Why shouldn’t I use a Guitar Amp to amplify a keyboard? Does it have something to do with impedance? What are some other no-no’s in mixing and matching audio equipment?
Additonally, a related question:
My Step-Dad insists on this procedure for using electric guitar with an amp. 1) Have the guitar and amp volumes turned all the way down, and the amp turned off. 2) Plug in the guitar. 3) Now turn on the amp and turn up the volumes. 4) Play. 5) Turn the guitar and amp volumes all the way down. 6) Turn the amp off, then unplug the guitar.
Now, is there really any harm in plugging a guitar into an amp that’s turned on, or unplugging a guitar from an amp that is turned on? My Step-Dad insists I am doing some harm the guitar electronics each time I do this.
Plugging into a “hot” amp can make a nice loud POP that might not be too good for the speakers, which is why, at least, you should have the volume turned all the way down first. Turning the amp off is overkill.
There’s no reason you can’t plug a keyboard into a guitar amp. Even from one guitar to another, there are slight variations in impedance, so you’ll almost never have a perfect match, anyway. I’ve never had any issues in the past with any keyboard/guitar amp combo. You should start out with the volume on the keyboard set low and gradually bring it up, so as not to overload the input of the amp, however. You want to avoid overdriving the amp too much, as this can cause damage to the output transistors, especially if there is a high level of clipping distortion. Tube amps are largely immune to overdriving damage, and many claim they sound better, too.
The reason you don’t plug a keyboard into a guitar amp is that you want to hear the clear, undistorted tone of your keyboard, be it acoustic piano, electric piano or synth. There are a few cases (e.g. B3 -> Marshall stack = Deep Purple) where you want the distortion, but those are rare.
With a guitar, on the other hand, the distortion provided by the amp is part of your sound.
Unless you overdrive the amp, no damage will be done. Admittedly that’s easier to do with a synth than with a guitar.
I don’t know about that. Most decent guitar amps are surprisingly linear, provided you’re not overdriving it. Many have a control that allows you to deliberately dial in the amount of distortion you want, but as long as this control is turned to its lowest setting, what you get out will be pretty close to what you put in, excepting cheap units that make no effort at fidelity.
I’m a keyboard player and one thing I’ve found is that often the guitar amplifiers manufacturers limit the frequency response of the device to suit guitars. Bravo to them for doing their jobs but it makes it hard for you and I on the keys.
There is a large range of responses and it varies dramatically among manufacturers and models but they almost all do it to what I think is an excessive amount. Usually, there’s not nearly enough low end. My brother has a bass amp/cab with a line-in jack that didn’t have the input mismatch but then the highs weren’t there.
Another downside is the single driver cabinets that are usually used. Often, it there are several speakers in the cab, they’re multiples of the same driver!
I got frustrated with the few high priced standalone ‘keyboard amplifiers’ that are available and I wound up going with a complete PA system. This has true compression driver highs and mids and low, low lows. It can be a bit much to transport, set up and take down but I have no regrets. Plus, you can use the system for home stereo, computer sounds, parties and DJ’s. The separation distance is a must for those 64M sampled stereo piano patches.
Mine: Mackie C300 speakers(bought new), Ramsa WP-1200 amp(120W/ch Ebay), Alesis 3630 compressor(long term loan). Its hard enough being heard at all over the drummer and distorted guitar. This system lets me be heard and retain the delicate sounds I want to use.
Guitar amps are not designed to produce the huge range of frequencies that a keyboard will put out. You can use a guitar amp but it may not give you very good reproduction of the sound.
For the record, when I play keys I play through my mixer straight into the main PA. We all have in-ear monitors with individual mixes, so I can hear whatever I want–no need for an on-stage amplification system.
Excellent advice from your father, i.e. do not screw around with input connections unless the amplifier’s gain control is adjusted to its lowest setting. (Or the speaker is deactivated. Or the amp is in standby. Or the amp is off. You get the drift…)
I learned this hard way. I’m now $220 poorer because of the experience.
First, many keyboards operate a much higher output levels than guitars so you will have to adjust gain and volume on the amp accordingly, even they you may be overdriving the input circuitry of the amp. Fortunately many (if not all) modern amps have a ‘line level’ input or sometimes just a switch. Look for a different input or a stitch that has -20 or +20, this pads (adjusts) the input volume by a +/- 20dB. Adjusting this setting can make a big difference particularly if you are getting unwanted distortion when volume and gain are already way down.
Second, what Q.E.D. said. I’m strictly a second-rate-two-bit-amateur live sound guy but plugging a guitar into an amp on a hot channel can be a very bad thing. Your amp goes ‘pop’ but what can come out of the house mains can be a truly thunderous crash. No damage may result to your amp but damage could result elsewhere. True, the sound man should be aware of what is going on and have the channel muted but it is also your responsibility as a performer to have good (read safe) technique. Guitar and amps DOWN when plugging in and if you have active pickups please dear please don’t unplug every time you leave stage. Us sound guys have more nine volts and will share if you ask.
A couple thoughts about impedances-
Sending a signal from a source to a destination, when the energy in the signal is not expensive, generally works fine as long as the source impedance is no higher than the destination impedance.
When the energy is expensive, because you are handling high power (which costs alot to create), then matching impedances uses the energy more efficiently. That’s why there’s at least some effort to match power amp output impedances with speaker input impedances. Quadrupling the amp power to fix an impedance mismatch is expensive.
The energy may also be expensive because it’s very small. For example, a television antenna is expensive and is alot of trouble to maintain on a tower, but it generates very tiny energies. So you wouldn’t want to waste these either, and therefore you use 50 ohm or 75 ohm or 300 ohm specifically, or use matching transformers.
An exception to this generality is when the wavelength of your signal is not huge compared to your system dimensions. In this case, sudden changes of impedance cause reflections back into the line and confuse things. Data transmission cables used in computers and networks have to keep impedances constant for this reason. But audio wavelengths (in the electronic form, not the accoustic form) are thousands of miles long, bare minimum.
