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Apreamplifier, also known as apreamp, is anelectronic amplifier that converts a weakelectrical signal into an output signal strong enough to be noise-tolerant and strong enough for further processing, or for sending to apower amplifier and aloudspeaker.[1] Without this, the final signal would be noisy or distorted. They are typically used to amplify signals from analog sensors such asmicrophones andpickups.[2] Because of this, the preamplifier is often placed close to thesensor to reduce the effects ofnoise andinterference.
An ideal preamp will be linear (have a constantgain through its operating range) and have highinput impedance (requiring only a minimal amount of current to sense the input signal) and lowoutput impedance (when current is drawn from the output there is minimal change in the output voltage). It is used to boost the signal strength to drive the cable to the main instrument without significantly degrading thesignal-to-noise ratio (SNR). The noise performance of a preamplifier is critical. According toFriis's formula, when the gain of the preamplifier is high, the SNR of the final signal is determined by the SNR of the input signal and thenoise figure of the preamplifier.
Three basic types of preamplifiers are available:
In an audio system, they are typically used to amplify signals from analog sensors toline level. The second amplifier is typically apower amplifier (power amp). The preamplifier providesvoltage gain (e.g., from 10 mV to 1 V) but no significantcurrent gain. The power amplifier provides the higher current necessary to driveloudspeakers. For these systems, some common sensors aremicrophones,instrument pickups, andphonographs. Preamplifiers are often integrated into the audio inputs onmixing consoles,DJ mixers, andsound cards. They can also be stand-alone devices.
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