Conrad-Johnson GAT Triode Preamplifier (HiFi-Plus 67)

The GAT drew the same reaction from every one of the grockles. The real people, muggles… non audiophile types:

“What the hell’s that?”

“It’s a preamplifier. It takes signals from the CD player and controls the big power amp.”

“It looks like something Captain Nemo might have used. How much is it?”

“Er, about £19,000.”

“[expletives deleted due to need to stay within the 1957 Obscene Publications Act, the 1697 Blasphemy Act, and the physical impossibility of getting a horse to do that to an archbishop]. Sounds bloody great, though!”

The dialogue, repeated more than once (although few were quite as creatively sweary), highlights much about the new conrad-johnson GAT preamplifier. It’s big. It’s visually distinctive. It’s expensive. And it sounds so good you don’t care. The GAT is the latest in a long line of limited-edition flagship preamplifiers from conrad-johnson, following in the traditions of ARTs and ACTs from the brand. There will be just 250 lucky GATters. The name is short for Great Anniversary Triode, but insiders (like Wes Philips) think it’s there as tribute to c-j’s well-loved customer service team-leader, Carwell Gatling.

Like the ACT before it, the GAT is a one-box valve line-only preamp, which only features single-ended inputs (five, two loops for processors or recording and two sets of single-ended outputs) and one that makes extensive use of microprocessor control. Channel switching relays, the 100-step volume control, balance and basic operation are all powered by a microprocessor, and the main ‘head’ section (where the main controls and displays live) looks very similar to the preamp that preceded it. Anyone you has used an ACT will also be used to the ticka-ticka-ticka sound as you work through those 0.7dB volume steps.

Unlike the ACT, with its offset, back-set control panel and the four clear plastic protectors for the quartet of tubes, the GAT looks very symmetrical. The centre control unit is flanked either side by a single 6922 triode, protected from the outside world by four quartered clear plastic protectors. The overall look does highlight the substantial feel of the preamp, and opinions converge on the GAT having a 1950s aesthetic… in a good way, more ’57 Chevy Bel Air than ’59 Edsel.

One triode per side might invite some questions from those who know their way around a preamp circuit. Digging deeper finds the GAT with a high-current MOSFET buffer stage and a solid-state discrete DC voltage regulator. From a strict valve-fascist standing that would make this a hybrid design, but few will call it that in reality. The advantage of solid-state voltage regulation is complete isolation from the mains circuit, while the MOSFET buffer means very low output impedance. That makes it more power amp friendly, or rather makes the use of long interconnect cables a distinct possibility. Like all c-j preamps, it inverts absolute phase, so turn your cables hot to cold and cold to hot at the loudspeaker end.

The typical c-j ‘no feedback, no electrolytics’ rule has been adhered to in the GAT. Every capacitor in the audio circuits (and their power supplies) is either a polypropylene or custom-designed Teflon type, while the circuit bristles with metal foil resistors and gold-plated silver contact relays that are sealed from the outside world. This is, of course, what you’d expect from a top-class preamplifier.

I’d say the clever part of the GAT is the blending of 21^st Century control circuitry with mid-20^th Century amplifier technology, but I guess the point of the GAT is it’s one big clever part. The microprocessor controlled start and stop processes are an example of the kind of forethought that went into the design. It goes into a minute-long auto-mute, to eliminate the sort of transients that occasionally hit during the first few seconds of tubes powering up and down. Most don’t bother, assuming that these early stage transients are not much of an issue if the power amp hasn’t started up. If you use these preamps with powerhouse solid-state amps that come to life in a second, those transients can get a touch alarming. In other words, if it wasn’t for the two tubes staring at you from either side of the front panel, you’d never guess this was a valve preamp.