Have you asked C-J? They're pretty good at getting back and providing any info they have, try them via their website. conradjohnson.com Good luck.
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I have a CJ MF-200 which is good into 1 ohms. These amps have alot of current. You should have no issues with these amps concerning power into 4 ohms. I believe my amp puts out 250 watts per channel into 8 ohms and over 400 watts into 4 ohms. I have an old review somewhere. The Mf-2300A is basically the same amp just tweaked with more exotic parts. I spoke to Bill Thallman who used to design this stuff. He said the 2500 has better bass and drive, but the 2300 has a warmer more natural midrange. I will be selling my amp soon since I upgraded to a Pass amp. I kept my CJ a long time. I tried many highly rated amps in my system to try and better the CJ. I kept coming back to the CJ, and sold the other amps (Llano, Odyessey, Belles, McCormack) until I got the Pass amp. I remember reading someone else who owned the MF-200 with speakers dipping into 1 ohm. The CJ amp had no problems. The transformer on this amp is monsterous.
Hi Chuck, Thiel 3.5's. These speakers are 89db at 1 watt/meter and a use an active equalizer with an in-put impdeance of 91 KOhms and an out-put impdeance of 130 Ohms (RCA's only) that draws up to 12 db of boost below 70Hz. Thiel recommends between 50-250 watts per channel, but, that is based on an amps 8 Ohm rating and ASSUMING that the amp can double down. That boost coupled with the 4 Ohm nomial/minimal rating is what concerns me. If I'm correct, and assuming that the speaker could regularly draw 15 watts that after boost it could be drawing 240 watts. Knowing how amps could actually perform in it's intended use could narrow my choices down to a reasonable number. Thiel recommends c-j amongst others and c-j claims that their amps work with Thiel, but, I think it's fair to suggest that I deserve more concrete answers. The equalizer also adds a bit of complexity with regard to impdeance matching and to the fact that it doesn't offer balanced in and out between pre and amp, but, I think this might be less of a concern, unless of course any one has other ideas. I'm open to suggestions.
I own Thiel 3.6's and my MF2500A had no problems driving them and sounded very good. I did upgrade to the premier 350 and obviuosly it does a better job in all aspects. But I would not be concerned about the 2500A driving your Thiels. Thiels are not nesessarily difficult to drive because their impedence curve, at least the 3.6's, is relatively flat. What makes them a challenge to drive and why they need current is because their impedence curve does dip below 2 ohms at least the 3.6's do over certain frequencies. Difficult loads are when impedence curves bounce all over the place creating a constantly changing load to the amplifier.
Having siad all this I would be more intersted in what the impedence curve of the 3.5 looks like as I am assuming it is similar to the 3.6 which may be a poor assumption. If you have not already I would contact Thiel and ask them.
Chuck, Thiel rates the 3.5's as having a 4 Ohm nominal, 4 Ohm minimal load. I have seen two independent tests that both show this to be pretty accurate. Both tests show a slight peak at about 33 Hz where the impedance rises to between 8 and 10 Ohms and basicaly flat across 4 Ohms the rest of the way. The testers attributed the peak to the sealed box resonance. I agree with you that Thiel's present a constant steady load with out the peaks and valleys most speakers present. Most amplifiers appreciate this kind (of) load. That the 3.5's don't drop below 4 Ohms is even easier on amps. It's the demands of the equalizer that concerns me. I'm sure you are aware that your 3.6's dip into 2 Ohms will require an amps 8 Ohm rating to double down twice to provide the appropriate power. If I am corect in my assumption(?) the equalizer's 12 db push will require the amp to double out(?) 4 X to provide appropriate power. That might be like a -2 Ohm power requirement (not really, but you get the idea). If my assumptions are correct(?) then perhaps Thiels maximum recommendation, may be their best. I take that to mean 500 watts into 4 Ohms. C-J has quoted different opinons on their 4 Ohm rating to me at different times. Once it was "we don't offer 4 Ohm ratings on our solid state amps". Once it was "close to to doubling down". Once it was "close to 400 watts". Once it was "480 watts". Well what it is it? This inquiring mind would like to know. Mind you I have been using c-j solid state pre and power on Thiels CS 2's for years and have always recieved very good customer service from c-j. I don't have an axe to grind, I'd just like to have needed information to make informed choices.
I had an MF2300A for a while. Only reason I sold it was to go back to tubes.
That amp drove a pair of CS2s with significantly more authority that some other 100W and 150W SS amps I borrowed to try. As mentioned before, it is a warm sounding amp and that was a very good match for those Thiels. I bought it from an other agon member who, if i recall correctly, stated that he blew a circuit breaker without causing the 2300As clip indicator to illuminate. Hyperbole? Possibly, but I never clipped it and I played the Thiels very loud at times. (imagine me cranking ozzy when the neighbors were playing abba on repeat over the deck speakers)
Mcmiller, I also have a pair of CS 2's which I used a c-j MF 80 on. Worked great! Not to beat a dead horse, but, it's the 3.5's equalizer that concerns me. Though the 3.5's are 2 db more sensitive than the 2's, the 2's unequalized impdeance at 5/6 Ohms is pretty easy compared to the 3.5's equalized 4/4 Ohm load. I think the sound starts to get hard when moderately pushed. I think, I just need more power. I was happy with MF 80, so I naturally thought of a bigger c-j for the 3.5's.
Hi Unsound, Stereophile reviewed and tested the mf2500. I'm pretty sure that they test 4 and 2 ohm loads, as well as 8 ohm loads. It's all part of thier normal bench tests that they do on a lot of reviewed equipment. If you go to Stereophile's web site, you should be able to pull up thier review of the mf2500 at no cost. The mf2500 is a very nice and musical amp. Best of luck. Stan
Hi Unsound, It's been about six months since I've been to Stereophile's web site. I visited it today and they changed the look of it. Also, you can't access as many reviews as you used to be able to--(but I did count 72 solid state amp reviews that are offered for free)--unfortunately the cj mf2500 wasn't one of them anymore. Sorry. I have read the review and it does have the information that you're looking for. Good Luck. Stan
Stereophile's latest buying guide lists the c-j 2500A as capable of 250 watts per channel into 8 Ohms and 400 watts into 4 Ohms.
In Stereophile's December 1999 issue the 2500 was reported by Martin Colloms as "Tested with the UK's 242V, 50Hz power supply, the MF2500 reached 309W into 8 ohms, one channel driven, and 295Wpc, both channels driven. It wasn't shy at 4 Ohms, and the shared power supply was man enough for 451Wpc into 4 ohms. This, only 1.3dB below the 8 ohm single channel test result, indicates good regulation and load driving ability.
Playing music-related (IHF tone-burst) signals, the MF2500 pushed 24.9dBW inot 8 ohms (315W) and 24.77dBW into 4 ohms (600W), but began to current-limit a little into 2 ohm loads with 23,9dbW (976W) available. This relative indifference to loading provides good verification of the easygoing muscularity identified in the listening trials. The maximum peak current capability was approximately +/-35A--good enough for all but the most severe speaker loads, and certainly those nominally rated at 4 or 8 ohms."
Unsound, I'm glad that you received your copy of the Stereophile test. The mf2500a amp is a powerhouse for a 250 watt amp- -( NOTE LOL- the mf2500 is 240 wpc). I was using a MF2500a, until I bought a Jeff Rowland 302 amp. The Jeff Rowland is a 300 watt amp @ 8 ohms and I have to set my preamp volume higher for the Rowland than I did for the CJ MF2500a to get the same level of loudness. I guess the Rowland doesn't double down as much. I hope that you found everything that you were looking for. Best wishes. Stan