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Vox MVX150H

Guitar Amplifier By Bob Thomas
Published November 2019

Vox MVX150H

Vox's hybrid approach to electronics has yielded a natural–sounding amp that won't break your back.

Since 2017, the NuTube miniature dual-triode valve has been employed in the preamp stages of Vox's small-format VX and MX amps, but in their new MVX150H amp head, this tiny tube steps up to the big-time. As with the earlier Valvetronix range, the final 'welly' comes courtesy of a Class-D power amp, but those amps used modelling in the preamp stage. In contrast, the MVX150H employs a 6P1 in the channel preamps and in the power amp of this two–channel, full–size, 150W guitar amp head — an intriguing idea, which presumably is intended to deliver a more tube-amp-like playing experience.

Overview

From the front, the MVX150H looks just like a conventional two-channel head. On the extreme left of the control panel you'll find the single input jack, with the Ch1/Ch2/FSW (footswitch, not included) mini-toggle switch sitting above it. The Channel 1 controls (Gain, Tone and Volume knobs plus Clean/Crunch, Bright and Fat mini switches) come next, and a blue LED lights when the channel is selected. Channel 2 retains the indicator LED, the Bright and Fat switches, and the Gain and Volume knobs, but also adds a more comprehensive Treble, Mid and Bass EQ and a Mid-Shift switch, and toggles between Rhythm/Lead rather than Clean/Crunch. A global, footswitchable reverb is available, and both Presence (higher frequencies) and Resonance (low–frequency cabinet thump) are there to tailor the overall output to your taste. Finally, there are two Master Volume controls, the second of which can only be selected via a footswitch.

The rear panel starts out quite conventionally with the IEC input to the multi-voltage (100-240 Volts AC) power supply, which is followed by the soft-switching momentary On/Off switch and the now commonplace Eco Mode On/Off switch, with the power-off period being 30 minutes. Restarting after the power-off requires powering the amp up again.

Sitting next to these is an unusual Wet Only output — an independent loudspeaker-level quarter-inch jack output that, when active, is driven by one half of the MVX150H's power amplifier. Using this output removes the reverb and effects return 'wet' signals completely from the MVX150H's speaker outputs. This is a Bridge Tied Load (BTL) output, which means that the socket's tip and earth form the signal path, and that therefore there is no connection to earth. This jack is only active when a plug is inserted, and is followed by the rotary 4/8/16 Ω impedance selector switch for the MVX150H's two main loudspeaker outputs. These, in turn, are followed by a rotary Power Level selector switch that ranges from Mute, through 1/1000, 1/30, 1/5 and 1/2 to Full power. Full power is impedance–dependent (150W into 4Ω, 75W into 8Ω, 37.5W into 16Ω). If you're using the Wet Only output to carry your effects, then the output power is half that in each speaker.

Next in line is the quarter-inch jack Emulated Line Out, which carries the sound of a "well-known dynamic microphone" in front of a guitar loudspeaker — my guess is that this is intended to sound like a Shure SM57 — and has an associated level control. Following these are the TRS quarter-inch jack sockets for two sets of twin footswitches, the first of which switches between Ch1 and Ch2 and between Master 1 and Master 2, with the second switching the effects loop and reverb off and on individually. These are followed by the send and return for the mono effects loop, which can be switched between series and parallel operation.

Finally, on the extreme left of the rear panel, sit separate Bias voltage controls for the Ch1 and Ch2 NuTubes. Decreasing the bias of a NuTube drops its gain and results in a looser, more saturated vintage feel, whereas increasing it provides more level, a tighter response and a smoother tone, with more headroom.

It isn't immediately apparent when first switched on, but the MVX150H has an internal fan. It's quiet, though, and I can't see it causing problems in the real world. The MVX150H didn't get overly warm in normal use, but things could be different in a hot, sweaty club with everything set to 11!

The rear panel of the MVX150H includes a novel Wet Only output.The rear panel of the MVX150H includes a novel Wet Only output.

Sounds

On its high-headroom Clean setting, Channel 1 can sound a bit plain at low gains, but wind the Gain control past two o'clock and you'll first find edge, and then the start of touch-sensitive crunch that has overtones of Vox and Fender amps. Switch to Crunch mode and you'll find Vox-ish chime to hard-pushed Fender-ish sounds — both of which are sweetly touch-sensitive. The Bright switch adds a tight overall edge that can be dialled back with the Tone control's high-cut action, and the Fat switch adds weight and girth. If you're into pedals, this is the input for you.

Channel 2 brings you into overdrive and high-gain territory, with its Rhythm setting capable of delivering a familiar Vox crunchy chime, while the Lead setting, aided and abetted by a low-end 4x12 cabinet thump courtesy of the Resonance control, does one of the best JTM45 impressions that I've heard for a while. Get a bit more hooligan with the Gain control and the channel and master volumes and you can sculpt stunning, superbly defined high-gain sounds that wouldn't sound out of place in any really heavy metal genre.

The Emulated Line Out, taken after the Master Volume section, delivers a reasonably good facsimile of the MVX150H heard/miked via a cab, and would certainly work well live as a FOH feed. In a studio situation, it would be perfectly adequate — but that said, I was impressed enough with the sound of the Celestion Redback (see 'Cabinet Meeting' box) to want to mic this cab up every time.

This combination sounds great and yet it is so much lighter to lug around than an all-tube 100W head and a 4x12.

So overall, then, the MVX150H is a decent amp. But I do have a couple of personal caveats. The first is that I feel the amp's designers have missed a major trick with their implementation of the Wet Only output and the effects loop. Don't get me wrong, the idea of an amplified Wet Only loudspeaker output to give us all the option of a dry/wet rig is a great one, but I can't help feeling it would have been much better if they'd made both the effects return and the internal reverb stereo, and given us the option of running a stereo setup with a dry guitar down the middle and the reverb and effects returns panned across the two cabs. That would have been killer! (Mind you, you could still achieve that effect by running from the send of the effects loop in parallel mode to a Larry Carlton–style setup of an external stereo effects unit feeding a powered PA cab on either side.) Speaking of the internal reverb, I'm not a huge fan. A reverb's sound character is a question of personal taste, of course, but to my ears it sounds more like a hall than a spring, and it just doesn't work for me.

Despite the very realistic efforts of the Resonance control, the experience of playing through the MVX150H and the 1x12 BC112-150 still isn't quite the same as playing through a 100W tube amp and a 4x12. It's not that it's bad by any means — it certainly feels much more 'real' than playing though an amp modeller, and that's probably due in some part to the interaction between the different tube stages. But I did still feel that the sound hadn't quite managed to get 'into the room' with me, something which could, I suppose, be due to the power-stage tube feeding a Class-D amp rather than a reactive load (like a speaker). With the cleaner-into-crunchy sounds and at lower volumes, this wasn't a particular issue for me, but once I wound the distortion and the volume up, the sound seemed to retreat towards the speaker cab just a little further than I'd hoped. Nonetheless, the amp's versatile range of sounds — which behave pretty much as you'd expect from a similarly structured all-tube amp — give you something to work with, and I never felt that I'd reached a dead end while I was experimenting.

Published November 2019