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Post by guitarman1 on Dec 11, 2007 7:04:36 GMT -7
Will I damage the transformer in my MAZ Jr., by running a 16 ohm speaker from the 8 ohm output?
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Post by dixiechicken on Dec 11, 2007 7:53:57 GMT -7
Perhaps NOT - but it's a BAD practice. I think you may void any warranties - if you do. Running with wrong load may cause eddy currents in the output transformer and cause the OT to run hot due changes of the magnetic flux in the ironcore - or something like that - and also influence the working point of the output tubes I believe. My recollection of things that CAN go wrong is somewhat hazy - as you can read. You had better CHECK THIS with Dr-Z himself - before doing anything that can be that dangerous. Cheers: Dixiechicken!
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Post by benttop (Steve) on Dec 11, 2007 9:04:15 GMT -7
DC is right - you don't want to do this as a matter of course. Once in a while if you're in a pinch it may be ok for a night, but you wouldn't want to do it all the time.
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Post by guitarman1 on Dec 11, 2007 13:29:16 GMT -7
We have an answer from the good Doctor, himself!
"Yes you can , going up in ohmage only limits the amps full output wattage, Ohms Law, going lower will over heat transformer."
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Post by dixiechicken on Dec 11, 2007 14:48:57 GMT -7
Keep in mind - that as a general rule: Tubeamplifiers is indeed more forgiving than Solidstate amplifiers - when it come to the matter of impedance mismatch.
Still you should avoid doing so - if only for the simple reason that somewhere down the line you may get a little over confident - and suddenly do that little extra bit that will blow your amp.
It doesnt cost anything to play it safe - unless you only bought a head without cab. ;D
Cheers: Dixiechicken!
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Post by benttop (Steve) on Dec 11, 2007 19:03:07 GMT -7
My problem is I can never remember the rule, so I always match.
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Post by Jones'n for Tone on Dec 12, 2007 7:06:08 GMT -7
Similar but different question..... Can I run a 8ohm load and a 4ohm load from the same head at the same time? Seems to me like this should be ok since there is no impedence mismatch. Just thought I should check first though.
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Post by benttop (Steve) on Dec 12, 2007 9:26:21 GMT -7
Similar but different question..... Can I run a 8ohm load and a 4ohm load from the same head at the same time? Seems to me like this should be ok since there is no impedence mismatch. Just thought I should check first though. If you mean plug two speakers into two jacks on the back at the same time, the answer is no way! Those jacks are hooked to different taps on the transformer. You never want to use more than one at a time. If you have two speakers, you get a Y cord and combine them. Unfortunately, if your speakers are two different impedances, it's not going to work as well as you would like - one speaker will be louder than the other. If you combine 8 ohms and 4 ohms in parallel, your net impedance is going to be less than 4 ohms (2.6 ohms actually) which is not a very good thing. If you combine them in series, it will be twelve ohms, which doesn't really match any of your outputs very well, and besides, one will be louder than the other. But you can do it and use the 8 ohm jack or the 16 ohm jack (I think the Doc recommends the 8 ohm jack in this case). HTH
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Post by Jones'n for Tone on Dec 12, 2007 10:21:03 GMT -7
Steve,
Thanks for the reply and yes I meant to hook up one 4 ohm cab to the 4ohm ouput jack and one 8ohm cab to the 8ohm output jack.
Your answer may well be correct, that it shouldn't be done. But I would like to dig a bit deeper though. The transformer itself should not care that there are two separate loads tied to different taps. After all that's how the transformers on the utility pole work, 240V from one tap, 120V from another. There may be something else in the amp design that doesn't like two separate loads?
The reason I ask is that I want to hook up each cabinet to a separate air brake for more control over the mix of the speakers. I'm sure this can be done from one output jack, but the cables become a nightmare. With two separate outputs this is a breeze.
Any other thoughts on why this should not be done? Obviously I don't want to do this if it will damage my amp in any way. Other experts please feel free to chime in as well.
Thanks,
Brian
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Post by benttop (Steve) on Dec 12, 2007 11:53:50 GMT -7
Steve, Thanks for the reply and yes I meant to hook up one 4 ohm cab to the 4ohm ouput jack and one 8ohm cab to the 8ohm output jack. Your answer may well be correct, that it shouldn't be done. But I would like to dig a bit deeper though. The transformer itself should not care that there are two separate loads tied to different taps. After all that's how the transformers on the utility pole work, 240V from one tap, 120V from another. There may be something else in the amp design that doesn't like two separate loads? The reason I ask is that I want to hook up each cabinet to a separate air brake for more control over the mix of the speakers. I'm sure this can be done from one output jack, but the cables become a nightmare. With two separate outputs this is a breeze. Any other thoughts on why this should not be done? Obviously I don't want to do this if it will damage my amp in any way. Other experts please feel free to chime in as well. Thanks, Brian Well I'm not the designer of the amp, so it's hard for me to say except that the designer (Doc Z) doesn't recommend it. Part of it is that when you look at how transformers are wound, I'm pretty sure you'll find that if you put two loads on there, there are parts of the tranny that are going to be overloaded. Those two jacks on the back share certain windings that are rated as they are. Doubling up might not be the best thing from a load perspective. But also the impedance connected to the output of the transformer is reflected back into the amp. A good design has maximum power transfer at the proper impedance. Doubling the load out there is going to throw those calculations off and who knows what will happen? I bet the Doc knows, but in any event, it is likely it will be sub-optimal. But you really need the designer's input to know absolutely for certain what might happen if you do that.
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Post by Jones'n for Tone on Dec 13, 2007 21:08:58 GMT -7
Steve,
You are correct. I asked the good Doc and he said although it probably wouldn't hurt anything to do it briefly, he didn't recommend it long term. He said that he'd have to do the calculations to give me any hard facts, but felt that the reflected impedance of the two loads would be mismatched enough to be an issue. That's good enough for me.
I have to say that both this forum and the Doc himself are very responsive and informative. What a great way to share the love and the knowlege of Z amps!
+1 to you Steve for all your helpful posts and +1 to the MAN (Dr Z).
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Post by benttop (Steve) on Dec 13, 2007 21:49:28 GMT -7
Thanks, I'm glad you asked the Doc, because this comes up all the time.
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