I am thinking of buying a Fender Super Champ amp, but it's only 15 watts. This is fine when I am micing the amp but may not be enough power for a larger venue unmiced. I figure I could always plug into a speaker cabinet for a little extra volume but couldn't I just plug into a 2nd backup guitar amp? The Fender Champ is 8 ohms and has an output jack. I've been told I could plug into an 8 ohm or 4 ohm speaker, but why not just use either an 8 ohm or 4 ohm combo amp that I already have instead of buying a speaker?
Here is what I have found through trial and error:
The Super Champ, while an amazing amp, is under-powered for live performance. The easy solution is to mic the amp,but that is not always an option.
My Super Champ is the XD Model.
There are two outputs on the back
(1) speaker out. Should be currently connected to the internal speaker. You can use this to substitute the internal speaker for a different speaker cabinet(like a 2x10 or 1x15 or whatever cab does it for you). In most cases you will not get more volume, just a change to your sound. Keep in mind plugging in the new speaker turns off the old one. You want to make sure your new speaker cab is the same impedance as well.
(2) The other output, the line-out is going to be the better solution for you. This is NOT a speaker out, this is line-level out. You can send this to a direct box and into the PA, you can send this to a powered speaker (like a powered PA speaker) or to a 2nd amp. If you plug a non powered speaker into this you will get....nothing.
In this scenario, Super Champ internal speaker DOES stay on and produces full sound. You are running the Super Champ plus whatever secondary device as well. You will get much more volume from this, depending on how powerful the secondary source is.
If you send line-level to a 2nd amp, be VERY careful about the levels out and levels in. If you crank the Super Champ the 2nd amp is getting too much signal. You should be able to balance the two in a way that makes sense.
The line out was built for recording and for running sound to the PA without needed to mic the amp, but keep in mind that the line out sound does not utilize the tube in the amp, so it can be less warm and tube sounding.
Personally, I've found this amp, with the line out going to a powered speaker, PA or second amp all work well and make this amp sound fuller (more hifi). I have used all three options in a live band setting with good results.
One trick I have seen used to get louder when you have two amps available and one of the amps has two input jacks on one channel as many Fender models do, is to plug your instrument into one of the input jacks and plug a patch cable into the other input jack, and then plug the other end of the patch cable into the input on the second amp. This allows adjustable volume and tone on each amp and increases power output level at the same time. Hendrix, Clapton, Leslie West and others took this technique to an extreme with their Marshall stacks in the late 60's and early 70's.
Connecting another speaker won't necessarily make your amp sound louder. It's possible that the placement of an extension speaker closer to the audience will make it sound louder (because of its proximity to their ears) but you don't get something for nothing. What you need is a 'line out' socket on your amp so you can run it to the input of your second amp. Running from a speaker output to the input of a second amp is asking for distortion, and I suspect that electronically-literate contributors are queuing up to explain why.