Guitar Amp / Keyboard Question

[JoeJoe]

I have a Behringer V-Tone GMX212 amp which I would like to use with four keyboards ( I'm not a gigging musician - just an home player ).
I'm currently using two small keyboard amps, the output of which is going through a Behringer 8 channel mixer - 1 amp to main output L and the other amp to main output R.
Having the four keyboards through the mixer enables me to play late at night ( both amps switched off ) through headphones.
I'm wanting to use the effects built into the GMX212 with my keyboards......I'm aware that keyboards and mixers use a low impedance signal and that a guitar amp is of high impedance.
Iv'e seen advertised on different music sites DI boxes but I'm not very conversant with these type of things if anyone could offer advice it would be appreciated.
Am I correct in the way I think using one should be:
Cable from GMX212 guitar input jack into the DI box, then out of the DI box and into either the left or right main output jack of the mixer ?
Would this convert the high impedance signal from the GMX212 guitar jack input to a low impedance signal suitable for use with the mixer and keyboards ?

[Enzo]

Really, impedance is not an issue here. A DI box will convert to low impedance, and more importantly usually to a balanced line. But that is generally to send it some distance, like down a snake to the PA.

The output of a keyboard will drive any high impedance amp input just fine.


Let me get it straight, you are currently sending the mixer L and R outputs to separate keyboard amps? And in essence, you want to replace one of those amps with your GMX212? And that way, whatever is coming out the mixer can then be reverberated or chorused or whatever by the Behringer FX system, yes?

If that is the case, pull the cord out of the keuboard amp and plug it into the GMX, thats it.


And just to be nitpicky, as a general rule, when describing cable connectiongs, we describe it from the signal source to the signal destination. In other words, when you have a cord between guitar and amp, we should say the cord is from the guitar out to the amp in. Not I ran a cord from the amplifier input to the guitar output. It is a small thing, I know.

[JoeJoe]

Hi Enzo, Instead of playing through the two keyboard amps as described in my last post, I tried the keyboards through the guitar input of the Behringer GMX212......not a very good sound at all !
The sound is pretty good if I use the Behringer CD / MP3 input and send that to the L + R main outputs of the Behringer 802 mixer and also means I get a stereo output rather than a mono one in playing it through the guitar input......only problem with this is I can't use the FX on the GMX212.
What I don't understand is the fact that you say ' Impedance is not an issue '....... guitar amps are of high impedance whilst keyboards are of low impendance, why do manufacturers make dedicated amps for keyboards for a player to get all the frequencies ( mid, low and high ) if impedance is not an issue ?
All I'm wanting to do is to use one amp which will provide me with a stereo output and be able to use the onboard FX - take the signals from the 4 keyboards I'm using and put them through the mixer.
This is why I asked the question: about putting a DI box inline with both the guitar input and using either the L or R main output of the mixer.......... in doing so I assume that I would get all the signals ( low, mid and high ).

[Enzo]

why do manufacturers make dedicated amps for keyboards for a player to get all the frequencies ( mid, low and high ) if impedance is not an issue ?

The answer is in your question. Keyboard amps and guitar amps do completely different jobs. The keyboard amp is basically a small PA system in a box. Since keydoards are full range instruments, the amp must reproduce everything from snorting bass to sparkling highs. And it should do so more or less in a neutral manner. We don;t want keyboard amps adding their own character to the sound, any more than we want PA systems to do so. The keyboard amp does indeed cover all frequencies, and the speakers are full range, usually including a tweeter.


On the other hand, a guitar amp should be considered part of the instrumemt, it is not there to REproduce the sound, it is there to add its own character to the sound. Guitar amps are SUPPOSED to have their own sound. Otherwise, like PA systems, they'd all sound alike. One can plug a guitar into a PA system to hear how thin and unexciting the guitar is without its amp. That is why guys will say "I play a Marshall" or "I play a Fender." Guitar amps are not full range either. They don;t have tweeters, and guitar speakers are specific for the task, they are not the same as PA speakers. Guitar amps start rolling off somewhere in the 3kHz-5kHz range typically.


It has nothing to do with impedance, the difference has to do with performance desired.



The keyboard puts out a line level signal, which is a stronger signal than a guitar. So the guitar amp usually has more gain. Not only that, unless you were going for a particular effect, you would not generally want to overdrive a keyboard amp. But overdriving guitar amps is a daily fact of life, so yet another reason for lots of gain. You found that you thought it sounded OK played through the GMX power amp and speakers, but not through the whole amp. That is not an impedance issue, it is a matter of you not liking the sound of the guitar amp preamp for your keys.

guitar amps are of high impedance whilst keyboards are of low impendance

I know you believe this, but where did it come from? I have never heard this before, and I have been runniong a pro audio shop for 25 years. DO not confuse frequency and impedance, they are not remotely the same thing.


There are stand alone effect units that you could connect between the keys and the mixer or betwen mixer and amps, that would allow you to add teh chorus or reverb or whatever without having the whole guitar preamp baggage.

[Rhodesplyr]

I know of some keyboard players who've used guitar amps for amplification, but they usually do it because they want a colored sound.

And they usually end up damaging the guitar amp speaker, if it's an open-backed cabinet because they try to drive too much bass through it. I have to lecture musicians about the limits of open-backed cabs all the time, as in, "This is why you keep blowing speakers." And, "Don't lend your guitar amp to a bass player."

Some older keyboards actually work better into high impedance inputs because that was what was standard when they were built. For example, my Vox Continental sounds better driving a >100k input as opposed to the 10-20k inputs common in many modern mixing boards.