If I were to ask for anyone not familiar with the name (or memory) of a Vox AC30 to raise their hands, not many metacarpi would grace the sky! Many modern musicians probably remember cutting their teeth on a "Vox box", stacked up on beer crates, between the inevitable piano tuned to concert pitch and a juke box — good old days!

I was surprised when asked to review a Vox amplifier; I was expecting something totally different, up to the point of unpacking. I believe they say "surprises always come in great heavy packages", so here goes.

Cabinet

The 27" x 20" x 10" cabinet was neatly hidden beneath a black plastic cover with three cut-outs for the handles. Removing the cover showed these carry handles to be of a heavy-duty suitcase type mounted on top of the cabinet; one at each end and one in the centre.

Black grained, cloth backed plastic material covers the ¾" chip board and plywood construction. Edge facings and corners are radiused, but the eight plastic corner cups are destined for an early retirement. Metal fittings would be stronger. The front plywood speaker baffle board is fitted to an internal one inch square wooden frame work. Two sides are doubly secured to the top and bottom panels using four large corner wedges; very strong, and necessary for taking the weight when carrying. A double panel open back construction allows good airflow, but does nothing for standing waves. Of course, wires and attachments can be neatly stowed away inside without hassle, along with the drummer's broken sticks and empty cigarette packets.

Around the front, a large gold finished plastic Vox motif cheers things up a bit, along with a gold strip separating the baffle covering from the traditional diamond pattern speaker cloth. Completing the aesthetics is the inevitable white edge trim. Three recessed plastic ventilation grilles and a lengthy control panel complete the cabinet top, and the 70lb baby stands proudly on four rubber feet. Perhaps castors would have been better, instead of feet, to prolong an active spine.

The overall visual impression one receives is of a clean, straitlaced, no nonsense, get down to business amplifier and indeed, that's just what the AC30 is.

Controls

Recessed in the back of the cabinet top lurks a control panel sporting an array of sockets and pointer knobs. The panel is finished in RAF grey with trim and legend in gold. Musicians are obviously intended to stand behind the amplifier when reading the control descriptions. As most of us would perform in front of the stage, with cabinets stacked behind, a good memory of control positions is essential, if twisted necks and injured drummers are to be avoided

Looking at the controls (from behind) from left to right; we have two vibrato/tremolo channel input sockets, two normal channel input sockets and two brilliant channel sockets.

All input jacks are standard 0.25 inch fitting. The outer three sockets are high impedance inputs (not indicated!) rating 250k; while the inner three sockets are of lower impedance, rating 68k, and of lower sensitivity.

The first two rotary controls are vibrato/tremolo speed and effect select. Three volume controls follow, one for each input channel, and tone correction is provided for with treble, bass, and separate treble cut controls. A chrome toggle on/off switch controls the volts, a red LED serves to indicate switch on, while a panel mounted 3.15A fuse monitors continued good behaviour.

After removing the rear cabinet covers I discovered the 220/240V voltage selector switch, mounted on the chassis beneath the control panel. A small recess had been made in the top back cover, into which the switch slider fitted. Finally, control of the effects was via a remote footswitch, complete with eight feet of connecting cable, and wired directly to the amplifier.

Visually, the control panel appears drab and somewhat austere, probably due to the black pointer knobs and dark colours used.

Circuitry

The AC30 has an all valve line-up using such stalwarts as five ECC83s, one ECC82 and four EL84s. Obviously one way to achieve true "valve sound". All valves, except for the EL84s which are retained by spring clips, are fitted with screening cans. HT rectification is by four silicon diodes and large 450V reservoir capacitors. Valve bases are wired to two small PCBs holding biasing and coupling components. A massive output transformer couples the amplifier to two eight ohm speakers connected in series. I must admit, they look very much like Group range Fanes complete with VSL labels glued on.

Vibrato and tremolo are the only effects built in. Tremolo (amplitude modulation) has preset depth as has the vibrato circuitry. Modulation rate (speed) is variable from four to twelve cycles (4Hz to 12Hz) but I would prefer a slower rate (1Hz) for a chorus quality. A rotary switch selects either effect (with a loud plop).

The effect foot switch cable along with the speaker wires are longer than required, to allow removal of the substantial chassis without disconnecting everything. The chassis bolts on to a 10mm plywood base and slides into place from the rear of the cabinet. Two wooden wedges support the chassis at each end, and tighten up to hold everything in place. Access and removal for servicing etc is simple and fast; often a problem in some units, but not here.

Test Results

Power output:	33W RMS into 16R
Distortion:	5% THD @ 33W, 1kHz
	1.5% @ 18W (-3dB), 1kHz
Input sensitivity for rated output:
(Normal and vibrato channels)	High = 15mV, Low = 30mV
(Brilliant channel)	High = 10mV, Low = 20mV
Power bandwidth:	15Hz to 12kHz (-3dB)
(Brilliant channel):	400Hz to 15kHz (-3dB)
Tone controls —
	Treble: +14dB @ 10kHz (brilliant channel only)
	Bass: +10dB @ 100Hz (brilliant channel only)
	Cut: -3dB @ 1kHz, -23dB @ 10kHz
Input overload margin:	+16dB (100mV) on normal input.
Hum and noise:	-45dB, volume at maximum.
Vibrato/tremolo speed:	4Hz to 12Hz.

The Sound

Plug in, switch on and... where's the noise? Being spoilt with modern "instant" technology, I forgot that valves prefer a gradual start to the day. Time for a quick coffee and tune up the old guitar. The statutory ten minutes passed and all was ready, judging by the quantities of hiss, hum and heat in the room. Switching the tremolo off, along with turning back volume and treble controls, removed much of the problem.

First I plugged in to the vibrato/tremolo channel, and played a few bars with tremolo effect on. The going is pretty heavy without control of depth and I developed a feeling of motion sickness, but nevertheless, the effect works adequately. Switching to vibrato gave an effect similar to a weak tremolo, almost not there at all. Perhaps this particular sample needs a bit of tweaking, or an input signal rich in harmonics such as a synth or organ. So, not over excited by the effects department on this one. Incidentally, the bass and treble controls have no effect on this channel.

Changing inputs to the normal channel produced a richer sound with increased depth over the previous channel. Winding up the volume control produced a fantastically loud over-driven sound, and good smooth sustain without signal break-up, so often apparent in transistor units. (Back to the old valves versus transistors battle!) As before, tone controls were inoperative on this channel, but who needs them? Great, plenty of drive, a degree of top cut and filtering ideal for good rock and blues guitar work. This amplifier produces a sound output apparently closer to 100 watts than to 30 watts, and certainly had not lost any of its ancestor's performance.

Finally, I tried the brilliant channel. As the description implies, this one has better high frequency response, and control of bass and treble at last. Full treble boost also cut bass response here, but adequate control of range exists and both controls could be used very effectively, if not excessively. The top cut control could be adjusted from a flat response up to a point where everything above 700Hz disappeared, and was operative on all three input channels. So, there we have the Vox AC30. Ludicrously loud, for the stage heavy rocker, tantalisingly tonal for the MOR artiste and destined to keep its place (if not by weight) as a good performer. I wonder if Rose Morris will send me a free sample — Christmas spirit and all that?