BOSS MG80 / Vox Valvetronix Modelling Valve Guitar Preamp LAB
80 watt, solid state / 2 x 5″ speakers / 1/4″ inputs high/low / Gain, Volume, Master Volume, Bass (w/Pull Warp control), Middle, Treble, Presence / 1/4″ Headphone Jack / optional 1/4″ output for ext 8 ohm
The Vox Valvetronix Tone Lab is a spin-off from Vox’s AD60/120VT modelling amplifiers, which take the approach of combining digital modelling and signal processing with both solid-state and analogue amplification stages, rather than trying to emulate absolutely everything digitally. Conceptually, the Valvetronix Tone Lab fits into the same camp as products like the Line 6 Pod (amp/speaker modelling plus effects) and can be used either for DI recording or to feed an amplifier for live performance. However, whereas the Pod takes the all-digital approach, the Tone Lab includes a miniature power-amp stage based around a 12AX7/ECC83 dual-triode tube, where some clever ‘pseudo-transformer’ circuitry has been used to make this influence the sound much as a real power stage would. Such innovative technology has to be given a fancy name, and in this case it is the Vox Valve Reactor. Much of the effort has gone into recreating the effect of an output transformer without actually having one, an important factor given that the output transformer and the way it interacts with the loudspeaker load forms a crucial part of the tube-amp sound. The Presence control on those amps that feature one also relies on the output transformer — rather than simply being EQ as you might imagine, Presence controls adjust the amount of negative feedback in the power amp section from the output side of the transformer, which means that the effect is actually quite complex. Furthermore, this miniature power stage automatically switches between Class A and Class AB depending on the amp model selected, and the output tubes of the original amp are shown in the display window for whatever model is active. Vox AC15s and AC30s used Class-A circuits, whereas the majority of Marshall and Fender designs, other than very low-power models such as the Fender Champ, have Class-AB push-pull output stages. Not only does the correct choice of power amp characteristic affect the sound, but it also changes the way the guitar feels to the player, which is a vitally important element of any guitar amplification system, and one that probably makes no sense at all to keyboard players!