Effects FX Loop: Considerations and Tips
By Eric Jacobs (*)
Effects Loop or FX Loop, an extremely practical tool when looking for a variety of audios. We tell you what to consider so that it does not become a headache when putting together your sound.
What is the FX Loop or FX Loop?
The effects loop or FX loop is actually a separation into blocks of the amplifier, where it is divided into preamplifier and power amplifier. The input is the input of the preamp and the Send is its output. The Return is the input of the power stage and its output is the connection to speakers. Because the Input, Send and Return can be connected to pedals, the same signal level is handled at all these points: on the order of -10dBm. In this partition we can insert pedals between the send and the return and that way they remain after the pre in the audio sequence. Therefore they are low level signal points that are susceptible to noise capture.
Signal to Noise Ratio
This is where the Signal / Noise ratio parameter is important. It is impossible to completely eliminate noise, but if we have a good signal-to-noise ratio, it will no longer bother us so much, it will only be heard in the audio silences, which can be cleaned with a noise gate.
Since the amp is a few meters away from our pedalboard, we need to bring the signal from the pedalboard to the input, then back from Send to the pedalboard and finally back to the Return of the amp. Those three cables are the same length and must be shielded because they handle signal, which implies that their shield must be connected to ground. If we think about it a bit, we realize that we are causing a great mass loop with these cables. In fact there are three loops.
What is a mass loop?
A mass loop is a closed mass ring in which alternating currents of large values can be induced due to nearby transformers radiating stray magnetic flux.
But the amount of induction depends more on the area of the loop than on the length of the cables. So the way to reduce that induction is to pack all three wires – or four if we include the channel control wire, etc. of the ampli- so that the cables do not enclose area or surface between them. This can be done with tape, frequent seals, or a special container in the form of a flat spring that comes to do this. To facilitate the connections it is necessary to label each of the plugs at both ends.
(*) The author is the renowned manufacturer of amplifiers, pedals and other products “Jake Amps”.
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