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Old 4th October 2005, 09:27 PM   #1
jud_fry is offline jud_fry  United States
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Default ohms and watts

I'm still trying to find out how to go about putting together a cab with a head. If the cab is 600w and 8ohms, what is the minimum power i should look for in a head, and what is the maximum power i should look for in head, i don't want to overpower the speaker. I just don't know anything about this, and i can't seem to find any info anywhere. Thanks to anyone for some clarification, preferrably in layman's terms.
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Old 5th October 2005, 02:00 AM   #2
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Rule of thumb -- you're not nearly as likely to blow your speakers from an amplifier that is OVER powered as you are from one that is UNDER powered and driven into clipping. This may seem counter-intuitive, but it's true!

As for more specific numbers, somebody else will have to help.

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Old 11th October 2005, 02:30 AM   #3
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600 watts is extremely high for guitar. i have a 40w tube combo and it sings like crazy.. marshall plexis are like 100 watts, and i've never heard of anything over 300 watts. An old half-stack i had had four 30 watt celections in it and the head was like 150 watts. i could crank it no problem.
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Old 11th October 2005, 08:40 PM   #4
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My housemate plays in a very loud metal band and uses a 100W tube head and doesn't put that near full volume most of the time.

100W is the max I'd recommend in a tube head for guitar, and 30-40W will likely be heaps. For a solidstate head, maybe 200W (max) as you usually don't want it to go into hard clipping because it sounds awful. With SS you'll need to get any distortion reqd from a pedal, tube preamp and the speakers overdriving/breaking up rather than the poweramp's contribution. May need a compressor pedal too, depending on what sound you're after.

Go and play as many amps as you can to get an idea what you need, as power and tone in guitar amps can be two entirely seperate things.
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Old 11th October 2005, 08:59 PM   #5
Byrd is offline Byrd  South Africa
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Just a fact to note in terms of "Loudness" - 60 Watts into 8 (One tenth of 600 Watts) will be 1/2 the loudness of 600 Watts into 8

Or to put it another way - To double the loudness of an amplifier, you will need to increase wattage by a factor of 10.

Any wattage above 100 Watts "SHOULD" be fine - however the best way to make this decision is to remember the first fact mentioned (2 times loudness = 10 times power) while looking at prices of heads.

The more power the better as long as you get value for money in terms of loudness.

I wouldn't worry too much about clipping as usualy only tweeters are affected by this distoriton.
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Old 12th October 2005, 04:11 PM   #6
AndrewT is offline AndrewT  Scotland
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Hi,
is a head something to do with a guitar amp?
Let's assume it is.
Guitar speakers are generally fairly efficient with an spl of between 95db/W and 100db/W.
At this level of output in an appropriately sized cabinets (for PA work) it is capable of 115db at 1m when driven at 100W. This is loud. It will completely drown out your voice.
The very big numbers of watts are more appropriate to wideband speakers that need big volts to drive low frequencies into speakers of much lower efficiency, often between 82db/W and 90db/W
I would tend to agree that smaller venues will work with 30W to 100W with a true PA speaker.
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