Guitar preamps that use digital modelling technology have found their way into vast numbers of studios. But do they have a useful place on stage, and what do you need to know if you want to use one live?
One of the biggest challenges in live engineering for small venues is managing the contribution of the backline amplification to the overall sound. Guitar rigs are often the most problematical, as guitar players usually want to turn up their amps to their own personal comfort level, to achieve the right amount of sustain and distortion. This can mean, however, that the guitar sound coming off the stage is already louder than it needs to be to balance with the rest of the band, before you even think about miking it up.
Effectively, the sound engineer has been deprived of the ability to mix the show. His/her only options are to turn up everything else (assuming that's possible without running into feedback) or to attempt the delicate task of negotiating with the guitar player(s) about their on-stage level. If backline amps can't be turned down without compromising the guitar sounds, they can at least be pointed somewhere other than straight out into the audience, but high levels on stage will inevitably make their way into other open mics as 'spill', compromising both the guitar sound and the other sources.
Of course, there was a time when the only way to get a good guitar sound on stage was to use a high-powered tube amplifier and a stack of speaker cabs to get the sound directly out into the audience. Then it became fashionable to use smaller tube amps miked up into the PA, but these are still pretty loud on stage, relative to acoustic instruments or vocals. In the last few years, however, digital amp-modelling preamps and pedals have become good enough to be considered a viable alternative even by discerning players, and guitarists are increasingly looking to such products to solve the problem of tone being dependent on level.
The first product to really get this message across to guitar players was undoubtedly the Line 6 Pod— still in production after nine years, and now sounding even better in the form of the Pod XT and its variants — but there are now many alternatives from Roland/Boss, Digitech, Korg/Vox, Behringer and Zoom, to name just a few. There are also analogue alternatives, often including real tube circuitry, that can give you a first-class guitar sound right out of the box, although the majority of this type don't include effects, so you may need to combine them with other pedals to create your signature sound. Guitar sounds remain highly personal, however, so there's no way to say which of these is the best, or even whether you'll actually be happy using any of them instead of a real guitar amplifier.
The big advantage of all the digital devices is that they emulate not only the amplifier but also the speaker cabinet, the way the cabinet would be miked in the studio and the entire effects chain, giving you a DI-ready sound — or, in fact, a selection of DI-ready sounds, as the vast majority allow you to save multiple user patches, ready to be called up when you need them.
Although digital modelling preamps initially took off as a convenient and repeatable way to record the electric guitar in the studio, it didn't take long for musicians and manufacturers to work out that they could be just as useful on stage, not least because they enable you to reproduce your sound at any level. However, there's a whole lot more to getting a good on-stage sound than simply plugging your Pod into the front of a combo.
A modelling preamp is generally optimised to produce the best sound when fed into a full-range sound system with a flat frequency response, such as a PA system or a studio monitoring system. Guitar combos, on the other hand, have inbuilt tonal voicing that varies from one combo to another, and tone controls that also affect the sound. Usually this results in a sound that gets brighter towards the upper mid-range but then falls off rapidly above 3kHz or so, where the guitar speaker's response starts to drop away. If you simply plug a modelling preamp into the front of your combo, you'll probably end up with an aggressive, harsh sound, lacking in low end, and adjusting the amp's tone controls is very unlikely to be able to fix the problem.
Manufacturers soon began to add an output-mode switching system to compensate for the coloration introduced by a typical guitar stack or combo, and DI preamps often now feature dedicated connections with specific voicings for feeding into guitar amps on the one hand and full-range systems on the other. Of course, there are no typical settings that will work for every amplifier, as each one has its own electronic voicing, and the speaker and cabinet will also affect the tonality in different, unpredictable ways. Nevertheless, starting from an output specifically voiced for a guitar amp, you should be able to get somewhere close to the sound you want if you spend a little time tweaking the amplifier tone controls.
If you always use the same amplifier with your preamp, you can fine-tune the patches in your preamp to get the sound just the way you like it. One point that I must stress, though, is that you should always use your guitar amplifer on a clean setting, as the preamp will add any distortion you require and it may not react well to additional distortion added later in the signal chain (you can add overdrive pedals and so on before the preamp if you wish to, though, just as you can with any conventional guitar amplifier). It's good practice to do a couple of experiments to ensure that the level coming out of your preamp is roughly the same as the level you get when you plug your guitar directly into the amplifier. If the level is too low you may not be able to get the sound loud enough, whereas if it's too high it may cause your guitar amplifier to distort in a way that compromises the tone you intended. Remember that the goal is to achieve the tonality you want without needing to have the on-stage amp at a high level, so it's best to let the preamp do all the distorting and set your amp to be no louder than you need in order to hear it.
There is another interfacing option, provided your guitar amplifier has an effects-loop return jack or a line input that bypasses the preamp entirely. In this case you can use the 'PA' (or studio DI) output setting of your preamp, although the character of the speaker cabinet will still influence your tone. If you're lucky enough to have a preamp with a setting specifically for plugging into a guitar-amp power stage, you should certainly try this, as the sound will have been pre-voiced to take account of a typical guitar speaker's response. Again, no general compensation will be right for all speakers, so you may need to tweak your preamp patches to get the sound just right, but it's a step closer.
I tend to use the guitar amp's power-stage input where possible, as it enables me to use my other preamp output (they're invariably stereo) to feed the main PA without compromising the tonality too much. You'll have to experiment to see whether the 'PA' (flat DI) or 'guitar power-amp' output setting gives the best result, but in my experience you can often get away with using the flat DI setting to feed your amp's power stage with this kind of split arrangement. That way the PA gets an appropriate tonality that needs no more than a little gentle EQ to optimise it.
At smaller gigs, the direct sound from the amp combined with the sound via the PA system creates a pseudo-stereo effect (albeit with two sides and one middle!), but don't worry too much about this, as most guitar effects sound perfectly acceptable in mono. On the other hand, if stereo effects are important to you a far simpler option is to do away with your guitar amplifier altogether, plug your preamp directly into the PA in stereo, then use the PA's full-range foldback monitors to let you hear yourself as you're playing. This approach does away with the uncertainty of which voicing option sounds best, as you always stick with the straight DI setting, but it takes quite a leap of faith for guitar players to give up their amplifiers altogether.
A halfway house for the less confident is to buy your own full-range monitor or small keyboard amp and then split the feed from one of the preamp outs to feed both the PA and the monitor. A cheap DI box with a through connection is fine for this purpose. You can also use the same approach if you feel that your guitar combo (using whatever input option is available to you) produces an acceptable on-stage sound when fed from the full-range DI output of your preamp. The advantage is that you can then adjust your volume as normal, so that you feel comfortable playing. To avoid the problem of the on-stage sound being too loud, it can help to place the amp or monitor in front of the player and pointing upwards, monitor-style, rather than behind the guitarist pointing forwards.
I often use a Pod XT Live at my own gigs and, depending on the size of the gig, I sometimes rely entirely on the main PA and monitoring, or I use an amplifier with a return jack (via the DI setting, so as not to colour the sound being sent to the PA) to give me my on-stage sound. From my experiences with this type of rig, I would strongly advise against trying to optimise all your sounds when you're sitting in front of your studio monitors or hi-fi speakers, as everything changes when you're playing with other performers at higher sound levels. I tend to do the preliminary programming of sounds and effects in my studio, but at rehearsals I'm constantly refining the patches (mainly via the tone controls or choice of speaker-emulation model) to get the sound that works best with the band. It also helps to program patches in the order you need to access them, so that you don't have to change banks mid-song.
Most preamps only have four or five patches per bank, but unless you have very sophisticated requirements you can probably set up all the sounds you need for a typical gig, if you're careful. Even if you need to increase the overdrive for a solo, you don't necessarily have to use two patches, providing your floor unit lets you switch off the modelled pre-pedal effects, such as overdrive and distortion. For example, I'll often set up a sound that's more or less clean with the guitar turned three-quarters up and slightly edgy with it flat-out. Then I'll add an overdrive, such as a modelled Tube Screamer, to the front of the chain and use that to set the degree of overdrive and level increase needed for the solo. The same applies to patches that use echo, where you need a different echo time for each song. Often you can simply use the tap-tempo input to enter a new delay time, rather than changing to another patch.
Ultimately, whether this approach is for you or not depends very much on the type of guitar sound you prefer. Purists may always want to stick with their boutique tube amps, but if you need to be able to switch between multiple sounds during the course of an evening, and especially if you need to achieve the singing sustain of a flat-out tube amp at low levels, a digital modelling preamp may be the most effective solution, benefiting both your sound and the overall sound of the band Don't dismiss it until you've tried it!