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FenderBender72
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#1
What are some wattage "no-no's". Like using an amp head with XXX amps with a cabinet with speakers rated for XXX amps. What all do I need to know about wattage before I buy a new head and cab?

seljer
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#2
The cabinet's wattage rating should be higher than the amps output wattage and the impedance should match.

More is louder, in theory. Though other factors play just a large as role as power (speaker efficiency, number of speaker, tube vs solid state). If you have two different amps playing through the same speaker, to the volume get twice as loud (psychoacoustically) you need roughly 3.5 as much bare power. Tube amps sound louder because of the overload in a different way.

5 watts is enough to piss of any neighbours if you live in an apartment
tubetime86
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#3
Your cab should be able to handle the number of watts your head puts out... Or even better; a little more. That's really it.
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Dave_Mc
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#4
^ pretty much. and also be the correct impedance.
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FenderBender72
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#5
Quote by tubetime86
Your cab should be able to handle the number of watts your head puts out... Or even better; a little more. That's really it.


Sounds simple enough. I dont know why I am over-thinking this so much. I guess I'm just undecided on what the hell to buy. Like a Peavey Vypyr 120 head with some type of cab (although I'm not sure what cab to get), or spend the extra money to get the 6505+ but I dont know if I need to spend the extra money to be happy with the sound I will get. I dont know; I have a lot of research to do...

Captaincranky
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#6
"Wattage" actually means different things in different contexts.

When the term is applied to a speaker, (or a cabinet full of them), it's an indicator of how much "wattage"they should dissipate, before damage can occur.

When "wattage" is applied to any amplifier, it is a measure of how much power the amp will generate.

So, as a rule, your speaker system, should be able to dissipate more power than the amp can supply.

However, You don't need 100 watts, to drive a 100 watt cabinet. You might blast yourself out of the house inputting perhaps as little as 10 watts.

More powerful amps, "hit harder", in the sense that they generate high dynamic range information much more rapidly than smaller amp, but it takes ten times the power, to generate 2 times the perceived loudness.

Speaker efficiency is more relevant than maximum amplifier power to overall volume.

However, more important than that, is speaker "impedance". This is measured in "ohms", and indicates the systems resistance to passing electricity.

The speaker system must be chosen, as a first priority, to match the suggested output impedance of the power amplifier involved.

Amps can have their power rated @ 2, 4, 8, or perhaps as high a 16 oms. It is especially critical with solid state amps, to match the impedance of the cabinets, to the amp's optimum impedance. Otherwise, she dun gonna blow....!
Last edited by Captaincranky at Oct 4, 2012,
CodeMonk
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#7
Quote by Captaincranky
"Wattage" actually means different things in different contexts.

When the term is applied to a speaker, (or a cabinet full of them), it's an indicator of how much "wattage"they should dissipate, before damage can occur.

When "wattage" is applied to any amplifier, it is a measure of how much power the amp will generate.

So, as a rule, your speaker system, should be able to dissipate more power than the amp can supply.

However, You don't need 100 watts, to drive a 100 watt cabinet. You might blast yourself out of the house inputting perhaps as little as 10 watts.

More powerful amps, "hit harder", in the sense that they generate high dynamic range information much more rapidly than smaller amp, but it takes ten times the power, to generate 2 times the perceived loudness.

Speaker efficiency is more relevant than maximum amplifier power to overall volume.

However, more important than that, is speaker "impedance". This is measured in "ohms", and indicates the systems resistance to passing electricity.

The speaker system must be chosen, as a first priority, to match the suggested output impedance of the power amplifier involved.

Amps can have their power rated @ 2, 4, 8, or perhaps as high a 16 oms. It is especially critical with solid state amps, to match the impedance of the cabinets, to the amp's optimum impedance. Otherwise, she dun gonna blow....!



I agree with everything except that last bit.
The main reason why you want to match impedance is so you don't blow the output transformer.
SS amps don't have output transformers.
Arby911
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#8
Quote by seljer
The cabinet's wattage rating should be higher than the amps output wattage and the impedance should match.

More is louder, in theory. Though other factors play just a large as role as power (speaker efficiency, number of speaker, tube vs solid state). If you have two different amps playing through the same speaker, to the volume get twice as loud (psychoacoustically) you need roughly 3.5 as much bare power. Tube amps sound louder because of the overload in a different way.

5 watts is enough to piss of any neighbours if you live in an apartment



Heed the first and last lines in the above, ignore the middle paragraph.
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CodeMonk
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#9
Quote by Arby911
Heed the first and last lines in the above, ignore the middle paragraph.


And more watts does not necessarily mean louder, it means more clean headroom.
Captaincranky
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#10
Quote by CodeMonk
I agree with everything except that last bit.
The main reason why you want to match impedance is so you don't blow the output transformer.
SS amps don't have output transformers.
No, solid states amps DON'T have output transformers, and that makes impedance matching MORE critical.

A tube amp is loaded through the transormer' s primary coils, the speaker system resides at the secondary coils of the tranny.

When the impedance is reduced in a solid state amp, the rise in current flow is born directly by the output transistor. The heat gets excessive, and the transistor junctions melt.

In the tube amp, the load across the output tube, for the most part, never varies, it only changes in the secondaries.
Arby911
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#11
Quote by Captaincranky
No, solid states amps DON'T have output transformers, and that makes impedance matching MORE critical.
.


Nope.
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#12
Quote by Arby911
Nope.

I gotta agree with Arby, I have built a few SS amps (very small/weak but still SS) and they didn't seem to care abotu impedance

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Captaincranky
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#13
Quote by Arby911
Nope.
Really? Take notice of the huge heat sinks on transistor output stages. What they're for, is to lead heat away from the transistors. If the transistor were suspended in air, its failure would be many orders of magnitude faster.
Heat will destroy transistor, and does so in every place they're used. The modern classic example is a computer CPU. Check out the heat sink fan assembly on a high performance computer sometime.

Modern solid state amps supply so much power, many multiples of what is available with the largest tube amps. So, it would seem they're harder to break, but watt for watt, they're not.
Kevin Saale
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#14
Yeah, thats not true. Solid state amps only have a minimum impedance for a reason. Almost every solid state amp made currently will list its wattage an minimum impedance (usually 4 ohms, sometimes 2) and its wattage at 8 ohms as well (or 4 or and 8 for 2 ohm minimum amps).

Yes, its true if you go below the minimum impedance you can cook the output transistors, but you won't do that by going over the minimum impedance.

Quote by Captaincranky
Really? Take notice of the huge heat sinks on transistor output stages. What they're for, is to lead heat away from the transistors. If the transistor were suspended in air, its failure would be many orders of magnitude faster.
Heat will destroy transistor, and does so in every place they're used. The modern classic example is a computer CPU. Check out the heat sink fan assembly on a high performance computer sometime.

Modern solid state amps supply so much power, many multiples of what is available with the largest tube amps. So, it would seem they're harder to break, but watt for watt, they're not.


Thats all true, but when you increase the impedance you're lowering current which will in turn lower the heat to the transistors. You could even say running the amp at a higher impedance would put less strain on the amp. Thats generally cancelled out by the fact you have to turn the amp up more to achieve the same volume if you're running a higher impedance load.
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Last edited by Kevin Saale at Oct 4, 2012,
AcousticMirror
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#15
nope solid state amps without ot's impedance bridge instead of match.

they'll put out max wattage at their optimal impedance and half with a 2 to 1 mismatch.

you just have to make sure you don't go under because you'll get twice as much nominal power.
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FenderBender72
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#16
so how the fudge do i figure out "suggested impedence" of amp "A" vs amp "B", and cab "A" and cab "B"?

AcousticMirror
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#17
if you have a tube amp match your ohms.

if you have a solid state amp get a new amp.

easy peasy.
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Kevin Saale
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#18
Its all in the technical specs. Most higher end tube amps will have select-able impedance, and most SS amps will have a minimum impedance of 4 ohms.
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Captaincranky
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#19
Quote by Kevin Saale

Yes, its true if you go below the minimum impedance you can cook the output transistors, but you won't do that by going over the minimum impedance.


Say WUT?

Yeah, higher impedance reduces current flow, which reduces heat. However, too low impedance simply put, is a "short circuit".

I didn't realize I had to explain what too high impedance causes, which is much reduced power output. But, speaker impedance which is, "too high", won't damage a tube or a transistor amp.

The reason you hear a "click" a few seconds after you turn a home entertainment receiver, is because it disconnects the output transistors from the speaker circuit, and only connects the speakers after the PSU caps are charged.

This is done to prevent "current inrush", caused the caps charging, from damaging the output transistors...
Last edited by Captaincranky at Oct 4, 2012,
AcousticMirror
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#20
too high an impedance will damage a tube amp.
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Captaincranky
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#21
Quote by AcousticMirror
too high an impedance will damage a tube amp.
And that depends on what you call "too high"? I seen to recall output transformers that had different taps for different impedance loudspeakers.
AcousticMirror
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#22
dawg if you plug a cab into the tap it was meant for then it's by definition not too high. it is just right.
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Captaincranky
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#23
Quote by AcousticMirror
dawg if you plug a cab into the tap it was meant for then it's by definition not too high. it is just right.
And then it won't damage the amp, now will it?
AcousticMirror
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#24
no of course not plugging the right cab into the right tap will not damage the amp.

going too high will.

is this hard to understand.
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Arby911
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#25
Quote by Captaincranky
Say WUT?

Yeah, higher impedance reduces current flow, which reduces heat. However, too low impedance simply put, is a "short circuit".

I didn't realize I had to explain what too high impedance causes, which is much reduced power output. But, speaker impedance which is, "too high", won't damage a tube or a transistor amp.

The reason you hear a "click" a few seconds after you turn a home entertainment receiver, is because it disconnects the output transistors from the speaker circuit, and only connects the speakers after the PSU caps are charged.

This is done to prevent "current inrush", caused the caps charging, from damaging the output transistors...


Quote by Captaincranky
No, solid states amps DON'T have output transformers, and that makes impedance matching MORE critical.




Make up your mind...

The simple fact is that SS amps have a minimum impedance, but not a maximum. Tube amps have both, although there are of course design criteria that allow a certain degree of mismatch, but it's nowhere near the order of what can be done with a SS amp.

Being wrong, and then trying to cover it up by saying 'I didn't know I had to explain THAT part' is childish.
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Captaincranky
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#26
Quote by Arby911
Make up your mind...

The simple fact is that SS amps have a minimum impedance, but not a maximum. Tube amps have both, although there are of course design criteria that allow a certain degree of mismatch, but it's nowhere near the order of what can be done with a SS amp.
Being wrong, and then trying to cover it up by saying 'I didn't know I had to explain THAT part' is childish.
No, too little current won't cause heating, too high current will. High current comes from low impedance. I really didn't think I had to explain that. In your case, I was wrong.
Kevin Saale
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#27
It is especially critical with solid state amps, to match the impedance of the cabinets, to the amp's optimum impedance. Otherwise, she dun gonna blow....!


Those are your exact words. What other way should someone take that then to mean any mismatch will cause the amp damage?
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Arby911
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#28
Quote by Captaincranky
No, too little current won't cause heating, too high current will. High current comes from low impedance. I really didn't think I had to explain that. In your case, I was wrong.


Yes, because I'm the one that's been wrong repeatedly above....

You are priceless!

There are a fair few folks here that know more about electricity and electronics than I do, but you don't appear to be one of them.

And in all fairness, perhaps you do know a good bit, but it's pretty clear you don't know as much as you think you do. (Or if you do, you really suck at presentation...)
“Ignorance more frequently begets confidence than does knowledge.”
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Captaincranky
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#29
Quote by Arby911


There are a fair few folks here that know more about electricity and electronics than I do, but you don't appear to be one of them.


OK, lets deal with specs. Since you are more knowledgeable than most folks here, well start with series and parallel resistance,

Two four ohm speakers in parallel present 2 ohms of impedance. With a SS amp rated @ 8 ohms, that likely would damage the amp. It could even hurt an amp rated a 4 ohms minimum.

Two 8 ohm speakers wired in series would present 16 ohms to a amp. I'm reasonably sure a tube amp rated @ 8 ohms, would tolerate that much mismatch. Nor would a single 4 ohm speaker likely damage the same a tube amp either.

Within the confines of those limits, I suggest a tube amp is less vulnerable to damage than a SS amp.

But yeah, the transistor amp is only at risk to the low side. Too high an impedance across its output transistors, by and large, just shuts it off.
Last edited by Captaincranky at Oct 4, 2012,
Arby911
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#30
Quote by Captaincranky
OK, lets deal with specs. Since you are more knowledgeable than most folks here, well start with series an parallel resistance,

Two four ohm speakers in parallel present 2 ohms of impedance. With a SS amp rated @ 8 ohms, that likely would damage the amp. It could even hurt an amp rated a 4 ohms minimum.

Two 8 ohm speakers wired in series would present 16 ohms to a amp. I'm reasonably sure a tube amp rated @ 8 ohms, would tolerate that much mismatch. Nor would a single 4 ohm speaker likely damage the same a tube amp either.

Within the confines of those limits, I suggest a tube amp is less vulnerable than a SS amp.

But yeah, the transistor amp is only at risk to the low side. Too high an impedance across its output transistors, by and large, just shuts it off.


It's amusing that you've artificially set the question, and then determined the answer to your preconception based on arbitrary values of your own making.

Look, I've taken a gander at several of your other postings as well as the circumstances of your warning, and from what I can see you take great pleasure in stirring up controversy (as often as not by posting marginal or outright false information).

That won't go over well in this particular forum.

Don't go away mad, just go away. Or learn to play well with others.
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Captaincranky
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#31
Quote by Arby911
It's amusing that you've artificially set the question, and then determined the answer to your preconception based on arbitrary values of your own making.
Are those values realistic or not? They're not really, "values of my own making", nor are they "arbitrary". They're simply factors of 1/2 or 2 times the typical load impedance of typical SS or tube amplifiers. So, what is the likely effect of a 1/2X or 2X impedance mismatch on either type of amp?
Kevin Saale
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#32
Quote by Captaincranky
OK, lets deal with specs. Since you are more knowledgeable than most folks here, well start with series and parallel resistance,

Two four ohm speakers in parallel present 2 ohms of impedance. With a SS amp rated @ 8 ohms, that likely would damage the amp. It could even hurt an amp rated a 4 ohms minimum.

Two 8 ohm speakers wired in series would present 16 ohms to a amp. I'm reasonably sure a tube amp rated @ 8 ohms, would tolerate that much mismatch. Nor would a single 4 ohm speaker likely damage the same a tube amp either.

Within the confines of those limits, I suggest a tube amp is less vulnerable to damage than a SS amp.

But yeah, the transistor amp is only at risk to the low side. Too high an impedance across its output transistors, by and large, just shuts it off.


I don't agree with the 4 ohm load on an 8 ohm tube amp. I've done that before, to a MESA of all amps which are DESIGNED to handle that and it ended up red plating the output tubes in no time. Mesa brand tubes as well. Yes, it didn't destroy the amp, but MESAs are purposely over spec'd to handle this mismatch, in general most tube amps aren't.

In general mismatching the load ohms over the output ohms is safe for all amps, but it will be some strain on the output tubes of a tube amp. As for an SS amp, if anything it'll be less strain. Your assertion that tube amps can handle more of a mismatch is too general for one thing, not backed up by any evidence, and, in the end, generally not true.
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Captaincranky
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#33
Quote by Kevin Saale
I don't agree with the 4 ohm load on an 8 ohm tube amp. I've done that before, to a MESA of all amps which are DESIGNED to handle that and it ended up red plating the output tubes in no time. Mesa brand tubes as well. Yes, it didn't destroy the amp, but MESAs are purposely over spec'd to handle this mismatch, in general most tube amps aren't.
Part of problem of even entertaining this entire discussion in relation to musical instrument amps, is that they undergo quite a lot of abuse. Low impedance causes high current flow, on that we agree. If we used these amps in a sensible manner, who knows what the disposition would be..

However, overdrives, distortion pedals, and whatnot, add really deviant signal waveforms and bandwidth to the equation. Amp clipping is notoriously deadly for speakers. To much signal delivered to the output stage isn't good for any amp.

Suppose we abandon this altogether, and suggest to the OP, "just make certain the impedance of the cabinet you choose, is matched to the amp's output impedance, or you may have problems".

On that note, I suggest the TS pick out the amp first, then the cabinet last.

That shouldn't be too contentious, but who knows.
Kevin Saale
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#34
Quote by Captaincranky
Part of problem of even entertaining this entire discussion in relation to musical instrument amps, is that they undergo quite a lot of abuse. Low impedance causes high current flow, on that we agree. If we used these amps in a sensible manner, who knows what the disposition would be..

However, overdrives, distortion pedals, and whatnot, add really deviant signal waveforms and bandwidth to the equation. Amp clipping is notoriously deadly for speakers. To much signal delivered to the output stage isn't good for any amp.

Suppose we abandon this altogether, and suggest to the OP, "just make certain the impedance of the cabinet you choose, is matched to the amp's output impedance, or you may have problems".

On that note, I suggest the TS pick out the amp first, then the cabinet last.

That shouldn't be too contentious, but who knows.


That IS what the first posters said. Then you come out of left field with bullshit, get called on it then back pedal into a debate. Just sayin.
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CodeMonk
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#35
Quote by Captaincranky
, "just make certain the impedance of the cabinet you choose, is matched to the amp's output impedance, or you may have problems".
.


/thread
gumbilicious
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#36
this is so confusing, what with all the posturing

tube amp -> match impedance (cab impedance should match the speakers out).

solid state -> use a speaker that is >= amp's min impedance.

...and i thought i was long winded.

cab's power handling needs to be rated at the amp's output or greater.
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Last edited by gumbilicious at Oct 5, 2012,
FenderBender72
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#37
I didn't realize when I started this thread, I would have commenced this great debate over something that I am now EXTREMELY confused on . So I will just check back when the fact checking has been done and a winner has been chosen.

tubetime86
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#38
Quote by Kevin Saale
That IS what the first posters said. Then you come out of left field with bullshit, get called on it then back pedal into a debate. Just sayin.

I'm just sayin' too.
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Arby911
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#39
Quote by FenderBender72
I didn't realize when I started this thread, I would have commenced this great debate over something that I am now EXTREMELY confused on . So I will just check back when the fact checking has been done and a winner has been chosen.


Don't be confused, the first line of post #2 is correct and was all you needed.

Ignore the rest.
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dementiacaptain
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#40
Dude, don't be confused. On a tube amp, match the impedance. period. It is generally a good idea to get a cab that is at bare minimum rated for the wattage of your amp, and many folks would suggest a cab rated over the output of the amp, but that is getting into another debate about different speakers being rated more conservatively than others.

This thread kinda turned silly, but that is what happens when you have a person arguing for the sake of arguing, who isn't even particularly good at presenting their argument.
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