The UA has a protect circuit that must be switched on by passing a signal through the unit. This is simply accomplished by turning on the amp and turning it and the guitar up enough to open the circuit. The circuit was included to protect parts in the UA vulnerable to the voltages it would see if plugged in backward. This saves time and money on costly repairs and in no way affects tone. Once on, you need not open the circuit again until the unit is unplugged from the AC main, and plugged back in again (to the power).
RECOMMENDED POWER UP SEQUENCE
1. Make cable connections with the “speaker” jack going to the cabinet and the “amp” jack going to the speaker out on your amp.
2. Set the UA to off. Turn on the amp and listen for blowby or signal to make sure the proper connections are made and that the cables are working properly.
3. Set the amp volume halfway or more to your intended volume setting.
4. Set the UA volume all the way to the left (no sound) and turn the switch “up” to
ON.
4. Turn guitar volume all the way up and spank a chord. The protect will now be off
and you won’t hear a sound. If you want to hear the protect defeated, turn up the
UA slightly when you spank the chord.
5. Turn up the UA to your desired volume.
If you experience hum or squealing from your amp, lift the ground on the UA using a 3 to 2 prong adaptor.