Amplification Part 2: Pre Amp and Power Amp

As touched upon in part one of my guitar amplification guide, one important thing to understand about guitar amps is the difference between the pre amp and power amp stages. A good understanding of the stages of an amp will allow you, as a player, to really experiment with the placement of effects and try different setups in order to get the best possible sound from your gear.

The smaller tubes make up the pre amp, while the two bigger ones at the back are part of the power amp

The smaller tubes make up the pre amp, while the two bigger ones at the back are part of the power amp

Basically, most amplifiers consist of two main stages, the pre amp stage and the power amp stage. When you plug your guitar into the main input (located on the front of the amplifier head), your signal goes through the pre amp, where the EQ and gain controls can alter the tone, then moves on to the power amp stage which provides the raw power used to make the signal stronger before going to the loudspeaker. Bass, middle, trebble and gain are usually part of the pre amp, while master volume is part of the power amp stage. This idea becomes really useful to musicians when we consider one other thing that good amplifiers tend to have: an effects loop. Effects loops are a send and a return jack usually found on the back of the amp. The send jack takes the signal straight from the pre amp, and the return jack goes straight into the power amp, which basically means that by taking advantage of the effects loop you are able to place effects both before and after the pre amp. By plugging directly into the return jack you can even bypass the pre amp completely, and just use the power amp stage to amplify your sound.

Baring in mind that compressors should always be placed first in an effects chain (see my guide on compressors here), and that overdrive pedals are designed to naturally boost the signal going into the pre amp to force it into overdrive, it makes sense that these pedals should be placed between the guitar and the pre amp, and not in the effects loop after the pre amp.

Effects that can be placed in an effects loop to great results are distortions, modulation pedals like flangers or choruses and delay pedals. The setup might look something like this:

Guitar > Compressor > Overdrive > Pre amp > (Distortion > Chorus > Delay) > Power Amp > Loudspeaker.

Alternatively, distortions could also be placed before the pre amp for different tones, but modulations are best after, as it is usually better to modulate a distorted signal rather than distort a modulated signal.

As for bypassing the pre amp stage altogether and going straight into the power amp, remember that you will need a good powerful overdrive to provide the necessary gain and act as a kind of pre amp in its stead. Also, preferably one which allows for control over bass, middle and treble levels so that you don’t lose the option of EQ. A setup going straight into the power amp might look like this:

Guitar > Compressor > Pre amp substitute > Distortion > Chorus > Delay > Power amp > Loudspeaker.

All of the above methods will yield completely different results, and so being aware of the different stages of the amplifier and exactly what each stage is responsible for can really open up your playing. There are many different ways to connect the same gear to get different tones, and the best way is to just sit down with your guitar and spend some quality time getting to know your amp!

Thanks for reading, please feel free to share this article if you found it interesting!

See you next time.

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  1. […] mentioned in my previous blog post about the different stages of amplification, a tube amp works with two main stages, the pre amp and the power amp. The pre amp is responsible […]

  2. […] same, and the only real difference is the positioning of the pre amp in the chain. As stated in a previous article on the subject, many good guitar tube amps have a built-in effects loop which allows a player to place effects […]

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