How do I connect my cab to my combo? - ohm related

I've got a combo with tree outputs: 1 x 8 ohm and 2 x 4 ohm. The internal speaker in the combo is connected through one of the 4 ohm outputs. I've also got an external cab that runs at 8 ohms and I want to use both the external cab and the internal speaker in the combo at the same time. Is it just as simple as connecting the cab to the 8 ohm output on the amp? Or are there any "rules" that says your shouldn't run two different ohms (in other words, should I connect both to the 4 ohm outputs)?

The combo is a Mesa Mark IIC+ and the cab a 1x12" Mesa Thiele.

Thanks!

Run both the internal and external speakers from the two 4 ohm outputs.
When using only the internal combo speaker, it's best to use the 8 ohm jack, but you won't kill the amp using the 4 ohm jack. The sound will be different, and some like it that way.

Thanks!

Didn’t know that I was supposed to use the 8 ohm jack when only using the internal speaker. It was connected to the 4 ohm jack when I bought the amp and since I’ve never had an extension cab before now, I’ve really never bother to look at how the speaker was connected, just assuming it was correct. I’ll try the 8 ohm jack when only running the internal speaker to see if it sounds different.

I've heard that for the HRG IIC+, to get it to sound closer to a simul, to plug into the 4 ohm tap and turn the presence down. much easier than swapping output tranny and whatever else bogie would do.

scott

MrMarkIII said:

Run both the internal and external speakers from the two 4 ohm outputs.
When using only the internal combo speaker, it's best to use the 8 ohm jack, but you won't kill the amp using the 4 ohm jack. The sound will be different, and some like it that way.

Click to expand...

Yup (confirmation), you should hook up your combo (I suppose its a 1-12" 8 ohm) and your external speaker (assuming it too is an 8 ohm load) into the two 4 ohm jacks.

Originally, the combo single speaker should have been in the 8 ohm jack. But no ill-effect if you input into one of the 4 ohm jack. There may be slight different tone, I don't know.

[side note] One technician told me in an A / B comparison, he could hear the difference between two 8 ohm speaker wired in parallel (4 ohms) and the identical model speakers two 8 ohm speaker wired in series (16 ohms).

As far as impedance on the output transformer Gerald Weber of Kendrick Amplifiers claimed he prefers running two 8 ohm speakers in series claiming he prefers the output transformer to use the outer taps.

note: I'm just reporting these theories, so don't shoot the messenger. :wink: