In this configuration the headphone amplifier can still provide power, but it cannot provide good control over the transducers. It is very common to find a resistor of at least 30 Ohms wired in series with the headphone output. The series resistor increases the output impedance and this decreases the damping factor. This shortcut provides stability but it completely destroys the damping factor of the headphone amplifier. This cheap solution is a series resistor between the amplifier and the headphone. Most headphone amplifiers use a simple and cheap shortcut to provide stability without the need for special circuitry. But, very few headphone amplifiers are built like power amplifiers. A good power amplifier will include circuitry that is designed to keep the amplifier stable while driving capacitive loads. Amplifiers can become unstable when driving a capacitive load. These transducers can act just like capacitors at certain frequencies. Headphones and speakers present the amplifier with a load that varies with frequency. It also prevents variations in frequency response that are caused by the impedance variations of the transducers. A high damping factor can improve the transient response, and reduce some of the distortion caused by the transducers. Like speakers, headphones perform best when driven by an amplifier with a high damping factor. The importance of a high damping factor is well understood for amplifiers that are designed to drive speakers, but it is often overlooked in amplifiers that are designed to drive headphones. This means that the damping factor is highest when the amplifier output impedance is designed to be as low as possible. By definition, the damping factor is the load impedance divided by the amplifier output impedance. An amplifier with a high damping factor will provide good acceleration and damping of moving diaphragms. Damping Factorĭamping factor is one measurement of an amplifier's ability to provide control. A good power amplifier can also provide an output voltage that does not change when the load impedance changes. The complex load produced by an electromechanical transducer is much different than the load produced by a simple resistor.Ī good power amplifier can initiate and damp transducer motions quickly, and it can do so without introducing distortion. Both have input impedances that change with frequency. Both have moving diaphragms that must be started and stopped in response to the audio signal. Both place a continually varying load on the amplifier. The only real differences are size and power of the transducers. Speakers and headphones are both electromechanical devices. Control is the ability to maintain a precise distortion-free output into a dynamic load. Power is determined by the ability to deliver a combination of current and voltage. What makes the HPA2™ different, and what do we mean when we say that the HPA2™ is a "power amplifier"? What is a Power Amplifier?Ī power amplifier provides two things power and control. Unlike most headphone amplifiers, the HPA2™ is designed to behave like a small but very clean power amplifier. Many Benchmark products include our HPA2™ headphone power amplifier.
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