In Research & Development for three years, Rockford Fosgate's new high-efficiency amplifier technology was shown to the press at the 1999 CES Show and has now been incorporated into a new digital amplifier topology, called Class bd. Rockford engineers have been granted U.S. Patent 6,097,249 for the Class bd technology. This patent involves a new technology, known as STARDUST (Single Terminal Alternating Rail DUal Sampling Topology), for audio applications - a novel form of Class BD amplification. STARDUST allows the bd class amplifier to put more than 1000 watts of RMS power in the hands of the serious car audio user - and does so in a relatively small size. This improvement has been in commercial products since the January 2000 introduction of the Rockford Fosgate model bd1000.1. Rockford Fosgate reports that STARDUST is expected to be a common element of the company's continuing program of digital amplifier development.When considering what you are getting for your dollar in relationship to the power output, the STARDUST technology makes the Class bd amplifiers (1,100 watts for $699.99) more affordable in relationship to other typical class AB amplifiers since there is less current consumption from the charging system. In the case of Class bd amps, there is less heat generated due to the Class bd STARDUST technology. As a result, the cooler internals makes the overall performance more reliable.
Class D amplifiers work by altering the "balance" of an ultrasonic, square-wave carrier, set at equal positive and negative time duration-called 50 percent duty cycle--for no audio output. Audio output is achieved by modulating the ratio of the time the wave stays at its positive and negative states. Audio is recovered by passing the varying average value of this wave through a low-pass LC filter.
A serious drawback of this type of Class D is the large rail-to-rail square-wave "carrier" produced, leading to heating and complexity. A typical Class BD amplifier solves this problem by subtracting away this carrier in the external load. However, because the subtraction is external, it is well known to specialists of this field that it leaves an untamed, full rail-to-rail switching signal on both output leads, a nightmare RFI problem which has eluded solution during the 30 year Class BD history.
Rockford's Class bd amplifier, with its Stardust topology, suppresses the generation of this carrier wave in the modulation process itself-somewhat analogous to single side-band (SSB) radio practice. This novel solution allows all the advantages of Class BD to finally be employed-without an RFI output problem.
Link for more info: www.rockfordfosgate.com
