The NTBT-918 is a tone control preamp with fully Bass and Treble controls with very low noise and wide boostcut range. It is 23 the size of a 9V battery. The sound is very clear and transparent. Distortion is well below 0.001%. This preamp can be used with either one 9V battery (9V operation) or two 9V batteries (18V operation) which yields 6dB extra headroom. In 9V operation the NTBT-918 uses approximately 750 microamperes of current from a 9V battery. This means one month of continuous duty or more than six months of average usage. In 18V operation, the NTBT-918 uses approximately 1,000 microamperes of current from two 9V batteries. This means more than three weeks of continuous duty or more than four months of average usage.