dumb question ... speaker cabs

[mylilss]

i have two avatar speaker cabs ... they are both wired for 8 ohms. can i plug each cab into a corresponding 8 ohm channel ?? or since plugging in two do i need to use the 4 ohm channels ??

i know when using my old peavey amps if i was plugging these two cabs into the back of the amps jacks i had to set the ohm level for half of what the cabs were, which to me was the same basic thing as daisy chaining the cabs... and i was curious if the dual rec's were wired the same way ??

 

[MrMarkIII]

Use the two 4 ohm speaker jacks. The 8 ohm speaker jacks are for two 16 ohm cabs.

 

[mylilss]

sounds good. wasnt sure if it was setup the same way or not, since these amps seem to be very different from others in other aspects of the wiring :mrgreen:

 

[echoes420]

I don't think it's a dumb question at all. In fact, I have another aspect of it to ask about. I own a Rectifier 4x12 and a Rectifier 2x12... both of which are rated at 8 ohms. If I were to ever want to run both cabs, how would I do that? And what would be the difference between hooking up both cabs to the head as opposed to running the 4x12 from the head and the 2x12 from the output of the 4x12?

 

[MrMarkIII]

I don't think it's a dumb question at all. In fact, I have another aspect of it to ask about. I own a Rectifier 4x12 and a Rectifier 2x12... both of which are rated at 8 ohms. If I were to ever want to run both cabs, how would I do that? And what would be the difference between hooking up both cabs to the head as opposed to running the 4x12 from the head and the 2x12 from the output of the 4x12?

Two 8 ohm cabs =
One into each 4 ohm speaker jack. 4 ohms total load.

4x12 from the head and the 2x12 from the output of the 4x12 =
4 x 12 into a 4 ohm speaker jack on the amp. 2 x 12 into the PARALLEL OUT of the 4 x 12 cab. Also 4 ohms total load.

Download the Lone Star manual at the Mesa website, and there are pages and pages of speaker hook-up minutiae at the end of the manual.

 

[94Tremoverb]

It's not a dumb question, and most amp companies (including Mesa) do a poor job of labeling their amps - it's confusing because the rules for multiple speakers or cabs are different from one. Modern Laneys show the way to do it - around each jack or pair of jacks there is a printed box telling you exactly what combination of cab impedances to plug in there.

In fact, on the Mesa amps, the jacks that are labeled 4 ohms are not 4 ohms *each*, they're 4 ohms *for the pair*... big difference. (Same with the amps that have two 8-ohm jacks.)

Next, when you connect two cabs, either directly to the amp or by daisy-chaining, the total impedance is half that of either cab - so if you're using two 8-ohm cabs, that's a 4-ohm load in total... so you use the 4-ohm jacks (one or both). Almost all amps and cabs are wired so that pairs of jacks are in parallel, even when daisy-chaining - series wiring is different and I won't confuse you just yet!

But - only daisy-chain if your amp doesn't have two of the right impedance jacks (eg if you have two 16-ohm cabs and an amp with only one 8-ohm jack), or if you don't have a cable long enough to reach the lower cab - because, if the first cable from the amp to the top cab fails or comes out, the amp has no load and you'll quite likely blow something (tubes or output transformer)... whereas if you run two separate cables from the amp to the cabs, it would need a problem with *both* cables to do that.

You can run cabs of different sizes if they're the same impedance - only the impedance and power handling matters... for cabs of the same impedance, half the amp's power goes to each cab, you don't just add them up. (eg a 50W cab and a 300W cab is a 100W pair, not a 350W pair, because half the power goes to the 50W cab and if you go over 100W input to both, you'll blow it.)

You can even run cabs of different impedance if you know what you're doing - the easiest rule to remember is that you treat the pair as if both are the *lower* of the two impedances (eg an 8 ohm and a 16 ohm together should still be run at 4 ohms on the amp, as if both were 8 ohms) and that the majority of the power goes to the lower impedance too (2/3 to the lower, if one cab is half the impedance of the other).

 

[plapnab]

Wow! All of this is making my head spin?!?! I was going to post this exact same topic because I have a similar question. Specifically, I have a Mesa 4X12 wired at 8 ohms and a 2X12 ART cabinet also at 8 ohms that I wanted to know how to run together. Regardless, according to what I'm reading I've been plugging into the wrong output on my head. Specifically, I've been using one of the 8 ohm outs into the 8 ohm 4X12 because I thought you were always supposed to match the impedence between cab and head...It's better to run the 4 ohm out into the 8 ohm cab??? My second question is if I wanted to run both cabs at the same time do I run them each separatley into the 4 ohm outs on the head...and is this safe being that I'm guessing the output load is different between the two. Also, is there any wrong way to do this...can I experiment without worrying about damaging the amp?

 

[mylilss]

Wow! All of this is making my head spin?!?! I was going to post this exact same topic because I have a similar question. Specifically, I have a Mesa 4X12 wired at 8 ohms and a 2X12 ART cabinet also at 8 ohms that I wanted to know how to run together. Regardless, according to what I'm reading I've been plugging into the wrong output on my head. Specifically, I've been using one of the 8 ohm outs into the 8 ohm 4X12 because I thought you were always supposed to match the impedence between cab and head...It's better to run the 4 ohm out into the 8 ohm cab??? My second question is if I wanted to run both cabs at the same time do I run them each separatley into the 4 ohm outs on the head...and is this safe being that I'm guessing the output load is different between the two. Also, is there any wrong way to do this...can I experiment without worrying about damaging the amp?

if you are running 1 8ohm cab, then you will plug it into one of the 8ohm outputs on the back of the amp. if both cabs you have are wired to 8 ohms, then when running both cabs you plug each one of the cabs into the 4ohm outputs ... if using one cab you want to use the proper ohm output, but when using two cabs you need to split the ohms, wheras in this case you have two 8ohm cabs you will use the 4 ohm outputs since 8(ohms)divided by 2(cabs) is 4(ohms) output

 

[94Tremoverb]

Very simple: with one 8-ohm cab, connect it to the 8-ohm jack; with two 8-ohm cabs, connect both of them to both *4-ohm* jacks.

So you've been running the 8-ohm 4x12" correctly on its own.

If you want to run both cabs together, the *total* load that the amp sees is 4 ohms, because you have two 8-ohm cabs in parallel. So they need to be connected to the 4-ohm tap on the transformer, which is wired to *both* 4-ohm jacks.

Mesa amps are pretty tough and not very impedance-sensitive. There's really nothing you can do with two 8-ohm cabs in any combination that will kill the amp, the worst that will happen is that you might shorten the tube life a bit - but only if you're cranking it up... impedance matching only really matters a lot when the power section is running hard. The only connection that might even come close to being a serious risk is to daisy-chain both cabs from a 16-ohm jack (which not all Mesas even have).

 

[plapnab]

Tremendous help from everyone…thank you so much!

 

[thunda1216]

thanks for this thread - I've been so confused with my multiple ohmage cabs and my Heartbreaker. The manual leaves a bit to be desired in this respect.

ty

 

[echoes420]

I know this is a Mesa forum, but since some of you seem to be so knowledgeable in the ohms department, I want to see what you guys say about this...

My Silverface Fender Twin combo has two 8ohm speakers in it that I wired in parallel to hook up to one of the 4ohm outputs... no problem there. But sometimes, I want to run a 4x12 with it... and it just so happens that I have a Fender Metalhead 4x12 that is wired at 4ohms. Now, the amp has two separate outputs, both labeled 4ohm. My question is, is it safe to run both the speakers in the combo off of one of the outputs and the 4x12 off of the other? I haven't ever even tried it, for fear of blowing up a 33 year old transformer... I always just unhook the combo speakers when I run the 4x12.

 

[YellowJacket]

Build a series box. Hook both speaker leads into the box and then hook the box into the 8 ohm jack on your amp. Problem solved.

 

[94Tremoverb]

It's not even that complicated - just run both cabs from the amp. If it's a 135W Twin (which if it's a '77 it should be - it will say on the back panel under the speaker jacks) - the Ext Speaker jack has a switch in it so the amp automatically sets itself for two 4-ohm cabs, which is why it says 4 ohms under *each* jack, not under both as it does on the 100W ones. (In fact, the jacks are in series inside the amp and the transformer is switched to 8 ohms, not 2 ohms, but you don't really need to know this!)

Even with the 100W and older ones, Fenders were specifically designed to handle a load of half the matching impedance, that's why the jacks are in parallel and there is no impedance selection. Leo knew that keeping things simple and building them to take a mismatch was less likely to cause trouble... which is one of the reasons you see far less Fenders with blown OTs than Marshalls. In fact, it's *more* risky to run an old Fender like that with an 8 or (especially) 16-ohm load than a 2-ohm one.

 

[echoes420]

It's not even that complicated - just run both cabs from the amp. If it's a 135W Twin (which if it's a '77 it should be - it will say on the back panel under the speaker jacks) - the Ext Speaker jack has a switch in it so the amp automatically sets itself for two 4-ohm cabs, which is why it says 4 ohms under *each* jack, not under both as it does on the 100W ones. (In fact, the jacks are in series inside the amp and the transformer is switched to 8 ohms, not 2 ohms, but you don't really need to know this!)

Even with the 100W and older ones, Fenders were specifically designed to handle a load of half the matching impedance, that's why the jacks are in parallel and there is no impedance selection. Leo knew that keeping things simple and building them to take a mismatch was less likely to cause trouble... which is one of the reasons you see far less Fenders with blown OTs than Marshalls. In fact, it's *more* risky to run an old Fender like that with an 8 or (especially) 16-ohm load than a 2-ohm one.

This answered everything I needed to know. Thanks so much! It is a 135W... with the push/pull master volume. I think 77 was the first year that had the push/pull... though I rarely use it.

 

[94Tremoverb]

No, the push-pull MV came in a lot earlier, around 1972. It's hard to tell unless you try pulling it, because it isn't labeled on the panel - I've known many people who have owned the amps for years and never knew about it! For what it's worth, I like to remove the whole bad-sound 'pull distortion' circuit, and replace it with a pull-to-engage post-phase-inverter MV using the same pot, which works beautifully and gives the option of the true non-MV circuit if you want it.

The 135W circuit came in around late 1976, so yours is a fairly early one of those. If you want you can make some changes to it which make it sound more like the earlier 100W model (which is a little softer and warmer-sounding) but you can't easily fully convert it to the earlier circuit, or 'Blackface' it, without a lot of expensive and non-reversible work... not worth it IMO, the amp is actually pretty decent-sounding as it is, providing you understand its limitations - it's loud and clean, takes pedals well, is loud, and... clean!

I like them, they sound great with a Mesa V-Twin pedal.

 

[echoes420]

Yeah... I use it for clean only... and it does it well! I have read all about the mods that are done to them, but I really like the way it sounds. It really reacted well to NOS tubes and I wouldn't change a thing about it now. I did change out the old Utah speakers out of it and have tried a couple different speakers in it, but I think I have settled on the Eminence Cannibus Rex.