VOX CT-04TB Over The Top Boost Pedal

The COOLTRON Over the Top Boost effect pedal uses a 12AU7 preamp-type tube at low voltage to deliver the kind of tone that, until now, would have been impossible to achieve in a battery-powered pedal.

Blast your tone over the edge and back. The OTTB puts the top boost channel of a VOX AC30 into an effect pedal. The Treble control can take your tone from cutting attack at one extreme to smooth and liquidy at the other, while the Bass control adds low-end girth at higher settings and a warm round smoothness at lower settings.

The OTTB even comes with a Cut control to add or remove higher frequencies at the turn of a knob. Vary the overall gain of the pedal from bluesy and mellow to fat and saturated. Or use the Standard/Custom switch to either make the EQ very interactive in Standard mode, or have it behave more like a traditional AC30 Hand Wired in Custom mode. You can use the Vox OTTB as a booster pedal to drive the input of your amp by setting the Gain low and the Volume high. Conversely, set the Gain high and the Volume low for an overdrive from the pedal itself.

Want to know how it all works?
Normally, tubes are used at high voltages and this restricts their use in battery-powered devices such as guitar effects pedals. Historically, attempts have been made to use tubes at low voltages in what has been dubbed "starvation" mode, but these circuits don't allow the tube to function in an acceptable manner. The tube simply cannot be biased to a satisfactory operating condition. Plus, the necessary heater (filament) current is too high to deliver acceptable battery life. Imagine how annoying it would be to have to change batteries every ten minutes during a gig!

Here's what makes the Vox COOLTRON system tick. The COOLTRON circuit basically operates by using two very special signal paths. The first is the servo circuit, which provides the right conditions between the plate of the tube and the grid. This achieves controllable, stable parameters for the tube and provides the correct operating conditions for the tube to function as it would if it ran at a higher voltage. The second circuit is a patented power supply that provides a low voltage, low current supply to the heater elements in the tube. Since the tube is now running at such a reduced supply level, the anode current is much smaller than normal. This means that the amount of heat required at the cathode to achieve sufficient cathode current emission is much smaller ” hence the ability to run the heaters at a lower level and for COOLTRON guitar pedals to run for 16 hours on 4 x AA batteries!

The COOLTRON system provides true tube sonic performance at very low voltage and at reduced heater current ” ideal for inclusion into the COOLTRON OTTB effects pedal.

• Connections: Input: x1 (guitar input), Output: x1 (line output)
• Input / Output Impedance: 830 k-ohm / 4 k-ohm
• Tube: 12AU7 (ECC82)
• Power Supply: Four AA alkaline batteries or DC9V AC adapter
• Battery Life: Approx. 18 hours
• Current Consumption: 95 mA
• Dimensions: 168.8 (W) x 155.5 (D) x 64.0 (H) mm / 6.63" (W) x 6.12" (D) x 2.52" (H)
• Weight: 1,000 g (excluding batteries) / 1,095 g (including batteries)