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Audio Amp Load

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JohnS_AZ:
Anyone know of any reasons this would NOT be a good dummy load for a 35W audio amp?



http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=RHRD-8.0-ND

Balaur:
That's a good choice. There are no reasons not to use it.

One could object that a loudspeaker has a complex impedance (resistive, inductive and even capacitive components) and it's also nonlinear (inductance, phase varying with frequency, etc).
However, using a resistor it's an accepted practice. In any case, the amplifier characteristics and performances are usually specified using a resistive load.

Also, a quick comment on using resistors that will have to dissipate a lot of power: the temperature coefficient is very important since it could modify the resistance for different output powers. However, in your case, the tempco is only 50ppm, which is perfectly usable.

Cheers

JohnS_AZ:
Thanks Balaur.

The datasheet specifies a pretty hefty heat sink to hold that 50ppm spec. (291 sq in surface area).

What I also learned from the datasheet and hadn't thought of before (although it makes perfect sense) is that you have to HUGELY derate this resistor if you run it without a heat sink. This is a 50W resistor, but without a heatsink you can only run it at 20W.

Luckily I have a beefy heat sink, and I'll probably add a small fan to it.

NiHaoMike:
Just use a coil of nichrome wire at the length needed to get the impedance you want. Very high power rating and very cheap.

Zad:
If it is relatively low power, use a 20W (or whatever) car lamp. NOT a halogen one, their 'cold' resistance is incredibly low.

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