# Jumper in FX loop....why??



## Verne (Dec 29, 2018)

I've seen many pictures of amps with a patch cord jumping the FX loop. I suppose for me to really get it can you explain in layman explanation, why is this? Does whatever it does work on every amp? I have my TM36 and my Fender London Reverb that have FX loops. Will it work on either or both of those? Just curious. 

I've seen it done on multi input amps as well, but mine don't have the multiple inputs for that, so not really wondering about that at this point.


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## knight_yyz (Mar 14, 2015)

Only works on some amps. Not sure what it does though. Try it see what happens


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## Budda (May 29, 2007)

Gets the full headroom/wattage of the amp in some cases. Thats how it was with my peavey jsx.


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## mhammer (Nov 30, 2007)

It's the manufacturer's choice whether to wire up the jacks as "normalized" (i.e., automatically connected to each other unless something is plugged in)...or not.


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## Latole (Aug 11, 2020)

There are two types of FX loops to my knowledge and to make a long story short:

In many amps internal contacts to the IN and OUT jacks do exactly the same as a patch cord:
Connect the preamps to the power amp.
Installing one won't change anything.
Sometimes these contacts become out of order and the use of a patch cord is used to put the amp back into operation.

Other amps have a special FX Loop circuit.
Installing a patch cord allows you to bypass this circuit which can undoubtedly have an effect on the sound? Or these circuit may have a little signal loss. With patch cord you may have more gain ? I do not know.

By the way subject is more for a Amp sub-forum than Guitars sub-forum


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## greco (Jul 15, 2007)

Latole said:


> By the way subject is more for a Amp sub-forum than Guitars sub-forum


That is an excellent point. Maybe @davetcan will move the this thread and that will result in it getting more exposure and traction.


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## davetcan (Feb 27, 2006)

Some loops have a volume/level control, I used to use it as an attenuator.


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## Pewtershmit (Jun 13, 2014)

davetcan said:


> Some loops have a volume/level control, I used to use it as an attenuator.


or in some cases a boost!


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## colchar (May 22, 2010)

davetcan said:


> Some loops have a volume/level control, I used to use it as an attenuator.



Exactly. I used to have a Marshall TSL and on that jumping the loop worked like an attenuator.


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## Verne (Dec 29, 2018)

My London Reverb has an FX loop level control, but it's SS anyway. My TM36 does not have this. I'll try jumping it and then pull it and see. I generally use the 5w setting now anyway so I can push the volume up a little more and use the tubes.


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## jb welder (Sep 14, 2010)

It's often used for reliability. The return jack often has switch contacts which are closed when the loop is not being used. It routes the preamp signal through to the power amp (and 'breaks in' to the circuit when loop in use).
If those jack contacts get dirty or oxidized, you will have problems with signal fade, or cutting in and out.
Putting a patch cord between the send & return bypasses those switch contacts so the preamp is 'hard-wired' to the power amp and the intermittent cutting out issues are eliminated.


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## Verne (Dec 29, 2018)

@jb welder So it's a good idea to put a jumper in regardless if it does anything or not? I have plenty of short pedal cables in a box. If no harm can come from it, and it could avoid an issue, I'm going down and jumping them right now.


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## jb welder (Sep 14, 2010)

Verne said:


> @jb welder So it's a good idea to put a jumper in regardless if it does anything or not? I have plenty of short pedal cables in a box. If no harm can come from it, and it could avoid an issue, I'm going down and jumping them right now.


No harm can come from it.
If you want to know if your loop has the switching jack, while you are playing, plug one end of a patch cord into the 'fx return' (or 'power amp in') jack. If it kills the sound, it's the switching type jack (series fx loop). Then plug the other end of the patch cord into the 'fx send' (or 'pre-amp out') jack and the sound shoud be restored.


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## Verne (Dec 29, 2018)

My London reverb has FX loop and also Preamp out and Power amp in. TM36 only has FX loop. I'll try on both later.


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## BlueRocker (Jan 5, 2020)

jb welder said:


> It's often used for reliability. The return jack often has switch contacts which are closed when the loop is not being used. It routes the preamp signal through to the power amp (and 'breaks in' to the circuit when loop in use).
> If those jack contacts get dirty or oxidized, you will have problems with signal fade, or cutting in and out.
> Putting a patch cord between the send & return bypasses those switch contacts so the preamp is 'hard-wired' to the power amp and the intermittent cutting out issues are eliminated.


The best answer by far. Better than I could have described it for sure.


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## jb welder (Sep 14, 2010)

Verne said:


> My London reverb has FX loop and also Preamp out and Power amp in.


Hmm. According to the schematic, they both have switched returns. So you could use 2 patch cords. But I'm not sure if they are both active all the time or you select a loop with footswitch or front panel switch?




BlueRocker said:


> Better than I could have described it for sure.


I'm not so sure about that.


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## BGood (Feb 20, 2015)

Will several patch cords linked with pedals have the same effect as a single patch cord ?


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## jb welder (Sep 14, 2010)

BGood said:


> Will several patch cords linked with pedals have the same effect as a single patch cord ?


I'm not sure I understand your question. 
If you mean, will it still get around the potential problems with the fx loops' switching jacks? Then yes. But all your pedals and patch cords and connections have to be good or you can introduce the same kind of cutting out issues.


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## BGood (Feb 20, 2015)

jb welder said:


> I'm not sure I understand your question.


It was a tongue in cheek comment. Does it matter if the loop is closed by a single patch cord or a chain of them (with pedals in between) ?


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## jb welder (Sep 14, 2010)

BGood said:


> It was a tongue in cheek comment. Does it matter if the loop is closed by a single patch cord or a chain of them (with pedals in between) ?


The single patch cord often has superior sound (compared to with pedals).


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