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I have an acoustic guitar which has a built-in preamp and is suited to be directly plugged in into an acoustic amplifier - for which I do not know whether it has an additional preamp or not. Side question: Do acoustic amplifiers usually have one, respectively do acoustic amplifiers work with both active and passive pickups?

For my electric guitar I am planning to buy a new amp. In contrast to my acoustic guitar, the electric one has passive pickups. My questions now is basically the same as for the acoustic amp, namely whether a normal amp like e.g. the Engl e315 expects a pre-amplified signal or not. Until now I never thought about it and was sure that it is supposed to work with passive pickups, but I got confused along the way since the amp head itself also has a built-in preamp and the internet states that passive electric guitars need an external preamp.

However, normal amps should also work with guitars having active preamps?

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The difference between a preamped signal and a direct magnetic pickup signal is actually not as much the level but the impedance. Since the input on amps mainly reacts to voltage changes, the main difference when connecting a preamped signal is that the input is more sensitive to noise than necessary since the preamp could easily deliver larger currents (and thus more energy at the same voltage). Many amps have both a "Hi" and "Lo" input and you'd usually put a magnetic pickup on the "Hi" input while using "Lo" for preamped pickups.

  • This means that with a preamped signal I am able to reduce noise and to modify the sound before the preamp of the amp adds another layer of sound modifications (which in result is then the typical sound of that amp). However, for acoustic amps I wonder why the amp itself also has a preamp, since an acoustic amp should amplify the signal as natural as possible, right? – Big X Aug 8 '18 at 13:20
  • Additionally: What benefits do I get if I have a guitar having active pickups, pluging it into a preamp and additionally plugging it into the amp (which also has a preamp). I stumble over this recommendation on various sites on the internet stating a preamp as the "must-have" effect for acoustic guitars (in general!). – Big X Aug 8 '18 at 13:54
  • @BigX: Many amplifiers either include effects like reverb, or include a provision called an "effects loop" by which such things can be added externally. If an amp is being given a signal that is at 25% of the maximum volume for the reverb unit, feeding it to the reverb without amplifying it first, and then boosting it 150x and feeding it to the speaker, will amplify any background noise in the reverb unit by 150x. Pre-amplifying by 3x, then applying reverb, and then amplifying by 50x would cause the reverb-unit background noise to be multiplied by 50x (instead of 150x). – supercat Aug 9 '18 at 18:50
  • Even if a guitar has its own volume knob, being able to set the amp head's pre-amp gain so that playing loudly with the guitar's volume at max will drive the reverb with a level that's maybe 25% below its limits, and adjusting the main amp for the desired loudness in that scenario, would allow the player to make optimal use of the instrument's volume control. – supercat Aug 9 '18 at 18:52
  • @supercat And in the case that the output level of an active guitar pickup is quite low (which is the case for my 2017er taylor) and one does not want the PA guy to complain that the output is really low, or if you just want to use an additional (and better one than the three knobs on the guitar) equalizer then a preamp-"pedal" also makes sense if you do not plug your guitar into an amp, but directly into the PA. In the case of a passive pickup the noise amplifying is a really good point. A preamp in the end allows one to reduce noise and improve sound. Thus the general recommendation, right? – Big X Aug 10 '18 at 19:21

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