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Old 08-01-2014, 03:47 PM   #1
markusm
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Default Replacements for ceramic "cement" resistors on crossover?

I'm trying to help a friend replace the cement resistors in his Gemini GSM-3200 but I'm having a hard time finding replacements.

The values are:

100 Watt 20 Ohm 5% (100W20Rj)
10 Watt 75 Ohm 5% (10W20RJ)

I think I might have found a replacement for the 10W on parts express, but wont know for sure until I can get the lead spacing measurements from the crossover. The other one I'm having an even harder time. I did find one cement resistor, but it has the wrong type of leads (sort of like a double lead sticking out the bottom on each end rather than regular axial leads, I think it might be called "chassis mount"?) and another aluminum chassis mount resistor.

I'm just wondering if the aluminum would work in it's place, or if I need to stick with the ceramic "cement" type? Both would need a bit of modification to work. The aluminum ones appear to have a hole in the "leads" on each end to solder a wire into, and on the cement one with different leads, I'd have to try to modify those by bending the leads out and cutting to get it to go into the hole if possible.

Anyone have any advice on this? The speakers are 300W speakers if that matters.
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Old 08-01-2014, 04:01 PM   #2
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Default Re: Replacements for ceramic "cement" resistors on crossover?

They should be non-inductive type resistors. 100 Watt 20 Ohms is a big resistor. Do you know how it is connected in the cross over network? It will work as long as the resistance is the same, higher wattage is OK but not lower, also must be non-inductive type.
Any pictures?
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Last edited by budm; 08-01-2014 at 04:02 PM..
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Old 08-02-2014, 05:40 PM   #3
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Lightbulb Re: Replacements for ceramic "cement" resistors on crossover?

Quote:
Originally Posted by markusm View Post
I'm trying to help a friend replace the cement resistors in his Gemini GSM-3200 but I'm having a hard time finding replacements.

The values are:

100 Watt 20 Ohm 5% (100W20Rj)
10 Watt 75 Ohm 5% (10W20RJ)

I think I might have found a replacement for the 10W on parts express, but wont know for sure until I can get the lead spacing measurements from the crossover. The other one I'm having an even harder time. I did find one cement resistor, but it has the wrong type of leads (sort of like a double lead sticking out the bottom on each end rather than regular axial leads, I think it might be called "chassis mount"?) and another aluminum chassis mount resistor.

I'm just wondering if the aluminum would work in it's place, or if I need to stick with the ceramic "cement" type? Both would need a bit of modification to work. The aluminum ones appear to have a hole in the "leads" on each end to solder a wire into, and on the cement one with different leads, I'd have to try to modify those by bending the leads out and cutting to get it to go into the hole if possible.

Anyone have any advice on this? The speakers are 300W speakers if that matters.
Cement resistors? On the outside, but inside is usually its a wirewound resistor. Just look for axial leaded high power/wattage wirewound resistors. With an axial type resistor, you don't have to worry about lead pitch (just bend the leads around to fit). May be easy to find for the 10W resistor. But for the 20 Ohms 100W type, usually comes with heatsinks or in power TO-2xx style packages requiring heatsinks. You could use several axial resistors of lower wattage in parallel (but total wattage of those resistors must be 100W or higher, and the total resistance in parallel must be 20 Ohms). I had use this method before actually...
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Old 08-02-2014, 08:46 PM   #4
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Default Re: Replacements for ceramic "cement" resistors on crossover?

Quote:
Originally Posted by budm View Post
They should be non-inductive type resistors. 100 Watt 20 Ohms is a big resistor. Do you know how it is connected in the cross over network? It will work as long as the resistance is the same, higher wattage is OK but not lower, also must be non-inductive type.
Any pictures?
I'm not sure how they are connected as far as where they are in the circuit if that's what you mean. I have included a picture to show where they mount on the board below. As far as the actual resistors they look like this http://i04.c.aliimg.com/img/ibank/20...61.220x220.jpg

The closest replacement I have found that's not on alibaba or aliexpress (I don't know these sites, and don't want to deal with wire transfers, etc... look like this: http://img03.taobaocdn.com/bao/uploa...pg_310x310.jpg

Below is the best picture of the crossover I have (I didn't expect to run into this much trouble.)

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Old 08-02-2014, 09:12 PM   #5
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Default Re: Replacements for ceramic "cement" resistors on crossover?

Can we see the bottom side of the board? It looks like you will have room to mount the resistors on the solder side (bottom side) of the board if you have to use the resistors in parallel to get the value you need.
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Old 08-02-2014, 09:27 PM   #6
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Default Re: Replacements for ceramic "cement" resistors on crossover?

Mouser: 75 Ohms, 10 Watts
http://www.mouser.com/ProductDetail/...hp3NlPuOgmE%3d

20 Ohms 100 Watts, you may have to use this ( I do not believe they are non-inductive):
http://www.mouser.com/ProductDetail/...jTnQLGtedTM%3d

or this:
http://www.mouser.com/ProductDetail/...HRrmZhntshI%3d

If you do not use non-inductive the impedance of the resistor which is in series with the high frequency speaker will have an affect in the corssover network. I always use non-inductive resistors in my speakers.
http://www.audioholics.com/loudspeak...aker-crossover
"Another very well documented issue with resistors is inductance. While high impedance, small wattage resistors are most often made from a metal film, higher wattage parts of low impedances (the kind most likely to be used in crossover networks) are often wire-wound parts. (If you have never noticed before, the symbol for the resistor is a bunch of wire scrunched up). Some old wire-wound types have a inductance high enough to cause issues in a crossover at very high frequencies. You may often find wire-wound resistors being referred to as "non inductive" to let the buyer or engineer know these parts have eliminated this potential flaw. Modern day parts are often wound with a serpentine pattern so the windings have self canceling inductance without having an effect on their intrinsic resistance."
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Old 08-02-2014, 09:38 PM   #7
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Default Re: Replacements for ceramic "cement" resistors on crossover?

Quote:
Originally Posted by budm View Post
Can we see the bottom side of the board? It looks like you will have room to mount the resistors on the solder side (bottom side) of the board if you have to use the resistors in parallel to get the value you need.
I can't at the moment. I do have pictures from the side (from before we pulled the x-over out) that show there's nothing mounted on the backside, so I don't think mounting anything parallel would be an issue, but the speakers are at my friends house so I wouldn't be able to get any more pics till after work on Tuesday. (Son has piano lessons after work on Mondays.)
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Old 08-02-2014, 09:43 PM   #8
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Default Re: Replacements for ceramic "cement" resistors on crossover?

I like to see the bottom side so I may get some idea why they use such high wattage resistor, it seems to me that it is not efficient since lots of power being dissipate in the resistor, i am surprised that the 100W one was damaged, I wonder the speakers could have been damaged also since it is more likely to be connected in series with the resistor.
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Old 08-02-2014, 09:43 PM   #9
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Default Re: Replacements for ceramic "cement" resistors on crossover?

Quote:
Originally Posted by budm View Post
Mouser: 75 Ohms, 10 Watts
http://www.mouser.com/ProductDetail/...hp3NlPuOgmE%3d

20 Ohms 100 Watts, you may have to use this ( I do not believe they are non-inductive):
http://www.mouser.com/ProductDetail/...jTnQLGtedTM%3d

or this:
http://www.mouser.com/ProductDetail/...HRrmZhntshI%3d

If you do not use non-inductive the impedance of the resistor which is in series with the high frequency speaker will have an affect in the corssover network. I always use non-inductive resistors in my speakers.
http://www.audioholics.com/loudspeak...aker-crossover
"Another very well documented issue with resistors is inductance. While high impedance, small wattage resistors are most often made from a metal film, higher wattage parts of low impedances (the kind most likely to be used in crossover networks) are often wire-wound parts. (If you have never noticed before, the symbol for the resistor is a bunch of wire scrunched up). Some old wire-wound types have a inductance high enough to cause issues in a crossover at very high frequencies. You may often find wire-wound resistors being referred to as "non inductive" to let the buyer or engineer know these parts have eliminated this potential flaw. Modern day parts are often wound with a serpentine pattern so the windings have self canceling inductance without having an effect on their intrinsic resistance."
Yeah those types are all I could come up with as well. I could be wrong, but at some point in my research I thought I read that those were in fact inductive. (the originals I mean).

If I'm right and the originals are inductive, using non-inductive resistors would cause no problems if I'm understanding the text you posted correct?
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Old 08-02-2014, 09:55 PM   #10
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Default Re: Replacements for ceramic "cement" resistors on crossover?

It should be non-inductive if they did not cheap out on the design to cut cost unless they count the inductive value of the resistor into account during the design process, the impedance will get higher as the frequency goes up so less voltage will be on the tweeter. You want the pad to be as pure resistance as possible. Inductor (if resistor is inductive) blocks high frequency (the higher the frequency the higher Xl), Capacitor passes high frequency (higher frequency lower Xc)

Last edited by budm; 08-02-2014 at 09:58 PM..
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Old 08-02-2014, 10:20 PM   #11
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Default Re: Replacements for ceramic "cement" resistors on crossover?

Quote:
Originally Posted by budm View Post
It should be non-inductive if they did not cheap out on the design to cut cost unless they count the inductive value of the resistor into account during the design process, the impedance will get higher as the frequency goes up so less voltage will be on the tweeter. You want the pad to be as pure resistance as possible. Inductor (if resistor is inductive) blocks high frequency (the higher the frequency the higher Xl), Capacitor passes high frequency (higher frequency lower Xc)
Ok, I could be wrong about that. At the time I was more focused on trying to find the exact type of resistor, appearance-wise, than other details so I was kind of skimming over what I was reading. What you're saying makes sense though, if the resistors go to the tweeters (these things have 4 or 5 tweeters, a horn, and two woofers) it doesn't make sense to use something that would block the high frequencies.

Just in case, I'll go by his house after work Tuesday and get pics of the bottom of board so you can take a look at it. (actually, just texted him and asked him to send me a pic)

Thanks for your help bud.
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Old 08-03-2014, 12:11 PM   #12
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Default Re: Replacements for ceramic "cement" resistors on crossover?

Ok... here's a pic of the bottom of the board.



Now heres the weird thing... these pics are from one of the other speakers (not the one I looked at). In one picture you can see there's a 10 Watt 20 ohm resistor. In the other if you look close you can tell the other missing resistor is the 10W 75 ohm resistor. (it's blurry as hell).





Is it possible the 100W is a misprint on the board? I never actually saw the 100W resistor as he lost it, I only saw the markings on the board.

I'm waiting on him to check the other 2 speakers and see what they have in them.
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Old 08-03-2014, 01:29 PM   #13
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Default Re: Replacements for ceramic "cement" resistors on crossover?

probably 10w
a 100w resistor would either be clad in a heatsink that you bolt down, or it would be huge.

on that board, both resistors have the same amount of space to mount them.
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Old 08-03-2014, 04:18 PM   #14
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Default Re: Replacements for ceramic "cement" resistors on crossover?

OK, that is more like it for not to be 100W resistor which is no way for it to fit that footprint on the circuit board.
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Old 08-03-2014, 05:11 PM   #15
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Default Re: Replacements for ceramic "cement" resistors on crossover?

Ok thanks guys. Is it common for there to be misprinted values on boards like that?
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Old 08-03-2014, 05:13 PM   #16
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Default Re: Replacements for ceramic "cement" resistors on crossover?

no, but shit happens - as the saying goes.
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Old 03-03-2016, 12:45 AM   #17
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Default Re: Replacements for ceramic "cement" resistors on crossover?

Quote:
Originally Posted by markusm View Post
I'm trying to help a friend replace the cement resistors in his Gemini GSM-3200 but I'm having a hard time finding replacements.

The values are:

100 Watt 20 Ohm 5% (100W20Rj)
10 Watt 75 Ohm 5% (10W20RJ)

I think I might have found a replacement for the 10W on parts express, but wont know for sure until I can get the lead spacing measurements from the crossover. The other one I'm having an even harder time. I did find one cement resistor, but it has the wrong type of leads (sort of like a double lead sticking out the bottom on each end rather than regular axial leads, I think it might be called "chassis mount"?) and another aluminum chassis mount resistor.

I'm just wondering if the aluminum would work in it's place, or if I need to stick with the ceramic "cement" type? Both would need a bit of modification to work. The aluminum ones appear to have a hole in the "leads" on each end to solder a wire into, and on the cement one with different leads, I'd have to try to modify those by bending the leads out and cutting to get it to go into the hole if possible.

Anyone have any advice on this? The speakers are 300W speakers if that matters.
dID YOU EVER GET YOUR gsm 3200 cROSSOVERS REPAIRED
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Old 07-13-2019, 01:55 PM   #18
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Default Re: Replacements for ceramic "cement" resistors on crossover?

I have the same problem with a gemini gsm-1250 it has ceramic 10w39rj and 10w20rj and needs a new circuit board and I was thinking of changing them to the aluminium ones can this be done and how
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Old 07-13-2019, 08:44 PM   #19
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Default Re: Replacements for ceramic "cement" resistors on crossover?

What ever style you change them to, they have to be non-inductive type resistors.
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