We've all done it.
We've all come to use a professional grade amplifier for the first time in our lives, spotted something labelled as an "Effects Loop" ( or FX Loop ) and thought "Why do my effects need a loop...and what the hell is a loop!?".
Fear not, for its actually a really easy concept to get your head around and on top of that, a very useful feature to have at your disposal.
The effects loop of an amp is designed to give you the ability to put certain types of effects AFTER the preamp stage of the amplifier in question. "Whats a preamp?", a hear you moan, lifelessly. Well my damp little squib, an amplifier is made up of two main sections; the preamp, which is what shapes the sound ( think bass, middle, treble and the overall amount of input gain ) and a power amp, which is what pushes that sound to the speakers ( this section can also add gain of it's own, if the amp is turned up too loud and overdriven. You should always turn the amp up too loud. ).
So why would you want to put certain effects after the preamp section? Well if you are using the amps overdrive for your dirty sounds ( like you wound on say a Peavey 5150 ) then time based effects like delay and reverbs may sound a little mushy and lost, running straight into an already distorted amp. In the effects loop they would only ever run into the much cleaner poweramp, meaning your delays and reverbs would be considerably clearer overall, even when you've got your dirty channel cranked!
Not all amps have effects loops such as vintage amplifiers and pedal platform amps ( very clean amps that are perfect for running pedalboards into ) however exactly the same theory applies for your pedalboard. Time based effects tend to live AFTER your overdrive and distortion pedals for the sake of clarity.
None of us can quite agree where chorus should go. Personally I like it in the loop but several of my friends have stopped inviting me over for dinner since I vocalised the above at a party one time...
The most important piece of advice as always, is to experiment! If you like your delays in front of your amp then you run them in the front! Enjoy a fuzz pedal in the loop? Well that may make you psychotic but whatever! Fill your boots!
Just be careful not to tell people at parties.
See you soon!