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Vox Valvetronix

Modelling Guitar Amplifier By Paul White
Published September 2002

This hybrid physical modelling, valve and solid-state design, presented in a classic AC30-style format, aims to offer the best of all possible worlds. How far does it succeed?

The Vox Valvetronix Amp (designed by Korg, who now own title to the Vox name) is a modelling amplifier with a difference -- instead of trying to use digital modelling to emulate absolutely every aspect of the sound, the designers have instead created a hybrid of a conventional guitar stage amplifier and a modelling amplifier. Physical modelling is used to take care of that part of the amplifier responsible for voicing, EQ and overdrive characteristics, and the built-in effects are all-digital too. Then the digital technology is married to a hybrid valve/solid-state signal path feeding a pair of 12-inch Vox loudspeakers, mounted in an open-backed cabinet styled very closely on that of the original Vox AC30. Even the panel cosmetics and pointer knobs are classic Vox. Indeed, if you didn't examine the panel controls you could easily believe the Valvetronix was an AC30.

VOX VALVETRONIXPhoto: Mark EwingBecause effects like reverb sound better in stereo, each speaker is fed from its own power amplifier. A number of power settings are available, via a rear-panel selector switch, to allow optimum audio performance at different sound levels. The available power settings on the 120W review model were 1, 15, 30 and 60 Watts per channel (a 60W Valvetronix is also available). To allow the user to gain a wider stereo spread, there are also sockets for adding external 8Ω speakers. There's an optional foot controller (not available for review) that facilitates easy patch switching, as well as pedal control over certain of the built-in effects (such as rotary-speaker speed or wah) and volume. A stereo effects loop allows external rack effects to be integrated into the system and, for use with a PA or recording system, there's also a stereo line out and a headphone outlet with volume control.

Control Zone

Everything about the Valvetronix is extremely intuitive. It utilises familiar guitar-amp controls (Gain, Volume, Treble, Middle, Bass, Presence and Master volume), augmented by a rotary Amp Type selector switch, plus dedicated effects sections that each have controls very similar to what you'd expect on a simple stomp box.

There are four effects sections in all, the first of which emulates pedals connected before the amplifier, while the remaining three deal with modulation effects, delay and reverb. All that remains is a very simple patch-memory section, where up to eight banks of four programs each can be accessed. Pressing the Bank Up and Bank Down buttons together puts the amp into manual mode, so that what you dial up on the control panel is exactly what you get. A single numeric display shows the bank number -- not, as you might expect, numbered 1-8, but 1-4, then 1-4 again with a dot after the number. Four numbered buttons with status LEDs access the programs within the currently selected bank. In this area there's also a guitar tuner, which uses the patch buttons' status LEDs as a readout.

Amp & Effect Types

A fair description of the amp models available might be 'the usual suspects'. Oblique references are made to classic Marshall, Fender, Boogie, Soldano and 'boutique' models, though the only types named directly are, not surprisingly, the Vox amp models (AC15, AC15 Top Boost, AC30 and AC30 Top Boost). There are two input jacks for high- and low-sensitivity pickups, just as there was on the original AC30. In conjunction with 20-bit conversion at the input to the digital section, this means that there's no need for any additional gain trim.

The first set of effects is designated 'Pedal', because these treatments come before the amplifier in the signal path. Here you'll find Compressor, Acoustic (acoustic guitar simulator), Vox Wah, Autowah, U-Vibe, Octave, Treble Boost, Tube OD, Fat OD and Fuzz. They are all addressed using just two rotary controls, labelled Drive and Level, the functions of which change slightly depending on the pedal type selected. Most of these effects can be used without an external pedal, with the exception of wah, which needs a pedal to sweep through the wah filter range.

To the right of this area on the control panel is the modulation effects section, where Chorus, Flanger, Phaser, Tremolo or Rotary effects can be chosen. These have Speed and Depth controls, with the option of controlling Speed via the external pedal, if connected. When the Rotary effect is being controlled in this way, the speed ramps up and down gradually, as it does with the real thing.

Delay effects comprise a straight delay, a tape-style delay (with limited bandwidth and a bit of degeneration thrown in), and a multi-tap delay. A Tap Tempo button sets the repeat rate, and there are rotary controls for delay Level and Feedback -- very simple, but perfectly effective. Finally, there's the Reverb, offering a choice of Plate, Spring and Room, with just a single knob to adjust the relative reverb level.

As the amplifier was designed in conjunction with the Korg Toneworks team, it comes as no surprise that the effects function to the same high standard as Korg's range of dedicated guitar-processor pedal effects. All the effect types have status LEDs, so it's really just a matter of using the selector button to step to the one you want, then adjusting settings with the rotary controls.


While the Valvetronix has two line outputs that can be used for direct recording, there's no official way to turn off the internal speaker. Both the line outs and the headphone out are controlled by the same knob on the rear panel, and plugging in headphones does mute the amplifier, as you'd expect. Of course, you don't want your headphones buzzing away when you're trying to record, so if you need to DI the amp you can simply plug in a stereo jack with nothing attached, to fool the output into muting.

The line output is fed through an integral speaker simulator. Unfortunately, I found that it didn't sound nearly as nice as the speakers, being thinner and a little buzzy. Even readjusting the EQ wasn't a complete solution. I also had problems with ground-loop hum as soon as I connected the amp into my mixer, so my conclusion is that the best way to record this amplifier is to mic it up. This is reasonably convenient, given the choice of power settings; even the 2W setting produces a powerful sound, with no loss of character.

The Sound

Taking the amp sounds first, I was quite favourably impressed with the Valvetronix, not only because it captures the essential character of the different amp types, but also because it seems more responsive than some of the modelling amps I've tried, and it has a reasonable playing 'feel'. It is also honest in modelling the leaden, overstuffed sound of the original Vox AC30 (I sold both mine for 30 quid each and never looked back!), though the AC30 Top Boost is a different story altogether -- this model really sings. In fact, the only amp model that I think really doesn't do full justice to the original is the 'Recto', no doubt based on the sound of a Mesa Boogie, which I felt to be over-edgy and lacking in weight. The American Tweed-style amps do work well, however, as do the classic British rock models, and if any of these are lacking in overdrive you can always use the Pedal section to add Tube OD, Fat OD or Fuzz. For blues, I really like the Tweed or AC30 Top Boost models, with a little compression up front and a hint of spring reverb. The only problem I encountered was a fairly loud buzz if I wasn't touching some metal part on my guitar. While this is partly down to the quality of the guitar screening (I was using noise-cancelling pickups), it is also related to amplifier input-stage design, particularly impedance. In comparative tests, my other amplifiers fared better in this respect.

VOX VALVETRONIX controls.Photo: Mark Ewing

There are few surprises in the effects section, though the U-Vibe and Octave settings in the pedal section are rather unexpected. These work much like their pedal equivalents, so when using the Octave (octave divider) setting you need to play monophonically. U-Vibe is based on the Univibe pedal and sounds like a hybrid of phasing and modulated EQ -- perfect for those slow Hendrix numbers.

In the main modulation section, the chorus stands up well against analogue pedals, while the flanger is the closest I've heard to an Electro-Harmonix Electric Mistress for a long time. While not entirely accurate, the rotary effect is nice, too. The unproblematic phaser and tremolo do pretty much as you'd expect.

In the delay section, the Tape Delay gives a good impression of the overall tonality of a tape-loop echo machine, while the Multi-tap version is great for those old 'Surf' sounds and Shadows covers. Delay settings are stored within a patch, but you can quickly reset the repeat rate using the Tap button.

Finally, there's the reverb, which is pretty limited in that you can't vary the decay time, but sounds absolutely right for use with a guitar amplifier. The Spring emulation is especially effective. All three variations have a hint of spring-like flutter, but on an electric guitar they sound quite authentic.

Summing Up

While modelling amps have yet to equal the amplifiers they set out to imitate (in terms of feel as well as sound), they're getting closer all the time. The Valvetronix comes closer than most, no doubt due to its ingenious hybrid design, which features a miniature valve power stage followed by a pair of 60W solid-state amplifiers. I found it much easier to get a usable and believable sound than I did from my old Line 6 Flextone combo, but then the Flextone is now quite an old design, and was also very much cheaper than the Valvetronix.

Because of the less-than-ideal speaker-simulated line output (see the 'Recording' box), my recommendation is to mic the amp rather than to DI it (which you can do without deafening the neighbours, thanks to the switchable power settings). That being the case, the Valvetronix will probably appeal most to the gigging guitarist who wants an amp capable of emulating most of the classic guitar amp and effects combinations at the touch of a button. If that same guitarist has a project studio, the Valvetronix also makes a great recording amplifier, because it sounds and feels like a real amplifier, despite its chameleon-like sonic abilities. It may not be the cheapest modelling amplifier around, but it looks and plays like a true thoroughbred.


  • Very friendly user interface.
  • Sounds and feels very much like a valve stage amp.
  • Can be switched to a number of power settings, from a couple of Watts to 120 Watts.
  • Includes simple yet good sounding on-board effects.


  • Speaker-simulated line output disappointing.


This is one of the better-sounding modelling amps I've used to date, but to get the best results from it in the studio you need to mic it up, not DI it.


120W version £799; 60W version £599. Prices include VAT.

Korg UK Brochure Line +44 (0)1908 857150.