Impedance (No ELT101 Lectures Please!)

[kirk]

OK, I've spent the last two years in an Electronics Technology program; I thought I was Georg Ohm himself. Of course, I had a hard time staying awake in these classes; theory bores me, which is why I probably still can't answer this question (and why I haven't gotten a diploma yet!).

Please, no theory lessons!

The head has three settings, 4, 8 or 16 ohms. There are two speaker outputs. They are not stereo.

Two cabs. The cabs have switches, for stereo (8ohms) or mono (16ohms.)

Someone please tell me how to run both cabs mono? What are my options, and what impedance should I be using on the head?

This is probably the most elementary of questions, but your help is greatly appreciated.

[Platypus]

You should set the amp on 8 ohms and the cabs on 16 ohms. 2*16 ohms in parallell=8 ohms.

[kirk]

Should I use both speaker outs from the head, or one and connect the cabs together?

[Kevan]

Kirk- I have this diagram printed out and always handy.

http://www.webervst.com/pics/zplot.gif

For more stuff about speakers and ohmage, check out the Weber VST site...specifically the Lets Talk Speakers Q & A. Info galore there.

http://www.webervst.com/sptalk.html

[ScottB]

What has me confused is how a Marshall 1960 4x12 containing 4 - 16 ohm speakers can have a total impedance of 16 ohms.

Any diagrams of this available?

[rty13ibz98]

Originally Posted by kirk

Should I use both speaker outs from the head, or one and connect the cabs together?

either way, the load is still paralleled to the head. so it's all good. i prefer coming from the head, but don't we all.....


rich

[rty13ibz98]

Originally Posted by ScreamJem7

What has me confused is how a Marshall 1960 4x12 containing 4 - 16 ohm speakers can have a total impedance of 16 ohms.

Any diagrams of this available?

its a series/parallel wiring job. my 5150 cabs were wired up this way to be only 16ohm mono.

platypus is right, 2 16ohm loads in parallel are 8 ohms. just remember your basic resistance diagrams.


rich

[bammbamm]

I'll try and keep this as basic as I can.
Open up your windows calc and put it into Sci mode.
Now the way to calculate your parallel resistance is this (x = your 1st resistance value) 1/x + 1/x /1 = your parallel res.
So for a marshall cab with say, 4 -16 ohm speakers it would look like this in all parallel : 1/16+1/16+1/16+1/16= 0.25 then take the reciprocal of the sum 1/0.25 = 4, giving us a 4 Ohm load. seems difficult at 1st but its pretty easy once you use it a few times. Series resistance is calculated by just adding each value. so if we have this same cab but we don't want a 4 Ohm load, then we need to figure our how to break this up. so... we take 2 of the speakers and run them paralell giving us an 8 Ohm load, then do the same with the other 2, then run them in series with the other pair giving us 16 Ohms total.

The reason we try to match impedences is that a signal will transfer more efficiantly from source to load if the impedences of each are the same.
If anyone has ever run too low a load on an amp knows lowering your load in a cab will burn up your output transformer on your amp. The other way around however, putting more resistance on will just lower your overall volume. I hope this helps, let me know if any clarification is needed.

Bamm

[Greg RG7]

My live set up is a Peavey Triple X (with switchable 4, 8, 16 ohm output)head into a Carvin 2x12 cab with option of 4 or 16 ohms.

I usually set the amp to 4 ohms, and match it up with the cabinet at 4 ohms. Isnt that what you do? just match it up? or is that wrong?

I've been playing 10 years and still can't figure this out.

What would be the ideal setting?

Second question : if you switch ohm settings on a tube amp while playing a gig, is that bad?

thanks for your help.

- Greg
www.srmrocks.com (are website plugs allowed?)[/b]

[Lonely Raven]

Greg,

Yes, you're supposed to match up the impedence settings on the amp,
according to what your cabs are loaded as.

Generally it's not good to switch any impedence or voltage settings
while the amp is on, or at very least put it in standby mode.

You might also want to try your amp/cab at 16 Ohms. Some amps
really shine when they have a heavy load on them (16 vs 4), while
some amps are just the opposite and the extra volume you get running
at 4 Ohms might just "wake it up".

I was playing with a XXX the other day at Sam Ash music. I thought it
wasn't very "present and live" compaired to the XXL. But the XXL got
very hard to listen to after a while because of it's lack of warmth.

[Greg RG7]

Ok, I'll try a 16 ohm/16 ohm combination with the amp and cab.

thanks for your help! I figured matching it up is the way to go...

As far as the Peavey Triple X, I dont want to turn this forum string into an amp discussion, but that's the #$@%@#! best amp I ever heard / bought in my life. For at least 3 years I was a Sansamp PSA-1 solid state fanatic! that unit is still the best solid state preamp you can buy, but playing live through a P.A. system, you can REALLY hear the difference, and I no longer care about amp maintainence as an issue with my sound, tube is the way to go. Over and over I tried Mesa Triple rectifiers and my ears kept telling me : "Greg, somone shoved a hendrix Fuzz face in this amp!" I just dont hear what is so good about those amps (with 2x as many tubes as a XXX) directly out of the box. Sure, with a rack of EQs and post-preamp effects, a Mesa could be sculpted to be pretty sick, but for half the price and half the tubes and twice the gain, the Peavey Triple X is hands down the best amp I ever heard, and for a former solid state militant like myself to say that, it says alot.

Thanks for you help, any comments on my XXX I guess are welcome (oh no! a forum subject change!! NOOO)

[kirk]

I am still as confused as a monkey trying to f a football.

Here's what I am working with right now (different than the original post but same idea.)

I am using an MTS combo, which has two 8 ohm speakers. According to Carvin, I am supposed to run the combo on 4 ohms. OK, now I am adding an 8 ohm cab to the combo.

What setting do I use now - 4, 8, 16?

[bammbamm]

It depends on the configuration. If you run the 2nd cab in paralell, you run the risk of hitting about 2.66 Ohms If you run it series, then it'll be 12 Ohms. Find out the config before using it or you'll burn up your output transformer trying.

IM or Pm me if you want some quick advice.

Bamm

[Lonely Raven]

I second what Bamm said.

Put the football away and message him.

In my (limited) experience. When you run two cabs off one head, it's usually parallel which would mean your running WAY to low impedence and rea very likely to blow some stuffs up.

Kinda like the ass-tard did to the Laney heads I got. It's costing me about
$250 per head to fix!