With the gain knob set to zero you get a completely clean tone, and by gradually increasing it you will introduce a creamy distortion and more sustain. Adding more distortion does not introduce any unpleasant high frequencies, so you can use the Tone control to simply shape your sound.
The Secret-1 LTD can be powered by a high quality stabilized power supply or with a regular 9V battery. To replace it you have to open the four hinges around the box. The accepted supply voltages range from 9V DC to 24V DC, and higher voltages will result in more dynamics and harmonic complexity. The recommended voltage is 18V DC. The pedal has a standard tip negative connector (the same as used by Boss pedals).
The Secret-1 LTD circuit is housed in a military case which was used by the German army to house their radio equipment. Enclosure dimensions: 14 x 14 x 6,5 cm.
The pedal has a true-bypass on/off switch. It preserves the input signal even when switched off.