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jask
Joined: 17 Mar 2006
Posts: 10187
Location: kamloops BC
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| Posted: Wed Apr 15, 2009 10:21 pm Post subject: subwoofer "pop" repair? |
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I have been playing with an old JBL sub that was given to me. The plate amp was working but motorboating,so I went over the obvious hotspots on the amp section as this is often caused by poor ground ( so I was told...) and replaced a couple of sketchy caps. The amp now works but will sometimes "pop" when it powers up or down, this happens even when it has no input signal. Someone suggested it might be a voltage regulator?!! ( damn, I didn't even see an alternator in there.... )
Anyone have any experience/ideas they want to toss out?
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AnalogRocks
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Joined: 08 Mar 2006
Posts: 26706
Location: Toronto, Ontario, Canada
TV/Projector: Sony 1252Q, AMPRO 4000G
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| Posted: Wed Apr 15, 2009 10:49 pm Post subject: |
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Switch to Sunoco 94 gas. It'll help it run better
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ecrabb
Forum Moderator
Joined: 13 Mar 2006
Posts: 15909
Location: Utah
TV/Projector: JVC RS40, Epson 5010
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| Posted: Wed Apr 15, 2009 10:53 pm Post subject: |
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Yeah, and maybe a new set of plugs would help with that pop when you start up and shut down. 
SC
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AnalogRocks
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Joined: 08 Mar 2006
Posts: 26706
Location: Toronto, Ontario, Canada
TV/Projector: Sony 1252Q, AMPRO 4000G
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| Posted: Wed Apr 15, 2009 10:56 pm Post subject: |
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Hmmm just had a thought. Could need a new left handed flem baffle, or a new mufler bearing.
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bbfarmht
Joined: 27 May 2006
Posts: 1273
Location: Where the Mississippi runs east to west!!
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| Posted: Thu Apr 16, 2009 12:35 am Post subject: |
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What about the windows rotator bearing. Those often pop when going bad.
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"Any society that would give up a little liberty to gain a little security will deserve neither and lose both"
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jask
Joined: 17 Mar 2006
Posts: 10187
Location: kamloops BC
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| Posted: Thu Apr 16, 2009 6:20 am Post subject: |
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thank you mr goodwrench
I am going to try and put some of Cliffs magic smoke into it.
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AnalogRocks
Forum Moderator
Joined: 08 Mar 2006
Posts: 26706
Location: Toronto, Ontario, Canada
TV/Projector: Sony 1252Q, AMPRO 4000G
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| Posted: Thu Apr 16, 2009 1:40 pm Post subject: |
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| jask wrote: | thank you mr goodwrench
I am going to try and put some of Cliffs magic smoke into it. |
Glad we could help. 
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Curt Palme
CRT Tech
Joined: 08 Mar 2006
Posts: 24396
Location: Langley, BC
TV/Projector: All of them!
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| Posted: Thu Apr 16, 2009 3:23 pm Post subject: |
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It might just be fine. I'd say change some more caps in it, otherwise leave it alone. You won't blow the woofer.
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jask
Joined: 17 Mar 2006
Posts: 10187
Location: kamloops BC
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| Posted: Thu Apr 16, 2009 4:00 pm Post subject: |
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| Curt Palme wrote: | | It might just be fine. I'd say change some more caps in it, otherwise leave it alone. You won't blow the woofer. |
One of the obvious bad caps was in a pair of polar caps wired back to back, I might just pull that out and replace it with the correct non-polar. When I had it on the bench I was using an old POS 8"sub to load the output and the pop was really loud,now that it is back in the cabinet it is not as severe a pop.
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Curt Palme
CRT Tech
Joined: 08 Mar 2006
Posts: 24396
Location: Langley, BC
TV/Projector: All of them!
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| Posted: Thu Apr 16, 2009 4:36 pm Post subject: |
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That could well be it!
You can get around nonpolar caps by doubling the value, and putting in two electrolytic caps in series, the two positive terminals connecting to the circuit, the negative leads of the caps tied together to each other.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Thu Apr 16, 2009 8:04 pm Post subject: |
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The popping noise in itself is not a sign of a direct problem but a problem in the circuitry that tries to control it. Its mostly caused by voltage spikes and can come from either the input side or the output side. Different manufacturers use different methods to try to eliminate the noise. Some use caps and some use bi polar or FET transistors. Caps would be used in conjunction with each others to bias the input upon start up and shut down. Transistors are usually used on the output side to pull the output to gnd on shut down and release slower on startup. Without a schematic to look at your kinda just hunting around but look at the output line to the speaker and see if there are any transistors tying that line to ground and test there. Also look at the input side for inline caps and caps to ground and test there. I dont know what type of suppression your amp uses.
Anyways the pop is normal but you have a problem in the circuits that try to eliminate it. If its not really loud or annoying then you dont even have to worry about it. Happy hunting...... 
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HK-Steve
Joined: 15 Jul 2006
Posts: 849
Location: Switzerland
TV/Projector: Marquee 9500, Epson 8100
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| Posted: Fri Aug 28, 2009 2:22 pm Post subject: |
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My M&K MX 150 made a poping noise,
When I contacted the service dept. they said to replace the level pot and crossover pot.
Pot = Potentiometer
They deteriate over time, with dust contaminating the resitance track.
Solved my problem.
Hope this helps,
Cheers
Steve
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