An ultrasonic generator for an ultrasonic welding system, comprising: a chassis having an AC power line input and housing a motherboard that includes connectors (16, 18, 19, 23, 24, 25) for directly connecting the motherboard to a plurality of modules (10, 11, 12) without wire harnesses to form a modular system, one of the connectors being an option module connector for connection to an option module; the modular system being characterized in that it is operable to: rectify and filter the AC power from the AC power line input to DC power; convert the DC power to AC power having an ultrasonic frequency and match an impedance of the AC power having an ultrasonic frequency to efficiently transfer that AC power to an ultrasonic transducer that delivers the ultrasonic frequency energy to a load; wherein the motherboard further includes a digital controller configured to control and monitor the plurality of modules (10, 11, 12), the digital controller being configured to: control a probe actuator device in a welding process; begin the welding process by applying a low level of adjustable ultrasound output to parts being joined by the welding process; monitor an ultrasonic power level as a force applied by the probe actuator device to the parts increases; and start a welding cycle in response to detecting a user-programmed trigger power level, without using a load cell or force transducer to directly measure the force applied to the parts. a chassis having an AC power line input and housing a motherboard that includes connectors (16, 18, 19, 23, 24, 25) for directly connecting the motherboard to a plurality of modules (10, 11, 12) without wire harnesses to form a modular system, one of the connectors being an option module connector for connection to an option module; the modular system being characterized in that it is operable to: rectify and filter the AC power from the AC power line input to DC power; convert the DC power to AC power having an ultrasonic frequency and match an impedance of the AC power having an ultrasonic frequency to efficiently transfer that AC power to an ultrasonic transducer that delivers the ultrasonic frequency energy to a load; rectify and filter the AC power from the AC power line input to DC power; convert the DC power to AC power having an ultrasonic frequency and match an impedance of the AC power having an ultrasonic frequency to efficiently transfer that AC power to an ultrasonic transducer that delivers the ultrasonic frequency energy to a load; wherein the motherboard further includes a digital controller configured to control and monitor the plurality of modules (10, 11, 12), the digital controller being configured to: control a probe actuator device in a welding process; begin the welding process by applying a low level of adjustable ultrasound output to parts being joined by the welding process; monitor an ultrasonic power level as a force applied by the probe actuator device to the parts increases; and start a welding cycle in response to detecting a user-programmed trigger power level, without using a load cell or force transducer to directly measure the force applied to the parts. control a probe actuator device in a welding process; begin the welding process by applying a low level of adjustable ultrasound output to parts being joined by the welding process; monitor an ultrasonic power level as a force applied by the probe actuator device to the parts increases; and start a welding cycle in response to detecting a user-programmed trigger power level, without using a load cell or force transducer to directly measure the force applied to the parts.