Ultra-Phonix HRM recreates the much sought after Dumble HRM overdrive tone that pushed the tweaked Overdrive Special Amplifier into stardom. Amongst the limited amount of ODS amplifiers produced by the legendary amp maker, a handful were armed with EL-34 power amp tubes rather than the 6L6 tubes found in most ODS amps. This gives the HRM edition of the Ultraphonix a quintessentially British voicing and EQ shift compared to the original version. The Master control determines the total output of the pedal. The Volume control adjusts how hard the pedals preamp is working, giving you more control over the amount of gain coming from the preamp. Turn up the Accent control to increase presence and slowly introduce more saturation into your signal. The Ratio control allows you to blend your distorted and clean signal, and the Tone knob allows you to accentuate different upper-mid frequencies, ranging from 800-1.6k Hz.