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Old 24th June 2013, 11:25 PM   #1
Msr898 is offline Msr898  United States
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Default Double amplification

I am new here and just wanted some advice. I play an American made Martin acoustic/electric guitar and a Peavey T-40 bass, I want to build a rack mount system to run both at the same time. I'm pretty sure it I possible but I wouldn't even know where to begin. Any advice is appreciated and welcomed. Thank you for your time- MSR in Texas
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Old 25th June 2013, 04:34 PM   #2
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The problem isn't in the double preamp (you might even be able to find a dual input guitar amp which can do two decent clean channels) or the mixing; it's in the speaker requirements. An acoustic guitar wants a lot of clarity in the high frequencies, and doesn't worry about real low frequencies at all, whereas a bass needs its clarity in the mid range, but wants real solid power in the lows. An electric bass is going to tend to need much more power than an acoustic to balance with other instruments or voices, while the acoustic will feed back much faster, even with contact mics. A speaker that can deliver all this loud enough to be useful for outside gigs is going to be a studio monitor, or one designed for reproducing full range premixed music.

Assuming, of course, that you're not intending to run the output through a remote PA, with what you're planning just a local monitor. In that case you're probably better off feeding the two instruments out separately, (full balanced outputs and ground lift, the works) and only mixing for yourself; PA guys don't tend to trust anybody else's eq or balance.

So, apart from the standard preamplifier functions (gain and equalisation), what do you generally use? Compression on the bass, or a short reverb on the guitar, for example, or completely clean? It would be handy to know what kind of performance you're planning on, and if there will be other musicians involved.
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Old 25th June 2013, 04:53 PM   #3
Struth is offline Struth  Canada
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Hi Guys

Where amps intended for acoustic guitars are traditionally built as minim hifi amps and speakers, this is not the universally appealing or acceptable approach.

Most players I know who play both acoustic and electric instruments use a straight guitar amp for both. The treble roll off afforded by the guitar speaker makes the acoustic much more listenable.

Dedicated acoustic amps use tiny drivers or woofer-tweeters that give ice-pick treble. This emphasises finger slide and fret noise and makes the guitar tone more "jangly" with less of the actual note sound coming through. Very distracting.

Most acoustic instruments have built in preamps if they have a pickup (peizo or dynamic), so there is no specific impedance matching issue to deal with. On the other hand, if the instrument has just a raw piezo, then this needs a very high-impedance input to capture its tone - >10M. A tube amp input is easily modified just by changing the input grid-leak to 10M.

The Martin guitar likely has a preamp built in, and the PV bass has high output passive pickups. Any preamp will handle both easily, so you just have to decide if you want it to be tube or solid-state. If tube, the basic Fender pre is useful for both: gain stage > EQ+volume > gain stage. If you are taking a line out to the mixing board, add an output level control and a buffer.

With the first volume and output level, you can get a mild overdrive sound for either instrument. Or, set it one way to compress the bass a bit and then set it for clean headroom for the guitar. Very easy to adjust.

Others will tell you that the "requirements" for bass and guitar are too different to use the same signal path for both. That is lethargic thinking. Some of the best bass sounds were recorded using guitar amps, and similarly some of the best guitar sounds were made using bass amps. Our TUT-series books describe how to achieve great tone with any instrument.

Have fun
Kevin O'Connor
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Old 25th June 2013, 04:58 PM   #4
Msr898 is offline Msr898  United States
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Quote:
Originally Posted by chrispenycate View Post
The problem isn't in the double preamp (you might even be able to find a dual input guitar amp which can do two decent clean channels) or the mixing; it's in the speaker requirements. An acoustic guitar wants a lot of clarity in the high frequencies, and doesn't worry about real low frequencies at all, whereas a bass needs its clarity in the mid range, but wants real solid power in the lows. An electric bass is going to tend to need much more power than an acoustic to balance with other instruments or voices, while the acoustic will feed back much faster, even with contact mics. A speaker that can deliver all this loud enough to be useful for outside gigs is going to be a studio monitor, or one designed for reproducing full range premixed music.

Assuming, of course, that you're not intending to run the output through a remote PA, with what you're planning just a local monitor. In that case you're probably better off feeding the two instruments out separately, (full balanced outputs and ground lift, the works) and only mixing for yourself; PA guys don't tend to trust anybody else's eq or balance.

So, apart from the standard preamplifier functions (gain and equalisation), what do you generally use? Compression on the bass, or a short reverb on the guitar, for example, or completely clean? It would be handy to know what kind of performance you're planning on, and if there will be other musicians involved.
I play mostly clean. So basically what ur saying is really I need 2 amps hooked to 2 different sets of speakers. Is there any way to run one 2 channel amp through 2 eq's then to one set of speakers?
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Old 25th June 2013, 05:23 PM   #5
Struth is offline Struth  Canada
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Hi Guys

A Fender Twin Reverb amp has two preamps that mix together. With a simple mod, both can have reverb and trem.

No need for multiple amps for the two instruments. Just play within the capability of loudness that the amp you choose can provide.

Have fun
Kevin O'Connor
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