# whats does a Pre-amp do



## Rick31797 (Apr 20, 2007)

On my amp i have a pre-amp output.. can you plug the preamp out to a mixer and the run your mics and pa speakers from the mixer.

Rick


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## mhammer (Nov 30, 2007)

Power amplifiers expect to receive a certain signal level, and are designed and rated in anticipation of that signal level. Everything that leads up to the point where the power stage begins can be collectively referred to as "preamplification", including all pedals used between the guitar and amp input.

In a perfect world, what leaves the guitar amp from any jack labeled "pre-out", or similar, is the sort of signal that the power amp stage gets.

Now, while that is, _in theory_, something that can be sent to a mixer, keep in mind that mixers take in several different types of signal. One is "mic level", which assumes a signal on the order of a few millivolts that will need to be boosted considerably. Another might be "instrument level", which is much higher than voice mic, but still noticeably lower than what feeds a power amp. Finally, it might be able to receive "line level" signals, such as what might come from a CD or tape deck, another mixer, or _the pre-amp output of a guitar amp_.


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## Andy (Sep 23, 2007)

In short, yes. If you plugged it into the line-in on your mixer, and adjusted the gain to bring it to the proper level, yes, you would get some decent signal.

That being said, if there is no speaker emulation, it's going to sound like utter garbage. Overdriving a guitar signal produces a huge amount of treble above 5k that is usually filtered off by the speaker (guitar speakers are *incredibly* low fidelity). Not only do PA systems not have this filtering effect, but the horn drivers in the speakers are very bright and actually emphasize them. For a good approximation of what it will sound like, listen to the solo in Sympathy for the Devil. Cool effect? Sure, but it would suck having that as your main tone.


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## keeperofthegood (Apr 30, 2008)

So, if you designed for a "pre-amp" out-put point in an amp design, it would benefit you to put in a low-pass filter with a 4K or 5K knee point and a leveler so that your signal out doesn't fry whatever you want that signal put to?


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## Andy (Sep 23, 2007)

keeperofthegood said:


> So, if you designed for a "pre-amp" out-put point in an amp design, it would benefit you to put in a low-pass filter with a 4K or 5K knee point and a leveler so that your signal out doesn't fry whatever you want that signal put to?


Frequency filtering is only one part of the equation. I'm *well* out of my league on this, but I'd imagine a simple low pass (and high pass -- there's alot of rumble from your hands and misc resonances that a guitar speaker doesn't reproduce) would give you a really clinical, EV-like sound. Not that that's a bad thing. I love that sound in the right application.

I'd rip one of these apart and put it in the amp. There's more to speaker emulation than just a low pass -- a guitar speaker has all kinds of nonlinearity, weird frequency dispersion, etc., that make it ridiculously hard to model electronically, and give us the familar guitar tone. From what I've heard, Palmer has gotten rather close. Close enough for live use or quick recording, I'm sure.

The closest thing would probably be to use an impulse response, but that's rather hard to incorporate into a live rig.


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