Audio Amp Load

[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.

[Zero999]

Any filament lamp will have a low cold resistance, halogens might be the worst but it's also true for standard incandescent.

Has anyone blown a resistor like that? I've found they explode, the ends pop out.

It's true that real speakers aren't purely resistive so the only way to really test it is to use a speaker, compete with crossover and enclosure but a resistor is fine for most applications.

[JohnS_AZ]

I'll do the regular bench testing using a pair of real speakers but I want to do a long burn-in of the amp under full power, thus the need for a dummy load.