The Blackstar HT-Dual is a modern classic in the world of tube-driven distortion. Unlike "starved plate" designs that run tubes at low voltages for show, the HT-Dual uses a high-voltage internal power supply to get genuine valve compression and harmonic richness.
The pedal takes 16V AC and boosts it internally to roughly 300V DC. This "B+" voltage is what allows the 12AX7 (ECC83) tube to operate in its linear region, providing real headroom. Blackstar Ht Dual Pedal Schematic
A dedicated filtering circuit at the end of the chain that rolls off high frequencies to mimic a 4x12 cabinet. The Blackstar HT-Dual is a modern classic in