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Old 10-04-2012, 04:18 PM   #1
FenderBender72
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Wattage???

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?
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Old 10-04-2012, 04:26 PM   #2
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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
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Old 10-04-2012, 04:26 PM   #3
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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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Old 10-04-2012, 04:31 PM   #4
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^ pretty much. and also be the correct impedance.
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Old 10-04-2012, 04:33 PM   #5
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Originally Posted 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...
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Old 10-04-2012, 04:35 PM   #6
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"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 : 10-04-2012 at 04:39 PM.
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Old 10-04-2012, 04:42 PM   #7
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Quote:
Originally Posted 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.
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Old 10-04-2012, 04:50 PM   #8
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Quote:
Originally Posted 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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Old 10-04-2012, 04:58 PM   #9
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Quote:
Originally Posted 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.
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Old 10-04-2012, 04:59 PM   #10
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Originally Posted 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.
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Old 10-04-2012, 05:01 PM   #11
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Quote:
Originally Posted by Captaincranky
No, solid states amps DON'T have output transformers, and that makes impedance matching MORE critical.
.


Nope.
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Old 10-04-2012, 05:05 PM   #12
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Quote:
Originally Posted 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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Old 10-04-2012, 05:07 PM   #13
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Originally Posted 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.
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Old 10-04-2012, 05:10 PM   #14
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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:
Originally Posted 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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Old 10-04-2012, 05:11 PM   #15
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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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Old 10-04-2012, 05:16 PM   #16
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so how the fudge do i figure out "suggested impedence" of amp "A" vs amp "B", and cab "A" and cab "B"?
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Old 10-04-2012, 05:20 PM   #17
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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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Old 10-04-2012, 05:21 PM   #18
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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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Old 10-04-2012, 05:28 PM   #19
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Originally Posted 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 : 10-04-2012 at 05:31 PM.
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Old 10-04-2012, 05:30 PM   #20
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too high an impedance will damage a tube amp.
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