Hey, Electronics guys, need help!

[simple]

I have these old but formidable Yamaha monitors, (remember the ones with the white 15s and silver horns?), and there's been something rattling around in one for quite some time. Well I just took it apart and found this that fell off the crossover network. My question is how badly do I need it? The monitor is working OK and I need it for a gig so I have to put it back together. I am worried about damaging something by it not being attached to the circuit board. And the other larger one is spinning on its wire...

The piece that is loose came from the lower left on this circuit board

 

[yyz2112]

Not being able to see the trace side of the board, I can't be sure, but it looks like one end of the resistor is connected to the positive out of the LF (low frequency?) side. If the resistor is in series, you MUST replace it or risk blowing a speaker. If the other end goes to ground, it's not as critical, but will affect frequency response.

 

[Patrick from Davis]

The resistor itself is a cement power resistor.  It looks like 20 KOhm (the k is in an odd place, might be a part number), but the board lists it as 20 Ohm.  You should check it with a multimeter to be sure.  If it is a 20 Ohm, 10W resistor than you can pick them up here

http://www.mouser.com/ProductDetail/Vishay-Dale/CP001020R00KB14/?qs=sGAEpiMZZMvhlCB8CTbT5NGrTjI6xvgZSDjVnczJoEs%3d

At 50 some cents a piece, you can get a number of them and squirrel them away.  The shipping, however, will be 5-10 bucks.  Hope that helps.
Patrick

 

[simple]

Yes, this is all helpful, thank you!

 

[Patrick from Davis]

Check the other one as well for a value.  If you are going to buy them from a place like Mouser, it is much easier to buy both kinds and replace the lot of them in both cabs.  Mouser can be difficult to locate the part if you are not used to their system.  If you have trouble, just post the specs.
Patrick

 

[dbw]

Careful, it's not 20 kilo-ohms, it's 20 ohms.  The "K" is an old-fashioned tolerance code... I have no clue what it translates to, probably 5% or so.

 

[-CB-]

Yes 20ohms.  The final K is either tolorance, where K is 10 percent, the temperture co-efficient, which is 1ppm for the letter K.  My guess, 10 percent resistive tolorance.

There is one little caveat....

The resistor you show has both resistive and inductive properties.  This is taken into consideration when designing things like... crossovers.

The inductive property must be taken into effect - simply because what you have is an encased wire wound resistor.  The wire may be thin and short, or thick and longer.  Its coiled and shaped, hence there is an inductive value.

You could just wing it.  It will work but the frequency of the "crossover" is likely to be altered slightly.  The caveat is if the components were very close to their limit, changing the frequency could put them beyond their limit. For instance, letting too much low frequency go to the HF drivers (thats tweeters for those in Port St. Lucie)  With a quality product like Yamaha... not likely, but worth knowing.

If these are part of a pair of monitors - get TWO resistors, and change both, one in each unit.  That way they will remain matched in their performance. 

Hope that helps.

 

[KwazyTwang]

To go along with CB. Some Tweeters or Drivers are very efficient. So the resistor helps balance out the speaker's response by not allowing one of the drivers to pull more of the energy.
If the tweeter was more efficient you might get unbalanced highs. The opposite if the woofer was more efficient. So it's important for your monitor.

 

[-CB-]

Nudder thing... maybe get some 20w resistors in the metal case... still wound, still wingin' it on the uH factor, but... better able to take the heat, and get rid of the heat.  If those were mine, I'd put the aluminum cased 20 or even 25 watt units in and never look back.  They take HEAT.  Look at the board and see the holes beind it - for ventilation and getting rid of the heat.  Those little aluminum bodied ones come packaged in their own heat sink.  Very efficient to use those.

Mouser has all the physical sizes and you'll probably find the aluminum one is smaller, and able to fit the space provided just fine.

 

[simple]

Great info! I like the idea of the aluminum replacements. I'll delve into mouser and see if I can find what you're referring to. Yes, I do have a pair of those monitors; they're old but they always sound great and keep working decade after decade.