Roemtech's HummBuster technology was specifically devoloped to remove audio noise such as hums or buzzes. The primary reason audio technicians get called back to an audio installation is because the system has devoloped an unpleasant noise. Typically this happens when something has gone wrong that is not the fault of the sound system itself. This seems to be very common in classroom audio installations, especially with older buildings. Most commonly, there is an improper ground in the 110/120v electrical system that is the real problem. This is known as a ground loop and typically manifests itself as a 60/120/180Hz hum. Another common issue is the sound card on the computer. Some do not handle their grounds properly, so when plugged into an amplifier, undesirable noises are heard, frequently described as a buzzing sound. In a perfect world, when these problems arise, it should not be the audio technician that is called, but instead, the high voltage electrician or the computer company that made the computer. In reality, it is the audio company that gets the call every time. Knowing that this burden typically falls to the A/V dealer, Roemtech wanted to come up with a solution for its dealers. After years of testing classroom audio systems on location, the HummBuster technology was perfected. When properly used, it easily solves both of the above-mentioned issues. The first amplifier to feature this technology was the PMA-245H. It came equipped with two switches that either engaged or disengaged the HummBuster filters for optimal results. The PMA-245H was later replaced with the PMA-245H+. This feature has saved installers many hours of troubleshooting and lots of heartache. In addition to the PMA-245H+, the HummBuster feature is currently available on the PMA-285H+, DMA-355H, Q55 and the Q100. The PMA-350H+ features our patented Auto HummBuster discussed below.