Your Macro-Tech amplifier incorporates several advanced technological features including realtime computer simulation of output transistor stress, low-stress output stages, an advanced heat sink embodiment and the PIP2 (Programmable Input Processor) expansion system. Custom circuitry is incorporated to limit temperature and current to safe levels, making it highly reliable and tolerant of faults. Unlike many lesser amplifiers, it can operate at its voltage and current limits without selfd-estructing. Real-time computer simulation is used to create an analogue of the junction temperature of the output transistors (hereafter referred to as “output devices”).
Current is limited only when the device temperature becomes excessive (and by the minimum amount required). This patented approach is called Output Device Emulation Protection (or ODEP). It maximizes the available output power and protects against overheating-the major cause of device failure. The amplifier is protected from all common hazards that plague high-power amplifiers including shorted, open or mismatched loads; overloaded power supplies, excessive temperature, chain-destruction phenomena, input overload and high-frequency blowups.
The unit protects loudspeakers from input and output DC, as well as turn-on and turn-off transients. The four-quadrant topology used in a MacroTech’s grounded output stages is called the Grounded Bridge. This patented topology makes full use of the power supplies providing peak-to-peak voltages to the load that are twice the voltage seen by the output devices (see Figure 7.1). As its name suggests, the Grounded Bridge topology is referenced to ground. Composite devices are constructed to function as gigantic NPN and PNP devices to handle currents which exceed the limits of available devices. Each output stage has two composite NPN devices and two composite PNP devices.
The devices connected to the load are referred to as “high-side NPN and PNP” and the devices connected to ground are referred to as “lowside NPN and PNP.” Positive current is delivered to the load by increasing conductance simultaneously in the high-side NPN and lowside PNP stage, while synchronously decreasing conductance of the high-side PNP and lowside NPN. The two channels may be used together to double the voltage (Bridge-Mono) or the current (Parallel-Mono) presented to the load. This feature gives you flexibility to maximize the power available to the load. A wide bandwidth, multiloop design is used for state-of-the-art compensation. This produces ideal behavior and results in ultra-low distortion values. Aluminum extrusions have been widely used for heat sinks in power amplifiers due to their low cost and reasonable performance. However, measured on a watts- per-pound or watts-pervolume basis, the extrusion technology doesn’t perform nearly as well as the heat sink technology developed for Macro-Tech amplifiers.
Our heat sinks are fabricated from custom convoluted fin stock that provides an extremely high ratio of area to volume, or area to weight. All power devices are mounted directly to massive heat spreaders that are electrically at the Vcc potential. Electrifying the heat spreaders improves thermal performance by eliminating the insulating interface underneath the power devices. The chassis itself is even used as part of the thermal circuit to maximize utilization of the available cooling resources.