Question About Amps

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Member Since: Nov 29, 2004

Okay, maybe more then one…

I am slightly confused about the concept of preamps. What are they for? What do they do? I know I need one – whether its part of the mixer of separate – but I also know there are things that “work as a preamp” such as the Pod. I ask this question because I feel that if I know the function of a preamp, I will be able to decide what can do the same job and what can’t.

Also, if I put my guitar into the POD, should I then put THAT through the mixer or right to the card?


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Since: Apr 03, 2002

Nov 29, 2004 09:04 pm

Preamps boost the signal of a mic to the level that recording equipment require for a decent signal, if you plug a mic straight into a sound card you will get a very weak and thin sound, preamps provide some power to the sound, as well as a place to loop effects thru and shape the sound.

Since: May 09, 2004

Nov 29, 2004 09:35 pm

There are also different types of preamps. But they all pretty much have the same function:

To slightly boost a very weak signal such as those generated mics and instrument pick-ups. (remember, they usually generate their electricity from sound waves causing deviations in a magnetic field.)

The POD you mentioned has a preamp meant for pickups but wouldn't be suitable for mics. With the POD you really don't need a mixer just plug the lineout from the pod into a/the 'line in' on the sound card. You could use a mixer in between but I don't recommend it unless you have a specific need for it as it may color or degrade the signal a bit.

Good luck.

Chief Cook and Bottle Washer
Since: May 10, 2002

Nov 29, 2004 11:14 pm

It's all about Unity gain or that place on the VU meter that shows 0. To get a signal to that amplitude in professional gear the signal has to be amplified to +4dB (Yup another industry wierdism, 0dB on professional equipment is actually +4dB) or .775 volts RMS (DC equivalant). This is also called line level on professional equipment. Mixers, sound cards, recorders, power amplifiers, etc. need a line level input. Microphones and most instrument pickups do not achieve this level and need to be amplified to line level. And so walla! the pre amp. Instrument amplifiers, PA amplifiers and many mixers have pre amps built or integrated into them.

The ohter consideration with pre amps is the tonal characteristics of the signal. Solid state amplifiers have a degree of enherent "hiss", "air" or crisp sterile sound. Tube pre amps are generaly warmer, less linear across the audible frequeny range, and at high levels of amplification offer a unique distortion that is precieved as "soft" or pleasant compared to their solid state counter parts.

Many units have pre amps built into them. The POD for example has a pre amp as well as a sound effects generator, and a DI or direct injection impedience matching unit. Please forgive me for not expounding on impedience matching. It is yet another physical law that governs the flow of electricity and effects the tonal charistics of a signal. Sufice to say most instrument pickups do not have impediance characteristics that work well with standard line input gear. A DI circuit is needed to correct these characteristics.

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