What are the differences between Serial and Parallel loop on a guitar/bass amplifiers. What are the benefits for each of them in the use of G-Force, G-Major, G-System, G-Sharp?
Many combo amplifiers and heads have an effect loop, however, there are no standards for these loops. At times it can be hard to even see it is a serial or parallel loop.
A serial loop interrupts the signal path between the preamp and the power amp - just as if theywere two separate units. This means the entire signal from the preamp travels through the processor and re-enters the power stage. It is basically a one-lane road going from one place to another.
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Parallel loops offer two paths from the preamp to the power amp. One path is a direct connection from the preamp to the power amp as if the amp had no loop at all. The other path sends the preamp signal to the effect processor (via the loop) and then routes it back to the power amp, mixing it with the direct (dry) signal.
Most amps that offer a parallel effects loop have a variable mix knob, so that you can control how much of the effect you want mixed in with the dry signal.
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In a parallel loop situation you wish to avoid direct signal to pass the unit. Therefore set all mix levels in the G•Major/G Force (and set Killdry to ON)/ G-System to 100% and control the effect amount using the Output parameter in each effect. The Mix between dry signal and wet signal will be done with the amp MIX control. Note that most amp do not offer a programmable mix control, and the mix position will be the same for all effects.
How do you choose one over the other?
Optimum performance of the G•Major / G-Force / G-System is achieved using a serial loop. With a serial loop you will get maximum performance from especially level changing effects such as tremolo and compression but also chorus and EQ. As mentioned previously, it is worth noting that due to the high quality AD/DA converters used in TC units the sound quality will not be degraded. Furthermore, the mix settings are saved by preset and that is a huge advantage: a chorus Mix will often be around 50%, while a delay or reverb mix might be at a quite different value.
The parallel loop is preferred when using vintage effects and effects that don't have any kind of mix function and that sometimes suffer from bad signal-to-noise-ratios. Lately it seems as if there has been more of a return to vintage effects and stomp boxes, which has probably caused more of an interest in the parallel loop.
However, as mentioned above a parallel loop does not work well when using effects that change the volume of the signal (such as tremolo, compression, or noise gates). Mixing the wet and dry signals on these loops can also at times cause an "out of phase situation". Also, as mentioned above, on most amps the mix control is not programmable, and you'll have to use the same mix level for dry/wet.
Technically, if you turn the mix to 100% on a parallel effect loop, it should operate exactly as a serial loop, however, this is not the case with all amplifiers on the market.
Conclusion: the G•Major / G-Force/ G-System/ Nova system (most TC guitar multieffects) will work with both serial and parallel loops but for the reasons mentioned above, we recommend using them in a true serial loop if possible.
To find out what type of loop your current amp is equipped with, please contact the manufacturer of your amp.