London Power’s VCK Voltage Clamp Kit stabilizes voltages in a tube preamp, helping to keep tone consistent with fluctuations of incoming power. This is particularly important in cathode-biased amplifiers fitted with Power Scaling.
- maximum input voltage: 550V (most cathode-biased amps are 400V or less)
- maximum input/output voltage difference: 200V
- trimpot allows easy voltage setting
- modest hum reduction of 22dB typical
Cathode-biased amplifiers demand full power even at idle, which pulls the supply voltage down to a value that stays approximately the same, even when the amp is driven to full output. In a Power Scaled cathode-biased amp, as the Power Scale control is dialed down, the supply voltage will rise as it becomes “unloaded”. This will change the tonal contribution of the preamp at low power settings. Adding VCK to stabilize the preamp voltage to the stock “loaded” value will keep the tonal contribution of the preamp constant with any Power Scale setting.
The unloaded voltage in a cathode-biased amp can be 20% higher than the normal idle voltage. VCK is designed to minimize this rise of voltage and keep tone the same.
VCK can be used in other situations where the incoming supply voltage varies due to, say, poor mains regulation in the locale.
VCK has been designed to occupy as little space as possible in the amp chassis, requiring less than one-square-inch of space (1″x1″, 25x25mm)
Available Kit Configurations:
The Standard DIY Kit requires assembly, and includes all the components that go on the PCB, the PCB, and notes for installation and set-up.
The Built Kit configuration includes pre-assembly of the kit, and notes
If you require a high-voltage version of the VCK, see VCK-HV.
PCB size: 1.4″ x 1″, 36mm x 25mm
See our Power Scaling FAQ.