The MF2550 - not just an ordinary amplifier

Big Dog RJ

Well-Known Member
Feb 3, 2012
708
41
113
Melbourne
#1
I was looking for the particular MF2500 series tag... Anyway this one I'll keep as brief as possible, since it's now past 5am, and just about to finish up my late night / early am session.

One of the monoblocks had to go upto QLD for a service, so my trusted good CJ mate lent me this SS beast, assuring me that it "will drive" the CLX's to their full potential. Ah! So I thought great, another good one from CJ, brings back memories of their previous MF series power amps, which had the MOSFET output stage.

CJ redesigned their MF series and launched a massive mothership called the Premier 350. This was some serious amp, rated at 350w of CJ's musicality and finesse, it could drive anything! Sadly no longer in production, CJ continued to focus their efforts in tube design, which they've been doing since the 60's...

A few other SS amps came and went, along with a few Hybrids, input stage being tubes and output stage being Mosfets. Those were great but always seemed to fall short compared to their top line tube designs.

Now we have the latest iteration of that production line, introducing the MF2550 but sadly this has been discontinued as well! CJ then changed ownership, Mr. C & J went fishing and now Jeff Fischel is in charge. He's a perfectionist and for whatever reason, he's decided not to proceed with another SS... For now just focusing on all tube design.

So, I brought this thing home, hauled it in to the living room, after correcting my hernia, dam thing weighs a tonne, (need to beef up that bench press or perhaps the deadlift...) Hooked it up, fired it up and oh my! What a performance!

This is designed with a MOSFET gain at the input stage, if I'm correct, then an additional buffer stage directly coupled to an output stage consisting of Bi-polar devices, the very same used in the Premier 350.
Rated about 100w less than the Prem 350, it can put out a very healthy and lethal dose of 250w of CJ power and finesse!

Has total grip on the stats, handles that notorious impedence drop of 0.7 ohms effortlessly and handles the top end which soars to over 20 ohms at lightening speed, no stress on this amp whatsoever!

The highs are very airy, and extend beyond the horizon, the mids are very smooth, plenty of open detail, air around the instruments, those subtle nuances, the soundstage depth and imaging are superb! And the bass, very very nice! It's super fast, tight, articulate and very agile, it also captures all the low notes, provided your speakers can deliver it. The specs on the CLX's bass is not extended to anywhere near 30Hz or 40Hz for that matter but those are just specs. Once you listen you'll know straight away what kind of superlative bass I'm referring to.

I've used and sold many SS amps in the past, from ARC, Krell, Plinius, Parasound, Bryston, Jeff Rowland, and Mark Levinson. These are all top dog brands and makes, and the few SS that have me fairly excited have been Pass Labs of lately, and of course my all time favourite, the Relentless amps by Dan D'Augostino.

Now, similar to CH Precision and Solution amplifiers, the Relentless are in that category of 200 grand price tag and above, depending on how much Class A bias you wish to choose. However, I do know it's definitely unfair to compare that ultra high-end category with this particular SS amp. But that's just the beauty of true high-end, and this is definitely not just an ordinary amplifier, hell no!

Even at the finest and stunning power of superb performance on the Relentless monoblocks, the CJ MF2550 can hold itself steady all the way towards the most notorious impedence swing, and it handled it just beautifully!

For those of you who do own the Dan D' Momentums or Relentless amps, no disrespect at all, in fact hats off to you! All I'm saying is that if anyone is very serious in putting out about 10 grand of pure power amplification at its finest, I very highly recommend this one!

Well done to CJ's team and at the same time, sad to see it go... Which is why this is one of a kind, simply because this is the very last MF2500 series you're going to ever find!

Cheers to all and keep those tunes alive
Best, RJ
 
Likes: Marcus

Big Dog RJ

Well-Known Member
Feb 3, 2012
708
41
113
Melbourne
#3
G'day mate, just saw this notice, beeped on my phone...

Used the MF2550 previously with CJ's ACT2 preamp, driving Quads ESL2905. That was great! Everything was mighty fine, couldn't flaw it one bit other than the limitations on the Quads...

After a while, when I got the ML CLX Art's, I ventured back towards tube monoblocks and this time partnered them with CJ's CT5 preamp. Its a fairly moded CT5, perhaps could be termed as an ACT2 series 3, if one ever existed. I had access towards the GAT/S2 but for some reason I just prefer the 6H30Pi Sovteks. The ACT2 has 4 of these tubes, whereas the CT5 has just 2. If not for the ongoing issues I had with the ACT2, I would've certainly kept it, and probably upgraded to the version 2 for that matter. However, I sold it off and found the CT5 through my trusted CJ dealer in Melbourne, and couldn't be happier!

The SS amplifier version I then used with the CLX's was the MF2550SE. Quite a margin higher than the standard non SE version but both are equally fine I would say. Its just that the SE version has a finer sense of balance and purer drive, plus takes awfully longer to sound right. Due to the number of Teflon caps plus top grade resistors used, it takes quite a few hours to really get going. I also noticed on soft to moderate levels its ok, that is sounds like background music... then turn it up a few notches and the lifelike performance kicks in, with a superb sense of realism.

Whereas, compared to the tube monoblocks I'm currently using, even on the lowest level and softest passages, I get all the realism required, no need to turn things up at all. It also helps during my after midnight listening sessions. Of course when levels are turned up it reaches a different dimension but not as significantly different compared to the MF2550SE.

Just last week Friday, I dropped off the car for a scheduled service, and popped into my dealer mates store for a small upgrade with the Nordost speaker cables, towards a version 2. There and behold sitting in the middle was the beautiful MF2550SE! I nearly walked out with it...but it was not meant to be. What on earth would I do with another amplifier, plus a SS for that matter. Might as well use the monoblocks for as long as I can maintain them. After that time comes, I will probably get back to SS.

The way it griped, controlled and handled the CLX's was extraordinary. Maybe I should have just kept it!

Cheers and have a good one,
RJ
 
May 30, 2010
16,605
1,484
420
Portugal
#4
(...) CJ redesigned their MF series and launched a massive mothership called the Premier 350. This was some serious amp, rated at 350w of CJ's musicality and finesse, it could drive anything! Sadly no longer in production, CJ continued to focus their efforts in tube design, which they've been doing since the 60's...

A few other SS amps came and went, along with a few Hybrids, input stage being tubes and output stage being Mosfets. Those were great but always seemed to fall short compared to their top line tube designs. (...)
Although the MF 2500 series is very nice sounding, IMHO they are far from the Premier 350. It is why I still keep one for very hot days! Paired with the CT5 or the GAT is sounds great, different but on line with their tube products. The big drawback of keeping a Premier 350 in storage is the long time of burn-in every time I put it in service - at less a full week playing 24/24. Cold from the box it sounds like a poor transistor design.
 
Likes: XCop5089

kach22i

WBF Founding Member
Apr 21, 2010
1,502
172
225
Ann Arbor, Michigan
www.kachadoorian.com
#5
It takes 3 days plugged in for my Martin Logan speakers to sound their best, and both sides of an LP for my Grado Sonata to get warmed up.

However, my tube preamp and solid state amp(s) seem to be up to the task quickly.

Are CJ products known for long warm up times?
 

Big Dog RJ

Well-Known Member
Feb 3, 2012
708
41
113
Melbourne
#6
Not necessarily anything excessive in warm up... other than what's stated in the owner's manual; warm up make take around 15mins. However, this I found to be normal operating conditions. That is, after the few 100hrs of those fine Teflon caps and top grade Vishay resistors to properly burn-in.

Those components, let alone the metal foil resistors found in every SE version of CJ's amplifiers, takes several 100hrs to run in as well.
So, I figure once these components and its related parameters have been run in properly, only then after an initial 15min warm up would everything reach optimal performance.

Speaking of which, I just upgraded the Nordost Frey2 speaker cables and its connections to those beautiful top grade spades, wow wee! What an outstanding presentation! Superb, superb superb!

The frequency extension on the highs is extended further. The finer details of the top end comes through very sharply with razor edge focus. The low frequency detail is deeper and tighter in the bass, extended beyond the previous cables by quite a margin. The most significant improvement is in the mid-band. There are finer and subtle details that are more profound and the 3D effect is even greater. This feeling of reaching out and touching the performers is quite spooky! I didn't think that aspect would be such an impressive area but it was. The pick up energy and detail is superb. Everything else pretty much remains the same, soundstage and depth, the disappearing act of the CLX's and that sort of thing is similar to the previous cables. I also noticed the levels don't need to be increased to experience a true sense of realism. On low levels it's all there, so this is even better for my late night sessions. Don't want to wake up the household... I better hit the sack, it's nearly 4:30am.

Now, I understand why those of you who use the Tyr, Valhalla and Odin's have these cables installed in a special way based on the exact specifications of the system and its connections. The secure link in using spades, Z-plugs, and whatever else your systems offer to be the highest secure connection, is very critical in getting that basic element right. It's a marvellous thing!

Cheers, and do enjoy those fine tunes!
Woofty woof!
RJ
 

Attachments

#7
Not necessarily anything excessive in warm up... other than what's stated in the owner's manual; warm up make take around 15mins. However, this I found to be normal operating conditions. That is, after the few 100hrs of those fine Teflon caps and top grade Vishay resistors to properly burn-in.

Those components, let alone the metal foil resistors found in every SE version of CJ's amplifiers, takes several 100hrs to run in as well.
So, I figure once these components and its related parameters have been run in properly, only then after an initial 15min warm up would everything reach optimal performance.

Speaking of which, I just upgraded the Nordost Frey2 speaker cables and its connections to those beautiful top grade spades, wow wee! What an outstanding presentation! Superb, superb superb!

The frequency extension on the highs is extended further. The finer details of the top end comes through very sharply with razor edge focus. The low frequency detail is deeper and tighter in the bass, extended beyond the previous cables by quite a margin. The most significant improvement is in the mid-band. There are finer and subtle details that are more profound and the 3D effect is even greater. This feeling of reaching out and touching the performers is quite spooky! I didn't think that aspect would be such an impressive area but it was. The pick up energy and detail is superb. Everything else pretty much remains the same, soundstage and depth, the disappearing act of the CLX's and that sort of thing is similar to the previous cables. I also noticed the levels don't need to be increased to experience a true sense of realism. On low levels it's all there, so this is even better for my late night sessions. Don't want to wake up the household... I better hit the sack, it's nearly 4:30am.

Now, I understand why those of you who use the Tyr, Valhalla and Odin's have these cables installed in a special way based on the exact specifications of the system and its connections. The secure link in using spades, Z-plugs, and whatever else your systems offer to be the highest secure connection, is very critical in getting that basic element right. It's a marvellous thing!

Cheers, and do enjoy those fine tunes!
Woofty woof!
RJ
If this system were mine, I would tape those two speaker ribbon cables together tightly to get inductive coupling. This reduces inductance and usually results in a faster, snappier presentation. You could start with tie-wraps and then if you like it use tape.
 

Alrainbow

Well-Known Member
Dec 12, 2013
1,517
350
155
NYC , USA
#8
I would go for an upgrade on the amp ,
MoFo 2500 ...
 

Big Dog RJ

Well-Known Member
Feb 3, 2012
708
41
113
Melbourne
#9
Emp Audio:

I've been in contact with Nordost regarding this suggestion of tying up the cables or taping them up at the ends... Apparently didn't make any difference. Maybe I wasn't tying them properly but there was no improvement.
I also suggested this to another Nordost user using the Odin's, nothing there as well.

Anyway, was wondering if you could elaborate on the science behind your tying method or what's the rationale...
Im sure Nordost have already thought about this, especially at this level. Always good to learn something new. Maybe I'll check with another Nordost user who has the Valhalla speaker cables and full connection of Tyr2 interconnects and power cords.

Do let me know if I've missed something or there's a particular way of tieing these up.
Cheers,
RJ
 
#10
Emp Audio:

I've been in contact with Nordost regarding this suggestion of tying up the cables or taping them up at the ends... Apparently didn't make any difference. Maybe I wasn't tying them properly but there was no improvement.
I also suggested this to another Nordost user using the Odin's, nothing there as well.

Anyway, was wondering if you could elaborate on the science behind your tying method or what's the rationale...
Im sure Nordost have already thought about this, especially at this level. Always good to learn something new. Maybe I'll check with another Nordost user who has the Valhalla speaker cables and full connection of Tyr2 interconnects and power cords.

Do let me know if I've missed something or there's a particular way of tieing these up.
Cheers,
RJ
The rationale is to reduce inductance, the enemy of dynamics in speaker cables. Coupling the + and - wires tightly makes a big difference in reducing inductance. This is not just about resistance or wire gauge.

It may be that the twisted-pair arrangement of the Nordost cables makes this inductive coupling difficult. Each wire in the cable carries a small amount of the total current, so there is not a large magnetic field to couple to the wires in the other cable. This means that the two cable must be very close together for any coupling advantage to take place. The two flat cables must be tightly pressed together from end-to-end.

IMO, the way these should be wired is one flat cable containing both + and - currents, with every pair carrying + and - currents, not two separate flat cables, one carrying + currents and one carrying - currents.

Another beneficial thing is to space the twisted-pairs from each other, so that the stray fields do not interact. I performed many experiments and computer simulations that showed the benefit of this arrangement.
 

Big Dog RJ

Well-Known Member
Feb 3, 2012
708
41
113
Melbourne
#11
Mmm, ok seems to make sense from a scientific perspective Emp Audio. I see your points.

I've received some feedback from a few people in this very case as well, since I started inquiring.
1. The representative for Nordost claims that they've already addressed this issue one way or the other.... Of course they have!
Considering the labour intensive process it takes to make just 1m length of cable, process takes 8hrs.
2. These particular cables were hooked up to Wilson's before, and no difference their either. If I'm correct, the previous owner upgraded to Valhalla or Odin's supreme reference series but is still using the Tyr2 somewhere in the system. Didn't receive any significant results from him either.
3. I did try my best to tape these up but it looks awful. Even the good wife thought I've lost the plot, as if I've not lost it already...

Anyway, was just wondering on which Nordost cables have you tried this? And what was the difference in performance percentage?
Was it a 15 - 20% improvement or more?

Nordost cables are definitely something out of the ordinary and although I've used so many brands, Cardas, Kimber, MIT, Chord, Audio Quest, Audio Note, Van Den Hull, DH Labs, some i can't even remember... at some point in time, either changing gear and upgrading or relocating components, for some reason I head back to Nordost. Not sure what it is but I guess it's a good thing.

I will continue to pursue this suggestion and see what other Nordost users have done, especially using the same csbles in similar applications with full range stats. After all, this was feedback from just three people, so perhaps more info coming from actual users who have done this or are considering it may have better results to share.

Thanks for your help Emp Audio, always good to learn something new. Every small percentage of improvement counts. BTW what kind of tape do you suggest?

RJ
 
#12
I would try double-sided tape and essentially laminate them together. May not be enough though..
 

kach22i

WBF Founding Member
Apr 21, 2010
1,502
172
225
Ann Arbor, Michigan
www.kachadoorian.com
#14
As far as coiling up Nordost speaker wire and hearing differences, I had too many variables to conclude anything. However, starting with post #20 in another forum extending reading on the subject says no difference.

https://www.audiosciencereview.com/forum/index.php?threads/speaker-cables.11961/

The current has to be flowing in opposite directions to have any hope of having an affect.

Coiled up, electrons are moving in same direction.
 

Big Dog RJ

Well-Known Member
Feb 3, 2012
708
41
113
Melbourne
#15
Exactly Kach, that's what I thought plus the feedback received so far.

However, Emp Audio has done some computer simulations, and claims to have obtained positive results, hence his rationale behind the suggestion of taping them up.

I've also mentioned this to other Nordost users, including the previous owner who has now upgraded towards Odin's but again no apparent differences other than looks awful...

I specifically asked Emp Audio to confirm on which Nordost cables he's tried this taping method but no answer as yet. Which leaves me wondering if they've ever been tried on Nordost cables or something else. I'm a bit over it now, and just enjoying the music through the CLX's, it's a marvellous thing!

Cheers mate, enjoy those fine tunes!
RJ
 
#16
Exactly Kach, that's what I thought plus the feedback received so far.

However, Emp Audio has done some computer simulations, and claims to have obtained positive results, hence his rationale behind the suggestion of taping them up.

I've also mentioned this to other Nordost users, including the previous owner who has now upgraded towards Odin's but again no apparent differences other than looks awful...

I specifically asked Emp Audio to confirm on which Nordost cables he's tried this taping method but no answer as yet. Which leaves me wondering if they've ever been tried on Nordost cables or something else. I'm a bit over it now, and just enjoying the music through the CLX's, it's a marvellous thing!

Cheers mate, enjoy those fine tunes!
RJ
ANY cable that uses two separate sets of wires for the + and - currents, not just Nordost should be coupled.

I have even twisted bi-wire jumpers together at shows for exhibitors and demonstrated an improvement in SQ. These are typically only about 8 inches long. I used to sell tightly coupled jumpers when I made cables. Some were flex-circuits with two adjacent planes to get maximum coupling. Worked great, sounded great.
 

Big Dog RJ

Well-Known Member
Feb 3, 2012
708
41
113
Melbourne
#18
Atm, I'm enjoying a few LP's from Three Blind Mice jazz, and a limited edition of the 4 LP box set from Impex Records. By adding in the Frey2 the speed, definition and resolution is superb! Very very nice. Whatever Nordost is doing here, they're definitely onto the right path, also matches with their slogan "making the connection!"

Getting back to the original topic in this thread, finally picking up the MF2550SE on Friday. I've had this for a while on the CLX's at our previous place whiles the monoblocks went upstate for a SE upgrade. Not yet tried this beauty at the new place, I'm sure it will be awe-inspiring!

I'll let the thing run in a while just to make sure those Teflons and big power supplies get upto speed then things should fall into place nicely.

If anyone is considering this particular amplifier from CJ's MF series, this is the last ever made and very sadly no longer in production. I definitely highly recommend it, especially to drive difficult loads and reactive loads typical with full range stats.

Cheers and enjoy those fine tunes!
RJ
 

About us

  • What’s Best Forum is THE forum for high-end audio, product reviews, advice and sharing experiences on the best of everything else. A place where audiophiles and audio companies discuss existing and new audio products, music servers, music streamers and computer audio, digital to audio converters, turntables, phono stages, cartridges, reel to reel, speakers, headphones, tube amplifiers and solid state amplification. Founded in 2010 What's Best Forum invites intelligent and courteous people of all interests and backgrounds to describe and discuss the best of everything. From beginners to life-long hobbyists to industry professionals we enjoy learning about new things and meeting new people and participating in spirited debates.

Quick Navigation

User Menu

Steve Williams
Site Founder | Site Owner | Administrator
Ron Resnick
Site Co-Owner | Administrator
Julian (The Fixer)
Website Build | Marketing Managersing