Re: Speaker impedance?

Posted by induction on Jun 08, 2017; 3:42am
URL: http://guitar-fx-layouts.238.s1.nabble.com/Speaker-impedance-tp38463p38479.html

ibanez48 wrote

I burnt the transformer out before the guy rewired the cab.
...
And my crate is a solid state.

Do you mean you burnt the output transistors? Solid state amps generally do not have output transformers.

The detail that your amp is solid state is fairly important in this case. For solid state amps, Neil is partly right, you can use a higher impedance cab with no worries (but less volume). You can even run it just fine without a speaker at all.* But if the cab's impedance is too low, you risk running the output transistors into thermal overload. In the extreme case, a short circuit in the speaker cable can kill the output transistors very quickly.

For tube amps, it's the other way around and Travis is right. Lower impedance cabs are fine, though they'll burn your output tubes faster. Tube amps can usually even handle short circuits fine.* But too high cab impedance causes flyback voltage that can instantly kill the output transformer.

This is actual reason you can't use a guitar cable as a speaker cable. (For some reason, nearly everyone I've ever overheard at GC says 'you can't use shielded cable for speakers'. I don't know where this idea came from, but there's no problem using shielded cable for speakers, though it's mostly pointless from a noise perspective and the increased capacitance could cause treble bleed.) The real problem with guitar cables is that the conductor in the core is tiny and therefore easily breakable/shortable. A short can kill most SS amps, and a break can kill some tube amps.

* Neither of these are entirely risk-free, so please don't.