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Sansui 7070 receiver Hum

My Sansui 7070 receiver has developed a periodic 120 hz hum that is not responsive to the volume control. Hum comes about every 30 sec to minute, lasts for approx 4-5 sec, then quits

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  • JOE BURNS
    JOE BURNS May 06, 2015

    the reception on my 7070 is bad. there is a spot inside I can touch it and reception comes in good on all channel's I was thinking maybe loose solder. please help

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  • Sansui Master
  • 12,962 Answers

Your filter capacitors in the power supply section are to blame and they need to be replaced.

Posted on Mar 31, 2014

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Posted on Jan 02, 2017

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1 Answer

Subwoofer is hummig what is this noise


Hum is a constant low-frequency buzz, usually at about 60 Hz or 120 Hz, which results from voltage differences between true "ground" (what you'd get shoving a copper pipe into the ground) and the electrical "ground" of your receiver's chassis When this voltage differential exists, it's called a "ground loop," and the hum it produces is darned annoying. You'll hear the hum mainly from the subwoofer because it's a low-frequency noise, you will need a ground loop insulator they are about $20 at any electronic store

Dec 28, 2013 | Vizio 2.1 ch. Sound Bar with Wireless...

1 Answer

My 8000s has developed a hum which is audible in both speakers. When the amp is first switched on I do not hear it but after about an hours use it becomes apparent. The volume of the hum is constant and...


My first thoughts are to replace the large electrolytic capacitor(s) their will be at least two I think, as they could be getting leaky. Though they could be fully charged up on switch on (hence no noise) they could lose it as time passes and let the 50/60 Hz mains hum in (which they stop). Another cause could be a semi-conductor that has become heat sensitive. This again could be in the power supply or something that has both channels running in and out of it. This is because the noise is in both channels, so can't be something that deals with only one channel, even if there are two of them!
Replace the caps first, if that doesn't solve your problem, then get some Servisol Freezer spray and spray any suspect part (one at a time) when it acts up! If the noise goes you have the culprit.

May 20, 2010 | NAD C372 Amplifier

2 Answers

Older Harman Kardon computer speakers have loud hum


The hum (50 or 60 Hz) is caused by the AC power getting into the entry point of the amplifier. Either the filtering capacitors from the powersource of the speakers have dried up - replace them - or there is a short in the cables.
There is another possibility: if you have kicked the subwoofer  box its transformer might have slipped from its fixings and now is touching the subwoofer speaker frame.
The only way to find which is to open the cases.

Nov 28, 2009 | Harman Kardon HK695 Computer Speakers

1 Answer

Older Harman Kardon computer speakers have loud hum


Most probably it's an internal problem with their power supply (a capacitor with broken soldering).
It can be quite easily repaired by a person knowing which side of a soldering iron to grip ;) If you have a friend that's familiar with electronics, you can ask to take a look. If you don't, the repair shop will most probably want a flat charge, which will not be feasible.

Nov 28, 2009 | Audio Players & Recorders

1 Answer

60 cycle hum at the same constant level, even if you turn the volume up all the way, it does not get any louder. What might that be caused from? A bad ground solider joint maybe? The Balance (L&R)...


If the volume control does not effect the hum volume, then the hum is being introduced directly to the final amp section. Check for defective caps in the power supply for the amp section. This will be the nigher voltage supply usually 40V or more.

Dan

Nov 04, 2009 | Teac AG-370 Receiver

1 Answer

Reel to reel tape recorder hum


Try replacing the Electrolytic Capacitor(s) on the power supply. They will be big value anywhere between 2,000UF and 6800UF. But capacitors of this type are notorious for causing hum, any on the deck could do it!

Apr 05, 2009 | Audio Players & Recorders

1 Answer

Wire antena (that came with SS5 system) causes a hum


It is assumed that the hum is coming down the aerial wire it self....The hum should be eliminated
dissappear if you remove the wire from its connector at the rear of the receiver.

If this is the case then reconnect the aerial and try to find a radio station to listen to..

When you find a station you will find the hum dissappears as follows:

When there is no station detected the receiver tweaks up its sensitivity via the Automatic Gain Control, (AGC) and when this happens any thing that is detected on the aerial is reproduced at the speakers and in your case its just a hum.

I have heard this event lots of times and mostly its scrackles or scratchs or other weird sounds which come down the aerial while the AGC is flat out at maximum..

The radio station transmits a sound "carrier" and within this carrier there is the music content.

The receiver detects the "carrier" when you tune to the radio station, and then it sets its receive
level to the setting made by the volume control and then lovely music is presented at the speakers..

So in fact your receiver is working as it should be ,.,,, no worries mate....

Now if the hum is still there when the music is there then you have a fault, but as you havent mentiond this aspect your receiver is in my view quite "normal".

Cheers For Now
From YUBEUT..


Sep 19, 2008 | Nakamichi SoundSpace 5 Shelf System

1 Answer

Onkyo HT-SR800 buzzing noise present then vanishes


The hum a fluorescent light makes is the 50 or 60 Hz hum of the alternating current mains supply. Inside the light fitting is a choke which when less than perfect tends to hum. When the choke is loose internally or externally is when the hum becomes an annoying buzz.

When an audio system has a similar tone of buzzing or humming the source will invariably be the same AC mains but how it got in there is difficult to answer...

It could possibly be poor smoothing and regulation of the power supply or an accidental hum loop caused by careless design and/or poor grounding. It could be caused by being induced in the input by connecting leads that are too long and poorly positioned/screened or it could be caused by mismatch between different components causing a poor signal-to-noise-ratio.

I am not sure why it should come and go but the fact it does would indicate a power supply problem more than the other possible causes.

If the Onkyo system has it's own volume control and it is being used witha tv or similar, it is worth trying to imporove things by turning up the tv volume to near maximum and then controlling the volume with the system control.

May 12, 2017 | Onkyo HT-SR800 System

1 Answer

Bang & Olufsen beocentre 7007 stereo music centre


The frequencies do not sound right, unless you are in Europe.
Low frequency hum almost always results from:

1) stray input pickup = Damaged cables, poor shielding,
Missing ground connections,
or ground loops.

This pickup occurs at the power line frequency:
50 Hz in Europe and Asia
60 Hz in North America

Harmonics (multiples) may occur as Fourier components
from signal distortion:
50, 100, 150, 200 .... in Europe
60, 120, 180, 240 .... in North America

Sub-harmonics such as 25 Hz are mathematically
impossible to derive from power line frequencies unless
there is some kind of weird inter-modulation, mixing
or frequency beating going on.

2) Defective power supply most often occurs at twice the
power-line frequency because of full wave rectification.

100, 200, 300... In Europe
120, 240, 360... In North America

Except for switching supplies, like those in a computer,
which can produce a high freq whistle at any frequency.

3) Amplifier feed back and other malfunctions can produce
other low frequencies, often by rectifying and detecting
the envelope of very high frequencies in the tens or
hundreds of megahertz. This is called motor boating
and it sounds more like a revving motor boat than hum.

(This kind of behavior is unlikely in a well designed amplifier)

By correctly identifying the noise frequency and
the environment, it is possible to narrow down the culprit:

1) Have you actually measured or observed the frequency
on an oscilloscope ?

If not, do you have the equipment to do so?


2) Where are you, and what is your power line frequency?

=======

If you have line frequency noise, possibly stray pickup,
check the cables, shields, make sure the turntable is
grounded and check for ground loops created by long
runs of parallel shielded cables running multiple grounds
between two auxiliary devices.

If you have twice the line frequency noise, check the
power supply filter capacitors and voltage regulator
chips and/or transistors within the power supply.

Power supply filter capacitors (electrolytic type) can dry out,
degrade and die during long periods of not being used.
They need to be periodically charged to regenerate the
dielectric insulation coating.

Also if you are actually getting line frequency noise
from the power supply, then check the rectifiers.

Full wave rectifier => twice the line frequency
Half wave rectifier => line frequency

A full wave rectifier with a blown diode behaves like half-wave.

From the description of your symptoms, hum is not affected
by input switches nor controls, I would suspect the the
problem is in the power supply feeding the final amplifier,

or perhaps in a broken feed-back loop within the output
amp, causing excessive gain and motor-boating.

A burned out power transistor in the output amplifier
can also cause bizzare oscillations, as the negative
feed-back circuit is trying to balance the DC operating
point of the amplifier but it can't.

Forget the voltmeter. If you have an oscilloscope, check
the power supply ripple, and scope key points in the output
amplifier.

Martin

Apr 24, 2008 | Bang and Olufsen Beocenter 9300 Shelf...

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