#1
Just double checking here; an 8 ohm output can go into a 16 ohm speaker Ok, but not vice versa?
Quote by Cathbard
Quote by Raijouta
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#3
So what am I risking, the speaker or the head? And other than buying a new cab how do I correct?
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Quote by Raijouta
Unless its electronic drums.

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#4
Yes, that can work but it will result in a quieter/weaker output. The other way round (bigger load Ohmage than cab) would result in nasty distortion and, with more power, damage to the speakers and risking blowing them.
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#5
So the dangers are for the cab, not the head. I know damaging my speaker should still be avoided but I'd be alot more pissed if I screwed my head.
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Quote by Raijouta
Unless its electronic drums.

BURN THE WITCH!!!!!
#6
Quote by tubetime86
So the dangers are for the cab, not the head. I know damaging my speaker should still be avoided but I'd be alot more pissed if I screwed my head.

As far as I know, yes because I can't see why the speakers not giving enough resistance would be bad for the head

But yeah, the first way (weaker head ohmage than speakers), which I presume is your situation, shouldn't cause any problems apart from a quieter output.
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#7
If you put a 16ohm cab into an 8 ohm head, your power tubes work harder, because the resistance to current is higher.

If you put a 4ohm cab into an 8ohm head, the cab tries to draw more power then the amp puts out, overworking the amp. And so I don't get bitched at again, no, it won't always blow up your amp, but it pretty much will blow up your amp unless you have a Mesa/Boogie.

Quote by DisarmGoliath
Yes, that can work but it will result in a quieter/weaker output. The other way round (bigger load Ohmage than cab) would result in nasty distortion and, with more power, damage to the speakers and risking blowing them.

That's what happens when you mismatch the wattage of the speakers with the wattage of the amp.
Last edited by imicius at Feb 16, 2009,
#8
So Imicius, should I be in search of a new cab? I'm running an 8 ohm speaker jack into a 16 ohm cab... as I said I know thats not intended but is it CATASTROPHIC, or inconvenient?
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Quote by Raijouta
Unless its electronic drums.

BURN THE WITCH!!!!!
#9
Quote by imicius
If you put a 16ohm cab into an 8 ohm head, your power tubes work harder, because the resistance to current is higher.

If you put a 4ohm cab into an 8ohm head, the cab tries to draw more power then the amp puts out, overworking the amp. And so I don't get bitched at again, no, it won't always blow up your amp, but it pretty much will blow up your amp unless you have a Mesa/Boogie.


That's what happens when you mismatch the wattage of the speakers with the wattage of the amp.


So theoretically, assuming you aren't cranking the amp to its full, it will likely just wear out your tubes faster? It's not a problem I suffer, but I know many people who are careless with load-matching to put it politely haha.

Oh, and I use a Hughes & Kettner so shove your Mesa metaphor

P.S to not sound like a dick, the last part there was only a joke - Mesa are also nice amps and I am debating buying a Dual Recto I've been offered for £900 to run alongside my H&K Switchblade.
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#10
Quote by tubetime86
So Imicius, should I be in search of a new cab? I'm running an 8 ohm speaker jack into a 16 ohm cab... as I said I know thats not intended but is it CATASTROPHIC, or inconvenient?

It will wear out your power tubes at a slightly faster rate, depending on how hard you crank it, but nothing terrible should happen. You don't really need a different cab, but if you do get one, it will be slightly louder.

Or you could get another 16ohm cab and run them together; that would be an 8ohm load.

Quote by DisarmGoliath
So theoretically, assuming you aren't cranking the amp to its full, it will likely just wear out your tubes faster? It's not a problem I suffer, but I know many people who are careless with load-matching to put it politely haha.

Oh, and I use a Hughes & Kettner so shove your Mesa metaphor

P.S to not sound like a dick, the last part there was only a joke - Mesa are also nice amps and I am debating buying a Dual Recto I've been offered for £900 to run alongside my H&K Switchblade.

Even if you are dimeing your amp, it should only wear out the power tubes, provided your amp has a lower total ohmage then your speaker cab.

I don't actually own a Mesa; they are designed so that if they are mismatched, they won't blow up. I don't actually know of any other amps that do that.
Last edited by imicius at Feb 16, 2009,
#11
It really depends, some tube amp OTs are made in such a way that they are more than safe running 8 or 16 ohm cabs, some older peavey tube amps could run 4, 8 or 16 ohm without any switching. Most modern amps have a switch that make the amps run safely in with any normal load. What amp do you have? Typically with tube amps you are better off macth the impedence, although its ussually safer to run a lower resistance load than a higher one, but that is not always the case. Bottom line match the head and the cab, or check with the manual, or amp maker to not risk damage.
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#12
Crate V-33H, running into a Blackheart 1x12 cab. I'd love to get another Blackheart 1x12 then they be in 8 ohm, but that will be at least a few months.
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Quote by Raijouta
Unless its electronic drums.

BURN THE WITCH!!!!!
#13
I suffer from teh same proble friend except that mine goes into a vj cab, im planning on ordering an 8ohm warehouse veteran 30 and just switching the stock speaker with that.
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#14
Quote by Johnbryant
It really depends, some tube amp OTs are made in such a way that they are more than safe running 8 or 16 ohm cabs, some older peavey tube amps could run 4, 8 or 16 ohm without any switching. Most modern amps have a switch that make the amps run safely in with any normal load. What amp do you have? Typically with tube amps you are better off macth the impedence, although its ussually safer to run a lower resistance load than a higher one, but that is not always the case. Bottom line match the head and the cab, or check with the manual, or amp maker to not risk damage.

It's the other way around. Running a higher impedance load will usually just result in bad, overly compressed tone.
#15
^ A higher impedance load will risk damage to the OT!!!
ALWAYS MATCH THE HEAD AND CAB!!!!!
/thread
Quote by Cachao

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#16
Quote by Johnbryant
^ A higher impedance load will risk damage to the OT!!!
ALWAYS MATCH THE HEAD AND CAB!!!!!
/thread

care to explain to me how?

running a higher ohm load is NOT the same as not having a load connected.
#17
Quote by al112987
care to explain to me how?

running a higher ohm load is NOT the same as not having a load connected.
The OP is risking damage to his head. A much higher ohm load is like not having a speaker connected. And this is considered dangerous for a tube amp. I've even heard a manufacturer of tube amps state than a dead short is better than an open for a tube amp. It is common knowledge that tube amps are susceptible to damage with ohm mismatches. Anecdotal evidence to the contrary is not going to fix your amp.

Conversely. a dead short on a SS amp would be disastrous. Whereas an open circuit or no speaker on a SS is fine.
#18
Quote by bartdevil_metal
DO NOT MISMATCH VALVE AMPLIFICATION. DO NOT.

Here's why:

If the Cab Ohmage > Head Ohmage, It causes strain on the Output Transformer (the most expensive part of an amp) and can cause it to fail.

So 16 Ohm Cab into an 8 Ohm Head = BIG NO NO.

If the Head Ohmage > Cab Ohmage, It causes strain on the Power Valves and makes them wear out faster (less expensive, but still an annoyance that makes your amp that bit less reliable)

So 8 Ohm Cab into a 16 Ohm Head = Still bad, but not AS bad.

---

Solid State Mismatch is absolutley fine, though some dB loss will be experienced. Solid State mismatch must be made so that the Cab ALWAYS has higher ohmage than the head.

So 16 Ohm cab into an 8 Ohm head is ok.

The other way around will cause the head to fail. Irreparably.

Cross thread quoting FTW.

It should also be said that some small mismatches either way you can get away with. For example if you mix cabs of different ohmage, and are within a 20% tolerance-ish.
...
Last edited by bartdevil_metal at Mar 23, 2009,
#19
Quote by fly135
The OP is risking damage to his head. A much higher ohm load is like not having a speaker connected. And this is considered dangerous for a tube amp. I've even heard a manufacturer of tube amps state than a dead short is better than an open for a tube amp. It is common knowledge that tube amps are susceptible to damage with ohm mismatches. Anecdotal evidence to the contrary is not going to fix your amp.

Conversely. a dead short on a SS amp would be disastrous. Whereas an open circuit or no speaker on a SS is fine.

No, it is NOT like having no speaker connected.

Matching upwards will not damage your amp. It is not like having no load connected. Flyback voltages will not occur at a 1:2 mismatch.
Last edited by al112987 at Mar 23, 2009,
#20
Sorry al112987, but you seemed to overlook reading the line you highlighted. I said a *much* higher ohm load is like not having a speaker connected. Not really an arguable point since *much* is not defined. But a 1:2 mismatch wouldn't qualify as *much* in my mind.

Regardless, it looks like you went and did a little research since your last post where you seemed to have no knowledge that tube and SS amps are different when it comes to ohm mismatches. Reference you response to Johnbryant where you claimed his statement was....

It's the other way around.

Now that you are using the term "flyback" voltage it appears that you went and schooled yourself. However, I would not generalize by telling people a 1:2 mismatch is fine. But it appears you are on track with your new found knowledge.
#21
Quote by fly135
Sorry al112987, but you seemed to overlook reading the line you highlighted. I said a *much* higher ohm load is like not having a speaker connected. Not really an arguable point since *much* is not defined. But a 1:2 mismatch wouldn't qualify as *much* in my mind.

Regardless, it looks like you went and did a little research since your last post where you seemed to have no knowledge that tube and SS amps are different when it comes to ohm mismatches. Reference you response to Johnbryant where you claimed his statement was....

It's the other way around.

Now that you are using the term "flyback" voltage it appears that you went and schooled yourself. However, I would not generalize by telling people a 1:2 mismatch is fine. But it appears you are on track with your new found knowledge.

at you thinking I went off and picked up some sort of "new found knowledge."
I know about certain things that I picked up when building my amp, about a year back.

I know that tube and solid state amps are different, yet until you brought it up, there was no talk about how an impedance mismatch affects a solid state amp. I brought up flyback voltages because that is the usual response from people who say "do not mismatch up, you're subjecting yourself to flyback voltages" when flyback voltages will just about never occur at a 1:2 mismatch.
#22
Well that certainly is in contrast to saying Johnbryant had it backwards when he wrote....

Typically with tube amps you are better off macth the impedence, although its ussually safer to run a lower resistance load than a higher one, but that is not always the case.

Johnbryant's statement is in accordance with general knowledge about amps. Maybe you had something else in mind and didn't express yourself well.
#23
Quote by fly135
Well that certainly is in contrast to saying Johnbryant had it backwards when he wrote....

Typically with tube amps you are better off macth the impedence, although its ussually safer to run a lower resistance load than a higher one, but that is not always the case.

Johnbryant's statement is in accordance with general knowledge about amps. Maybe you had something else in mind and didn't express yourself well.

Running a lower ohm load is terrible for your tubes and puts a huge strain on your OT. That is a fact, but my point is that not having a speaker connected at all and having a higher ohm load are two different things. I have never heard that (ex: 16 ohm amp into 8 ohm cab) is generally ok, I know there are specific instances, but it's not the standard.

Everyone I have ever asked about mismatching up has told me it's ok. A few months ago. I wanted to run el34s in my JTM45 in which would have caused a 1:2 (even closer to 1:2.5) impedance mismatch (my amp's OT has a 8.5k primary) which when running with el34s which most efficiently run seeing a 3-4k primary, and I asked two well respected vintage-Marshall clone builders about this and they said that it would not do any damage, though it would be best to run a 1:2 underload for tone purposes. (one of the cases where it IS ok to run an underload) Even devices like the ultimate attenuator use a fixed impedance that you're running your amp into which will cause mismatches.

I'm no amp or electronics expert, but I've done enough dicking around with my gear that I do have a pretty good general clue about what is going on in there.
Last edited by al112987 at Mar 23, 2009,
#24
Well this guy says no to a 50% mismatch.

http://roccaforteamps.com/

Here's a quote from him on a thread on another forum where someone is asking about running an 8 ohm output into a 16 ohm load.

"Believe it or not, a direct short is safer than an 8 ohm amp into 16 ohm load.
The problem with the 8 ohm amp going into the 16 ohm load is power transfer.
That energy builds up and can cause a tube, socket, or transformer to arc.
Same thing if you have no load at all (worse)."


I agree with you that I would rather put my 8 ohm output into a 16 ohm speaker before shorting it, but that's from the mouth of an amp builder. That's why my advice will always be the same.... ask the manufacturer.

Also this thread did not have a specific amp in mind.
Last edited by fly135 at Mar 23, 2009,
#25
I've heard from others differing opinions... mainly on the basis that arcs from higher voltages from an upwards mismatch only happens in extreme cases (ie. no load), not from a 1:2 mismatch, it's a bit of practical advice, not theoretical advice (kind of like things like cathode stripping and cathode poisoning) as in the case with Roccaforte's. He is right, but it's shady area on whether not the damage will occur with a 8ohm->16ohm mismatch.

Regardless, I would never mismatch more than one step either way.