how to connect my carlsbro scorpion 2x12 combo to my 4x12 cab

[neilmay]

hi guys. 1st time here. i've got an old (very loud) carlsbro scorpion 2x12 combo. there is no line out for connecting up external speakers. i want to be able to connect it to my behringer 4x12 (400watt) speaker cab. is there any way to do this?

[teemuk]

Yes. There are many ways to do this. Do you want to connect the cabinet as external one (in series with the combo's speaker) or so that it disables the combo's internal speaker?

You need an isolated switching jack, where an internal N.C. (normally closed) switch mechanism connects a specific terminal to the jack's tip when no plug is in the jack. When a plug is inserted the switch opens and breaks the connection. Beware, there are many different switching jacks and unless you can improvise based on the instructions given you need this specific one. Also, use proper wire gauge that can handle the speaker currents.

Following are just some ways to do these mods:

Disabling:
- Clip the positive and negative speaker wires. (You might wish to do this so that the mod is reversible. In other words, you just pull off the connectors from the speakers and extend the speaker wires somehow. The main point is that for both of the speaker's terminals you have a wire coming from the amp and a wire coming from the speaker.)
- Wire the switching jack in between the wire ends as follows:
Both ends of the negative wire (one coming from the amp and one coming from the speaker) are soldered to jack's sleeve terminal
The positive wire coming from the amp is soldered to jack's tip terminal
The positive wire coming from the speaker is soldered to jack's switch terminal (now the internal speaker is disconnected each time there is a plug in the jack)
-Mount the jack to a convenient place e.g. metal L-profile mounted to the chassis. Do not ground the sleeve of the jack! Your amp takes care of grounding.

In series:
- Clip only the negative lead (see previous instructions)
- Solder the end of the wire that comes from the speaker to jack's tip terminal
- Connect the switch- and sleeve terminals together (now the jack is shorted from tip to sleeve when there is no plug inside it)
- Solder the end of the wire that comes from the amp to the sleeve terminal
-Mount the jack to a convenient place e.g. metal L-profile mounted to the chassis. Do not ground the sleeve of the jack! Your amp takes care of grounding.

[neilmay]

Series sounds best as i can connect to 4x12 for gigs but retain 2x12 combo for practice
bit more info, i'm not that techy minded, please. would this type of jack do?what wire/wires do i connect to which terminal? sorry for sounding dull.



5 connectors, Ground, Signal, Switch Common, Normally Closed and Normally Open.
Use as an input or output jack.
Ideal for use as an input jack when you want to interrupt the battery power when there's no jack insterted.
Unlike the Stereo swiched jack we offer, the switched terminals on this jack are completley isolated from the jack plug.
Originally designed for PCB through hole mount, but the lugs are plenty big enough to solder wires directly to them.
Lugs are numbered for easy identification. 1=Ground, 2=Signal, 5=Common switch, 4=NC switch, 6=NO switch. 5 is connected to 4 when there is no jack plug, and 5 is then connected to 6 when the jackplug is inserted.
Comes with retaining nut.

[teemuk]

To understand what each terminal does let's first examine the basic plug types.

TS (Tip-Sleeve) or "mono" plug:

TRS (Tip-Ring-Sleeve) or "stereo" plug:


A mono plug has two contacts. The "tip" contact, by standard, carries the signal while "sleeve" contact is for the signal common (meaning ground). A stereo plug also has a third contact known as "ring" (the reason for such name is pretty obvious). This is for the signal of the other channel. It is also worthwhile to notice that when a stereo plug is used with most mono jacks the ring becomes shorted to the sleeve.

Judging by the given description of the jack, I assume it is a mono one, as there is only one terminal for the signal. Naming them like that ("signal" and "ground") is pretty unprofessional, though since these contacts can be used for pretty much any purpose depending on the application. Therefore, I refer to signal terminal as (the standard) "tip" and to ground terminal as the standard "sleeve". Mono jack is allright for this application.

The jack also has a switch but the switch is isolated (therefore it doesn't work exactly like described in my previous post). It doesn't matter. The main idea is that you have the switch there, as you can always improvise and externally wire it to perform the needed tasks. It is also described that the switch is single pole-double throw -type (SPDT). It means it is like this:

The switch "common" is the contact labeled "COM". L1 is the NC "normally closed" terminal, while L2 is the NO "normally open" terminal. Pretty self explanatory.

Now, read my previous post carefully, as it describes how the switching jack in the concerned application should operate. Heck, I just rephrase the information: The switch's COM terminal should be in contact with the jack's "tip" when there is no plug in the jack. When a plug is inserted the contact breaks. You can easily wire the isolated switch to perform this operation.

---

Note that when you wire the speakers in series you are naturally increasing the load impedance. In case of solid-state amplifiers this means that there will be a corresponding reduction in the amplifier's output power. Loudness-wise the increased speaker cone area will compensate this, though. However, in case someone reading this didn't know, tube amps are not happy with the increase in load impedance unless you also reset their "impedance selector" to correspond the new load impedance. Not all combos have such feature. Personally, when it comes to switching like this I would try an arrangement where you can select between the "disabling" and "series" setups. The switching arrangement requires a bit more thought (and an additional switch or jack) but it can be done.

[teemuk]

...