Keyboard vs Guitar Amps. What the Diff?

Factual Questions
1

AIUI, you can’t plug a keyboard into a guitar amp (or vice versa) and expect to get decent (if any) sound.

What matters, and couldn’t I just plug either into my (old) stereo receiver’s “Line In”, flip the switch to “AUX” and listen - the same way I use a home audio system to listen to whatever the computer is generating? I used to have an old computer assigned to the role of CD player. My sister and her brood were blown away when I popped the CD player on the computer and the music stopped.

Line out - to - line in should work regardless of what is producing the line out, right?

2

The only difference between keyboard and guitar amps that I am aware of is that guitar amps have some extra circuitry to allow them to be overdriven without exploding. You should be able to use any one for any instrument, as long as you know its limitations.

3

The keyboard uses line level signals where the guitar amplifier uses mic level signals. If you plug a guitar into the line in input on your stereo, the guitar will be extremely quiet and weak. Likewise, plugging a keyboard line out into a mic level input will overdrive it and cause distortion.

If you run the guitar through a pre-amp then you can plug it into a keyboard amplifier. Also, some amplifiers are designed to take both types of inputs. Even on some that aren’t, if you turn down the pre-amp stage to a very low volume the keyboard won’t sound bad through it.

There’s also another difference. Guitar amplifiers often intentionally distort the signal to make the guitar sound “better”. This distortion won’t make the keyboard sound better. It will make it sound worse. A clean, non-distorting amplifier actually makes a guitar sound a bit flat. However, you can also use a non-distorting amplifier and a digital effects box which mimics the distortion of several different types of amplifiers.

Your stereo and your computer use line level signals, in general. Older sound cards had a separate line and mic level input jack. Putting line level signals into the mic input could cause distortion and sometimes could even damage the sound card. A lot of modern sound cards can use the same jack and will adjust the input type as needed. Some figure it out automatically. Others need you to tell it what type of input through the computer’s control panel or a control panel specifically designed for that sound card.

4

Keyboard amps are full range amps with minimal distortion–you want to hear the instrument, not the amp. Guitar amps are pretty much the opposite. Bass amps are generally closer to keyboard amps than guitar amps, but often lack the very high end.

5

Guitar amps tend to have a lot of mid range with not much bass or treble response because musicians have collectively decided it sounds “better”. The last thing an electric guitarist wants is a really accurate amplifier that faithfully reproduces the sound of the guitar. If you were amplifying an acoustic guitar though, you do want to hear the instrument and you’d use something closer to a keyboard amp than an electric guitar amp.

6

I’m beginning to remember why I never learned much about music - too many things to try to comprehend when every last person on earth knows what harmonizes and what clashes.

I have spent a few hours lately trying to comprehend the basics of music theory.

Now I need to know which amp will or will not work with what instrument.

If I tell a keyboard/sequencer - whatever, to sound like a guitar, will the amp self-destruct? :smiley:

7

It’s pretty simple, if you want a guitar amp, you walk into a shop and say “I’d like a guitar amp please!” and if you want a keyboard amp you walk into a shop and say “I want a keyboard amp please!”

8

Another slant is this - keyboard amps are designed to take the keyboard instrument’s sound and drive it through a loudspeaker. They should run clean and not colour the sound. A guitar amplifier is part of a musical instrument. You choose a particular guitar amplifier based upon its sound, and the sounds can vary wildly. The Fender sound is quite different to a Marshal, versus a VOX, versus a HiWatt, versus a Mega Boogie, and so on.

Keyboard amplifiers are often semiconductor designs. Good guitar amplifiers are almost always tube based. Guitar amplifiers started life as conventional amplifiers, but then guitarists started to explore what happened to the sound when the amplifiers were abused. Amplifier designers responded by tweaking the parameters of the amplifiers in interesting ways, and built amplifiers that were deliberately abusable, and often designed outside of the normal parameters of amplifier design. Things like way too may gain stages, undersized output transformers, soggy power supplies, feedback loops that deliberately were driven outside their limits, frequency shaping through the gain stages that tweaked the distortion characteristics.

One well known exception to the rule about not driving keyboards into guitar amps was the late John Lord. He drove his Hammond into a Marshal guitar amp. It formed part of the distinctive Deep Purple sound.

9

The synthesised output from the source (keyboard/sequencer) is already shaped as if it had been through a guitar amplifier (strong mid, rolled off treble/bass, distortion etc).

Think about this - the front-of-house sound system for a big venue has a generally flat frequency response - this system amplifies bass, drums, keys, guitars, vocals and whatever else to a venue-filling volume, and the only EQ applied is to compensate for the sound characteristics of the space itself. Ditto for the onstage (or in-ear) monitors (foldback) - they are simple with flat EQ.

A keyboard amp is usually a monitor - all the processing occurs on the instruments and effects rack, and the player just wants to hear that. The same sound is injected into the sound system. Many keyboard amps are for stand-alone rigs, and include a small mixer and mic inputs. Acoustic Guitar amps are the same, with some added reverb/EQ/chorus.

A Bass/Guitar amp is part of what defines the sound of the player, so the amp is usually mic-ed, and that mic is fed into the main system. If your rig is not based on a physical amp, and includes amp and cabinet simulation, then you can feed directly into the main sound system and use a simple monitor (like a keyboard amp or monitor wedge) to listen to the sound.

However, there is a risk when using a monitor with guitar distortion or heavy bass - you can drive the system harder than you intend. If you are feeding a heavily distorted guitar into a monitor amp - that is ok. But if you then turn it up to the point that the monitor amp also starts distorting, you may not hear it (you want to hear the distortion, after all) and you will then damage the monitor. Similarly with bass amps - the monitor speaker will reproduce all frequencies well, but will not cope well with heavy bass transients - bass amp speakers have heavier cones designed for low frequency reproduction and transients.

So - my rules of thumb:

Bass guitar -> Bass amp or D.I. to front-of-house with low volume monitor
Electric guitar without effects rack -> Guitar amp mic-ed or D.I.ed to front-of-house
Electric guitar with effects racks -> Monitor amp and/or D.I.ed to front-of-house
Acoustic guitar with or without rack -> Monitor amp and/or D.I.ed to front-of-house
Keyboards with or without rack -> Keyboard/Monitor amp and/or D.I.ed to front-of-house
Mics -> effects (reverb/EQ) -> front-of-house with monitors

(N.B. D.I. is direct injection - usually conversion from unbalanced signal to balanced signal for long runs to the mixing desk, sometimes taken from a pre-amp out jack on an amplifier)

Si

10

I think of a keyboard amp as a general purpose PA which could be used to amplify your ipod, tv, vocals, etc.

11

This is the first thing I thought of when I read the OP. An electric guitar by itself doesn’t have much going for it that can modify/fully produce its sound. You quite frequently going to want to tweak the basic signal. A modern synth keyboard is going to have nearly all the adjustments within it that an everyday player is going to want. What comes out of the keyboard is most likely going to the same signal you want the amplifier to produce. (Well, okay, you’re going to want an equalizer and whatever other goodies you can afford.)

12

Another difference is that the actual sound producing mechanism in a keyboard is entirely electronic. (some electric pianos excepted) That in a guitar is mechanical (the string). This means that if the guitar is placed close to the loudspeaker it is connected to, you can have feedback that will allow infinite sustain, or even runaway where the note gets louder over time. An electric guitar can be considered a rather dead mic with a very narrow bandwidth(s) (that of the note/chord that is being fingered )

For this reason many guitarists will want their guitar amp/speaker right next to them on stage, where they can manage the feedback by moving closer or farther away. So it needs to be reasonably compact and nice if it looks cool.

Conversely, it matters not at all where a keyboard amp/speaker is located, so long as there is a monitor near enough that the keyboard player can hear what they are doing.