FX Loop - Series or Parallel

[ChasFred]

OK now, My new Mesa Subway Rocket has a parallel FX Loop. I have never owned an amp with a FX Loop. I recall talk in the past some where about pros and cons to the two different types of FX Loop. What is the general thought on this. If I wanted to convert it to a series circuit it would be very simple.

Let me know your thoughts on this.

 

[RVA]

OK now, My new Mesa Subway Rocket has a parallel FX Loop. I have never owned an amp with a FX Loop. I recall talk in the past some where about pros and cons to the two different types of FX Loop. What is the general thought on this. If I wanted to convert it to a series circuit it would be very simple.

Let me know your thoughts on this.

Do you mean Serial/Parallel? I am no expert, but, as I understand it, a parallel loop has signal going into it that is unprocessed by the front end. A wet/dry dial allows you to mix the processed/unaffected (serial/parallel) singals in the FX loop. If it does not have a wet/dry and is truly parallel, you just get the dry/unprocessed signal from the guitar in the loop. Most people put things they want to keep "pure", like modulation and noise gates, in a parallel loop.

 

[Hackmaster]

I'm not much of a pedal user, but this is an interesting question. and I'd love to hear a good explanation.
Both my Mesa's have an effects loop, but the F30 has a parallel loop with the mix knob on the back.
The RectoVerb 25 has a series loop with no mix knob.

 

[ChasFred]

Mine has a mix knob in the back also.

Do you mean Serial/Parallel? I am no expert, but, as I understand it, a parallel loop has signal going into it that is unprocessed by the front end. A wet/dry dial allows you to mix the processed/unaffected (serial/parallel) singals in the FX loop. If it does not have a wet/dry and is truly parallel, you just get the dry/unprocessed signal from the guitar in the loop. Most people put things they want to keep "pure", like modulation and noise gates, in a parallel loop.

My amp has a parallel FX loop. There is a mix knob on the amp so that when /if I use it I can control how much dry and effects are fed to the power section.

Hack, how do you like your RectoVerb 25? The vids I have seen on it look pretty interesting.

 

[smitty_p]

In a serial FX loop, the signal is intercepted when you plug into the FX Send jack and is routed through your effects. The signal is injected back into the amplifier at the FX Return jack. The jacks are specially-constructed jacks that incorporate an extra set of contacts that as act a switch when the cable is inserted and removed. Consequently, with no cables inserted into the jacks, the signal just passes from preamp to the power amp section. This explains why there is no mix control with a series loop. You either have your effects in the loop, or you don't. Incidentally, series loops are the most common.

In a parallel FX Loop there is extra circuitry involved. As suggested earlier by others, there are two paths in a parallel loop. One is your "dry" guitar signal as it passes from preamp to power amp. The other path connects to the FX Send and FX Return jacks on the amplifier. This, of course, is where you connect your external effects. This signal path is the "wet" signal. The "mix" control essentially is a blend control that determines how much of the wet and dry signal you want to use. Theoretically, a mix control that is maxed out to the wet signal would effectively accomplish the same audible result as a series FX loop. However, the real result of using the mix control will depend on how the amp builder has designed the circuitry.

I've never used a parallel loop, though the idea does seem interesting.

 

[ChasFred]

That is a excellent description smitty. I have the schematic and can see it, just not patient enough to type it out as well as you did.
I have read that time based effects do not work well in parallel loops.
I was just curious as to whether anybody here had any first hand experience.

 

[Hackmaster]

Hack, how do you like your RectoVerb 25? The vids I have seen on it look pretty interesting.

I'm totally smitten with it, Chas.
I could sell all my other amps, and still be a happy camper with just that one.
But that won't happen anytime soon.

It does cleans, grind, crunch, and molten metal saturated with harmonics and sustain, all in one package.
All at reasonable volume levels. Did I mention how much I like it???

 

[gball]

In a serial FX loop, the signal is intercepted when you plug into the FX Send jack and is routed through your effects. The signal is injected back into the amplifier at the FX Return jack. The jacks are specially-constructed jacks that incorporate an extra set of contacts that as act a switch when the cable is inserted and removed. Consequently, with no cables inserted into the jacks, the signal just passes from preamp to the power amp section. This explains why there is no mix control with a series loop. You either have your effects in the loop, or you don't. Incidentally, series loops are the most common.

In a parallel FX Loop there is extra circuitry involved. As suggested earlier by others, there are two paths in a parallel loop. One is your "dry" guitar signal as it passes from preamp to power amp. The other path connects to the FX Send and FX Return jacks on the amplifier. This, of course, is where you connect your external effects. This signal path is the "wet" signal. The "mix" control essentially is a blend control that determines how much of the wet and dry signal you want to use. Theoretically, a mix control that is maxed out to the wet signal would effectively accomplish the same audible result as a series FX loop. However, the real result of using the mix control will depend on how the amp builder has designed the circuitry.

I've never used a parallel loop, though the idea does seem interesting.

Some parallel loops (like the Mesa ones) are buffered. In the case of the Mesas, it's a tube buffer. My Mini Rec is a 2011, and back then they had a switch on the back of the amp that is a hard bypass for the loop, so if you were not using it you could completely remove the buffer from the signal chain. In practice people said they preferred the sound with it engaged whether they had effect in the loop or not, so Mesa eventually removed the switch. I can tell you, there is a very noticeable difference between the buffered and unbuffered sound in my Mini-Rec. Low end is tighter with it switched out, but it sounds "bigger" with it engaged. Can't say I prefer one over the other, it's actually a cool extra tone shaping feature.