toxaris

Hello.
I have a JMP 2203 from 1981. To that I have a 4x12 1960AV.
My question is:
What difference in sound and loudness it makes when I go 4ohm mono, 8ohm mono (In Stereo mode) or 8ohm Stereo.
I guess that JMP 2203 does have two outputs and one ohm switch which switch between 4 and 8 ohm.

spikei

no difference, the important thing is to match the ohms of the amp to the cab, or you may cause damage to the amp.

amplifier

First off, tube amps can't handle ohm mismatches between head and cab the way SS amps can so don't go aimlessly experimenting. Back to your volume question...ohms are electrical resistance so the less you have the more current gets through. So technically 4 ohms mono would be louder than 8 ohms mono.

toxaris

Ok, thx for your answer.

Rocktiger74

ok...silly newbie question then...

If it is important to match the Ohm level between amps and cabs why have various different selections of Ohms like 4 Ohms, 8 Ohms etc, on the same amps/cabs?
Why not just stick to one, like 4 Ohms?

Thanks

Adwex

- There are different speaker cabs with different impedances, you need to be able to match the amp to any cab.

- What if you want to connect a pair of cabs, like a full stack? A full stack of 16 ohm cabs would be connected in parallel, so they would equal 8 ohms together, ...and a full stack of 8 ohm cabs would equal 4 ohms.

- What if you had a 2x12 cab instead of a 4x12? My 2x12 cab has a pair of 16 ohm speakers, but the total cab impedance is 8 ohms.


You MUST match the impedance of the amp and the cab (or combination of cabs). The whole impedance thing isn't too difficult to understand, but you MUST understand it, or you risk damaging your amp. Trust me, I know, because I forgot to switch the amp's impedance once when I switched from one cab to another, and it blew my output transformer. It cost me $300 to have it replaced, and it took a month.

Rocktiger74

Many thanks Adwex