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GT Electronics 'Studio Tube Pre-Amp'


Hate that 'dry' D.I. guitar sound? Want a genuine stage amp tone at recording levels? Groove Tubes reckon they've produced a major breakthrough in guitar amplification & recording. Gary Cooper investigates...


Ask a dozen professional guitarists how they record their sounds and you'll get a dozen different answers. Some use their stage amps and try to capture their live sound on tape by miking the speakers; others use an assortment of old, weird and wonderful mini valve amps of great antiquity and overdrive them to hell. Some use Scholz Rock-men, Rock Modules, Gallien Kruegers and the like, some use their amps' Master Volume arrangements. The methods are as many and as diverse as the players and engineers themselves. Why? Simply because whichever way you try to record a guitar sound, something seems to get lost from it, and that something can probably best be described as 'feel'.

Back in 1983, the Geordie valve amp maker Greg Burman (now, sadly, no longer in business) developed a small valve pre-amp (the Burman GX3) which, to a degree, overcame the problem, being a three gain control all-valve pre-amp for studio use. Several studios bought it and used it successfully, but it lacked a vital element: the effect of a valve power amp driven speaker. It's in this respect that all recording compromises tend to fail. However hard previous designers have attempted to provide a full power sound at low volume levels, it's the loudspeaker's contribution that has been missing. Fortunately, one electronics whizz at least has been beavering away at this problem, having experienced it for himself - Groove Tubes' Aspen Pitman. Old IT hands will recall the interview we ran with Aspen in Issue 2, where Aspen revealed himself to be unusually in touch with the guitarist's point of view. Well, the great man and his designers have been giving this recording problem some serious thought during the past three years, and the result is with us now — the GT Electronics Studio Tube Pre-Amp.

Having analysed the problem, GTE's designers have developed a mysterious 'black box' (now world patented, I gather) which they call the 'Emulator'. It seeks to simulate the effects of a valve-loaded speaker, regardless of the volumes being used (indeed, regardless of whether a speaker is connected or not). It's the key to the GTE's operation and sound.

What it does



The purpose behind the GT is threefold. Basically it's been designed to offer a realistic 'valve amp on full' sound for recording straight into a mixer, but it will equally well drive a separate power amp (enabling you to use it on stage at any power level) or, alternatively, deliver 25 watts into an 8 Ohm speaker, so that you can either monitor the recorded sound through a speaker or (possibly) use it on its own for small gigs.

The Details



Puritan plain in black sheet metal, the GT Studio Pre-Amp is a heavily built unit designed to be installed in any standard 19" rack. Particularly if you're the type of person impressed by flashing LED's and super-cosmic graphics, the GT might strike you as looking pretty boring; but remember this is no pseudo Hi-Fi box of gimmickry, it's a toughly made, professional piece of engineering, designed for people who realise that the icing on a cake is no guide to the quality of the gateau!

The GT's facilities are basic but complete. The back panel has just three outputs — 'Speaker', 'Line' and 'Emulator' (the latter being a tap to the GT's mystery factor, about which more anon) plus a fuse holder and a fixed mains lead. The front panel, meanwhile, provides a conventional ¼" jack input plus rotaries governing Gain and Pre-Amp levels, Treble, Middle (with a pull boost), 5-position Mid-Boost shaper and Bass plus Presence, Master Volume and Line Out, the array being rounded off with a standby. Driving the amp is an array of Groove Tubes valves — first stage, tone section, gain stage and phase inversion roles being performed by ECC83s with a pair of 'Matched Duet' 6V6s delivering final power. From a design and circuitry point of view the GTE isn't really very different from most other prime quality valve amps. As the handbook admits — with refreshing honesty and directness — it's 'a classic design similar to many of the old Fender amps you already know'. This is certainly true. In fact it's just a beautifully constructed traditional valve amp with an extra gain stage added to facilitate today's overdrive sounds.

Technically, the GT's specifications are impressive — particularly so for a valve unit, and well in keeping with the sort of quality required in the most demanding studios. I haven't had the opportunity to confirm the figures quoted by the manufacturers, but from a performance-based assessment of noise I see no reason to disbelieve them.

On Test



There's nothing at all to baffle the guitarist about how to use the GT, but just in case you have jettisoned a few too many brain cells on your way through life, a splendid handbook, written in Aspen Pitman's typically chatty and highly informative style, comes supplied and takes you through the amp stage by stage. I really can't commend this handbook too highly. Why so few other amp makers don't take the trouble to explain how to use their products to the best possible advantage has often mystified me. Here, in around ten pages, you're told how all the controls work, what they do, how the valves perform (even down to what sort of lifespan you should get from them), precisely which valve does what in the line-up, sample control settings (three pages of them, telling you how to get sounds like 'A Smooth Blues tone with mid-boost a la Stevie Ray Vaughan', 'Bright, crunchy solo tone a la Eric Clapton', 'Heavy Rock solo tone a la Edward van Halen, Jake E. Lee and Steve Vai' and so on. Of course, this isn't intended to be a 'dial a guitarist copy' guide, but it certainly helps you become familiar with the amp's multitude of sounds and could be a major asset to the session player called on to 'Gimme a Jimmy Page, like now!' by a demanding and harassed producer!

Of the three rear panel connections, the 'Emulator' output is designed for direct connection to either a studio or PA desk (it delivers 1.2 Volts RMS with an output impedance of 10K). This output stage gives the full 'on stage' sound (ie after the pre-amp section) and is affected by the 'black box' circuitry which is the key to the amp's ability to give a true on stage sound at low output levels. If, on the other hand, you want to slave up an additional guitar amp you should should use the Line Output, which gives a 1.2 volts feed. Here the signal is from the pre-amp section alone and is, in effect, 'dry'. Finally, if you want to use the GT's 25 watt power then, logically enough, just connect an 8 ohm speaker to the 'Speaker Out' socket.

Having got this far it's now time to start discussing what the amp sounds like. This isn't going to be easy, because if I don't restrain my overwhelming enthusiasm for this new device then I suspect that some of you out there are going to think that the old codger's really wigged-out this time, having taken a substantial back-hander to rave and drool. I hope I don't need to stress that this isn't the case! Having said that, I'll press on and trust that you accept my opinions at face value. Let's start with the tone stages. No, on second thoughts, let me first emphasise how noise free the GT is, only full overdrive bringing in some hiss and amp noise, as it inevitably will with any amp.

Right, now I'll get on to the tone stages. 12dB shelving types, they're designed to be set at 12 o'clock as their basic setting — though that doesn't actually mean they're 'flat'. The Treble and Middle rotaries are effective in a traditional valve-amp way. Pull the Mid control, however, and you get a significant 20dB boost in the mid frequencies, although when this is done the variation in mid tone comes not from rotating that control, but rather from using the 5-way click stopped Mid Boost selector beside it. This is marked A-E and adds what the handbook accurately describes as progressive degrees of 'overtones' to the mid frequencies, 'A' being basically bright and 'E' giving a richer, darker sound. This is a fairly subtle effect in many ways, but it's just the sort of tonal adjustment which gives its best when you're playing a high-class guitar; i.e. not a cheap Korean Strat copy! Try it with a Les Paul and see for yourself how well the mid-boost selector works.

But it isn't the tonal flexibility, nor the GT's noise-free characteristics that make it the remarkable product I feel it to be. Put bluntly, the GT Electronics Pre-Amp delivers an astonishingly accurate 'live at full power' sound at apparently impossibly low levels. Plugged straight into a desk, delivering the minute output demanded, the GTE still manages to sound like the finest quality valve amp at full output. Monitor your sound via control room speakers and you'd swear that what you were playing through was a steaming, smoking valve stack. Even more to the point, the amp responds to your playing exactly like a full-on valve unit. Notes squeezed out sound squeezed, the amp is touch-responsive in the way that only a valve amp is, and the guitar comes alive in your hands just like it would if you were plugged into a Mesa or a Marshall. How does it do it? The answer lies in the mysterious black metal clad box on the far left hand end of the GT's top surface - the heart of the 'Emulator'.

The Emulator



I can't pretend that I fully understand how the Emulator device functions, but I do have a small inkling of its secrets, which I'll try and explain. This, by the way, is very important stuff, because what the Emulator does will explain a lot to many of you who've wondered just why it is that valve guitar amps make a guitar 'breathe' with your playing, while transistor amps make you feel that the guitar is essentially inert — dead, if you prefer. You have to realise, firstly, that the once widely held belief that a valve amp sounds better because of its inherent emphasis on the even order harmonics is only a small part of the overall picture. I used to believe this myself, but became puzzled (especially as my playing improved over the years) that while the better transistorised amps were getting increasingly closer in their sounds to valve amps, they still didn't feel like them. Moreover, I found that when using a pro class valve amp there was a lot more to getting the overdriven sound I wanted, particularly when holding it on the edge of feedback overrun, than was being controlled by my hands alone. There was a definite physical 'body posture' relationship in the way I was playing, and I noticed that others were doing the same thing. The more I delved into it, the odder it seemed. Why did so many players use the position of their bodies against their speakers as part of the way they got their sounds? It certainly wasn't just to inhibit feedback, either. There was definitely something else going on. What was more, why did valve amps seem so much more touch responsive than transistorised types? The more you pushed a string, the greater the overload and power produced whereas, with a tranny amp, the guitar just responded inertly. Playing through a valve amp it felt as if you were pushing against something — a quality which meant that a valve amp enabled you to play infinitely more expressively than you could through a solid state confection.

Where all I could do, as a writer/reviewer, was speculate about what was going on, Aspen Pitman was busy assembling a design team to unearth a way of simulating this strange electromagnetic phenomenon. The Emulator is the result.

As far as I can glean, the Emulator comes in two parts. The 'black box' which resides on the top of the amp seems to be a mechanical device (electro-magnetic in operation) which simulates the way in which a vintage Celestion speaker reacts when being driven by a valve power amp. According to GTE, a speaker only uses part of the energy from the power amp's tubes to make a sound. What it doesn't use is fed back into the power amp (the loading factor I've often rambled about in the past), and it's this energy which makes the power tubes distort, relative to the amount of feedback. In other words, as Aspen puts it: 'The harder you push a speaker, the harder it pushes back and the more distortion you get'. In a few words that explains what it is that we guitar players experience when we talk about a valve amp's 'feel'. But there's more, too. A speaker radiates an electro-magnetic field, and it's inside this that the positioning of the guitar and the player's body adds yet a further complication to the equation. I found out how well the GTE handled this quality when seeing whether it was possible to work physically 'against' the black box on the GT's top surface in the same way that you would normally position your instrument and yourself against a loudspeaker — you can!

Back to the review...



The upshot of all this is that the GT feels positively freaky to use. Not only does it sound like the very finest tube amp when you're playing it, but it even feels like one, and allows you to use all the feedback/sustain tricks that are a natural part of the Rock guitarist's style. But does this mean that it's only suitable for overdriven use? Not at all! It's not just when a valve amp is being overdriven that it sounds good, because the GT works supremely well when set to deliver clean Country and Blues sounds — the sort of sounds which, again, would need a well driven valve amp to obtain under normal circumstances. It's that ability to deliver exactly the same sound and feel characteristics of a full-on 100 watt valve amp while delivering only a minute output level to a mixer that really singles out this amp as the advance that it is.

Conclusion



So who's going to spend £850 on a unit like this? Well, not me, because I can't afford it! On the other hand Tony Iommi (Black Sabbath) has just bought a dozen of these beasties to use in the studio and on stage, and I understand both American and British studios are flocking to buy them — I'm not at all surprised! Rather than wrestling with every guitarist who comes into your studio with his or her battered Marshall or whatever, the spending hours trying to find a sound on tape that still gives the artist the feel and sound they demand, engineers and studio owners are finding it cheaper and easier to buy one of these, rack it up and say to their customers: 'try this, sunshine, it'll flatten yer!'. I can't do anything other than agree.

Rather than fork out around a grand for a Mesa Boogie or similar (which you still have to mike and/or DI to record), any studio or any session player, any professional who records and wants their ultimate sound on tape, should certainly investigate this impressive new device. I realise that the GTE is an oddity, not the sort of thing that the majority of IT readers will be able to afford, let alone have the need for, but, should you ever find yourself in a studio trying to get a 'live' sound from your guitar, I hope you find one of these units there to help you!

RRP £850 inc. VAT

More details on GT Electronics and Groove Tubes from Scott-Cooper Marketing Ltd., (Contact Details).



Previous Article in this issue

FCN Cougar CLX100 Guitar Combo

Next article in this issue

Perfect Pitch?


In Tune - Copyright: Moving Music Ltd.

 

In Tune - Dec 1986

Donated by: Gordon Reid

Gear in this article:

Preamp > Groove Tubes > Studio Tube Pre-Amp

Review by Gary Cooper

Previous article in this issue:

> FCN Cougar CLX100 Guitar Com...

Next article in this issue:

> Perfect Pitch?


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