How to use the Effects Loop inputs on an Amplifier

Marshall MG102 CFX Effects Loop equipped Most of today's popular amps, such as the Marshall MG102 CFX pictured above, come equipped with Effects Loop inputs.

Have you ever wondered what those two inputs labeled “Effects loop” found behind many bass and guitar amps actually do, let alone how to use it properly? It’s not as hard as you might think! It essentially comes down to the basics of the signal path.

For those of you unfamiliar with the process, the whole thing starts from your electric guitar or bass. When the signal from the pickups reaches the amplifier, it goes through a preamp, an equalizer and power amp (in that order), after which it goes to the speakers. Not much more to it as far as the basics go but most musicians are not satisfied with just the basics! Most of them want to add effects, such as the kind you get from pedals – delays, distortions, compression and the like. Where would they go in the path?

Technically, you can put them anywhere you’d like as long as it’s between your guitar and the amplifier but if you want the best sound possible, certain effects sound better as specific points in the signal path. Distortion and compression effects for example sounds best before they hit the preamp, in other words, between the instrument and the amplifier.

But not all effects work best this way. Time-based effects for example work best when the signal from the instrument when it hits the amplifier’s preamp and EQ section first and then your effects, yielding a cleaner, more pronounced sound. In other words, between the amplifier’s preamp and power stages. This is exactly where the effects loop inputs play their part.

Most effects loop inputs let you do exactly that – designate outboard effects between the preamp and power of the signal path. Naturally, the effects loop inputs are usually found on the back of the amplifier and consist of two jacks – return and send. Some amp’s effects loop might even boast extra features such as their own level controls. When the loop is in effect, the signal is rerouted to your effects pedals through the ‘send’ after it has gone through the preamp and EQ stages. Afterwards, the signal is brought back to the amp through the ‘return’ until it passes the power amp.

Time-based (or modulation) effects like chorus, delay, phasing and flanging usually sound best when they aren’t colored by the amp’s preamp and EQ circuitry, which is why they work so well in an effects loop. For example, some of these effects—especially flanging and phase shifting—produce an ambient “whooshing” noise that is audibly accentuated by the preamp when these effects are placed between the instrument and the amp. To avoid such unwanted noise, these effects can be placed in the effects loop, where their ambient operational noise isn’t amplified as much because the signal isn’t sent to the outboard effects until after it has already gone through the preamp.

Well, there you have it – the effects loop – not such a big deal after all! In any case, the effects loop of an amplifier is just one of many helpful tools at your disposal. Be sure to make good use of and never be afraid to experiment with effects placement. You never know what sound lies just around the corner!

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