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The two 10 watt power resistors on the midrange for my house speakers extremely hot and shutting off the amplifier. What can I do to correct this problem with out changing the frequency response? If you need anymore information I can supply it for you.
Midrange power resistors extremely hot
- Thread starter david5559
- Start date
... a possibility is that one of the series capacitors has failed.
... There are two parallel capacitors in series with the 4 ohm resistors ... Looks like they are labeled C7 and C8. It might be worthwhile to desolder the larger capacitor ... 10uF? ... and check it's value to see if it has shorted out ... maybe the smaller one also.
.... at certain frequencies, the capacitors are supposed to act as impedances. Maybe one of them has worn out. How much use have the speakers seen?
... There are two parallel capacitors in series with the 4 ohm resistors ... Looks like they are labeled C7 and C8. It might be worthwhile to desolder the larger capacitor ... 10uF? ... and check it's value to see if it has shorted out ... maybe the smaller one also.
.... at certain frequencies, the capacitors are supposed to act as impedances. Maybe one of them has worn out. How much use have the speakers seen?
The capacitor C7 -19uF and C8 - .1uF have been replaced and the two 10 watt resistors will burn your fingers if you touch them. The amplifier does not get hot when there is no music playing. They are old but have had minimal use. What can I do with this heating problem because the midrange frequency keeps burning out? The midrange speaker is very clear and crisp until the croosover burns out.
It is a common problem in both speakers , excessive heating in the two 10 watt resistors. Anything past 1/3 volume.
DickCappels
- Joined Aug 21, 2008
- 10,661
Sounds like you need bigger resistors, or put the very hot resistors on a heatsink, or turn down the volume.
Is putting bigger resistors going to change the frequency response of the speakers? I am only driving the speaker at 1/3 volume which is nowhere near their capacity. Does anybody out there know how to put in the right components so it will work correctly. I need HELP !!!
no
and we need answers since post #2. HOW MANY WATTS DOES YOUR AMPLIFIER DELIVER?
What is the impedance of the speakers? 8 ohms?
You give no specs = we give no math.
It sounds to me that you are driving low powered speakers from a high power amplifier.
A good rule is to have your speaker RMS power rating (not "advertising brochure" power) higher that the RMS power of the amplifier.
Running a high power amp into low power speakers is not wise at all. Smoke results!
As noted above, you have not given any power info so your questions are almost meaningless.
A good rule is to have your speaker RMS power rating (not "advertising brochure" power) higher that the RMS power of the amplifier.
Running a high power amp into low power speakers is not wise at all. Smoke results!
As noted above, you have not given any power info so your questions are almost meaningless.
When we say "bigger" resistors in this context, it means the same ohm resistance, just higher power rating. Now, they are going to dissipate the same amount of heat but it will be spread across a bigger area.
Also, describe "hot". This ceramic bar (sand bar) resistors can withstand temps much hotter than your finger. Unless you smell plastic melting, I would say the resistors are ok.
I will be posting all the information on the speakers and the amplifier tomorrow or the next day. Thank you for all the information I have received so far.
I went poking around in an online resistor store and found that some of them are rated for 250 degrees CENTIGRADE.
That's 482 F. Way hotter than your fingers would enjoy! According to this chart. there are only 2 solders that DON'T melt at 250 C.
Code:
Solder Alloy Melting Point (°C) Melting Point (°F)
5Sn-95Pb 307 585
0.5Sn-92.5Pb-2.5Ag 280 536
Sn/5Sb 243 469
100Sn3 232 450
99.3Sn-0.7Cu 227 440
96.5Sn-3.5Ag 221 430
Sn/3.0Ag/0.5Cu 219 426
Sn/3.8Ag/1.0Cu 217 423
Sn/3.5Ag/1.0Cu/3Bi 213 415
50In-50Pb 209 402
45Sn-55Pb 204 400
55Sn-45Pb 193 379
60Sn-40Pb 186 368
63Sn-37Pb 183 361
62Sn-36Pb-2Ag 179 354
97In-3Ag 143 289
Sn/57Bi 139 282
52In-48Sn 118 244
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Just out of interest #12, that feature has been used in equipment. I have seen a power resistor soldered to the underside of a tag strip, the wires not twisted around the tags, just straight across, and it was used as a protection device, like a fuse. If excess current was drawn, the resistor would overheat and melt the solder so it would drop off the tags.
165W @ 8 ohms
That's 4.54 amps RMS per channel.
(2) 4 ohm in parallel makes 2 ohms
In series with the midrange speaker.
If the midrange speaker carries half the wattage, that's 3.2 watts dissipated by 20 watts worth of resistors.
If all the power went to the midrange speaker and the owner played it maxed out continuously, that would be 41.25 watts into 20 watts worth of resistors.
Considering average power content in music and a bass speaker taking half the power, the math doesn't demonstrate how those resistors can get too hot to survive.
This is, "not a problem" unless something else is broken.
Does the stereo sound right? If so, this is an imaginary problem.
If not, something else is wrong.
That's 4.54 amps RMS per channel.
(2) 4 ohm in parallel makes 2 ohms
In series with the midrange speaker.
If the midrange speaker carries half the wattage, that's 3.2 watts dissipated by 20 watts worth of resistors.
If all the power went to the midrange speaker and the owner played it maxed out continuously, that would be 41.25 watts into 20 watts worth of resistors.
Considering average power content in music and a bass speaker taking half the power, the math doesn't demonstrate how those resistors can get too hot to survive.
This is, "not a problem" unless something else is broken.
Does the stereo sound right? If so, this is an imaginary problem.
If not, something else is wrong.
That's one of the major reasons to hang 'em high. Those long legs have a resistance to heat flow, and besides that, they radiate.
I have read that you wouldn't want a solid silver spoon to stir your coffee because heat travels through silver so fast it would hurt your fingers.
Obviously, other metals have a lot less thermal conductivity, and restricting the diameter of the path enhances that effect.
Another reason to hang 'em high is so the resistor can radiate on 4 sides instead of 3, with better convection than being blocked on one side.
Why? Because resistors can be built to survive temperatures that would brown a circuit board and degrade the quality of the solder joints.
Anybody who has been in this business for a couple of years has seen that phenomenon.
Here's a chart. Look who's on top for thermal conductivity...silver.
http://www.tibtech.com/conductivity.php
I for one have never liked that crossover design. I know it's theoretical intent but it's very power wasteful for what little purpose it serves.
Over the years I've redesigned a number of those types of circuits to simplify them and reduce their power losses by taking out the resistors that ran parallel to the speaker circuit. The speaker units never showed any real change in performance other that being a bit louder in the mids and highs for the given power put into them.
Over the years I've redesigned a number of those types of circuits to simplify them and reduce their power losses by taking out the resistors that ran parallel to the speaker circuit. The speaker units never showed any real change in performance other that being a bit louder in the mids and highs for the given power put into them.
