Wiring combo with switching speaker jack input

[therealting]

I have a Fender Rumble 500 v3 Combo that I really like - lightweight, reasonably compact, affordable and actually sounds great. I’ve always used heads and cabs, and have usually brought a spare head along just in case.

The Rumble doesn’t have a speaker jack or cable accessible from the outside of the cab. Can I install a switching jack such that plugging in a speaker jack disables the connection to the built-in amp and allows me to use an external head?

Thanks!

[Mottlefeeder]

In theory, yes you can, but in practice it would not be a good idea. Jack sockets for speakers are fairly robust, and may cope with 500W, but jacks intended to switch signal inputs tend to be more fragile.

A better solution might be to install a double pole two way switch and switch the amplifier output between the internal speaker and a speakon or jack socket. Speakons are designed for that job, many jack sockets are not.

David

[therealting]

Thanks David. To clarify, I’d be switching the speaker input between the combo and an external amp, but I take your point. I wonder if it might be better to wire the internal amp to a jack plug, then plug that into the external socket to the speakers. 

[Mottlefeeder]

1 hour ago, therealting said:

Thanks David. To clarify, I’d be switching the speaker input between the combo and an external amp, but I take your point. I wonder if it might be better to wire the internal amp to a jack plug, then plug that into the external socket to the speakers. 

If you wire the amplifer output to a Jack plug, it will be shorted out momentarily every time you plug it into a socket when both the tip and the sleeve are moving passed the first contact, and possibly also when the Jack plug is unplugged and dangling free. On most occasions, the amp will be off, but one day it won't be, and since it was designed to be permanently connected to a speaker, it probably does not have short circuit protection built in.

I had a similar arrangement with a high-powered speaker in a low-powered combo, with the option of using an external higher-powered amp. Setting up in a hurry on a dark stage, I managed to connect the output of one amp to the output of the other. The bigger amp fried the smaller one. I've since redesigned it to make sure it can't happen again.

Whatever you do, it has to be idiot proof, so I'd suggest a 10 Amp two way switch with the speaker connected to the switch wiper, and one switch contact connected to the amp and the other to a speakon socket. No risk of shorting either amp, and nice big contacts on the switch and the plug/socket.

David