Bit of help please......

[sted]

Hey guys,

I just purchased a spanking Matamp 2x12 cab to use with my combo, very happy with the sound as I demo'd loads of speakers with my combo speaker and settled on the Celestion G12K 100's, very nice!
My question is one of impedances really, the combo speaker is usually plugged into the 8 ohm output and the new cab is 4 ohm, the guy from Matamp said it would be fine to just plug the cab into one of the 4 ohm outlets and keep the combo where it is, I cant find anything in the manual about an 8 ohm and 4 ohm setup though I'm assuming that running both the internal speaker and cab speakers from the 4 ohm sockets would also be a safe mis match?
I'm pretty sure the guy was right as Matamp make top notch handmade amps and cabs but I just want to be sure!

cheers guys

 

[MrMarkIII]

Here's a calculator for speaker impedance matching:

http://colomar.com/Shavano/impedance_proc.php

Values entered horizontally are for series connections.
Parallel connections are entered vertically.
Be sure to show all your work. This will be on the final.
Your example:
Row #1 = 8
Row #2 = 4
Total = 2.67 ohms.
This is safe, but at the limit. You can't go to 2 ohms or lower.
It'd be safer to re-wire the cab to 16 ohms, for a total load of 5.33 ohms.
If it was my amp, I'd try it both ways to see which sounded the best, because mis-matches change the sound. Only you can judge this.
Hope this helps.

 

[LPJunky]

Hi! I had a similar thread going I think last week. It followed from the fact that I got a pair of 1x12(8 ohms G12K100 yes those are great by the way) and I wanted to run both on the 4ohms output and run a 8ohms 2x12" (2x CL80 16ohms-parallel) in one of the other 8ohms. I lastly sent an email to Mesa - :x no reply! Thats not very good as customer service but that's for an other thread.

By the way MtMarkIII how come 2.67 is safe mismatch when they claim 4 ohms is what is required. May be at low power like 45w (half) it would be ok.

I think I might be able to figure out if its safe to do the fancy connection we want by figuring out the power consumption in the secondary winding of the transformer. I need a bit more time for that. From the schematics I don't know if both windings are electricaly connected or totaly independent, I guess I can get an ohmeter and check this on the amp.

 

[sted]

Woah! Youve lost me with that lot! :lol:

Using my common sense (I only have a small amount!) Mesa have several examples in the manual of cabs with a higher impedance being run on the lower impedance outlets, ie a 16 ohm cab plugged into an 8 ohm outlet etc
Surely running an 4 ohm cab in a 4 ohm outlet and an 8 ohm cab (The internal speaker) also in a 4 ohm outlet isnt going to cause any damage as its all on the safe or low side? I imagine the bigger problems would arise when trying to run a low impedance cab in a high impedance outlet? :?