal faceplate features a black rocker power switch sitting in a slightly recessed oval which is cleanly divided by a vertical groove. The font also has an understated Conrad Johnson logo and power LED light. The back side of the amp is similarly simple and elegant with a captive power cord and fuse holders to the left side (facing the back) while the right side features a pair of Cardas RCA input jacks and five-way binding posts. Notably the heat sink fins are only on the left side of the amplifier.
Upon opening the amplifier I found a clean and well dressed design. I also noted the cross wise orientation of the boards which lends itself to the single heat sink design. The interior is dominated by a rather large power supply. The MF2500 input section utilized FET’s and the output section uses bi-polar devices. According to Conrad Johnson the FET’s, when used in the input section, give the amplifier a more tube like sound due to their similar distortion characteristics. Furthermore, it was also found that FET’s almost eliminate amusical odd-order harmonics.
The output stage features bi-polars as low impedance is critical here and they have about one-quarter the output impedance of FETs. Conrad-Johnson feels that this design correlates into a faster and more solid response, particularly in the bass regions. Lastly, the MF2500 features extremely low levels of negative feedback, which greatly improves transient responses.
I placed the MF2500 into my reference two channel system where it was joined by another Conrad Johnson component, the Premier 17LS (review pending) driven by a Pioneer Elite CDR19RW digital front end. I used the MF2500 with a variety of speakers, including; RBH Sound MC-6T’s, Martin Logan Scenario’s and Ascents and finally, the new Final 0.3 hybrid electrostatic speakers.