Conrad Johnson MF2500 Stereo Power Amplifier 
Home Theater Power Amplifiers Stereo Amplifiers
Written by Brian Kahn   
Sunday, 01 April 2001

Introduction
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.

The Setup
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.

The Music
I left the amplifier running for nearly a week straight before sitting down for a serious listening session. During the break in period I noticed a slight humming sound coming from the amplifier itself. This mechanical noise faded, but never went away entirely, I found that lifting the ground provided the greatest improvement. I listened to the MF-2500 with all of the speakers mentioned above, with all of my critical listening done through the Martin-Logan Ascents.

I began my first critical listening session early on a Sunday evening with Bill Berry's "For Duke" (Realtime Records). This album has both truly great jazz, and is extremely well recorded. Through the first half of the album I was absolutely amazed by the presence and width of soundstage. I have been using this album as a reference in reviews for a long time and have never heard it sound this good on any of my systems. The second half of this disc is actually a second album, Earl Hines' "Fatha." The first track of the second half of the disc, Birdland, features Red Callendar on the tuba. I was floored by the first blast of the tuba, not only was it crystal clear and tonally accurate, it had a great sense of weight and solidity.

I then moved into listening to some more modern jazz including Fourplay's Between the Sheets (Warner Bros.) album. The title track features some good percussion work and Sade on vocals. I was able to listen more closely to the drums on this track than on the previous album. The initial drum hits were solid with a clean and detailed decay. Sade's voice came through clearly with solid imaging. I noticed the same characteristics when I listened to my next selection, Robbie Robertson's self titled album (Mobile Fidelity), except of course with Robertson's distinctive vocals replacing Sade's.

I listened to a variety of male singers including; Robbie Robertson, Elvis Presley, Mighty Sam McClain and Marc Cohn. The "Fallen Angel" and "Broken Arrow" tracks on Robbie Robertson's album displayed a, extremely deep and wide soundstage with good dynamic range. I felt that the MF-2500 did a superb job of capturing the nuances of differing male vocalists, from the Mighty Sam McClain's distinctively deep voice on "Give It Up To Love" (JVC XRCD) to Marc Cohn's smooth and detailed vocals on the "Walking In Memphis" track on his self titled album (Atlantic Records.) On Elvis' Elvis is Back (DCC Compact Classics), the "Fever" track had me think Elvis really was back in the building. This is a simple, low key track featuring a somewhat subdued Elvis and an acoustic guitar. Listening to this track it sounded as though Elvis was sitting ten feet in front of me, I could even hear what sounded like the jingling of cufflinks.

Going from the smaller environment of "fever" I switched to Harry Belafonte's At Carnegie Hall (Classic Compact Discs). The MF-2500 had no problems portraying this larger arena. This live album features a great deal of audience participation. The MF-2500 portrayed this overwhelmingly large soundstage as well as it did the intimate staging of Elvis' "Fever".

With the MF-2500's 240 watts per channel on tap I felt as though I had to crank it up a bit. During some mid day listening sessions when I figured I would not bother the neighbors too much, I cranked the amplifier up a bit. I first wanted to explore the amplifier's bass capabilities so I put on Crystal Method's Vegas album (Outpost Recordings) and went straight to track two, "Busy Child". This track features deep and powerful synthesized bass line. While the Ascent's are only rated down to 35 Hz, the MF-2500 had no problems driving them down to their lower limit with a great deal of control. While the sound was always well behaved and smooth without any hint of fatigue, there was a slight thinness to it in the lower registers.

I continued on with the almost obligatory Janet Jackson "Go Deep" track off of the Velvet Rope album (Virgin). This track, as many of you already know, features a very deep and detailed bass line, which the amplifier handled with aplomb, easily differentiating between the notes. Next up was Paula Cole's "Tiger" off of her This Fire album (Warner Brothers). This track has great dynamic range and at about 45 seconds in, this range, as well as bass extension are demonstrated. As with the previous listening sessions, the MF-2500 never hinted at being pushed to the limit and seemed to have much more in reserve. Throughout my listening the amplifier remained smooth and controlled; and with the exception of the slight thinness in the bass incredibly consistent from top to bottom.

Lastly I listened to one of my favorite albums of all time, Dire Straits' Brothers In Arms (Warner Brothers). The sounds that came out of my system were incredible, with that incredible guitar and drum intro coming to life followed by Mark Knopfler was wailing away in front of me. The MF-2500 capably provided a smooth, detailed and solid image. Despite the slight thinness described above, the amplifier was more than able to place me in the middle of some great music and let me forget about the world outside.

The Downside
The MF2500 lacks some of the features I expect to see on an amplifier of this level. A look at the back panel of the amplifier will reveal that the MF2500 does not have balanced inputs, dual binding posts for bi-wiring, nor a removable power cord for those who like to experiment with aftermarket audio toys. I am unsure if any of these omissions had a noticeable impact upon the sound quality, but for some, they may be limiting.

The sound quality of the MF2500 was generally very good. There was a slightly noticeable thinness in the lower registers that was evident on the majority of speakers utilized. For those with speakers accurate in this region it may prove to be a bit problematic, and one should avoid paring this amplifier with speakers that are themselves thin in this area. The level of control at the lowest frequencies was quite good, but not quite at the level of the newer Krell amplifiers.

Conclusion
The Conrad Johnson MF2500 is a serious amplifier with a great deal of muscle. I was unable to drive this amplifier hard enough, despite the use of varied electrostatics and high volumes, to cause any notable degradation of sound. The MF2500 always remained smooth and detailed, throwing up a large soundstage without the slightest bit of strain. Consider the MF2500 highly recommended to anyone searching for a refined amplifier with some serious balls.
Manufacturer Conrad Johnson
Model MF2500 Stereo Power Amplifier
Reviewer Brian Kahn





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