Mesa 412 only 4ohm port is working

chilldoggin · Jul 18, 2015

Hi guys. I got a 412 from a guy yesterday and have found that only the 4 ohm port is working. This is a problem as I'm playing an OR50 through it which runs 8 or 16 ohm. I'm not the best with wiring, but I was hoping someone could tell me where the disconnect is. I really just need to get the 8 ohm port working. Here are some pictures of the guts: http://m.imgur.com/uq8Hz5R,0eQsUQN,99FdoEv Any help is much appreciated!

morgan138 · Jul 18, 2015

If that 4x12 is like the one I had open just an hour ago, the 4 ohm jack you're referring to would normally only be connected to 2 of the 4 speakers. But it looks like someone has changed the cab's wiring, so if they've got it so that one jack (that's labeled "4 ohms") connects to all 4 speakers, the total impedance is 8 ohms.

chilldoggin · Jul 18, 2015

Thanks! So with this wiring job, I shouldn't have any issues running it at 8 ohms. What's this type of wiring called? Series?

morgan138 · Jul 18, 2015

chilldoggin said:
Thanks! So with this wiring job, I shouldn't have any issues running it at 8 ohms. What's this type of wiring called? Series?

I'm guessing it's either series/parallel or parallel/series. Either one will connect for 8 ohm speakers into a single 8 ohm load.

Mesa 412 only 4ohm port is working

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Mesa 412 only 4ohm port is working

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