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→Effects Loops
Most modern amps feature the availability of distortion in the pre-amp. Additionally, even when using distortion pedals in front the amp, the pre-amp still provides compression. Many effects should be processed completely after any distortion or compression affects the signal. For example, the delay trails of a delay effect should gradually decrease in volume until they are inaudible. With compression, the trails would have a more consistent volume level until suddenly dropping off. Similarly, reverb would seem to stagnate rather than decay. Distortion would be even worse, with delay trails and reverb being distorted just like the original signal, creating a noisy mess.
An effects loop <u>Effects Loop</u> gives you the option to run effects between the pre-amp and power amp. In some cases, the power amp may still be providing compression or distortion; but it's usually less than the pre-amp.
Amps traditionally have ''serial'' effects loops - the signal leaves the pre-amp from the effects loop send, is processed by any effects in the loop, and returns through the effects loop return to enter the power section. Most effects have mix controls - they split the signal in two as soon as it enters the effect and only process one of them. The resulting "wet" signal is mixed with the unprocessed "dry" signal, with the proportions determined by the mix control. 100% is totally wet, 0% is totally dry, and 50% is equal mixes of both. If all your effects have mix controls, or you always want to run your effects 100% wet, then a serial loop is fine.