Review: Rogue Audio Cronus Magnum Tube amp

Category: Amplifiers

Rogue Cronus Magnum Review

I owned the Cronus for a couple of years before sending it into Rogue for the conversion to the Magnum edition and Mark O'Brien was extremely patient with my very many questions about the upgrade. His excellent reputation is more than deserved.

The Magnum upgrade to the regular Cronus amp consists of
- Larger power supply
- Power supply mods
- Polypropylene bypass capacitors
- Precision Dale-Vishay resistors in critical spots
- Upgraded binding posts
- Gold tube sockets
- Upgraded small signal tubes
- KT90 output tubes
- Magnum logo on faceplate

I did not order the upgraded small signal tubes as I have a good supply of various new and NOS ones. I also did not order the KT90s as I had various other power tubes I wanted to try (more later). It is to be noted that the output coupling caps are upgraded as well as bypassed; something not listed above.

System is Mac Mini Sourced from an external hard drive to an ART Legato Async Converter (all plugged into an APC S15 power conditioner/surge protector), to a MHDT Havana (with upgraded caps, fuse and tube), to the Cronus (upgraded fuses), to Aural Acoustics Model B speakers (3 way, time and phase coherent, 87db efficient). Cables are db Labs Essential USB, KCI Pegasus Digital IC (BNC-BNC), Jena Labs Symphony Analog ICs, and Kimber 12TC speaker cables (with Cardas un-plated Cu spades on the amp end and Eichmann Cu Bayonet plugs on the speaker ends). Power cords are Kaplan and Pangea.

I enjoy most types of music with classical and folk/traditional forms being my favorites and rock and jazz close behind. I use a wide variety of recordings from these forms which are both well produced and of average quality. Tonal and harmonic accuracy are of the utmost importance to me with bright strident sound being the most off putting quality. PRAT and frequency extension and balance are next in importance followed by soundstaging and imaging qualities.

I enjoyed the base Cronus but was bothered by a few things. One, insufficient dynamics, was certainly occasioned by a power mis-match with the Aurals which need more than the Cronus's 55wpc. Two, congestion in complex musical passages, was partly, but not entirely, due to the same power issue. The third, a bit of hash and harshness in the upper mid-range and highs, was about half down to the amp, with the other half being down to cheap speaker binding posts, which I changed after the upgrade.

In any event, the changes, subsequent to the upgrade, were dramatic.

Obviously macro dynamics are much more pronounced. The bass is more powerful, focused and extended. Both traits hold even using the Black Treasure 6CA7 and Genalex KT66, previously utilized by me in the regular Cronus, which are limited to their 50-55 wpc output capability. What was somewhat surprising to me however, is how much micro dynamics were improved. Low level resolution, in terms of both ambience and the differentiation of individual lines (including background ones which are now much more discernible), is concomitantly greatly increased. Orchestral crescendos are not at all blurred and sound effortless while rock has real punch and drive.

Another pleasant surprise was just how much more natural the tonality is: for example pianos have a greater realism and lack the clatteriness I heard with the non-Magnum. Highs are now very clear and possess greater extension. The one (relative) weakness of the unit is refinement that is less than that of the best. The best, of course, being significantly more costly.

All of these improvements, as one would imagine, were magnified with more powerful tubes. I tried three different types: Penta KT88SC, NOS GE6550 and Tung-Sol KT120. These tubes, as well as the 6CA7 and KT66, it must be noted, all require the use of socket extenders as they do not fit into the holes in the chassis top of the Cronus (regular or Magnum), which only accommodate EL34/KT77/KT90 tubes. Also, the KT120s, although raised an eighth of an inch above the chassis by the extenders, overhang the holes completely. To avoid any issue of heat build up inside the unit, I had the holes punched out by a friend about an additional 7/32" in diameter. (Note: new production units of both the Cronus Magnum and Atlas Magnum, as of mid Febuary, now have a re-designed top to accommodate large bottle power tubes, which a lot of people have apparently been experimenting with. That is customer responsiveness.)

The Penta KT88SCs, while initially enjoyable, possess the overly emphasized bass that I have almost always heard from amps using that tube type, which is not to my taste. I have always preferred 6550s. They have a more even frequency balance to my ears than KT88s, even though their bass is slightly recessed compared to the mid-range and the highs. NOS GE6550s are of course superb (and very expensive), with a mid-range that is tonally naturalistic and incredibly three dimensional, and highs which are extended and sweet. Although the Magnum's circuit can output 90wpc, I do not know what the output was with these tubes. The spec'd output for KT88 amps usually range from 60-80wpc per quad of tubes but can reach 100wpc; for 6550 amps 60-70 wpc seems to be the maximum. The Pentas did sound more powerful and dynamic than the GEs but not as good.

The relatively new Tung Sol KT120 is a very good tube. Capable of outputting up to 75 watts per tube they have the best frequency balance of the three types; with bass that is as powerful and extended as that from KT88s, and a mid-range and treble that is equally prominent. If they don't have quite the three dimensional images or sweetness of the NOS GE, they still sound more natural to me given their range and dynamism. They also throw a larger soundstage than any of the others. They also obviously put out the full 90 watts per side the CM maxes out at but sound even more powerful, given the extra headroom resulting from their coasting at that output.

I have had several audio friends over who were equally impressed with the CM and also lent it out to a couple of them. In both my system and those of two others, the CM was preferred to several other amps, both integrated and power, that cost significantly more. And in fact, with the KT120s, the CM sounded more powerful and more dynamic than one tube power amp rated at 100wpc, and another at 125wpc (both using KT88s).

In conclusion, as so many others have already opined, the Cronus Magnum is an excellent integrated amp and a superb bargain.

Associated gear
Mac Mini (with external Hard Drive), ART Legato asynch converter, Havana DAC, Aural Acoustic Model B speakers.

Similar products
Primaluna Dialogue 2
I am planning to buy my first Tube integrated - I currently have a Cambridge 650 integrated with Revel F12 speakers NAD CD player and a vintage AR turntable from my college days - college days a LONG time ago I am 59 !

I have heard and read excellent things about the Cronus Magnum however I was suprised not to see it listed in the latest Stereophile reccomended componets issue - My budget is $2500 or less for the amp Has the Cronus Magnum been surpassed by newer improved designs ? Thank you Russ Dejulio Pittsburgh,PA
There are a lot of politics out there.i can tell you owning several Rogue
Pieces and the New Chronus Magnum with the kt-120
Vacuum tubes is outstanding.recntly we did a Comparison with he $2400
Prima Luna , the Rogue was much better balanced with very good image detail and front to back layering of instruments it was far more dynamic,
And Bass that was as good as any solid state amp I have owned
And 100 Vacuum tube watt per channel.
So... how does the Magnum compare to the PrimaLuna Dialogue 2???
Thanks guys I hope that my wife gets it for my 60yh bday on 9-10-13 !!

All Best !

Russ DeJulio
The Rogue is much better built and sounding then Prima luna
The amp is made in the U.S.A, transformers are also custom wound here
Mark Obrien is not only a very good designer,but also backs his products up without exception,and if there ever is a problem that can't be handled
Over the phone ,you send it to them and turn around time is Excellent.
I have owned several Rogue products and always competitive with products of more moneys. The 120 vacuum tubes are a nice improvement across the board then the current bade kt88 much better control ,dynamics
And great soundstaging, and imaging.use a good powercord truly makes
A Big difference.
I've been a fan of his products for a long time. Buy from him without hesitation. You won't be sorry.
My son and I compared it to the Prima Luna. To me the Rogue has a lot more presence and is very lively. I can't believe the value of this unit.
Have Any of you Cronus Magnum owners tried using 12bh7's in place of the 12au7's? As much as I thought my Cronus Magnum sounded very good, I thought this amp was lacking something. I expressed this with the tech I use to restore my vintage tube amps and he suggested swapping out the ECC82 / 12au7's for 12bh7's.
I had some extra 12bh7's that were for my Sansui AU-111 and decided to give them a try in the Cronus Magnum. After doing so all I can say is that I do not plan to ever put another 12au7 back in! The difference was immediately apparent.There was a much clearer separation of instruments, and with greater detail. IMHO the difference was night and day, and for the better! It was exactly what this amp needed.

The original tubes that came with my Cronus Magnum, Genalex ECC82 gold pins, were switched out for NOS Westinghouse black plate 12bh7's.
Hi Rob: Where can I buy tube socket extenders? Thanks, Jeff
I have been considering a Cayin A-50T or Rogue Audio Cronus. Anyone heard both? There are not stores in this area that sell high end gear of any kind. No stereo stores in all of Louisville area. There is a Rogue Audio dealer in Indianapolis. Thanks.
I had the Cayin for a couple of years and then gave it to my brother who still loves it. It is one of the better el34 amps I have owned. I almost bought the Cronus a few years back. So I judge that one. You can't go wrong with either one. I will add that the Cayin has function remote also. Good luck
Just ordered my bh7's to swap in, thanks!
bh7's sounded great...but they brought a bit of noise through the tweeter. A quiet ringing, audible on quiet passages, alas. Replaced with 3 au7 NOS RCA clear tops. Anyone else try this experiment?
Say also - has anyone biased their 120s beyond 35?