Guitar amp effects loop with only one jack: How does this work?

Cafe Society
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Since I started playing electric guitar again during the Covid lockdowns, I’ve just been using a Line6 interface into my computer + modeling software, listening with headphones. This has been mostly great, but the downside is that having both my guitar and the song I’m playing along with in the same speakers/headphones, there’s no separation. That’s fine for jamming along with a song I already know well. But if I’m trying to work something out by ear, the sound of my guitar tends to bury the recorded track as soon as I try to play along.

I came to the conclusion that I needed to get an amp, so that the recording can be over here, and my guitar sound can be over there, and I can keep them separate. Then I remembered I had a cheap practice amp, purchased more than 20 years ago, buried in a closet.

It’s this one here:

My question is about the EFX loop. I’ve seen effects loops on better amps, and those tended to have two jacks: “Send” and “Return”. I’m rather perplexed as to how it is supposed to work with only one jack. Obviously, I can’t plug my guitar into a pedal and then run that pedal into the “EFX Loop” jack and expect to get any sound out of it when there’s no cable running to the actual input jack. (Tried it anyway, got the expected result.)

Not having any actual previous experience using an FX loop, the only “obvious” solution to me is to use a Y-splitter to send my guitar’s signal to the pedal and to the amp’s input jack simultaneously. But I don’t know if that would be correct.

Alas, if this amp even came with an instruction manual, it’s long gone.

The pedal in question is a BOSS Metal Zone distortion. I’ve watched a number of videos about this pedal, addressing some of the complaints about it, and several of these videos reached the conclusion that the pedal is intended to be used in the FX loop. Indeed, they all seemed to get better results that way, as opposed to running it into the input jack.

In any case, using this pedal with the amp isn’t vital. I’m currently running a line from my Line6 interface to the amp, and that allows my modeled sounds to come through the amp. I’m mostly just curious how a one-jack loop is supposed to work.

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If I’m reading things correctly, and I may not be, I’m not a guitar player, it’s an input that bypasses the preamp and goes directly to the power amp side. Something about some pedals not playing nicely with the preamp side of things and causing issues/distortion.
ISTM, calling it a ‘loop’ has more to do with the internal circuitry than it being an external loop for you to add your own effects.
This thread on reddit seemed to have the best explanations that I, again a non-guitar player, found.

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1: You can probably get the manual online by contacting Kramer directly;

2: That jack is a “Tip, Ring, Sleeve.” Basically, it’s its own effects loop jack — an output and input in one. Using a stereo cable, wired correctly, will allow you to use pedals into the amp. It’s been decades since I’ve messed with amps, so there are things I can’t explain further, but that’s a start.

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I would be so tempted to try putting a pedal between the phone out and the EFX in.

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IMPEDANCE MISMATCH!! DANGER! DANGER!

That does not compute.

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This might make it clearer: https://www.henriksenamplifiers.com/product/trs-sendreturn-y-cable/

The same cable has different channels, and they can send or receive. In that example, the tip sends and the ring receives. A single jack becomes Y, and the two jacks it splits into doesn’t have the rings.

In other TRRS cables (like a stereo headphones + mic cable), there might be two channels send (left/right to headphones) and one receive (mic).

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This has a better diagram: https://www.tc2290.com/docs/cables_insertysplit.pdf

(It doesn’t necessarily need a Y though… it could be a TRS jack on both ends… but it looks like the MT-2 does have separate inputs/outputs, so a splitter there probably makes sense)

Here are some example cables: trs insert cable - Sweetwater (you can call them on the phone too, they’re usually pretty knowledgeable)

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Thanks, that clears things up nicely!

Yikes! That cable costs more than I think I paid for the amp! I’ll assume there are less pricey options out there. But it’s good to know what I’m looking for.

The main reason I’d like to use the distortion pedal with the amp is simply to be able to switch between clean/dirty sounds on the fly on songs that use both–something I can’t do at all with my computer-based modeling software. The amp itself has separate overdrive & clean channels, but there’s a push button on the amp itself to switch between them which is, again, not really doable on the fly while still playing.

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Yes, sorry, see the other link (trs insert cable - Sweetwater) for cheaper cables. That one was just the first one that came up, but you have a lot of options.

Though please double-check this with someone who’s done this setup before, or ask their salespeople. (I’m also not a musician, just someone with an interest in cables)

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FWIW, I believe the output from that jack is “post-pre-amp,” and the return is “pre-power amp,” so if you have a properly-wired (read: non-stereo) cable, you could run the guitar into the pedal(s) then directly into the power amp. I’m sure there are reasons for doing so but I’m not sure why you’d rig it that way; pretty sure someone will have a slam-bang explanation, though, so I’m anxious to hear it, too.

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@burpo_the_wonder_mutt , where have you been? We were worried.

Glad you’re here.

(Sorry for the hijack)

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You will need a breakout cable like this:

It is plastic, but Strymon is a highly regarded company (mainly for their boutique guitar pedals), and I would trust that anything they sell is of high quality.

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You could solder together such a cable out of wire and connectors. My very first attempt was rather… delicate with respect to rough handling, but it still worked.

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You used to be able to buy 100% of the components and tools needed to fabricate that yourself by walking into Radio Shack, back when they existed.

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Or Fry’s Electronics, back when they existed. Microcenter seems to carry a few parts and the tools needed to kludge up a solution, but it would be ugly.

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(Take all of the below with a grain of salt, as I am not an amp signal expert or an EE. I am open to being told I am wildly wrong).

Actually, not so obvious. Theoretically, you ought to be able. Think about the EFX loop as an output and an input (others have explained how that his happening on the same cable).

Based on this schematic the effects loop in this amp is splitting the signal after the amp section and sending some to the EFX out via the ‘R’ of the TRS cable, and then taking an input from the ‘T’ of that cable and proceeding through the EQ section and then to the speaker or headphones.

Note that the signal coming in from that loop doesn’t pass through any amp that you have output control over (this is… not great design). There is no knob on the amp that increases or decreases the level of the signal coming in from the EFX return.

All that is to say, other than amp design, there is no inherent reason why you would need to have signal running into the main input in order to hear something coming in on an FX in. It’s just another input. It all depends on where that input comes in in the signal chain. On this specific amp it looks like that input is post-amp, and so there is no way to adjust the ultimate output level of that signal. have no idea if the Boss Metal Zone output is hot enough to be heard.

I defer to others, but one thing I’d try is using a TRS like this ($9) from your pedal to the amp. Sometimes a jack expecting a TRS cable will not work at all with a TS cable. The Boss pedal will still send signal as expected (it will send through the Tip band, which is what the amp is expecting to receive on).

But, if you don’t already have a TRS cable to test with, I’d just buy what @Hoops recommended or even simpler this TRS breakout cable ($12), plug the guitar into the input of the amp, and run the Boss pedal off of the FX out, being sure to use the cable labeled “Ring” as the input to your pedal, and “Tip” as the output.

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I think this is backwards. I originally read this the same way as you so I could be wrong.

On the schematic (nice find BTW), the bottom conductor of the effects jack is Tip. This is the output to the amp. On the schematic it’s connected to the output of the preamp (upper-left), the reverb (lower-left), and normally the Ring of the jack which eventually connects to the treble input (upper-right).

The top connector is Ring and is an input to the amp, the output of the effects, shorted to Tip when not plugged in, and connected to the treble input.

As the plug is inserted, Tip will make contact and then Ring.

This site was useful: Understanding Audio Jack Switches and Schematics | Same Sky

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I gotta say I’m impressed at the sheer number of incompatible ways the audio industry has abused 1/4" phone jacks.

How about using discrete connector designs so if the plugs & sockets mate, the electronics (and power capacity and shielding of the cables) are compatible?

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I had no idea that connector was invented in 1877:

Consider it took us 119 more years to invent USB A connectors with the innovation that it requires an average of three attempts to plug in a connector that only has two options.

Then another 18 years to fix that with USB C connectors. Progress!

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Yeah, that was probably part of the issue. I didn’t know what the “TRS” meant, so plugging in a standard guitar cable was a mismatch.

In any case, I do have a suitable split cable coming, so I’ll see how that works out.