The 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 now in 2014, the new Icon Audio 845PP shows how.
In a word, it’s a showstopper. Whether you love, hate or simply don’t care about valve amps, there’s no denying the effect that one of these sitting on your sideboard has. As well as putting it under mortal strain (it weighs a whopping 35kg, and actually feels heavier), it will soon warm your room – which will give you a nice, comfortable glow inside until your electricity bill arrives! It also has another function, which is to amplify relatively low, line-level signals up to the level that will wake up your loudspeakers – and depending on what these are, your neighbours too. This is no shy, retiring violet of a valve amp then, rather in tube terms it’s the stormtrooper of the apocalypse, ready to ram its thirty eight (claimed, but totally believable) watts of power up right up the back of your sofa!
To maximise its power potential, the ST845 runs in push-pull mode, telling us that it is not one of the more specialist, far-out valve amplifiers. Other configurations such as single-ended give what tube aficionados would say is a sweeter, easier and more expansive sound – at the expense of vanishingly low output power, so horn loaded loudspeakers are called for. The ST845 however is more of a valve amplifier designed to fight it out in a modern solid-state world; you won’t need to change your loudspeakers or suddenly start listening to simple acoustic music with no bass to keep it happy.
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.
Launched in 2014, the £5,995 ST845 follows Icon Audio’s general best practice – a rigid steel chassis 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 large (440x400x240mm, 35kg) chassis is built well, but the finish isn’t as good as some price rivals. The copper top plate is lovely, 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, from Yamaha NS1000Ms to Sonus faber Olympica IIs, it’s 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, but in a very good way.
It might not come as a total 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. The Icon Audio had my current reference Sonus faber loudspeakers doing a passable impersonation of a PA stack at Glastonbury – now there’s an image one doesn’t conjure with very often!
Moving up to the midband, and the ST845 doesn’t lose much warmth, although it 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 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 quite 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!
Again, the 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 – rather like a large Harley Davidson motorcycle, it just 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. A flawed gem, Icon Audio’s ST845 PP makes people fall in love with what it does best, which is to make one of the most sumptuous sounds around.