From the Maxon website:
"This new RTO700 Tube Overdrive replaces the original Real Tube ROD880 Real Overdrive.
The RTO700 Tube Overdrive Pedal has no clipping diodes in the signal path - All distortion comes directly from the dual triode preamp tube and hi-gain amp circuit. This design makes the RTO the best tube overdrive pedal for use with clean and semi-clean amps to effectively add a 2nd or 3rd channel of pure tube tone to your rig.
Every aspect of the RTO700 has been re-thought and redesigned to provide a lifetime of trouble-free performance. As soon as power is applied to the pedal, an In-Rush Current control begins heating the tube at a very low voltage (much like a tube amp standby switch) to dramatically extend tube life. When the pedal is engaged, a charge pump circuit bumps incoming voltage to feed the tube with 12.6 VDC.
Unlike other tube overdrive pedals, the RTD800 places the tube AFTER the OD/Distortion circuits, making it the best tube overdrive pedal to recreate an authentic tube-amp tone.
Gain and Master Controls allow the user to dial the amount of distortion and output level. The three Tone controls are completely independent with no frequency overlap, allowing for an unprecedented degree of tonal options. Everything is kept clean and tight via the variable VCA Noise Reduction circuit, which features an LED status indicator and On/Off switch.
The RTO700's Front-Panel Controls are as follows -
GAIN - Controls Gain level.
MASTER - Controls output level allowing user to match effect and bypass levels .
BASS - Controls low frequency range.
MID - Controls middle frequency range.
TREBLE - Controls high frequency range.
NR - Controls amount of Noise Reduction when NR is switched on.
NR On/Off - Turns Noise Reduction on/off.
Like all Maxon products, the RTO700 features True Mechanical Bypass switching using a 3PDT switch. The RTO700 comes complete with the Maxon AC2009 9-Volt power supply, an auto sensing digital power supply that can be used anywhere in the world."