cedricsmods

So you have a combo (meaning that it contains both an amplifier and speaker(s) inside the same enclosure), and you want to use it as a cab (speaker(s) only) or a head (amp only).

This tutorial will show you two different types of mods. You can do one or the other, but not both.

Disclaimer: the new output jack on the amplifier should be used only with a cab that has impedance equal to the combo's stock speaker.

Option A: adding a speaker-out jack that disconnects the internal speaker when an external cab is connected.
This is useful if you want connect the amplifier section of the combo to an external speaker cab. For example, to plug a small combo into a 4x12 cab. This is especially useful for a combo with a small speaker, if you do not intend to connect an external head to the combo speaker, but do want to be able to use the combo's amp section with an external cab.
(if you use this method, you cannot use the combo's speaker with another amp.)
This requires a Neutrik-style switching jack like the one I use in the pictures.

Option B: using the amplifier section and speaker cabinet separately.
Use this option if you want to be able to plug a different amplifier into your combo's speaker(s). This is especially useful for a combo with a large speaker, in case you want to be able to plug a different head into the speaker. For example, to use a 2x12 combo as the speaker cab for a head.
You can use a Neutrik-style jack like I do, or a traditional Swithcraft-style jack.

Since this question is asked frequently, I have decided to do everyone a favor and provide some step-by-step instructions with accompanying pictures.
For this tutorial, I am using a Peavey Rage 158. It is a small, inexpensive practice combo that came with my first guitar in a starter pack. This combo is not really worth using as a head or speaker, but I am using it because it is the only unmodded combo I have on hand.

You will need a screwdriver to remove the amp from the enclosure (if you choose to do so), a soldering iron and solder, 1/4" (6.3mm) jacks (1 switching jack for Option A or 2 regular or switching jacks for Option B), electrical wire, a drill with bits designed for metal, bits for wood (if you want to mount a jack on that).
Unplug your amp before working on it. If it is a tube amp, you should safely drain the capacitors before working inside it. Wear safety glasses while soldering. Be smart and don't die or burn your house down.

A few tools



Part 1: Adding a speaker-out jack to the amplifier section.
1. Disconnect your speaker.
You might have to remove a back panel or something, depending on the design of your combo. Once you get to the speaker(s), find the wires leading from the amp to the speakers. For a single-speaker combo, this is easy, there are two. Disconnect them. They might be simply pushed on, or they might be soldered on. See if there is any indication which terminal on your speaker is positive and which is negative, sometimes they have symbols, or sometimes the + terminal on the speaker is painted red.
(For a 2 or 4 speaker combo it is a little more complicated, and I don't have pics because I don't own one, but if you ask I will help. If anyone wants to donate a Fender Twin, Mesa combo, or any Tophat, Matchless, or Dr. Z combo so that I can provide more comprehensive instructions, I will happily accept. )

Speaker wires. On my amp, Yellow is +.



2. Remove the amplifier
Once the speaker is disconnected, we remove the amplifier from the enclosure. How this is done will vary depending on your model of combo, so you are on your own for this step.

Here I have removed the amplifier, and you can see the same two wires that were removed from the speaker.



3. Wiring your new speaker-out jack
First locate where you want the new jack. Make sure you will not be damaging anything inside the amp by drilling it there. If you indent the spot you want the hole slightly with a nail-set tool and hammer, the drill will be less prone to slip out of place. Use a drill bit designed for metal.

About to indent where I am going to drill


I have now drilled the hole, and inserted the jack.
Now you take those two wires that used to connect to your speaker and wire them to your new speaker-out jack.

Positive goes to the tip, negative goes to the sleeve.
If you are using a Neutrik jack (as I am) you must be sure to connect the wires to the primary lugs (the ones with the long leaves.) There are some close-ups and explanation later in the tutorial.

Behold, the new speaker-out jack!


Make or buy a new enclosure for just the amp, and presto! you have a head.
You can now use a speaker cable to plug your head into a cab.
Please, please, please keep in mind that whatever cab you use must match the impedance for which the amp is rated.

The only thing that should be plugged into this speaker-out jack is a cable going to a speaker. No headphones, no second amp.

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cedricsmods

Part 2, Option A: Speaker-out jack that disconnects the internal speaker when a cab is connected.
This is especially useful for a combo with a small speaker, if you do not intend to connect an external head to the combo speaker, but do want to be able to use the combo's amp section with an external cab.

In order for this to work, you must have used a Neutrik-style jack in Part 1. Wire the jack to the amplifier output as shown in Part 1. Then you simply connected the + and - from the combo's speaker to the seconday lugs on the Neutrik jack. When nothing is plugged into the jack, the secondary lugs are connected to the primary lugs, and the signal goes to the internal speaker. When an external cab is connected, the plug lifts the switching leaves on the Neutrik jack which disconnects the internal speaker.

Pictures of how the jack works:


Here is a pic of a Neutrick Jack. The lugs with the long leaves (top row in the pic) I call the primary lugs. These are where the amplifier output connects.
The bottom row in the pic is the secondary lugs. These connect to the internal speaker.
Note that when nothing is plugged into the jack, the leaves make physical (and therefore electrical) contact between the primary and secondary lugs. This means that when nothing is plugged in, your signal goes to the internal speaker.



When the external cab is plugged in, the leaves are lifted which breaks contact and the secondary lugs (and therefore internal speaker) are disconnected.



Here it is all connected. Yellow is + from amp. Blue is - from amp. Red is + from internal speaker. Black is - from internal speaker.

Part 2, Option B: Adding a jack for the speaker cab section.
This is especially useful for a combo with a large speaker, in case you want to be able to plug a different head into the speaker.

We will do this in much the same way as step 1, by wiring the speaker to a 1/4" (6.3mm) female jack.


In this picture, the red wire is soldered to the tip lug of the jack and will connect to the "+" terminal on the speaker.
The black wire is soldered to the sleeve lug of the jack and will connect to the "-" terminal on the speaker.

1. Solder the wires to the jack.
2. Drill a hole and mount the jack.
3. Solder (or push on) the wires to the speaker terminals.
4. ????
5. PROFIT!!!

(As you can see, this time I used an open Switchcraft style jack instead of the Neutrik syle one. Either will work just fine. I used push-on connectors for the speaker, that makes it easier to switch out the speaker, but soldering the wires to it is fine.)

Here is a sketch of what you started with:
Before


Here is a sketch of what your setup should look like after adding the speaker-out jack to the amp and connecting the speaker to a jack:
After


You now have a much more versatile setup. To use it as a combo, simply plug a speaker cable between the head and cab. You can plug the amplifier section into a different speaker cab (just make sure the impedance matches!) Or you can plug a different amplifier into the speaker cab (again, match the impedance!)
You can leave them in the same enclosure or split them up. It's just up to what you want.

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cedricsmods

Reserved.

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blindsagacity

Just skimmed, but nice work Cedric.

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rootbeerjuice

Can this be performed on any combo amp? If so, I might do this to my Microcube, just for practice...

Also, the first part looks nice, very easy to follow.

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My Fireman Build (indefinitely delayed)

Little_Buster

It works on any combo.


Cedric, did you just now do this mod?

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cedricsmods

Nah, I did this weeks ago with the intention of typing it up then but I have been too busy with other stuff. If you are inquiring about how long it takes, I could to it in less than 10 minutes if I wasn't taking pictures.

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Little_Buster

Yeah I was wondering when you actually did this ;P

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Jango22

Can we just skip step 1 if we already have a speaker out jack?

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Gear:
Agile Ash RB 828
Schecter C-7 (old 90s style headstock)
Pod HD300

JoePerry4life

What kind of jack are you using?

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Agile AL3000
Douglas WRL90
SX SR1 STD Plus
J&D Strat
Squier Tele
Sammick TR2
Douglas Draco
Peavey JSX
Bugera V5
TWANGED VJ

Little_Buster

That is a neutrik jack.
You can also use a regular stereo jack

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Invader Jim

No, you gotta use a jack with a built-in N.C. switch. normal stereo jack won't work.

Little_Buster

I made one with a normal stereo jack and It works fine

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Invader Jim

Does it shut off the speaker? How did you wire it?

cedricsmods

If you already have a speaker out jack, then you do not need to wire this jack. However, you do need to ensure that the wires connecting the old speaker don't short on anything. So if you are not using the old speaker wires, cover them with heatshrink tubing.


That is a Neutrik stereo jack, as Buster said. I do not have it wired to disconnect a speaker because in the example I gave we are removing the speaker completely so that we just have a head. This is the most simple way to wire it. You could also use a Neutrik mono jack, a Switchcraft stereo jack, or a Switchcraft mono jack. I used this kind because I bought a bunch in bulk. The ring connector (middle lugs) are not being used in my pictures.

You can wire one like Jim is talking about, which would be useful if you wanted to add a speaker out to a combo, but still keep it as a combo. With that method, when you plug in an extension cab, the combo speaker is disconnected. This method requires a switching normally closed (N.C.) stereo amp (which coincidentally is the kind I used, though I did not wire it for switching).

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ice condition

now, say i took the amp out of my POS spider III 15, could i (just for the hell of it) use it as a rack-mount preamp, or would that just not work at all and blow up my neighborhood.

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The best bosom in all of UG.

cedricsmods

You should not run a chain that goes amp -> amp. The only thing that should be connected to the speaker out is a speaker cable going to a speaker. No second amp, no headphones. Thank you for asking, I will add this to the first post.

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Invader Jim

Added to the resource thread, cedric.

ice condition

what's wrong with doing that? I've used headphones from the output jack along with going into another amp from the output jack . . . with no noticeable damages.

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The best bosom in all of UG.