Stereo 4x12 and stereo amp questions

V

Vhyle

New member
I have a Line 6 Spider II 150w amp, and a stereo 4x12 cab. I just got this gear a few months ago, but I just recently noticed that the input jack plate on the back of the cab had a mysterious hole next to the jack, and it looked an awful lot like another jack may have been there. So today I removed that plate, and gee whiz, there it was - another input jack, dangling inside the cab. The washer and nut are missing from it, which is why it fell in there into the black abyss of the cab.

Now, my question. The Line 6 amp is 150 - 75x2. It has stereo left and right output jacks, at 8 ohms/75w each. Before I found the missing jack in the cab, I plugged in each input on the amp into the cab. Sure enough, it was either the left or right speakers that were working, depending on the amp output I had hooked up.

Now I have both jacks out and ready to use on the cab, meaning I can use the full cab at 150 watts. My question though is mainly based from my limited knowledge of electronics. Here's how the cab is wired up:

speakurz.jpg


Each speaker is 8 ohms. The way these are wired up, it's 16 ohms each side total, divided by two, which equals 8 ohms in each input. Am I correct on this? I want to make sure I won't blow anything up if I try to connect this thing in stereo. I'm skeptical because of the fact that the jack was dangling inside the cab; perhaps the previous owner did it on purpose because the amp wouldn't work for it? I don't really know. I just want to play it safe before I try plugging it all in.

So since each output on the amp is 8 ohms, and each input on the cab is 8 ohms (unless I'm wrong; if so, please correct me), then it should work no problem. Right?

Mainly, this whole thing is stemming from my confusion of series/parallel and the impedance. It's been a long time since I've had an electronics class. Thanks in advance.

EDIT: I made the pic myself, because I'm having a helluva time finding a pic of the wiring diagram for a 4x12 cab with stereo inputs. I made this pic based on my cab.
 
Unless your jack plate has some type of stereo/mono switch just use this diagram for each of the jacks. DO NOT connect the 2 jacks together the way your diagram shows.

spkr-dia-3.gif
 
Ok, so simply isolate each jack to 2 speakers in their own series? Essentially have two 2x12s in one cab.

If I do that, the jacks will be rated at 16 ohms, and the amp output jacks are at 8 ohms. Is that going to be an issue?
 
Line 6 amps are very finicky for impedance. I believe the jacks are rated at 8 ohms, so make sure you are running both sides at 8 ohms (or higher). Do not run a 4 ohm load to them as this will overwork the SS amp. Same thing running just one output jack. Check the FAQs at the Line 6 website
 
I was planning on isolating both pairs in the cab, making two separate 2x12 circuits. I'm going to wire them each in series, so each side will be 16 ohms. So from the research I've done, this shouldn't be a problem since it's an SS amp. Tube amps are another story, however.

ETA: Yes, each output on the amp is 8 ohms. 8 ohms from the amp into a 16 ohm input on the cab.
 
Seems a little bit overambitious wiring a stereo signal to speakers in the same cabinet.

How much separation are you going to get?
 
drstawl said:
Seems a little bit overambitious wiring a stereo signal to speakers in the same cabinet.

How much separation are you going to get?
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I'm not going for any sort of separation, really. I'm going for the fact that I'd like to utilize all 4 speakers. As of right now, I can only use 2 at a time - either the left or the right side. This was before I discovered the hanging second jack inside the cab. But with the stereo-only outputs in the amp, and the current wiring of the cab, I can still only use 2 speakers at a time. Well, what's the point of having a 4x12 when I can only use half of it at all times?

I'm going to wire them in an X-pattern anyway, so I'm not looking for stereo separation. If I want to jam out in a band practice, I can just plug in half the amp and use 2 speakers. If I ever play a gig, I can plug in both jacks and blast away with the whole cab.
 
Vhyle said:
I'm not going for any sort of separation, really. I'm going for the fact that I'd like to utilize all 4 speakers. As of right now, I can only use 2 at a time - .
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not according to that chart you drew. That's a series parallel circuit. If it's wired that way either jack would make all 4 speakers sound.

You also made the comment that before you discovered the 'missing' jack you got left or right speakers depending on which side of the amp you hooked up.
That's not possible if you only had one jack available in the cab.
The speakers wouldn't care which amp was hooked up and nothing would change regardless of which amp you used.
 
You would think that, but it did. It played either the left or right speakers, depending on which output on the amp I was using. I swear. I thought that is odd too, but it does. I double checked to make sure I just wasn't crazy. it does not power all 4 as it lies right now. I'll check it again tomorrow to be completely sure.
 
think about it .... how could 2 speakers work when you plug one amp in, and then 2 different speakers work instead when you plug the other amp in using the same jack?

not possible.

Also ..... either you have that circuit drawn wrong or all four speakers work when you plug into either of those jacks.
 
As Lt Bob has stated, the diagram as you have it (discounting the jack that was hanging down inside the amp for a moment) shows a series/parallel circuit which is driven by a single input (the lower one on the diagram) It should present a load of 8 Ohms at the input. The second input is just in parallel with the first. If you plug both sides of a stereo amplifier in using both inputs, then you will get a summed mono signal. The best thing to do is to rewire the cab as two separate 2-speaker series circuits, which will give a load of 16 Ohms per side, in proper stereo. There will be a slight drop in overall amp volume, but you can just turn up a bit. :)

On reflection, what might have been fooling you with regard to which speakers were working is if you were using a patch with a very noticable stereo effect, such as a dry signal on one channel and a modulated signal on the other; or a ping-pong delay, perhaps.

:thumbp:


:mad:
 
Vhyle said:
If I want to jam out in a band practice, I can just plug in half the amp and use 2 speakers. If I ever play a gig, I can plug in both jacks and blast away with the whole cab.
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As I said before, don't do that with the Line 6 amp -always use both left and right output circuits. Otherwise the imbalance will eventually wreck your amp.
 
mjbphotos said:
As I said before, don't do that with the Line 6 amp -always use both left and right output circuits. Otherwise the imbalance will eventually wreck your amp.
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Mjb, most stereo devices have an arrangement where one of the outputs functions as a L/R output when used on its own, don't they? Isn't that the case with a Line 6?
 
Bubba po said:
Mjb, most stereo devices have an arrangement where one of the outputs functions as a L/R output when used on its own, don't they? Isn't that the case with a Line 6?
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I don't know about Line 6 specifically but I do know that imbalance won't hurt anything. It's all about loads and in general you can run a SS amp with no load. A stereo amp is simply two amps in one casing. So there's no good reason running one amp in a two amp casing will damge the other one.
 
Bubba po said:
If you plug both sides of a stereo amplifier in using both inputs, then you will get a summed mono signal.
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well, what you'll likely get is a blowed up amp because you'd have the outputs of two amps running into each other.
 
Lt. Bob said:
I don't know about Line 6 specifically but I do know that imbalance won't hurt anything. It's all about loads and in general you can run a SS amp with no load. A stereo amp is simply two amps in one casing. So there's no good reason running one amp in a two amp casing will damge the other one.
Click to expand...

Hey, just go read the Line 6 FAQs. I'm not making it up.
 
mjbphotos said:
Hey, just go read the Line 6 FAQs. I'm not making it up.
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of course you're not making anything up ......... you're one of the good guys here.

I did go and look and it's actually not that clear.

Although it says you want to hook up both sides (amps) to a cab 8 ohms or higher to avoid amp failure .... above that it only says that if you don't connect both sides to a stereo cab half the speakers won't work ... but no mention of damage.

Also above THAT it says that "All Line 6 amplifiers (with the exception of the Spider valve series) are safe to run without any speaker load connected" ...... so personally I'm reading that as you can run one side with no load but don't hook them up to less than 8 ohms.

But it's pretty unclear to tell the truth. You could interpret it either way.







However, if I had a line 6 amp one of my desires would be to blow it up so maybe I'm not the best to ask!
:D
 
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