Recently I had a current spike in my house while using my stereo system that shut off all my components (turntable, preamplifier, amplifier and the two JBL PB10). The spike was about one second long, or so. I turned everything back
on and each component worked fine again. When I turned
all system off, using my surge protector, I heard a quite
loud thump in the left JBL PB10 subwoofer (that also was
turned off from the same surge protector). This thump was
heard for the first time in 2-3 years sicne I'be been using
the pair of the JBL PB10. Now is does the same every time
when I turned the system off. What might be wrong with
that JBL BP10 powered subwoofer? Or, how to eliminate
the thump (turning off manually the JBL before turning off
the other components?). Thank you in advance for any
possible assistance and support in this matter,
Emil - Harford, CT
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Re: Thump at the time of shutoff
The amplifier in the sub as with any other amplifier has a capacitor in it. Essentially a battery that holds a charge. When you trun things off such as subs or amps with a powerstrip instead of the intended on off button, the power supply has been cut, but the capacitor is still energizing the unit. So it catches the noise in the line.
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I live in California but I do have a memorex system with the same components. My belt fell off my turntable so it didn't turn. It took a bit of patience but I was able to get the belt back on. The turntable is held down by a clip on the spindle. The belt might have to be replaced if it keeps falling off. It will do that if its been used alot. While the turntable is off, if you move the arm you can see if the turntable motor will turn on too. That would be the only other problem you can have on that unit. The repair cost might be more than what the unit cost. Just be patient and careful and you probably can fix it yourself.
Electronic components are very sensitive to voltage surges, spikes or sags.
Voltage is not delivered at a constant 120 volts. With alternating current, the voltage rises and falls in a predetermined rhythm. The voltage oscillates from 0 to a peak voltage of 169 volts. Most appliances and electronics used in the United States are designed to be powered by this form of generated electricity.
During a power surge, the voltage exceeds the peak voltage of 169 volts.
A spike in voltage can be harmful to appliances and electrical devices in your home. An increase in voltage above an appliance's normal operating voltage can cause an arc of electrical current within the appliance. The heat generated in the arc causes damage to the electronic circuit boards and other electrical components.
(Smaller, repeated power surges may slowly damage your electronic equipment, over time too.)
Voltage sags, a.k.a voltage dips or brownouts, is another form of electrical disturbance that can damage appliances as well.
The bottom line, power surges, spikes, and sags can vary in duration and magnitude; and can damage electrical equipment ranging from stereos to computers to any household appliance that uses chip board circuitry sensitive enough to "blow" due to over or under-energizing it.
You have to use the "Auto-Off" feature, which is located on the same button as on/off:
The automatic shutoff time (ASO) can be
programmed to shut off immediately after
brewing (0:00) or up to 4 hours later. The
default shutoff time is 2 hours.
Press and hold the On/Off button to display
current shutoff time. To change the preset
time, press and hold the On/Off button until
the red power light and LCD display begin to
flash. This signals that you have entered the
Set automatic shutoff mode. Set the time
you want coffee to begin brewing by
following the instructions in “Entering Time
When the coffeemaker shuts itself off, two
tones will sound.
NOTE: Automatic shutoff may be
programmed either before or during coffee
brewing. If you program the auto shutoff
time after brewing is completed the unit
will automatically account for elapsed time.
For example, if you set the auto shutoff for
40 minutes and 25 minutes have already
elapsed, the unit will shut off automatically
after 15 minutes (40 minutes minus the 25
elapsed equals 15 minutes).
You need to check your ground connection. If there is a bad ground there will be feedback to the amp and it will just sit there and loop back with the Thump, Thump, Thump sound. I had to wire my amp's ground all the way back to the negative battery terminal. It was a pain but I have never had a problem since :)