Modelling Amps in the Studio

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Most recording guitar players have tried hardware modelling devices, such as the Line 6 Pod, and software amp emulations from the likes of Avid, Native Instruments, Line 6, IK Multimedia and so on. Most would agree that for certain styles they can produce fantastic results, all without annoying the neighbours, but there are occasions where nothing beats the experience of playing through a nice-sounding amplifier and then sticking a mic in front of it. Not only does mic’ing an amp avoid any latency issues, it also provides the player with the familiar experience of hearing their sound come out of a guitar amp rather than out of a pair of studio monitors. It also allows the engineer full flexibility in choosing the microphone type and position in order to capture exactly the right sound for the track.

Most traditional guitar players would agree that it doesn’t get any better than a boutique valve amp, cranked up until it hits the sweet spot — and they’re right — but even that dream scenario isn’t without its challenges. The best valve amp sounds are created when both the preamp and power amp are driven hard enough to hit that magical sweet spot, and in the case of most amps designed for stage use, that’s far too loud for home recording. A master volume control really doesn’t solve the problem because although that allows you to push the preamp hard, the power stage is no longer contributing its magic.

Of course you could buy a very small valve amp specifically for recording, and some of these sound wonderful, but even five watts of valve power can be fearsomely loud. What’s more, most valve amps have specific tonal character that might not suit all applications. And even a small valve amp needs to be played through a suitably large speaker to avoid it sounding boxy, so while you will find many low power valve amps that can do one thing really well, they probably won’t be any smaller than a stage amp and tend to be relatively expensive.

Modelling amps that combine DSP processing with a solid-state power amp have been with us for a while. They certainly look like an attractive proposition for the recording guitarist as their sound can be recreated at any volume from a whisper upwards while their on-board effects, amp and speaker models hold the promise of a tonal adventure park with virtually unlimited options. Though companies such as Line 6 and Roland started the ball rolling in this area, even traditional valve amp stalwarts such as Fender and Marshall have started integrating digital effects and modelling technology into their products. These modelling amps certainly meet the needs of tonal flexibility, scalable volume and affordability, but there are still those players who’ll never be happy with an amp that doesn’t have at least some valves in it.

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One of the neatest solutions in recent years is the hybrid amplifier — one that combines digital modelling with real valves and real speakers. A good example is the recent Line 6 DT 25, designed in collaboration with Reinhold Bognor. This is available as a combo or as a separate amp head, and teams a modelled preamp stage with a full-scale valve output stage. Indeed it goes rather further than that because the valve stage (one 12AX7 plus a pair of EL84s) can itself be configured in a number of ways via a built-in electronic switching matrix to emulate different amp types. For example, it can operate in class A/B mode when you’re after a Fender or Marshall type of vibe or can switch to Class A for a Vox or Matchless tonality. The feedback around the power stage also changes to match the mode you select and the output valves can be set to operate in either triode or pentode mode offering even more tonal scope. I know some players will resist the idea of a modelling front end but my bet is that these same players feel no pangs of guilt when plugging a solid-state overdrive pedal or a digital delay into the front of their valve amp. Ultimately what matters is the result. Does it sound like a real amp, does it feel like a real amp and can you get the sound you want to record at a realistic volume level?

In the case of the DT25, I’d say that the answer to the above questions would be yes — it even includes a low power mode that brings in some extra modelling to help create the character of an overdriven power amp stage allowing you to set a much lower master volume level without losing tone. This is just as well as with a 25 Watt capability in Class A/B mode and 10 Watts in Class A mode, the DT25 is loud enough to play pub gigs. Even in low power mode, the final output still comes via a real valve power stage with a real speaker pushing real air, which combined with the magic of modelling gives you the opportunity to explore a far wider range of amp tones than any conventional valve amp can offer. Even the built-in modelled spring reverb sounds wonderfully authentic — though it doesn’t go ‘sproing’ when you kick it! The amp also includes an effects loop for adding those effects that need to come after the preamp, and if you already own a POD HD floor unit, you can use the built-in Line 6 Link connector on both devices to combine the variety of amp models and effects available in your POD HD with the power, flexibility and tonal authenticity of the DT25.

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Another approach to hybrid amp design comes from Vox and I have to admit to being a real fan of their Valvetronix technology. What’s more these amps are unbelievably inexpensive. Vox have carried this technology through a number of versions of their VT amplifier range as well as their Tonelab stand-alone guitar effects products so it has been tried and tested now for a number of years, getting more refined with every revision. Again they start out with a modelled front end, so all the amp types, tone controls and effects are created using powerful DSP chips. The really clever part though is their valve stage, which is designed around a single dual-triode 12AX7/ECC83 valve in a miniature power amp circuit capable of delivering only around one watt maximum into a specially designed load that makes the valve ‘believe’ that it is feeding into a traditional output transformer and speaker. This valve stage switches from Class A to class A/B mode depending on the type of preamp model selected so gain retains the correct character of the type of amp being emulated.

The output from this mini power stage then feeds into a clean, solid-stage amp that boosts the power to an adequate level to drive the speaker with models available from 15 Watts to in excess of 100 Watts depending on your requirement. You can almost think of it as being akin to a small valve amp being fed through a PA system. For recording, I think the 30 and 50 Watts models are best-suited as their 10 and 12 inch speakers deliver the required amount of low end authority, though there’s also a 15 Watts version with an eight inch speaker if your needs are more modest. The great thing about all these amps is that no matter how low you turn the volume on the solid-state output stage, you can still push that miniature valve power stage as hard as you like so you get a consistent and highly believable sound at any volume level from ‘don’t wake the parents’ to full-on gig battle conditions. All the essential effects such as modulation and delay are built in along with an independent reverb and on the current VTX models you can store eight presets for fast access via the front panel or from an optional footswitch.

I use an older version of one of these Vox amps in my own studio and usually find myself gravitating towards the AC30 Top Boost emulation as it lends itself to most musical styles and also responds really well to a good overdrive pedal. I’ve tried many more expensive amps but keep going back to it. Back in the day I owned a couple of original AC30s and they sounded great, but the problem was that by the time you hit the sweet spot, the audience was already leaving clutching their ears! The Valvetronix amps really nail that AC30 sound, and at a civilised volume, but if the AC30 sound isn’t your thing, the VTX amps cover all the amp style essentials from clean US combos, via steaming Brit stacks to US High Gain and boutique metal amps.

I’ve done recordings using both these modelling amps and in most respects they really do manage to combine the best aspects of modelling flexibility with the sonic authority and responsiveness of a good valve amp. Sure there will always be individual valve amps that do a better job in a specific tonal area, but where you need to be in full control of both your volume and your tone, but you don’t want to rely on a DI modelling solution, I really think hybrid is the way to go.

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About Author

Paul White is editor in chief of "Sound On Sound" magazine where he shares his musical and recording experiences with other gear addicts. Paul plays live with the 'Pewke Band' and as part of an acoustic/electric guitar duo with Ray Mytton. Paul White Editor In Chief - Sound On Sound Magazine www.soundonsound.com

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