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Old 23rd January 2008, 02:02 AM   #1
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Default Help with power levels of components

Hey all

I just wanna know what power levels of components need to be in order to handle a certain watts rms load

For example what volts do a cap need and what watts do a resister need

I have an amp that does 120 watts rms or do need them to be slighly higher from peak levels?

I ask this here because no one answered in another thread?

I have access to crossover type 100 volt caps here? will they do

Thanks Cya
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Old 23rd January 2008, 09:04 AM   #2
simon5 is offline simon5  Canada
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It depends on what the component will dissipate by itself.

For example if your amp is powering a 7 ohms speaker with a 1 ohm resistor in series, that 1 ohm will only see 1/8th of the power so a resistor rated at 15W would do.

For the voltage it's the same, your capacitor should be rated slightly higher than the peak voltage it will ever see. If your amplifier is powering a 8 ohms speaker with a sinewave, and the capacitor is in parallel with the speaker, it will see the full voltage, 44 Volts peak. You could take a part rated at 50V or something.
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Old 23rd January 2008, 09:26 AM   #3
Andy G is offline Andy G  Australia
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I generally parallel a pair of 10w resistors twice the required value for PA speaker. ie 20w handling. (don't think you will find 15w resistors down here)

10 watt is probably more than adequate, but for the small amount extra, doesn't hurt to make sure.

You do know to make sure you are using Non-polar capacitors.. If they have a + or - marked on them.. wrong ones !!!

Again, WES have a couple of lines of poly caps, which are usually preferable to electrolytics.

Jaycar also sell poly caps.
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Old 23rd January 2008, 09:49 AM   #4
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100V should be plenty - on an 8 Ohm speaker 100V peak is 625W, much more than your amp size, even allowing for some safety margin.
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Old 23rd January 2008, 09:58 AM   #5
AndrewT is offline AndrewT  Scotland
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A safe guide for speaker capacitors is to exceed the amplifier supply rail voltage. Except when a bridged amp is used and then exceed rail to rail voltage.
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Old 23rd January 2008, 10:32 AM   #6
sreten is offline sreten  United Kingdom
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I'll just throw in the peak power capacity of a power resistor is
something like 20 times its continuous rating and at clipping levels
average amplifier output is < 1/10 of continuous output power.

So there is no need for very high power resistors in the positions
they are generally used. Some common sense needs to be applied
for their selection and speaker purpose, PA or hi-fi use differs.

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