CJ Solid State Amp Recommendations

[Timo62]

I might just give the MF2275 a try. I feel like it would be a good candidate for a back up amp on hot days. It should do fine with low to medium level volume listening. Plus , I have a chance to buy one for a very reasonable price.

[jahatl513]

Hello, The MF2500A is as solid a rock as needed. I too have a Classic 120SE and the MF2500A simply handles any speaker load and is pure CJ sound; forget the 2550SE and yes take a Premier 350 when you can but MF2500A is my recommendation.

[AnotherJohnson]

forget the 2550SE and yes take a Premier 350 when you can but MF2500A is my recommendation.

Is there a reason you would dismiss the MF2550SE?

Mine has been incredible and is my favorite solid state amp of all time. With some speakers, like the ML ESL Hybrids, I think it is a better match than my pair of LP275Ms.

Just curious to know what it has done in your system to recommend that it be forgotten.

[Big Dog RJ]

G'day Jahat,

Certainly understand your point of view and preference for the MF2500A. Infact the MF series of CJ's amplifiers are very fine musical instruments. You really can't fault any of them. Then comes along the Prem350 and its a rare beast! Brute force no doubt but it had bi-polar transistors in the output stage if I'm correct... and to me this was "hard hitting."

Since I'm very passionate about panels and full range stats, when I tried out the Prem350A with my ACT2, it was definitely overpowering. It has unlimited amount of current drive and power, as I've mentioned in one of my previous posts, this thing can launch the next shuttle for NASA if required... it's that powerful!

Partnered with the ACT2 it was a formidable force, nothing could hardly match that combination in that particular price range. This kind of raw power and drive, I've experienced with Boulder amplifiers, Momentums, Relentless, Pass Labs XS series, Hercules, CH Precision, Threshold and so on, these are the big boys. Plenty of power on tap and plenty of dollars on hand... we're talking 100grand over in amplification. This is the level the Prem350A is at.

However, with a slightly less gain on the linestage, you can tame the sudden burst / force of energy the Prem350A is capable of. Only a handful know this, and have tried it but have not posted their recommendations. Probably because they're too busy enjoying that explosive energy of the Prem350A.

This amplifier was then discontinued and came along the MF2550SE. Aaaah! Now that was like walking into a cool room on a very hot day. It was a perfect balance of both power, current drive, reactive load handling and delivered a fine balance of realism. When called for, it can produce some serious power and yet have all the subtle details without being overblown. This particular trait is thanks to the cleaver design of having both bi-polar and Mosfets used in conjunction. At the end of the day, Mosfets will always have that signature sound closer to tubes but with ample more drive factor involved.

It also takes an awful amount of time in order for the MF2550SE to really kick in. Once it reaches its pinnacle, it's an extraordinary opportunity to experience it, and the way it delivers the whole presentation, provided your speakers are upto the task!

Although I did enjoy my time with the Prem350A and for what it was capable of, that kind of power and level of brute force was not really required to drive the ribbon panels and stats that I was using at the time. Hence, my preference and overall favourite CJ SS amplifier is the MF2550SE, and I'll probably end up with one, once I get too old to bias and maintain tubes...

That's just my personal opinion and preference. I'm sure you've got your facts and reasons but I certainly wouldn't dismiss the MF2550SE. As I've stated earlier, it's no ordinary amplifier.

Cheers, RJ

[AnotherJohnson]

There is a NOS MF2550 on eBay right now for less than $2800 plus shipping.

I called CJ to see if they could upgrade it to the SE if I bought it and sent it in. Sadly, they cannot due to lack of all the specific precision resistors.

I expect that the non SE version is a killer amp ... but I want one to pair with my SE model, so I’m going to pass.

[Big Dog RJ]

$2800... jeeze, that low?

I would be very sceptical buying something like that on Ebay...

OTOH perhaps once you do get the unit, sending it off to CJ HQ to conduct a full service/check, would be worth it. I guess they would be able to confirm the serial number as well, which will authenticate its origin. In that case all should be well.

Anyone looking for a superb SS powerhouse with power and finesse, should consider this amplifier. The standard version is very good, its performance is truly top notch. The SE version has a few extra goodies that gives it a whole other dimension but that's something that is expected from CJ's SE versions.

All the best to the rightful owner or the new owner to be... As I've stated before, the MF2550SE is not just an ordinary amplifier.
Cheers, RJ

[AnotherJohnson]

$2800... jeeze, that low?

I would be very sceptical buying something like that on Ebay...

OTOH perhaps once you do get the unit, sending it off to CJ HQ to conduct a full service/check, would be worth it. I guess they would be able to confirm the serial number as well, which will authenticate its origin. In that case all should be well.

Anyone looking for a superb SS powerhouse with power and finesse, should consider this amplifier.

The offer is from a reliable supplier and it is in sealed factory packaging.

I’d just buy it and play it if it were me. Of course it’s easier for someone in the US to deal with a US based seller. I would be hesitant to buy if the offer were by a seller in another country.

I have bought from Hong Kong, Europe, Canada, and even California () in the past, but there’s always that feeling of uncertainty until the item shows up and proves good.

The only time I ever got screwed on eBay was back in 2006 when I needed a rare Whitworth wrench to complete my 1970 Royal Enfield Interceptor’s tool kit. I found one with a seller “down under” for a modest price with modest shipping charge. Of course it’s easy to undercharge if you have no intention of delivering the goods. I never saw the wrench .

[Rwclay]

Can someone describe the design goals of the MF2100 and where their use is best suited?

[Big Dog RJ]

MF2100, nice one!

This was my very first SS amplifier from CJ, it was a revelation being used to Musical Fidelity, NAD, Arcam, Audio Lab, Parasound, Bryston, and a host of other useless ones...
The CJ MF2100 was in a class of its own. I would say probably in the league of Krell, Sumo, Adcom, Plinius and Pass Labs at the time. These were considered the big boys / top dogs... and then we ordered in the MF2300 and boy did that drive virtually anything!

The MF series amplifiers are all based on Mosfet output stages and have that certain warmth to the sound after it gets going. It was rated at 100w/ch and also came equipped with a clipping circuit, LEDs on the front panel just in case the amplifier was over-driven. We first used it on all of our Paradigm, Energy and Sonus Faber speakers we sold at the time. These speakers were fairly easy to drive, with a benign load of 6ohms nominal, around 88/90dB sensitivity.

For lager panels, such as the Maggie's and Apogee's, we used either the MF2200 or the MF2300 or CJ's larger premier series monoblocks Prem12's and Prem8A's.
Mostly matched with the PFR preamp at the time and also with the original Art preamp used in our personal reference system, all of these combinations were top of class SOTA systems.

The MF2100 was a wonderful amplifier, given the right load and a equally high quality preamp to match it, it's a great combination to the entry level of SOTA. I really enjoyed my time with it, and at the moment I'm using their latest SS design the MF2550SE to drive CLX's but sadly the MF series amplifiers are discontinued. No more SS offered by CJ. Unfortunate.

Cheers, RJ

[Big Dog RJ]

Hey Rwclay,

Was just wondering, if by any chance you had the means of saving up a bit or coughing out the extra spend on a slightly better amplifier than the previous MF series?

When I say "slightly better " that is a serious understatement! It is actually supremely better, and far superior in every sense of the term power amplifier, and that amplifier I'm referring to is none other than the MF2550SE.

If you can get hold of one, this would be my highest recommendation. There are ones available for very reasonable pricing, it's just a matter of looking around.

I've got one right in front of me and I'm using it to drive my CLX's, it's superb!

However, that's only temporary until one of the monoblocks gets attended to and comes back...
Cheers, RJ

[Cremona]

Has anyone compared the sound of a MF2250A or MF2500A to a MF2275SE or MF2550SE?

[Big Dog RJ]

Wow! This is an old thread... and still going. Great.

Have consecutively heard and owned the MF series amplifiers by CJ in various system configs. Comprising of SF, Genesis, Apogee's, Maggie's, Paradigm, Energy and Infinity's IRS systems, they all were very good but totally different systems in completely different room settings. So, to answer specifically the question of comparing side-by-side... No.

This was mostly during my dealership years, so that's going way back to 1998 to 2004, when I closed & sold off. Those systems mentioned above were custom orders comprising of various gear from ARC, VTL, Manley Labs, Jadis, Cary, Melos, Musical Fidelity, Threshold, Forte, Sonic Frontiers and other audio gear we traded. I cannot recollect the exact type of sound, plus some performed extremely well with the right type of gear and speakers, whereas others not so great.

Just to summarise, although the earlier MF series amplifiers were quite good, from the MF2300 onwards, the MF2550SE is my preference of all time, with regards to CJ's SS line. It's truly an outstanding SS performer that really doesn't sound like SS at all. It has a special warmth to it, followed by a powerful Output stage comprising of MosFet devices, which provides that tonality that I'm looking for. The only issue is, the MF2550SE doesn't show its true attributes within the initial run... rather only after few hours of running in. Once it has reached that warm-up stage, which can take several hours, only then its performance shifts gears and goes beyond ordinary to extraordinary! It's a superb amplifier.

Then there's another very special CJ SS that was made with a certain type of DNA, one that elevated the performance to stratospheric levels! It could drive virtually any speaker system with a sneeze, ample power to launch the next mission to the moon, and can blow your roof off, provided your speakers can accommodate very very high input power. It didn't have much finesse as compared to the MF series, and that's mainly because the Output stages consisted of high powered Bi-polar devices, and its massive power supplies wouldn't flinch one bit, plus this particular SS amp also had a very high Class A bias, which CJ didn't divulge much... none other than the mighty Premier 350. I partnered it with the ACT2 preamp at the time, driving Apogee Diva's, that system was something else! Still to this day, I've come across only a handful that can match or surpass its performance, and even then would cost a bloody fortune!

The only downside or major problem I see with the MF series and the Premier 350A series of SS amplifiers is that they're all obsolete! In which case the parts aren't available for any of these original designs. Unless of course, you were to use alternative parts and modd the design... That may be viable.

The Premier 350 series and MF2550SE are the ones that I can recall instantly, simply because that type of sound and performance was something to reckon with. A true force of nature with power and finesse if matched right. The older MF series I can't recall too well because that's long time ago, sorry not much help there in your direct comparison question.

If I had access to the MF2550SE and also had access to a very skilled audio techie who can do mods and refurbs on audio circuits then I'd go for the MF2550SE without any hesitation. I wouldn't really bother with any of the others. It's a top notch SOTA SS power amplifier that didn't get much recognition it deserved. Neither the Premier 350 did but there were only a handful of those ever made.

Cheers, and do enjoy those finest tunes!
Woof! RJ

[microstrip]

(...) The only downside or major problem I see with the MF series and the Premier 350A series of SS amplifiers is that they're all obsolete! In which case the parts aren't available for any of these original designs. Unless of course, you were to use alternative parts and modd the design... That may be viable.
Woof! RJ (...)

Just to refer that all parts for the great sounding Premier 350A are available on the market - no experience with the MF series. And there is little to modify in the design - it is an extremely simple circuit, the schematic is available in this forum.

[Big Dog RJ]

(...) The only downside or major problem I see with the MF series and the Premier 350A series of SS amplifiers is that they're all obsolete! In which case the parts aren't available for any of these original designs. Unless of course, you were to use alternative parts and modd the design... That may be viable.
Woof! RJ (...)

Just to refer that all parts for the great sounding Premier 350A are available on the market - no experience with the MF series. And there is little to modify in the design - it is an extremely simple circuit, the schematic is available in this forum.

Oh! Wasn't aware of that at all. That's really good to know, especially when there are a few Prem350A units out there. Still sounding tops I suppose in that case. The last time I experienced one was a few years ago, driving older Infinity Kappa 9's I think they were. It was like a F1 zooming down the fwy, crossed lanes at blistering speed with effortless power. Just marvellous!

Although CJ HQ don't support any of their SS series any more, I suppose that parts or certain may be available with specific suppliers... don't know just wondering, in which case even the MF series could be serviced if needed. Then again CJ HQ may look into service / fixing things SS but would definitely charge a premium. Fair enough, considering age, parts & labour.

Mmm... must check this out with my Spore network maties. Perhaps a MF2550SE as second amp would be easier to access compared to a pair of top grade Pass Labs XA series amps. That's also an awful lot of savings. Always a good thing to have few $$$ on hand during rainy days.

Cheers MS! Thanks for your update matey.
Woof! RJ

[artoly]

Hi @BigDogRJ

To keep this interesting topic alive, I only just noted that way back in time (i.e. 2020 and top of page 2) , you mentioned: "However, with a slightly less gain on the linestage, you can tame the sudden burst / force of energy the Prem350A is capable of. Only a handful know this, and have tried it but have not posted their recommendations. Probably because they're too busy enjoying that explosive energy of the Prem350A." (sorry, Ican't quite see the correct way to quote on this site, but am betting you might see this post at some point anyway - t.b.c.).

Being a Prem 350 owner, with a limited knowledge on such things, can you please elaborate on what you think they did to reduce gain? I'm guessing I would need to find someone more knowledgeable to solder in some resisters in the right place. Is that about right? My 350 is between an Audio Research Ref 3 pre and Dynaudio Sapphire speakers.

[Big Dog RJ]

Ah, G'day mate, it's being a while...

So, you finally got the Prem350A, nice one! Yes, I did mention that the Prem350A has a sort of explosive character, such that it can sound quite harsh with a high gain Linestage. Hence, using a high gain Linestage, such as the ACT2, was a pre-power combination that could drive virtually any type of speakers.

With that particular combination, where both pre-power units are capable of very high levels, driving difficult loads of very notorious impedence swings from notorious speakers, proved to be far better matched than compared to other subtle or softer combinations of preamps & power amp matching. Those notorious speakers that really opened up with the Prem350A and ACT2 were: Energy Veritas, Infinity's IRS 1B's, Epsilon, Renaissance 90 and Kappa 9's, Maggie's MG20 series and of course those hard to drive older Apogee's, especially the Diva's.

So relatively speaking, based on those older speaker design monsters... (notorious impedence swings), most modern design speakers aren't that low in efficiency nor in impedence. Even the big Wilson's these days can be driven with a handful of watts, Class A watts even better, although Wilson's and other high performance speakers will benefit further from greater amplifier designs, with larger power supplies and higher stable voltages. In which case, the Prem350A will also be a superb match.

So, when I said that the Prem350A can be tamed by reducing the gain on the Linestage... I'm referring to the Preamp you're going to partner the Prem350A with. There are many designs to choose from, including SS preamps or tube preamps but the idea is to have a decent amount of gain on the preamp itself, not a high gain Linestage unless you were driving difficult impedence swings. When I refer to notorious/ impedence swings, we're talking about impedence going below 1 Ohm! Down to less than 1 Ohm is pretty much a short circuit! And most amplifiers go out with a puff!!! However, not the Prem350A, that thing doesn't flinch one bit.

You mentioned in your post that you're currently using an ARC Ref3 preamp, I'm not familiar with the exact specs. If the overall sound is smooth, with a very easy to follow musical lines, the presentation is not jumpy and doesn't throw you off your seat... so to speak, in which case allows you to enjoy the music then all is well!
If the sound is jumpy, edgy, very very sharp with a razor bite sharpness on every transient, explosive power and acceleration that keeps you always on edge, hardly allowing you to ever relax (a typical trait of overpowering horn type speakers...) which I can't stand, then this is the case where your preamps gain factor is far to high for the high performance of the Prem350A, and that's where the explosive nature of the Prem350A kicks in.

So, get a preamp / Linestage with a much lower gain, and it will Tame the Prem350A towards a more listenable and pleasurable approach, rather than having to fall off your seat all the time.

Cheers mate, RJ

**Note** forgot to mention, there is no modification required to do in the Prem350A inorder to lower its gain. I was referring matching with a preamp having less gain, would be a better approach, unless you listen at very high levels.

[artoly]

Thanks RJ. Very helpful indeed.

I've had the Prem 350 for about a year and like it a lot (as purchased during my Nov 2023 post 'Preamp (opposition) pairing with Prem 350').

I swap occasionally with an Audio Research Ref110 (I have not yet seen a valve C/J power amp for sale in NZ since starting looking, but maybe one day). I intended to just keep one power amp, but I know I would miss either one of them, and would probably regret selling. My music selections and volumes do vary to suit the amp (as you would understand, with the very powerful S/S and medium-powered valve power amp having differing strengths/advantages).

Re-reading your post above, it nicely describes the potential sound issues with too much gain. From this description, I am thinking the gain is not an issue with my speakers, ARC Ref 3 and C/J Prem 350.

I do have a speaker hum issue with the Prem 350 connected, but I'm quite certain it is a ground loop between the pre and pwr amps and presumably has nothing to do with gain. I can eliminate the hum with an iFi GND Defender, but need to use C13-C19 power cable converter plugs to make it fit the Prem 350 socket. However, the iFi or the converter plugs soften the 350's dynamics....to the point that I usually take the iFi out again. I'll get to the bottom of it one day, but still enjoy it as is.


PS. For what it's worth, being 5 years late on this thread topic - My Prem 350 needs the correct voltage to run at the reasonable design temperature. Mine is rated at 220V and the wall voltage is around the 244V range (+/- at different times, being a bit over 10% difference). 244V is too much for my 350 and made it idle at about 55 degrees C over the fins (131F). After it died and I had it repaired (either from this or a spike, I'll never know), I added a big custom step-down transformer to achieve the correct 220V for the C/J. The idle temperature dropped to about 35C (95F) with this in place. The temperature does not increase very much in-use with my speakers and my volume levels.

All the best.

[admin]

I've ran into ground loop issues before and that certainly sounds like what you are dealing with here.

They can be fixed but it does take some experimentation, careful power connection layout, and a little bit of luck.

[33 rpm]

From this description, I am thinking the gain is not an issue with my speakers, ARC Ref 3 and C/J Prem 350.

@artoly, when I look at some of the key specs (5.6db gain of the SE outputs of the ARC Ref 3, 1.1V input sensitivity of the Prem 350, 88db sensitivity of the Sapphires), your system seems, on paper, to be very well balanced. Hopefully, you can address the ground loop issue...and continue to enjoy the system.

[AnotherJohnson]

PS. For what it's worth, being 5 years late on this thread topic - My Prem 350 needs the correct voltage to run at the reasonable design temperature. Mine is rated at 220V and the wall voltage is around the 244V range (+/- at different times, being a bit over 10% difference). 244V is too much for my 350 and made it idle at about 55 degrees C over the fins (131F). After it died and I had it repaired (either from this or a spike, I'll never know), I added a big custom step-down transformer to achieve the correct 220V for the C/J. The idle temperature dropped to about 35C (95F) with this in place. The temperature does not increase very much in-use with my speakers and my volume levels.

I don’t know if there is an equivalent solution for voltages outside the US, but I was very pleased when I added the PS Audio power regenerators. My ARC gear manuals say their gear runs best at 117.5 Volts, and my experiments proved that my ears agree. Sadly, my various CJ amps were not compatible with the power regenerators, and CJ has told me that they do not recommend them.

FWIW, my Burmester gear likes 117.5 too, so even though I have two regenerators in my system, I’ve set them up to the same specifications.