Resistors

[ebenai]

Hi:

I'm just starting in this hobbie. I'm trying to assemble a LM4780 dual mono amp that I got from Audiosector. I have lots of questions.butThe first one is that I ruined some resistors and went to get replacement but they were larger (same specs) than the ones I got with the kit. Where can I get the "compact, metal film resistors" that came with the kit? Does it make any difference if you use a larger one (same specs)? Please forgieve the ignorance.

[rolandong]

Hi,

Not to worry my dear, big resistor has higher power rating.

[David94114]

For most, if not all, applications, it does not matter if you use a resistor with a higher wattage rating than what is called for in the spec. The other way around, however, is a serious problem. Don't do it.

Mouser and Digikey are two good comprehensive sources of supply. www.mouser.com and www.digikey.com

Electronics Goldmin www.goldmine-elec.com sells asssortments of 1/8 watt 1% tolerance metal film resistors which are very reasonably priced, if you think you will be doing several projects.

[rolandong]

is a serious problem

For educational purposes, could you kindly articulate ?

[jarthel]

Originally posted by rolandong


For educational purposes, could you kindly articulate ?

example: resistor in the circuit was originally has a 2W rating. putting anything below 2W might be asking for trouble.

at least that's how I understood his reply.

[Pars]

Another place with really cheap prices and looks to be pretty good quality, though I have never used them):

http://www.opamp-electronics.com

Look at the 1/4W metal film resistors.

[David94114]

Resistors resist the flow of electricity, but in doing so they heat up. The amount of electricity flowing through them determines the amount of heat generated. If you use a resistor that is below the recommended wattage, it will get hotter than it should. At a minimum, this will cause it to burn out earlier than otherwise, and your project will fail. The worst case is that it can start a fire, or its failure can damage some other equipment.

Think of it like choosing an extension cord. If you have a real heavy gauge extension and cord and use it to power a night light, no problem. But if you have a real light weight extension and use it to power something that uses a lot of power, like a large space heater, it could overheat and fail, and take your house with it.

There are formulas that are used to calculate the power that will flow through any given resistor, if you want to get into that. Google on ohm's law for starters.

[David94114]

Just to clarify....

When you said "larger" I took that to mean "higher wattage" since that is the way the term is typically used. Higher wattage resistors are usually physically larger, since they need to dissipate more heat. So the three parameters you need to pay attention to are resistance (specified in ohms) , tolerance (spec'd in percent) and power level (specified in watts). A higher wattage resister can safely dissipate more heat than a lower wattage resistor. So as long as the ohms are the same and the tolerance is the same and the type (probably metal film, in this case) is the same, you can safely use a higher wattage resistor than what is called for the in the original design. The only problem you may encounter is that if you are using someone's printed circuit board, the higher wattage resistor may not fit the spacing of the holes but you can usually deal with that by bending the leads carefully. Some circuits, though, only work well if the leads are extremely short, so be aware of this as a potential issue.

[ebenai]

Thank you very much. When I said larger I was refering to the size. It appear that the ones I got with the kit are smaller. Does it make any sense? Does compact mean a smaller version of the same metal film resistor?

[David94114]

I am not familiar with those particular resistors. Have you verified that the wattage ratings are the same even though the size is different?

If you are unsure what to do at this point I suggest you check with the person or company who provided you with the original kit.