See that little red light by the jack socket of this custom Strat copy? That means it's got the guitar equivalent of turbocharging, the Ampro Activator pre-amp system. Tim Glynne-Jones tested the boosted beast

In the same way as a good portrait photographer can take a well structured face and make it beautiful, so a good built-in active circuit can take a great guitar sound and make it magnificent, giving the instrument extra vitality by accentuating its character and polishing up some of its rougher features. If you want your guitar to be the Jane Seymour of the music world then you can't give it much better treatment than the Ampro CD-S Activator.

Designed by Tim De Whalley, a well known guitar craftsman, the CD-S was conceived to fit the Fender Strat or Strat copies. Tim has also designed activators to fit Precision basses, Jazz basses and Telecasters. The one I tried was fitted into a Strat with the addition of a Screen Kit and a Standy-by, retailing at £25 each.

There is an LED battery state indicator on the output plate which flashes instantaneously on plugging in if the battery is healthy. The stand-by switch enables you to switch between active and passive modes. This means that you can switch the activator off with the battery disconnected without having to unplug, thus allowing the guitar to be played even when the battery is dead and also saving wear on the output jack. In the passive mode the tone controls are disconnected leaving adjustments to be made with the volume control and the five-way selector switch.

In the active mode the selector switch is gain compensated with each pickup having extra gain including positions 2 and 4 so there is an output balance on all five positions. Performance irregularities are corrected by this slight gain coupled with high impedance buffering which prevents high frequency loading so your true sound enters the activator.

The tone controls have a centre notch indicating a flat response. Clockwise rotation produces a boost of 15dB max. Anticlockwise rotation produces a cut of 15dB max. They are also non-interactive, meaning that you can juggle with one control pot, without interfering with the frequencies on the other, so affording a wide range of sounds.

The screen kit consists of a wiring harness, pickup screening and 3 A/D boards and serves the purpose of eliminating humming and crackling when the activator is in operation.

Fitting the Ampro Activator requires very little modification of the recipient guitar. The only visible additions are the toggle switch for switching between active and passive modes, the LED battery indicator on the output plate and, round the back, the plate covering the battery cavity which is itself a very neat and simple cut-out job.

Whether or not you understand Tim De Whalley's electronic wizardry, you only need to turn the thing on to realise that, whatever the cause, the effect is fantastic, pumping vitality and clarity into the sound. In the passive mode the sound was pretty good and I was happy with the guitar in this mode for a little while wondering what difference the Activator would make and feeling a bit sceptical about the need to improve the sound quality from this already high standard. When my curiosity finally overcame me and I switched to active my questions and my doubts were obliterated in one gush of sparkling sound like the sun coming out on Cup Final day.

On a crystal clear background the reinforced sound still maintained the Strat character with the extra gain and slight treble lift increasing the sustain and bringing out the famous Strat harmonics.

As promised, the variation in tone was enormous. The non-interactive controls offer an assortment of tones ranging from a tinny treble sound to a hollow, boxy sound; from a chanking reggae sound to a hard-edged, driving punk sound, via a beautifully mellow blues sound. In fact just about any guitar sound you want.

Switching back to the passive mode was a bit of a let down after the brilliance of the active and I could only reflect that the Ampro Activator is a marvellous design in electronics which brings out excellence in a great guitar as well as giving it increased versatility.

For a total cost of £110 you can add a quality to your guitar which you could spend a lot more time and money trying to achieve with effects.

Ampro CD-S Activator: £60