Ohms....

[Big_dawg]

I think I know the answer but Im just after a second opinion as Ive no one else to ask...

currently I have 16ohm 1x12 cabs, but have been offered a Mesa 1x12 but its only 8ohm. Can I daisy chain it on to the back of the 16ohm 1x12 or am I going to damage something somewhere.

Also I have both 8 & 16ohm outputs on my amp Im pretty sure I cant plug the 8 into the 8 and the 16 into the 16 (or both into the 2 8 outputs) but please tell me im right!!

[Big John]

Do not plug the 8 ohm cab into the 8ohm output on the amp and the 16 cab into the 16 simultaneously. You will damage the output tranny. Those outputs jacks are wired to taps coming off the tranny's windings, and are meant to be "either/or" and not "both at the same time".

Paralleling an 8 ohm cab with a 16 ohm yeilds 5.33 ohms. Since you don't have a 4 ohm output jack on the back of your amp, this mis-matching of cabs isn't a good idea. However, since you have two 16 ohm cabs, you can plug each one into the 8 ohm output and you're good to go.

When there's two jacks on the back of an amp for a certain ohm rating, that means that the total impedance of both jack must equal that number. So, one cab at 8 ohms gets plugged into one 8 ohm jack. Two 16 ohm cabs get plugged into both 8 ohm jacks because the total ohms is 8.

[Big_dawg]

Thats what I thought. Shame guys knocking out 2 Mesa 1x12's for for £100 each ($200) - in this country thats about 1/3 of the price...

Thanks for the advice though...

Not quite understanding ohms at all is it better to run the 2 cabs Ive got (16ohms) straight from the 2 8ohm sockets or to 'chain' them together?? Or doesnt it make much difference?

[drewbertca]

Originally Posted by Big_dawg

Thats what I thought. Shame guys knocking out 2 Mesa 1x12's for for £100 each ($200) - in this country thats about 1/3 of the price...

Thanks for the advice though...

Not quite understanding ohms at all is it better to run the 2 cabs Ive got (16ohms) straight from the 2 8ohm sockets or to 'chain' them together?? Or doesnt it make much difference?

Won't make any difference....buth ways puts the cabs in parallel and results in 8 ohms....

Personally I plug into the head if there are 2 plugs - personal preference.....results in a shorter cable run to the 2nd cab...

[Big John]

dawg, does your amp have 4 ohm jacks?

[Big_dawg]

no
2 x 8ohm
1 x 16ohm

Am I right in thinking then that the lower the ohm number the more wattage it can handle??

[Big John]

Nope. A 100w Marshall at 16 ohms is still 100w Marshall at 4 ohms.

[Big_dawg]

oh, why is there a difference in ohms for the same speakers then??

ie the celestion G12h comes in either 15 or 8 ohm..

[ES350]

The mfg. puts out various voice coils with different impedances so there is some flexibility in wiring cabs to match the output impedance of different amps...

[Big John]

Yup, it comes down to compatibility. You can blame it largely on Fender. Back in the tweed combo days, there was only one impedance available for the output of the amp, and that impedance depended on which model amp was being used. In late-60/early-61 when Fender went to piggyback rigs, this openned up (although not at first) the options for mixing and matching different speakers. But because the model of amp determined the total ohms available (Bassmans could drop to 2 ohms!), it was determined to be a good idea by speaker makers at the time to offer different impedances to allow for more speaker configuration options. I was told all this by a very wise retired AirForce electronics technician.

[Big_dawg]

thanks for that, its slowly become clearer....

[dwagar]

general rule of thumb I go by, I want the speakers to be the same or higher than the head setting, never lower.
I've had guys tell me it doesn't really matter. But that's where I feel safest.

eg, I'd run a 16 ohm cab with an 8 ohm setting if I had to, but I wouldn't want to run the 5.33 (8+16) as above.

[Paul_Cat]

two 8ohm and one 16omh? Sounds like a TinyTerror... I was also wondering the same thing

[ES350]

Well, Fender used one supplier in the tweed days---Jensen, all of which were 8 ohms. So Fender designed the OTs to accomodate the possibilities of parallel wiring 8 ohm Jensen speakers and came up with 8, 4, and 2, which has been the standard at Fender ever since with few exceptions.

[Big_dawg]

Originally Posted by Paul_Cat

two 8ohm and one 16omh? Sounds like a TinyTerror... I was also wondering the same thing

you got it.... Love this little guy...

[Big_dawg]

ok now im beginning to understand about ohms, thanks for all the advice.

Save me starting a new thread, and whilst Ive got you all here lets talk wattage.... which I kinda understand...

with the aforementioned tiny terror a very loud 15w output (going through 2 16ohm 1x12 cabs). Ive also been offered a matamp 4x12 loaded with 16ohm celestion vintages. To power the 4x12 am I right in thinking the little terror just has to work twice as hard (ie warmer tubes) as with the 2 1x12's??

[dwagar]

the 4x12 cab is 16 ohms which will run fine with your head. I think you'll find the 4x12 louder as you are pushing more air, and due to its height it's projecting better.

As a matter of fact, I ended up having to use the 8 ohm + 16 ohm last night myself. I pulled one of my 2x12 cabs to use with my Hammond, so it messed my setup a bit.
Since that is (as Big John said above) 5.33 ohms, and since I'm running an 8 ohm Hotplate, I checked with THD, they confirmed it'll run fine with the head set on 4 ohms.