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RE: With modern sources putting out 2.5v why do I need a preamp

You are absolutely correct: most systems have much more gain than necessary and that extra gain adds noise and distortion to the signal. The primary reason to have a preamplifier is so you can show your audio buddies TWO BOXES: it adds verisimilitude to your high end audio credentials; it's audio fashion and we love our gear.

OK, that's a little sardonic; but the truth is the vast majority of systems don't need a preamplifier if there is a way to adjust the volume without it. You have checked the specs. of your source for output voltage and found that you have more voltage than you need to drive your amp to clipping. Now check the specifications for the output impedance of your source. I am confident you will find an output impedance low enough to drive ANY amplifier. All our modern high end sources use a high quality opamp as a buffer to lower the output impedance. Adding another buffer will only add a layer of noise and distortion.

So you will find all sorts of theories as to why you should have two boxes in your audio stream but, in fact, the signal is never going to be more accurate and clean than it is at the output of the source. That said, it should be clear that the source should be driving the speaker so there is no further corruption of the signal by adding gain stages and buffering stages. We all know that in the real world speakers need more voltage and more current, e.g. power, to be driven to acceptable levels. Amplification is, therefor a necessary evil and, as such, should be applied as judiciously as possible.

What should be clear is that a preamplifier should be absolutely transparent to the audio signal. In other words if the signal coming from the source is 2 Vrms and if the signal coming the preamp is also 2 Vrms they should be identical! If you have a dual channel oscilloscope and you invert one signal they should cancel each other out entirely. If that is not the case then the signal is being CORRUPTED by the preamplifier. Those that assert they like the sound better with a preamp like the corrupted signal better. It is that simple: the preamplifier is adding or subtracting something or shaping the signal in some way that the user finds appealing.

So, in the end, very few who buy their equipment in the store will give up their preamps no matter what I say. Things are very different in the DIY community right on this asylum. Builders realize that every component (resistor, capacitor, semiconductor, tube, transformer, RCA jack, and cable) the signal passes through corrupts that signal, even if it is minutely. Therefor, those with a scientific proclivity will assert, the fewer components the signal passes through, the less the signal will be corrupted and the cleaner and clearer the sound will be. The preponderance of two stage amplifiers (from the source to the speakers) and highly efficient speakers attests to that assertion. I understand that this is NOT mainstream thought in the audio community, so I am simply a voice in the wilderness. However, there is always the possibility someone will hear the message.



Edits: 08/14/16

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  • RE: With modern sources putting out 2.5v why do I need a preamp - Palustris 12:12:33 08/14/16 (0)

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