Carvin FET1000 Instruction Manual - Page 40

FET Series Power Amplifiers About the FET Series Amps Section 3 Section 3 About the FET Series Amps The primary considerations in the design of our new FET series amplifier were performance and reliability. The FET series amplifiers are designed using the latest generation MOSFET's (Metal Oxide Silicon Field Effects Transistor). These devices have a wide degree of thermal protection and inherent stability. They offer significant advantages in performance and reliability compared to conventional bipolar transistor technology. These devices coupled with Carvin's advanced computer aided design and test systems have allowed us to incorporate unique new circuits that exploit the MOSFETs advantages. The combination of intelligent engineering and manufacturing have allowed the FET series amplifiers to achieve a competitive edge in performance when compared to other amplifiers. The following information will help you become more familiar with the advantages of MOSFET technology and your new FET series Carvin amplifier. Why M SFETs? Carvin's MOSFET amps use a third generation MOSFET device quite different from transistors. These devices have a very high input impedance and, because of their high speed, cover an exceptionally wide frequency range. The net result of the MOSFETs extended frequency range is an amplifier with more transparent sound. The device's high speed also translates into improved "slew rate" performance. In many ways these MOSFETs resemble high impedance tubes but without the drawbacks of tubes. Don't be surprised if you hear a definite sonic improvement in your system when you switch to the Carvin FET series amps. MOSFETs exhibit properties of "self protection" from thermal stress. They offer high current capacity for increased reliability and quick response to high level transients. They are inherently more reliable than bipolar transistors for several reasons. Conventional bipolar transistors have a positive temperature coefficient. This means that as the device heats up its internal impedance decreases and the device tends to conduct more current...which heats the device more...etc. The result of this cycle of increasing temperature followed by increasing current is "thermal runaway". When transistors are used in parallel (as in most high power amps)this can lead to "current hogging" where the one hottest transistor tries to carry the entire load of the amplifier. Because of this characteristic amplifiers using bipolar transistors must be carefully compensated to control thermal runaway. This can result in compromised audio performance at best. At worst it can result in amp failure. MOSFETs have a negative temperature coefficient. This means that as a device heats up its internal impedance increases and the device becomes more resistive to current flow. MOSFETs effectively distribute the current demand among all the output devices. The result is an even temperature distribution among the devices and the elimination of problems associated with "thermal runaway" and "current hogging". • 3-1