Re: Speaker impedance?

Posted by Neil mcNasty on Jun 07, 2017; 5:10pm
URL: http://guitar-fx-layouts.238.s1.nabble.com/Speaker-impedance-tp38463p38464.html

Speaker impedance is very important to pay attention to!
If the speaker has lower Ohm than the amp... You destroy the amp!
It burns the output transformer, since there is not enough resistance and the coils overheat, burn the insulation and then short-circuit.
But if the speaker has a higher Ohm than the amp... You are OK! No problem!

My recommendation/how I would do it:
Check the Ohm output of your amp (check the speaker wiring and Ohm ratings of the speakers and calculate the Ohm rating if it is not already labeled on the amp).
Then add a switched jack between the amp's speaker output and the speakers, that breaks the connection to the built in speakers when a speaker jack is inserted, and then sends the signal to the external cabinet.

If you have a dedicated external cab that is not being used for anything else, I would probably rewire it to match the amp...
If you do not have a dedicated cab to use for this, the rules are as following:
If the external cab has a higher Ohm rating than the amp (example: amp is 8-Ohm, cab is 16-Ohm), then you can safely use it!
BUT! If the cab has a lower rating than the amp (example: amp is 8-Ohm, cab is 4-Ohm) you should not use it as it is. As it might damage the amp!
(sorry for the repetition, but it is so important that it is worth hammering in!)

I have done this mod to several of my small vintage amps (that has very poor and small speakers) and it works like a charm!
I sometimes run a 16-Ohm cab on my Silvertone's 8-Ohm output, with no problems, except that you might loose a tiny bit of top end and get slightly lower volume than usual...

Hope this helps you to accomplish your task!
Cheers and Good Luck!