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I have an Electrovoice MA-1212 That when I hook it up and power on all I get is a constant low frequency Hum. Checked the wiring and speakers on another amp and eliminated them? Any suggestions?

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WIth the speakers disconnected, measure the terminals using a DC voltmeter. I suspect that there is DC voltage there where there should be 0V. If that is the case, the output transistors are shorted and need to be replaced.

Dan

Posted on Jul 31, 2009

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I have a kenwood vr-505 receiver that has a content buzzing through the speakers. I have unplugged everything and hooked it all back up but the buzzing still persists. Is it fixable?


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or is it a hum like 50 or 60HZ mains
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The subwoofer output on my Kenwood VR-606 has suddenly stopped working. I have tried the "setup" several times, turning the subwoofer off and back on. Also, when I first power up the system, it emits a low...


It sounds like the problem is not with your VR-606. If you hear a hum from the sub, the problem is more likely to be in the sub's built-in power amplifier. However, it is worth resetting the amplifier to factory presets. To do this, unplug the power cable from the mains supply and reconnect whilst holding down the power on/standby key. If the hum persists, connect any powered speaker to the sub-out socket, power on and listen for the hum. If no hum then suspect the powered sub amp. Turn the sub on with no connection to the Kenwood VR-606. If hum persists, the sub has a problem and will need to be replaced or repaired. By the way, you said there is a low frequency hum through the 'speakers' for about 30 mins. Is that all speakers or just the sub? Hope this helps.
Cheers, Don.

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This is a nice speaker. You could get humming from the wires being crossed they actually do have polarity and better speakers will hum if the wires are crossed. The volume cloud also be too high without input. You also may have some interference with other audio wires or power wires close to the speaker.

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The radio is on, no sound comes on, all wires checked


Check if your speaker cables are connected very well.

Use a battery remove your speaker cables test them with the battery for signal.

Check and reconnect everything you connected to your bose radio.you will here a sound . take care.

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Wiring tweeters.


Yes you need them. I always put them inline on the positive side. They are to protect the speakers against low frequencies. Actually, I use oil bath capacitors sometimes on pro systems. I don't see how they would work between the positive & negative that is unless they have a positive & negative side with an out and an in? Hope this helps,

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Electro voice ma-1212 shorted 2sd5200 power transistors


Your best bet would be to contact EV. Search for either EV or Telex. Telex will be easier to find and contact the repair department. Ask for the part availability and cost. They are very helpful there. Please let them know the model number as well.

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Apr 16, 2009 | ElectroVoice...

2 Answers

Subwoofer probelm


I suspect you have a bad cable, a poor ground or a bad
power supply inside the speaker amplifier. The amplifier
(inside the sub-woofer) could also be defective.
===
1) Bad cable or connector:
If the (braided shield/outer tube) of the coaxial input cable is
not grounded, the cable will pickup line frequency "hum"
from surrounding power lines, house wires, lights and
appliances.

This hum is then amplified by the speaker's amplifier
causing the constant bass sound you speak of.

Because the hum frequency fundamental is 60 Hertz in
North America, 50 Hertz in Europe, you hear it coming
mostly out of the sub-woofer, because the midrange and
high speaker circuits filter it out.

Check the input connectors, cable at both ends, wiggle
the jacks at a low volume setting to see if it changes.

Make sure that you are indeed using a properly shielded
coaxial cable.

A coaxial cable consists of a thin inner conductor, surrounded
by a flexible tube made up of a braided metal shield, which
must be grounded. This prevents hum from being picked up
by the sensitive amplifier inputs.
===

2) If the power supply within the sub-woofer's internal amplifier
is defective, the the power supply hum will also get coupled
into the amplifier and speaker with same results as above.

Power supply hum is typically twice the line frequency,
i.e. 120 Hertz, but not always, depending on what
component failed: Rectifier diode, filter capacitor, or
the voltage regulator.

3) Ground loops:
When you run very long cables between the source and
destination of an audio signal, multiple ground paths (must)
exist between the two points in space, creating complete
loop circuits.

Power line hum from the environment can (will) induce
heavy AC currents around these loops, creating a voltage
gradient across these cables, and in-between the end
devices.

Once again, this AC hum is coupled into the amplifier inputs.

Ground loops become a problem with cables over 10
feet long, and an astronomical problem for stage audio
engineers. To avoid ground loops, they must break
the circuit's continuity by using isolation transformers,
optical isolators, and/or differential input amplifiers.

So how long are your cables?

Most house stereo components are only designed to
handle 6 to 10 feet of cabling max.

30 feet is already asking for major trouble.

4) Feed back oscillation: This occurs when the output of
an amplifier is fed back to the inputs with a round trip
gain greater or equal to unity. The tiniest little electrical
disturbance is then amplified and re-amplified, over and
over again, usually at one preferred frequency, causing
the typical (ear-splitting) microphone squeal or howl.

In your situation feedback and/ loss of original signal
could be the result of mis-wiring the input cables.

Note that this is NOT as silly nor as unlikely as it sounds,
because many computer audio cards and even some
home stereo systems have re-configurable inputs and
outputs.

SOFTWARE configuration decides which jack at the
back does what !!!!

On my computer, for example, the Realtek audio driver
tries to automatically figure out what cable is connected
to each jack (usually it gets it wrong)

Using the Realtek control panel applet, I can then
manually re-configure the gray jack as input,
the green jack as bass, pink jack as center.... etc.

If this situation also applies to your system, please check
the software configuration. Connecting an output cable to
an input jack will certainly cause a lot of HUM and not
much music.

5) Finally, don't rule out internal sub-woofer failure. Unlike
the passive stereo/hi-fi speakers of days gone by, modern
multi-channel theater systems with front, center, rear and
sub-woofer speakers are internally amplified, with active
frequency cross-over filters and special effect/ surround
sound capabilities.

Usually, the large sub-woofer contains most of the
electronics, amplifiers and filters.

It feeds the other speakers, and it is controlled by
an external volume control module which can be separate
or built into one of the tweeters.

These sub-woofer electronics are prone to poor design,
overheating and early failure. (Even fresh out of the box
like yours)

If you cannot get it working, take it back to the store,
and make the NICE salesmen **** with it.

Good luck
Please rate my answers
Martin.

Jul 20, 2008 | Yamaha 5.1-Ch. Surround Sound Home Theater...

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