American audio is big and expensive. Everyone knows that. Rogue Audio is the notable exception. Take the Cronus Stealth for example (what is it with ‘stealth’ now? It’s getting close to words like ‘quantum’ in the buzzword bingo stakes). This is a US built, 90 watt, KT90-based integrated amp with a built in phono stage, a headphone amp, a remote control, a relatively large footprint and an attitude. But it doesn’t weigh a ton and doesn’t cost a fortune.The amp is simplicity itself to use. Just power, volume, balance and source selection (three line inputs and a MM phono) and a full-sized headphone jack socket on the front panel, fixed (tape) and variable (preamp) line outputs, an IEC socket and a single set of gold-plated speaker terminals for each channel at the rear. Even the remote comprises an up and a down button for the volume. It really doesn’t come much simpler. If you want to adjust the impedance from eight to four ohms, you need to take the top plate of the amp, unscrew the positive terminals on both speaker sockets and swap the connected green wire with the unconnected yellow one, swopping over the protective poly tubing in the process. Rudimentary, but it works, even if it’s not the kind of thing that you want to experiment with too often.
If you are reading this outside of the EU, buy the optional protective cage (fortunately, the wise burghers of the CE mark insist that valves are things that can simultaneously burn you, cut you and electrocute you when you drop a screwdriver on them, so the cage is mandatory here). Although the amp looks classy with exposed valves, it’s probably best to retain the cage because there is also a gap around those transformers and caps on the top plate. Although you need to remove it when you bias the power valves, because the bias plate sits just behind the right channel pentodes.
Adjusting power pentode bias is easy. The spring-screw panel in between valves and transformer exposes four DIP-switches and pots controlled by tiny grub screws. The back left has a clipped beige plastic screwdriver for the task. After the amp has been powered up for half an hour, turn the volume down, switch each valve switch in succession to measure mode and turn the grub screw until the DC milliammeter in the centre of the top plate reads 35mA. Flip the DIP-switch back into ‘run’ mode and move on to the next valve.
The valve roll-out couldn’t be simpler, too. Two 12AX7, three 12AU7 and four EH KT90s, taking respectively the roles of input stage, gain and phono stage and power delivery. In the standard Cronus, these EL34 power pentodes deliver a healthy 55W per channel in Class AB1 push-pull mode, but in the Cronus Magnum, that figure rises to a very healthy 90W, also in Class AB1 push-pull. This is very much at odds with most audio amps today, which typically run the EL34 in Class A and at around 25-30W per channel. The key to the increased power delivery in the standard Cronus is the move from Class A to Class AB1, while in the Magnum it’s down to the change of tubes. The KT90 is a relatively uncommon valve, a beam ‘kinkless’ power tetrode that can often be used in place of the better known 6550 and KT88. The advantage of the KT90 is it can really take on a lot of plate voltage. If you think what’s needed to push out 90w per side with a relatively cold 35mA bias, we are talking big voltages indeed. I spent many hours waiting for the tubes to red-plate or screen-glow or any of the other things that happen to power valves when being driven past their limits, but they stayed healthy and happy. I guess if these valves can have relatively long lives inside the guitar amps of the loud and metallic, domestic use is a breeze.
Given that high plate voltage however, there are two points worth noting; if you are a tube-rolling addict, I’d suggest using the standard Cronus or sticking to playing with the double triodes at the front of the amp, and take the ‘do not use without connecting to loudspeakers’ warning very seriously. Swapping out the Electro Harmonix KT90s for even a set of NOS boxed KT88 might not be a bright move, and expect the unexpected when loading up a quartet of rancid no-name 6550s that you picked up for a song at a car boot sale, which had hitherto spent their nasty, brutish and short lives being profoundly roasted inside some questionable guitar amp.
The worry with the combination of Class AB1 operation and relatively high-power from comparatively cold-biased tubes can spell uninspired, undynamic sound. Fortunately, that isn’t the case here. The amp is more of a fine player of small-scale dynamics than one that goes for the sweeping bombast of single-ended designs, but it covers all the bases very well. So, you might not get the gut-churning drive of Mastodon in full graunch, but instead you get the delicacy needed to define the voice out of the mêlée.
It can really strike up the whole mêlée, though. No matter what kind of audio maelstrom you put in front of the Rogue, it takes up the challenge with all the boundless energy of a wiry terrier. Except that it’s also one of the biggest terriers around, because the Rogue throws out a huge, meaty, full-fat kind of sound. Not simply a big soundstage, but the sort of sound that seems big for its size. I’m really struggling to get this concept across in print; it’s closely allied to healthy power deliver, but it’s something more – the closest I can describe is like watching Alice Cooper (the man) walk on stage; he immediately seems taller and broader than he actually is. Precisely the same thing happens to the sound here; it becomes engorged with the music. Any kind of music, from a Shostakovich piano trio, to Charlie Christian redefining the sound of guitar, to the nu-country of The Low Anthem, to even the broken new-wave beat of Gang of Four, the Rogue takes all in its stride, and really fills the sound with sound, if that makes sense.
This enthusiasm for the task in hand almost completely glosses over the two blots on the copybook; it does deep well, but there are amps better at the excavating part of audio, and it’s a touch course-grained, both of which are especially noticeable next to solid-state designs. The former is not a great problem unless you choose to partner the amp with full-range speakers; and even here speakers with a bottom end tauter than the Brazilian women’s beach volleyball team will be fine here, but speakers like PMCs that are really destined to live comfortably with solid-state might show up a touch of thinness.
The grain is also not really an issue, unless you are a big fan of the blandness of audiophile recordings. In music where the music is uppermost, this will just come across as gutsy sound in the mids and top. On the other hand, if you listen intently to the sound of the background and focus on the tonality of the instruments instead of the way the music ebbs and flows, you might just detect a grittier, grainer sound than typical Class A valve and solid-state devices. This is no bad thing – it’s original Naim Nait-level grain – and could even add a spot of excitement to some of the more drab audiophile pressings.
I’m going to rattle out that little Naim Nait once again, because the sound has something of that device’s ability to cut through the hi-fi nonsense and just make bloody good sound. It is good with the beat, laying down a good sense of rhythm if the disc demands it. Most of all, the comparisons with the old Nait work simply because the thing is fun to use. It’s the sort of amp that isn’t content with just one disc; 20 minutes after it warmed up, it’s in its stride and you will spend a few hours more than you expected playing music through the Rogue.
The good news is what happens in line level also occurs through phono and – albeit to a lesser extent—through the headphone socket. The phono is quiet, well crafted and fun (although it’s relatively low gain for high-output MCs)—the perfect partner to the line stage. The headphone socket meanwhile is good, although no match for the ‘whole amp through the cans’ sound from the (admittedly more expensive) VTL IA-80 integrated.
This is one of those products that makes me think there is still hope for finding high-end sounds without the sort of high-end prices that currently dominate the market. Power, big valvey sound and a lot of fun, all wrapped up in a package that doesn’t need a banker’s bonus to own. Check it out now!
Power output: 90Wpc ?
Tube complement: 3 x 12AU7, 2 x 12AX7, 4 x KT90?
Inputs: Phono, CD, Aux 1, Aux 2?
Outputs: Fixed and Variable, headphone jack
Dimensions (WxHxD): 37 x 18 x 48cm
Weight: 22.7kg ?
Audiofreaks (UK) Ltd
Tel: +44(0)20 8948 4153