One problem that I briefly talked about a couple of months back with typical single-ended amps is that as a group they lack the power you need to drive your current speakers. And one problem with every OTL amp I know of is that to get the output impedance right you need to parallel a big bunch of tubes - which raises the cost of the amp, both to purchase and to re-tube. Jud Barber, the head of Joule Electra is very aware of both these issues, having quite a bit of experience in both design fields (actually, Marianne, his wife, runs J-E, but on occasion she allows Jud to think that he does). His line of justly praised OTL amps, which are very powerful single-ended beauties, are some of the most articulate, detailed and honest amps ever manufactured. However, the entry cost for this brand of sonic Nirvana is nearly as high as the joy they return, so Jud has come up with a more affordable variation on his OTL design.
On that issue he simultaneously addresses the power issues of SET design. Using the same circuit he employs in his OTL amps but then transformer coupling that circuit allows him to offer an amp that marries two important attributes. At 30 watts a side, he has, in single-ended terms, a powerful design. In addition, by using an output transformer but retaining the circuit of his OTL he has kept most of his signature sound but can use just two tubes a side to achieve it. The resulting Stargate amplifier is a monoblock design that retails for $5,500, which is a not insignificant amount of money, but is also considerably less than his entry level OTL.
Jud certainly seems to have started out right as the Stargate amps are a nice looking piece of industrial design. The chassis, transformer covers and even the acrylic pads to protect your rack from the supplied spikes are all black, leaving an inky night sky against which the Joule Electra logo, a subtle blue power LED and the tubes themselves glow. Especially the tubes. With a pair of the legendary Russian 6C33 "nipple" tubes and five small signal tubes per chassis, the glow, while not of solar dimensions, is certainly a nice little constellation.
Hiding behind those output transformers on the rear deck is an IEC power receptacle, three Cardas binding posts (one neutral post, and a four and eight ohm tap), and a Cardas RCA input jack. In the middle of all this is a rotary feedback adjustment knob. With feedback adjustable from 0 dB to around 6 dB, you can tailor the sound to your speakers, room and pleasure with but one drawback. While the knob has a position indicator, there are no markings to indicate the amount of feedback you have dialed in, which makes getting a precise match between channels is an eyeball affair. In actual use I cannot image a situation where being off a quarter or so of a dB or so between channels would be an issue, so this is probably more of a geek gripe than a real world issue.
Setting the Stargates up in my system was quick and easy, although that rear mounted feedback knob made frequent adjustments to it a hassle. After hooking them up with my Merlin VSM-SE speakers, and getting signal from my First Sound Present Statement pre-amp, I tried several feedback setting and eventually settled on right around 2 dB as the best overall setting (this number is derived from information on the feedback setting found in the manual). There were occasional recordings that benefited from a different setting, but the vast majority of albums sounded just right at this particular spot.
The Central Scrutinizer
After dialing the Stargates in I fed them a steady diet of music for about a month before setting down with pen and paper to listen critically. The major reason it took so long to get around to evaluation mode was that the new Joule-Electra amps, right from the instant they landed, were extremely involving. Sure, that last sentence is usually taken to be reviewer-speak for colored but interesting, but not here as the Stargates seemed to combine the often disparate attributes of SET and OTL amps. That is, right out of the box they had darn near all the clarity of the Atma-Sphere M-60 MK. II OTL amps that I've had around here for several years, and coupled that with a like measure of the tonal expressiveness of the Art Audio Gill Signature SET that I reviewed several months back. Nevertheless, I am here to serve so I forced myself to set pleasure aside, scrutinize, and report.
Under the microscope the Stargate showed itself to have superb extension. The highs though these amps reached to Himalayan levels with the clarity of the air at the top of Everest itself. Even better than sheer extension, the treble region had both snap and shimmer. Cymbals broke into sound like stars glittering on a cold December night, but, after the initial pop sat down and took on a keen burnished shine. And the topper, at least for me, was that all this detail and light never, ever took on a grating, harsh or biting edge.
Down low, the Stargates reached satisfactorily deep, and with a firm hand. Whether playing Radiohead, Bruckner or Bill Laswell, I never felt that these SET amps ran out of extension or power. On the other hand, the only tonal region that showed itself to lag behind the curve, at least in my system, was the mid-bass. While not thin, as compared to the bass regions above and below, it lacked that last little bit of resolution. This minimal lack of definition gave the mid-bass a slight sense of hollowness, even a slight paper quality. If you look below you can see that I still scored the mid-bass a high B, so even though critical you need to put these comments in context of the overall superb tonality of the Stargate.
The mids, in a word, were wonderful, and in a phrase combined SET and OTL seamlessly. Vividly textured, but also amazingly clear, the combination was, I believe, exactly what Jud was working for. Acoustic recordings combined quickness, definition and harmonic accuracy. Male vocals, especially, were presented with an astonishing accuracy, shrinking the gulf from recording to reality to a mere puddle.
Perhaps the single greatest contributor to the overall sound of the Stargate was the way it handled dynamics. With a quantum like leading edge, contrasts appeared suddenly and with intense impact. This snap carried with it no artificial or mechanical edge to distract or alter the illusion of reality. In addition, the trailing edge of things was as nearly superb, turning the tracking of note contrails in orchestra halls, churches and recording studios into an intensely enjoyable activity.
With all this speed came equal clarity. I felt that I was able to peer deeply into the stage and recording session. Small details, buried on the mix or laying at the corners of perception were not artificially hyped; rather they were laid open for anyone to look at. The long-suffering Robin even took notice of this. Much more of a holistic/groove listener than an obsessive audiogeek, she commented that with the Stargates in the system she was noticing details as never before, and enjoying it.
Reiterating what I've said in previous reviews, staging is something that I enjoy but since I rarely encounter it in live music, is not a mandatory part of my listening experience. That said, I fully understand that a well-made recording encodes a great deal of spatial information. With the Stargates I was able to see just how much. I've used the Joni Mitchell recording of the title track to Court and Spark [DCC GZS 1025] in the past to demonstrate how well a product draws a stage. The Stargates took me further into this session than I have been in the past. Left to right is a given with this recording, but depth is more problematical. Not with these amps. I heard and felt both the width and depth of the recording room, as well as the size and shape of the isolation booth that Joni is in. Other fave staging disks, such as the six settings of the Arvo Pärt work Fratres by I Fiamminghi [Telarc CD-80387] had me playing virtual architect as I explored space in all three dimensions, with the stage itself projecting quite nicely in to the room.
The Other Kids
I've used the OTL designed monoblock Atma-Sphere M-60 mk. II amps around here for a couple of years and have come to respect them for there skill at showing what is on a recording with utmost fidelity. Certain folks have characterized the Atma-Sphere as a tad cold, but my experience runs slightly counter to that. To be sure, they do not have the typical tube warmth, but they are neither cold nor threadbare, rather they are revealing of everything they contact. Especially tubes. Several of the people I have talked to about these amps who have had problems with them have resolved those issues by selecting the right driver tubes. Use the wrong 6SN7 in the wrong spot, and the sound does edge to the cold and slightly brittle. But find the right tubes and the sound is immediate, involving and precise. And at $4200, the price is amazingly good for what you get. Still, there are drawbacks.
With four 6SN7 and eight 6AS7 tubes a chassis, re-tubing is a planned expense, not a casual endeavor. And not everyone wants to hear everything going on in their system and on a recording all the time. Lastly, the top end of the M-60 mk. II can be ever so slightly ragged at times (I think that those who call the M-60 cold are responding in large part to this artifact).
Putting the Stargates up against the M-60, was an interesting battle. The M-60 had a very slight, overall edge in speed and in clarity, but the treble of the Stargate was just as open and revealing as that of the Atma-Sphere, but it also had a finesse that made it both more natural and enjoyable. Dynamically, the Atma-Sphere took the edge in the macro department while the Joule-Electra in the micro arena. In matters of tonality, the Stargate had a touch more harmonic richness and bloom, but the M-60 had a bit more bass definition. Overall, I would call the Stargate the more approachable of the two, as well as the easier to maintain and live with. To these ears, the Stargate offers 98% of the special OTL sound qualities of the M-60, but with a more refined treble and an increase in richness.
Up against the SET design, $3,800 Art Audio Gill Signature, the Art Audio showed itself to have an even richer tonal palette than the Stargate, most particularly in the upper-bass/lower-mid region, but the Joule-Electra has better mid and lower bass, stands on better dynamic footing and offers up more detail throughout the range. The Joule-Electra also has the edge in staging over the Art Audio. But it's not quite as cut and dried as that since the Art Audio amp is, at least in my view, is an outstanding overall amp. It concentrates its skills over the lower-bass to lower-treble region, where almost all music takes place, and so is a real pleasure to listen to, and it does so with a richly textured harmonic sense. With many speakers and sources that makes the Art Audio a perfect amp as it is forgiving and yet detailed. Still, the Stargate manages to capture a good 95% of this same sound, and add to it the clarity of an OTL, which makes it a compelling amp and one that edges the Art Audio out, in my opinion.
Off To Another World
At the end of the review period I was as enamored of the Stargate as I had been at the start. It neatly slays both the low power serpent of the SET jungles and the cost monster of the OTL forest. It also combines the skills of the SET and OTL designs, adding clarity to midrange texture, and with enough power for most real world loads. Above all, the Stargate is a completely honest amp. It never colors, and the few faults it has are subtractive, which makes it an easy long-term partner. This one is well worth looking up. In fact, I think I'll go give it a long last workout before the UPS guy comes round.
Driver Stage Differential Mu follower using: