#1
is there any problem of having a 8ohm cabinet into a 4 ohm ouput amp in a marshall avt ???

i know for solid state amplifier .. it only create a loss of volume which i dont really care about .

but is there any danger for a hybrid amp ( with a 12ax7 in the premap section ) ???

thank you .

my old valvestate cab is 8 ohm .. and the valvestate 2000 head are 4 ohm.
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Last edited by Skysc at Nov 2, 2009,
#3
Quote by i_am_metalhead
Wont hurt anything SS, hybrid, or tube as long as the cab is rated equal to or higher than the head.



+1

You will lose output. But it will work. Never plug an amp into a cabinet that has LESS impedance. Higher is fine.
Last edited by Matt420740 at Nov 2, 2009,
#4
it'll be a little bit of a power/volume drop but not much
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#5
Quote by i_am_metalhead
Wont hurt anything SS, hybrid, or tube as long as the cab is rated equal to or higher than the head.

Regardless of the power section, it's something you should avoid.
Although a solid-state amp is usually considerably more tolerant of impedance mismatches, it's bad for the amp to maintain one for a long period of time.
#6
Quote by kyle62
Regardless of the power section, it's something you should avoid.
Although a solid-state amp is usually considerably more tolerant of impedance mismatches, it's bad for the amp to maintain one for a long period of time.


Tell that to Matt Bruck (former tech for EVH). He's stated several times that impedance mismatch is perfectly fine as long as the cab is rated higher than the head - doesn't matter if its SS or tube.

I have a feeling that he knows just a bit more about the subject than you
#7
Quote by i_am_metalhead
Tell that to Matt Bruck (former tech for EVH). He's stated several times that impedance mismatch is perfectly fine as long as the cab is rated higher than the head - doesn't matter if its SS or tube.

I have a feeling that he knows just a bit more about the subject than you

You're completely right of course - that's what's called a 'safe mismatch'. After all, making any amp work less than it needs to is somewhat less catastrophic than making it provide more power than it physically can...

However, you must understand that a lot of less experienced kids use this forum. It's not a good idea to go telling this sort of thing to the ones who aren't well versed on amps as it only adds another layer of confusion, and no doubt leads to quite a few broken amps ("Wait, is 16 ohms higher or lower than 8? I don't get it...").

It's easier to teach people that impedance mismatches are a bad habit, full stop -although in reality of course it's no problem to more experienced gearheads.
Last edited by kyle62 at Nov 2, 2009,
#8
I picked up a very simple cheat sheet on this some time back and I hold it as true.


For Valve amps:
Amp Head Ohms > Cab Ohms = Worn Power Valves, Power Loss
Amp Head Ohms < Cab Ohms = Strain on the Output Transformer, Power Loss

For SS Amps:
Amp Head Ohms > Cab Ohms = Power Loss
Amp Head Ohms < Cab Ohms = Not sure


Will - Eddie Van Halen's rig does not count in the context of this board. Most people on here should just follow the basic principles. The TS will probably be fine but all tube amps are different. Eddie had the money and tone chasing mentality to do whatever the fuk he wanted to and ran a variac etc...basically abused the sh*t out the things.
Last edited by 311ZOSOVHJH at Nov 3, 2009,
#9
Quote by kyle62
You're completely right of course - that's what's called a 'safe mismatch'. After all, making any amp work less than it needs to is somewhat less catastrophic than making it provide more power than it physically can...

However, you must understand that a lot of less experienced kids use this forum. It's not a good idea to go telling this sort of thing to the ones who aren't well versed on amps as it only adds another layer of confusion, and no doubt leads to quite a few broken amps ("Wait, is 16 ohms higher or lower than 8? I don't get it...").

It's easier to teach people that impedance mismatches are a bad habit, full stop -although in reality of course it's no problem to more experienced gearheads.


Sorry if I came off as a jerk - I wasn't trying to insult you or anything. I was just stating something that has been said by a very knowledgeable and experienced tech (Trust me, I doubt working with Eddie's rig is something your average Joe could do).


Quote by 311ZOSOVHJH
Will - Eddie Van Halen's rig does not count in the context of this board. Most people on here should just follow the basic principles. The TS will probably be fine but all tube amps are different. Eddie had the money and tone chasing mentality to do whatever the fuk he wanted to and ran a variac etc...basically abused the sh*t out the things.


While you do have a point, I was repeating something that Eddie's tech has stated (not Eddie himself) when asked about mismatching impedance. I doubt someone with as much knowledge about the subject has Matt Bruck would give bad or misleading advice. And he stated in one response that its (a "safe mismatch") is safe to use on any amp.


Not trying to say that you're stupid or anything, just repeating what's came out of the mouth of someone who is very experienced and knowledgeable in the subject.
Last edited by i_am_metalhead at Nov 3, 2009,
#10
Still seems like undo stress on an output transformer for no good reason tho - when it is not that hard to match your cab. I can understand in situations where someone needs to gig one night and has to borrow a friends cab etc but do it on purpose as 'just the way my rig is' doesn't make sense to me.

I'm not an amp tech tho and I've lost track of what this thread was about
#11
Quote by i_am_metalhead
Sorry if I came off as a jerk - I wasn't trying to insult you or anything. I was just stating something that has been said by a very knowledgeable and experienced tech (Trust me, I doubt working with Eddie's rig is something your average Joe could do).


Not in the slightest; as I said, I agree completely.
It's just that some of the younger users of UG are going to be confused by the truth, so sometimes it's easier to tell a convenient lie!


Eddie was famously one of the most fussy musicians going - the 'brown M&Ms' story pays homage to that!
Last edited by kyle62 at Nov 3, 2009,
#12
Quote by 311ZOSOVHJH
Still seems like undo stress on an output transformer for no good reason tho

Should girls wear jockstraps?


bad joke.
SS amps don't have output transformers.
That's exactly why they can take any mistmatch as long as there's some load.
#14
Quote by 311ZOSOVHJH
Still seems like undo stress on an output transformer for no good reason tho - when it is not that hard to match your cab. I can understand in situations where someone needs to gig one night and has to borrow a friends cab etc but do it on purpose as 'just the way my rig is' doesn't make sense to me.

I'm not an amp tech tho and I've lost track of what this thread was about


I've never understood why someone would want the intentional mismatch. I think it doesn't sound that good but Eric Johnson runs an 8ohm output into a 16ohm cab and he sounds great. YMMV I guess.
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#15
The tone benefit varies a lot by amp. It just depends on if you want more transformer saturation, so if you've got a 5150 or something like that you probably won't like the result, whereas it can sound rather nice in an old plexi.
#16
Quote by 311ZOSOVHJH
Still seems like undo stress on an output transformer for no good reason tho - when it is not that hard to match your cab. I can understand in situations where someone needs to gig one night and has to borrow a friends cab etc but do it on purpose as 'just the way my rig is' doesn't make sense to me.

I'm not an amp tech tho and I've lost track of what this thread was about



In my defense I was talking about Eddie's rig (Not the OP's) when I said undo stress on an OT is not worth it.


A small cheap transformer will not be able to handle the irregularities as well for example.

yes. no.


FFS.

I need to correct myself again. I'm sure Eddie's OT was kick ass. The small cheap transformers I was referring to are the ones on the lower budget end of tube amps we see in here a lot....like my Valveking. It is dinky compared to the amps he uses.
Last edited by 311ZOSOVHJH at Nov 3, 2009,
#17
Quote by 311ZOSOVHJH
In my defense I was talking about Eddie's rig (Not the OP's) when I said undo stress on an OT is not worth it.


A small cheap transformer will not be able to handle the irregularities as well for example.

yes. no.


I guess for him it didn't really matter though. He was making enough money at that time blow up every Plexi OT in the world and have them rewound/replaced. I believe he did have to get his OT rewound on his main Plexi several times actually.
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#18
Quote by i_am_metalhead
Tell that to Matt Bruck (former tech for EVH). He's stated several times that impedance mismatch is perfectly fine as long as the cab is rated higher than the head - doesn't matter if its SS or tube.

I have a feeling that he knows just a bit more about the subject than you
WRONG. Either you read it wrong or he's full of shit.
Having a cab with higher impedance than the amp allows the voltage excursions to go much higher on the primary of the OT in a tube amp. This is dangerous to the health of your amp. The plates output tubes will experience much higher voltage peaks than the amp was designed for. The insulation on the primary windings of the output transformer is much more likely to punch through and fail.

You might be able to get by with a 2:1 mismatch, but if you dime your amp, don't count on it. Iron is expensive. You're actually safer to have a LOWER impedance cab connected to a tube amp. In fact, Fender has shorting jacks on the speaker output of their tube amps, to protect them from damage if the amp is accidentally used without a speaker connected. That's right. A dead short is safer for a tube amp output than an open circuit.
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Quote by Jackal58
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Quote by SK8RDUDE411
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Last edited by SomeoneYouKnew at Nov 3, 2009,
#19
Quote by SomeoneYouKnew
WRONG. Either you read it wrong or he's full of shit.
Having a cab with higher impedance than the amp allows the voltage excursions to go much higher on the primary of the OT in a tube amp. This is dangerous to the health of your amp. The plates output tubes will experience much higher voltage peaks than the amp was designed for. The insulation on the primary windings of the output transformer is much more likely to punch through and fail.

You might be able to get by with a 2:1 mismatch, but if you dime your amp, don't count on it. Iron is expensive. You're actually safer to have a LOWER impedance cab connected to a tube amp. In fact, Fender has shorting jacks on the speaker output of their tube amps, to protect them from damage if the amp is accidentally used without a speaker connected. That's right. A dead short is safer for a tube amp output than an open circuit.


Some OTs can take it better than others though. Old Fenders were known to take mismatches fairly well while others like Marshall weren't. There was an issue a while back with users of the Ultimate Attenuator blowing their OTs due to the input impedance on the UA being 30 ohms. The builder tried to say it was perfectly safe for every amp but after a while it became clear that he didn't know shit about tube amps or electronics for that matter. I believe he didn't even know what flyback voltages were.
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#20
Quote by SomeoneYouKnew
WRONG. Either you read it wrong or he's full of shit.
Having a cab with higher impedance than the amp allows the voltage excursions to go much higher on the primary of the OT in a tube amp. This is dangerous to the health of your amp. The plates output tubes will experience much higher voltage peaks than the amp was designed for. The insulation on the primary windings of the output transformer is much more likely to punch through and fail.

You might be able to get by with a 2:1 mismatch, but if you dime your amp, don't count on it. Iron is expensive. You're actually safer to have a LOWER impedance cab connected to a tube amp. In fact, Fender has shorting jacks on the speaker output of their tube amps, to protect them from damage if the amp is accidentally used without a speaker connected. That's right. A dead short is safer for a tube amp output than an open circuit.




No, I read it correctly and the man knows EXACTLY what he's talking about. I doubt he would have worked for Eddie for over a decade and now writes tech columns if he didn't know what he was talking about.

People like you are the reason I love UG.
#21
Quote by i_am_metalhead


No, I read it correctly and the man knows EXACTLY what he's talking about. I doubt he would have worked for Eddie for over a decade and now writes tech columns if he didn't know what he was talking about.

People like you are the reason I love UG.
nope.

There are a few idiots who don't know what they're talking about who write "tech" columns and plenty of fools like you who accept the garbage they write as gospel. Unfortunately there will also be gullible people who will listen to your advice. It just means more income for those of us who repair amps.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
#22
Quote by SomeoneYouKnew
nope.

There are a few idiots who don't know what they're talking about who write "tech" columns and plenty of fools like you who accept the garbage they write as gospel. Unfortunately there will also be gullible people who will listen to your advice. It just means more income for those of us who repair amps.


Yea.

There's just those of you who take any possibility - no matter how unlikely - and use it to scare people.

OR...

There are also "techs" who think they know what they are talking about and post on internet forums and post completely incorrect information.

You have a better chance of running into James Hetfield at your local grocery store than you do of doing serious damage to your amp by using a "safe mismatch".

And again, I'm forced to use the example of my brother (who has a masters in electrical engineering) has has told me that the resistance from a safe mismatch would not be enough to damage a transformer.

I get my info from professionals who have been at the game for decades and from people who actually know the sciences involved.


Seriously dude get a life and stop trying to play "Mr. Know-it-all".
#23
Quote by mmolteratx
I guess for him it didn't really matter though. He was making enough money at that time blow up every Plexi OT in the world and have them rewound/replaced. I believe he did have to get his OT rewound on his main Plexi several times actually.


What I said didn't come out right

The small cheap transformers was a reference to the cheap tube amps we see day in and day out around here. The Plexi's OT, like mine, are massive.
#24
Quote by i_am_metalhead
Yea.

There's just those of you who take any possibility - no matter how unlikely - and use it to scare people.
Nope.

Not at all "unlikely". I've replaced over 2 dozen output transformer in tube amps. It was absolutely clear what the failure mechanism was on almost half of those.

There's no benefit for me to scare people. Really, dude. Get a grip.
Quote by i_am_metalhead
I get my info from professionals who have been at the game for decades and from people who actually know the sciences involved.
I personally have experience. And I personally know the sciences involved. I don't need to flaunt "credentials" of my relatives.

Quote by i_am_metalhead
Seriously dude get a life and stop trying to play "Mr. Know-it-all".
You're dead wrong. You can't support your position with facts, because you don't have the understanding of the electronics and physics involved, so you say "get a life". Classic.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
#25
SYK - I've been a royal ass and I'm sorry. I'm not going to change my stance on the matter because I have facts to back up my point.

You've experienced problems with OTs due to mismatched impedance so it can be a problem. That's not to say that you can't safely run an amp while mismatching impedance.

You could get hit by a bus tomorrow - the odds of it happening are extremely small, but there are still those odds. Yet, no matter how small the odds there are still people in the hospital every day because they got hit by a bus.

We're both standing on complete opposite sides of the fence on this one and technically neither of us are wrong - as I said the chances of it actually damaging your amp are quite small, yet you've seen it happen first hand so it is actually a danger.


So there is no point arguing about this.