The famous 845 power triode started life as a radio transmitting vacuum tube – physically large and with an impressive anode dissipation of 75 watts, it ran 1,250V on the anode no less. The thoriated tungsten filament – which glowed like a lightbulb – was powered at 10 Volts and 3.25 Amps, so any transmitter that ran a large complement of them was always going to make the lights dim! The same goes for hi-fi amplifiers too, because the 845 went on to make excellent audio tubes and is now something of a cult.
Launched in 2014 for £5,995, Icon Audio’s Stereo 845PP was no shy, retiring violet of a valve amp, rather in tube terms it’s the stormtrooper of the apocalypse, running in push-pull mode to give a claimed 38W RMS per channel. Many smaller valve amplifiers have self-biasing, using resistors to set the cathode voltage correctly, but the sheer size of the 845 valve means that four resistors dissipating about 20W of power each would be needed – making for lots of wasted power and heat. That’s why Icon Audio has fitted a bias meter which helps users to manually set the biasing, as well as warning if a valve is on the way out – something you won’t know about with a self-biasing system. Seasoned valve sorts will know this is the right way to do things.
Indeed, the ST845 follows Icon Audio’s general best practice – which means a rigid steel chassis (measuring 440x400x240mm and weighing 35kg), into which good quality low distortion, tertiary wound output transformers are bolted, and these are potted to reduce noise. High quality passive components are used throughout, including Solen/SCR capacitors, with the option of Jensen copper foils. Silver plated copper internal wiring (all hand wired, point-to-point) is used, along with a Japanese sourced ALPS volume control. As well as the four Psvane 845 valves, two 6SL7 first stage valves and two 6SN7 output driver valves are used, along with a GZ34 driver stage rectifier. Two separate 10v AC heater supplies are provided, a separate power supply for the driver circuit, which uses a valve rectifier and another choke.
The ST845 is certainly built well, but then again so it should be at £6,000. Still, the finish isn’t quite as good as some price rivals, both tubular and transistor. For example, the Audio Research VSi60 or 75, whose prices the Icon Audio straddles, and the Musical Fidelity AMS35i, seem swisher. The Icon Audio amp’s copper top plate is lovely, and copper isn’t cheap these days, but some of its black powder coated steel casing parts aren’t as classy, and nor is the front panel switchgear.
Valve amplifiers are normally especially sensitive to the loudspeakers they are being used with, but in the case of the Icon Audio ST845 PP, it seemed far more sure-footed. Showing precious little fear of any loudspeakers I threw at it, it is one of the few I’ve reviewed over the years that sounds genuinely powerful and gutsy. But those hoping for it to be as transparent as a transistor amp shouldn’t hold their breath, because it is quite coloured. So much so that you might say it stamps its sonic personality all over the music, like a giant walking over your front lawn – this is a bold and characterful amplifier.
It won’t come as a complete surprise to learn that the ST845 is warm sounding, although in fairness it’s never gloopy and syrupy, with a bass like it is walking through treacle. Instead, the big Icon Audio is fast and lithe, but still has a vast thump down south, seeming like the audio equivalent of a JCB. It is solid yet surprisingly lithe; it’s pleasingly sumptuous but never sounds overblown in a well balanced system. For example, the walking bassline on Black Uhuru’s Party Next Door was a delight. Moving up to the midband, and the ST845 doesn’t lose much warmth, although does dry up slightly. Everything gets a nice, rosy glow, meaning that recordings which your previously viewed as a little acerbic – like The Bodines’ Scar Tissue – suddenly seem to calm down and chill out. There’s never any sense of the sound being laser-etched out right in front of you; instead you’re drawn into this wide and deep soundstage, with a lot of the action going on behind the plane of the speakers. Things hang back a little, yet this amplifier is so expansive left you right that you still feel immersed in the proceedings.
It’s a lovely sound, no matter what sort of music you like. It gives a beautiful clarity and ease to even some of the most uneasy human voices – like Bob Dylan’s for example. Highway 61 Revisited was a lot less strident than you normally hear it. There’s no doubt that the 845 is a wonderful power valve to have driving your speaker cones; it’s so clean yet warm in a way that almost all no other valves are. Yes, like lesser tubes it is coloured, but it’s far more resolute and detailed sounding, and doesn’t make the music descend into some sort of audio comfort blanket. It’s got more warmth and guts that a 300B, yet a sort of KT88-like get-up-and-go; in other words it’s a perfect combination!
Treble is lovely. Suddenly, cymbals played through even a top quality Class A solid-stater like the aforementioned Musical Fidelity AMS35i seem a bit steely and scratchy. Also, they don’t time as well; the filigree hi-hat work on Rush’s Subdivisions sounds more like it’s being played on a drum machine on lesser amps, whereas the ST845 PP seems to flatter the sound of both Neil Peart’s vast drum kit and his playing. In fact, the big Icon Audio has an easy sound and never seems to break into a sweat. No matter how complex the music gets, it just shrugs it off and keeps playing.
Even at high volumes, it displays grace under pressure in practically any British living room, although ask it to power the school disco and you’ll find it loses its sophisticated demeanour pretty sharpish. Running up to fairly high levels in a largish room with medium sensitivity speakers, it sounds powerful and assured – it’s just that you can’t push it as far as a solid-stater. There’s also something that never leaves you – that coloration. It’s lovely, but if we’re honest it should be there and makes the amp less able to pick out the tonal differences between recordings and even instruments. The studio where Stax recorded its classic soul catalogue in Memphis sounds a little too close to The Power Station in New York, for example. Some solid-state purists will find the bass just slightly slurred too; it is magnificent, but it doesn’t switch on and off with the speed of an LED.
This is a lovely thing which bestows luxury and a sense of occasion on its owner. It oozes character and charm, making a sound that virtually no other amplifier can. However, don’t expect it to be the last word in openness, subtlety, speed or clarity; others do better here. Still, most Icon Audio ST845 PP simply won’t care; they’ll fall in love with what it does best, which is to make some of the most sumptuous sounds around.