Quote Originally Posted by vibralux
can some one please help me as i am a hi-fi novice i have noticed that pre amps are not full size but phono pre amps look just look normal amps. please can someone explain the difference and can you use a pre amp instead of an amp?
The job of amplifying the small signal from a phonograph cartridge, tuner, CD player, etc. is performed by a number of job-specific stages. Sometimes these stages are integrated into a single box as with a receiver, or found as separate components. The phono preamp amplifies the weakest of the signals (ranging from 0.2 millivolts for moving coil types to 5 mv with moving magnet types) to a level equivalent to that of so call "high level" sources such as tuners, tape decks, and CD players. Also, phono preamps equalize the signal to reverse the effect of the RIAA compensation curve (done to reduce surface noise). The preamp is the next stage taking the 500 mv - 2 volt high level signal to 2 - 4 volts sufficient to drive the power amplifier. Preamps also serve as the control center having the source switching capability, volume and balance controls, tape monitor loops, and in some cases, tone controls. The final stage is the power amp. While the signal gain multiple is similar to that of the preamp stage (actually the phono preamp performs the greatest signal gain), the amp deals with the largest amounts of current required to drive a loudspeaker. That is why power amps are usually the largest stages.

Indeed as hifitommy indicated there are some phono stages that look like power amps in terms of their size. Audio Research, Aesthetix, ASR Basis, Manley Labs, Passlabs to mention just a few all make pretty sizable phono preamps, some of which have power supplies like you would find in a power amplifier. Most, however, are much smaller than a typical preamp.

No, you cannot use a preamp in lieu of a power amp. The signal is too weak and not suited for driving a loudspeaker. With some high gain sources, however, you can bypass using a preamp and have the source drive the amplifier directly.

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