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Sessionmaster Guitar Preamp

Instant rock guitar without all the hassle of amps and microphones.

What use a guitar amp and a microphone? Not Paul White, he just wants to plug in and go!

Most guitar players have their own approach to getting their live sound more or less as they want it, but in the studio, it's often difficult to recapture the same magic. I know this because I've been on the receiving end before now! If you take in your own amplifier, it's either too loud or the engineer mics it up so that it sounds totally different, and what's worse, you don't know just how different it does sound until you come to hear the playback. Conversely, if you try to DI the guitar through some sort of preamp, it invariably sounds dreadful. But does it have to? If only you could get the right sound from a preamp, it would save a lot of time and you'd hear the sound you were actually going to end up with right from the start.

Unfortunately, studio preamps have got themselves something of a bad name — the first models were pretty grim and, just like the stigma attached to early solid-state amps, the reputation persists. The good news is that some very serious work has gone into guitar preamp design over the past two or three years and some very tasty products are starting to emerge. These tend to fall into two categories: the guitar multi-effects preamp and the basic preamp with no effects of its own other than overdrive. In my experience to date, the latter type seem to produce the best guitar sound, at least in the overdrive department, though I admit to being quite taken with one or two of the newer multi-effects preamps as well. Most studios, even small home facilities, have some form of multi-effects unit, so it may be equally effective, and a lot cheaper, to plug a no-frills recording preamp into whatever you already own.

The Rock Sound

Why is it so difficult to make a guitar preamp that sounds good when plugged directly into a mixing desk? Getting a good clean sound isn't really the problem, but reproducing the sound of an overdriven amplifier is more problematic, since it is influenced by a very complex blend of factors. The rock guitar sound wasn't invented, it evolved, largely due to the shortcomings of the technology of the period — a combination of valve amplifier design limitations, the need to produce enough volume to compete with a drum kit, and the appalling frequency response of the only loudspeakers that could handle the power. If none of these limitations had existed, the modern rock guitar sound might be quite different.

A well-designed preamplifier can emulate the tone control section and overdrive characteristics of a real amplifier surprisingly accurately, but the real problem is in imitating the effect of the loudspeaker. A typical rock guitar speaker acts as a very efficient filter, removing all the high-frequency, buzzy harmonics — and because guitar speakers have always done this, the accepted rock guitar sound is smooth and raunchy, but with no real top end. If you've ever plugged an overdrive pedal directly into a mixing console and then wondered why the result sounds so thin and buzzy, it's simply because you're hearing all those high harmonics that the speaker normally takes out. Guitar speakers also become less efficient as they are played louder, which has the effect of compressing the sound. Consequently, some guitar preamps contain an element of compression to make their simulation more realistic.

Guitar preamplifiers intended for use in the studio are fitted with a filtered output designed to imitate the filtering effect of a typical guitar loudspeaker. This feature is often known as speaker simulation, and without it, it's virtually impossible to get a good DI'd rock sound. If the speaker simulator is well designed, the sound you get when you plug into your mixer is very similar to the sound you'd get by miking up a guitar amplifier. You may need to add a few effects, particularly reverb, to take the dry, clinical edge off it, but a good unit, properly used, can produce a wide range of clean and rock sounds which are virtually indistinguishable from the real thing.

Aside from the convenience aspect, these preamps allow you to record at any time of day without making too much noise, you don't have to worry about room acoustics or traffic noise, and you can record at the same time as other musicians without their sounds getting onto the guitar track or vice versa.

The Sessionmaster

Sessionmaster was designed by guitar guru Stewart Ward, the inventor of the popular Sessionette guitar combo. It is a simple, compact guitar preamplifier, capable of producing both clean and overdriven guitar sounds, with an integral speaker simulator so that it can be used straight into a recording console or Portastudio. There are no fancy effects or even channel switching, but the flexibility offered by the five knobs and three buttons is surprising.

"The unit is particularly good at producing mildly distorted guitar sounds that respond to picking intensity — great for recreating vintage blues sounds."

Sessionmaster is not a new concept — indeed, it has been on sale for around a year now, but what I have before me is the very first production model of the Mark II. I was so impressed with the original Sessionmaster that I use it for the majority of my studio work and also on the rare occasions I play live. However, the Mark II incorporates a couple of significant advances, enabling it to produce a much wider range of clean guitar sounds, while the overdrive sound has also been improved.

Though Sessionmaster is rack mounting, the box containing the electronics is only around 10" wide and is fixed to the back of a heavy-gauge, 1U rack panel. The model I have is finished in the same livery as the original — grey and green screening on a Mac-coloured cream/grey finish — and goes rather nicely with any Apple or Akai equipment you happen to have around. Powered by an external mains adaptor, the unit is configured as a single-channel guitar amplifier; there's no channel switching. This single channel can produce the whole gamut of guitar sounds from clean, through ragged to powerful overdrive, while the three-band passive tone network is based on that used in several classic valve-amp designs.

Control Options

Sessionmaster II has a single input jack located on the front panel, while the rear panel accommodates two output sockets; one unfiltered for use with a guitar amplifier and the other processed by the speaker simulator for DI'ing into a recording system. The mains adaptor plugs into the rear panel and a green LED on the front panel lights when the unit is powered up.

The control layout is deceptively simple, the Gain control being used to set the degree of overdrive. This works in conjunction with the Gain boost button and is arranged so that lower settings of the Gain control produce a brighter, cleaner sound. In addition to Gain, there are two more boost buttons, Bass and Mid, which are self-explanatory. The frequency ranges for these circuits have been selected very carefully and the Bass button really does bring in the low-end kick of a big amplifier. Again, by juggling the button combinations with the tone control settings, the tonal variety that can be achieved is impressive.

Many designers have tried to develop fancy equaliser circuits for guitar amplifiers, but in the end, the passive system used in the original Fender amplifiers still seems to sound the best. The Sessionmaster equaliser is based very firmly on this old design and faithfully recreates the characteristics of the original, including the imperfections and quirks which make it so distinctive. And, like the original, if you turn down all three tone controls, no sound gets through. Last in the list of controls comes the volume control, which sets the output level at both rear-panel jack sockets.

"As the gain control setting is increased, the sound takes on a slightly raggy edge which is very much like a valve amplifier used on the clean channel."

Clean Machine

The first noticeable improvement comes, surprisingly, in the clean sound department. The power supply design has been changed so that the circuit is less likely to clip when subjected to the input from a guitar with powerful pickups, while the voicing arrangement seems to have been extended, allowing far brighter sounds to be produced. Now you can get a really jangly, modern tone, but equally, it's easy to get a thicker, vintage tone. As the gain control setting is increased, the sound takes on a slightly raggy edge which is very much like a valve amplifier used on the clean channel. Further gain increases produce a raunchy overdrive, and different variations on this are possible by using either high gain settings and no gain boost, or low gain settings with gain boost on.

The boost controls produce a very noticeable effect, with the Bass control introducing a low, reassuring kick to both clean and dirty sounds. If I'm not mistaken, the mid-boost character has been changed and now seems more musically relevant to the guitar than on the original model. With the gain boost turned on and the input gain control turned up, the amount of overdrive that can be produced borders on the excessive — as it should — and even Strat-type guitars come over with plenty of power and sustain. Guitars fitted with humbuckers deliver a predictably thicker and more authoritative tone.

By combining various boost buttons and the three tone controls, just about any tone can be created, but you do have to experiment to get the best results. Though there seem to be few controls, subtle variations in settings can make a huge difference and the more you play around, the more you discover. You can just plug in and go, but a little patience is rewarded by an unexpected diversity of tone. The underlying overdrive sound is distinctly British rather than American and it works well on both chords and single notes without too much intermodulation (the dissonant jangling that occurs when two or more notes are played simultaneously).

Studio Use

The lack of a channel-switching facility might be considered a limitation for live work, but in the studio, where clean and dirty sounds tend to be recorded in separate takes, it is of little consequence. Both the clean and dirty sounds appear quite convincing when taken from the speaker-simulator output, though for very bright, clean sounds, it is perfectly acceptable to use the non-filtered output for recording. Electronically, the circuit is very quiet and any noise that does materialise at high overdrive/gain settings is invariably due to the guitar pickups falling prey to interference from mains transformers, wiring and computer monitors. Humbucking pickups are better in this respect, but in either case, the amount of background noise seems considerably less than you'd expect from a guitar amplifier set up to produce a similar sound.

Because there is no built-in reverb, the DI'd sound is rather dry and some form of effects processing is necessary to get a 'produced' sound from the unit — it takes only a hint of reverb to make the sound come alive. The unit is particularly good at producing mildly-distorted guitar sounds that respond to picking intensity — great for recreating vintage blues sounds. Like all overdrive systems, the more overdrive you add, the less incisive the sound, and it sometimes helps to use the sweep mid control on your mixing console to add bite when playing with a really dirty sound. As the exact frequency depends on the tonal qualities of the guitar being used, this has to be approached by ear, but the magic spot usually lies between 2kHz and 4kHz.

Overall I very much like the simplicity and flexibility of this unit. It produces very convincing rock guitar sounds without undue 'fizziness' and is quiet enough for even the most serious recording projects. Extra reverb or other effects are needed to get the best out of Sessionmaster, but when you consider that this unit costs only around the same as a couple of guitar pedals, it becomes a very attractive proposition for the guitarist involved in recording at any level. If you need instant Rock Guitar — just add Sessionmaster. And just in case your bass player is feeling left out, there's a bass version coming along any day now!

Further Information
Sessionmaster II £149 inc VAT.

Sessionmaster is available by direct mail from Radius or from selected dealers. Contact Radius for dealers in your area. (Contact Details)

Previous Article in this issue

Soundtracs Solo MIDI Mixing Console

Next article in this issue

Steal The Feel

Recording Musician - Copyright: SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.


Recording Musician - Jul 1992

Review by Paul White

Previous article in this issue:

> Soundtracs Solo MIDI Mixing ...

Next article in this issue:

> Steal The Feel

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