Yamaha P-2200 Owner's Manual - Page 16
Fig. 30B - Speaker Cone moved outward by Postive-Going - manual
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HUM AND NOISE Hum or noise from a power amplifier disrupts a program, and is irritating to a listener. Hum and noise could be considered a form of distortion. The P-2200's hum and noise are so low that they are completely inaudible under any normal listening circumstances. RISE TIME Rise time is a measurement of the amount of time an amplifier requires to respond to a square wave at a specified frequency. The rise time of an amplifier is an indication of its frequency response. A fast rise time corresponds to a wide frequency response. The P-2200's rise time specification is measured with a 1000Hz square wave output signal of one volt peak-to-peak amplitude. The rise time is the time the amplifier requires to change from 10% (0.1 volt) to 90% (0.9 volt) of its output. To improve measurement accuracy, the first and last 10% are normally not included in the test (any slight nonlinearities that occur in the test signal or the amplifier could lead to measurement error). SLEW RATE Slew rate is a measure of a power amplifier's ability to follow a fast rising waveform at higher frequencies and higher power outputs than the rise time measurement. The P-2200's slew rate is measured with a 200kHz square wave input signal, at 175 Watts output power into 8 ohms. It might seem reasonable to assume that the fastest slew rate for an audio waveform occurs at 20kHz. However, this is not the case. When one frequency is superimposed upon another, the combined waveform has a slew rate that is greater than the slew rate of either signal by itself. The actual value of the slew rate of one of these waveforms (or any waveform) depends not only on the frequency, but on the amplitude of the waveform as well. Thus, the criteria for a good slew rate specification, which indicates that an amplifier can reproduce these combination waveforms, varies with the maximum power output capability of the amplifier. The higher the power, the higher the required slew rate. With a 45 volts/microsecond slew rate, the P-2200 can easily reproduce even the most extreme audio waveforms at its full power output. INPUT IMPEDANCE The input impedance of the P-2200 is high enough to allow it to be used with most semi-pro devices, or to be used as a "bridging" load for a 600-ohm source. Page SIX 2 details input impedance and level matching for the P-2200. INPUT SENSITIVITY The P-2200's input sensitivity indicates the input drive voltage needed for the P-2200 to produce its rated output of 230 watts into 8 ohms (input attenuators are adjusted to maximum clockwise rotation for minimum attenuation). PROTECTION CIRCUITS AND THERMAL SPECIFICATIONS See the discussions under INSTALLATION, on Page SIX 13. GAIN Gain is the ratio of the P-2200's output voltage to its input voltage. Maximum gain occurs when the input attenuators are set for minimum attenuation. If the input and output voltage are specified in dB, the voltage gain is equal to the difference of the two dB numbers. As stated under INPUT SENSITIVITY, an input voltage of +4dB (1.23 volts) produces an output power of 230 watts into an 8-ohm load. 230 watts into 8 ohms implies an output voltage of 43 volts which corresponds to +35dB (referenced to 0.775 volts, as used in this manual). The voltage gain of the P-2200, with its input attenuators set for minimum attenuation, then, is 31dB [(+35dB)-(+4dB)]. OUTPUT IMPEDANCE (Refer to Figures 9 & 20) The output impedance of the P-2200 is extremely low. Thus, within its operating limits, the P-2200 is a good approximation of a perfect voltage source and will deliver increasing power levels into lower impedance loads in a linear fashion according to Ohm's law. The Appendix discusses Ohm's law and the concept of a perfect voltage source. DAMPING FACTOR Damping factor is a term that is derived by dividing the load impedance (speaker or other load) by the amplifier's output impedance. Thus, a high damping factor indicates a low output impedance at a specified load. The cone/voice-coil assembly of a loudspeaker gains inertia during its back and forth movements. This inertia can cause it to "overshoot," that is, to continue movement in one direction, even when the amplifier is trying to pull it back in the other direction. An amplifier with a low output impedance can "damp" (reduce) unwanted loudspeaker motions, as explained below. Fig. 30A - Speaker Cone at Rest Fig. 30B - Speaker Cone moved outward by Postive-Going Voltage from Amplifier. Fig. 30C - Voltage from Amplifier has dropped to Zero but Speaker Cone has moved back PAST its rest position (overshoot) and is producing a voltage of its own: "Back EMF"