The Noble Amplifier Company Preamp will only power the Cali76-TX in standard mode. Use one of the 9V outlets to power your Cali76-TX if using this preamp. The transformer circuitry is switched in by relays when provided with 14.6V. If the -TX has powered up with the transformer engaged then dropping the voltage below 12.6V will switch out the transformer circuitry; the Cali76-TX will then perform like a Cali76 Standard. We do not recommend using a supply of 12V – 15V as possible variation in regulation of mains voltage could cause the transformer stage to switch in and out of operation. 18V is recommended for best results when using the transformer output stage. UPDATE: Noble Amplifier Company now offers an optional 18V boost cable to power the Cali76-TX at 18V directly from the Noble preamp. When using this cable the transformer will be engaged.