Humming Sound

Hi all,

I hear a humming sound whenever I connect by HATHWAY cable setup box audio to my AVR, especially when the AVR volume is increased. When I tried once connecting my PC audio out to the AVR AUX IN (using fairly good Philips stereo cable), the humming sound was again present, and it was actually louder now.

More information for suggestions:

1. AVR is Yamaha RX-V459; This has only 2-pin power cord, no earth pin
2. Cable Box is HUMAX ND-1000C (HATHWAY) - has only 2-pin power cord
3. PC has Antec Power Supply, with regular 3-pin power cord
4. There is no shock or leakage current which can be felt on touching any of these equipment
5. Sound seems to be coming from Sub-woofer. When I switch off the sub-woofer, there is no audible hum (maybe if volume is pumped up without any signal)

6. The humming sound is much less when I connect DVD (on coaxial IN), but you can hear it only at very high volumes with no signal. So this is not an issue

7. When I connect IPOD (internal battery) to AUX IN, there is almost no hum at all

Please suggest possible causes and solutions.
I searched the forum and found one thread with similar problem. But it is not clear how it was solved.

Thanks
Churfsan

Humming sound can come due to -

1. Audio Cable earthing
2. Voltage transformer has faulty or bad coil
3. Dry soldering of the cable connectors joints

Please check the cable for any cuts or loose connections.
Also check the connection points for dry soldering.

It can be an issue with Hathway transformer put inside the STB as if its of poor quality or due to earthing issues it can produce a humming sound.

I faced similar issue with my bpl diva world space receiver that used to give humming sound on low volumes,

This could be due to a number of reasons.

If you hear the hum only from sub, then disconnect and reconnect the cable to the appropriate connection.

Also I am assuming you connected your PC via a Y cable and not stereo. For now, don't connect this until you resolve the issue (less variables to try out).

This may not be due to the power circuit as you do not get this when you connect the DVD to AVR right?

Try the following:

Re-connect the cables going into and out of the STB & AVR.
If you aren't using a surge protector, use this and see if it goes away.

Finally, hook up the AVR onto a separate power outlet diff. from other components if possible.

You should not hear any hum at all even when volume knob is turned high.

Let us know the results.

Hi marsilians,

Thanks for the suggestions, I will check and post back the results

Hi Dushie,

Thanks for the suggestions, I will check and post back the results

The problem is more pronounced when I connect the STB, so I think that the problem may be with the STB quality. It is a cheap, mass product given by the cable operator, no choice

I thought that the BPL Worldspace would be better quality. So how did you solve the issue?

Thanks

Hi:

The culprit here is the cable feed to STB. Your STB is perfect. If you have a LCD/Plasma TV, you can notice running lines and humming noise if there is a rogue signal. Otherwise, if you have a CRT, nothing is exposed. In your case, the subwoofer is able to expose the rougue signal, so is the humming noise.

Do you have a single cable feed from outside to your STB or is there a break in cable feed from outside which inturn joins another cable in your hall ?

Hi Vinod_David

After seeing your post, I cross checked that there does seem to be some running lines on the LCD TV, especially visible in darker scenes.

There is a single feed coming from outside. Of course, outside I do not know how it is connected. These guys just twist around exposed cable ends, no professional connections really

Can we do something inside the house, or we are at the mercy of the cable operator?? Any filters, anything?

One more thing, I tried connecting my desktop PC (just for testing purpose). I connected my audio stereo out from Creative Live 5.1 card; Again I could hear a loud hum. Maybe interference from PC power supply / fan??

I would be nice if HTPC experts can also suggest in this regard

Thanks very much
Churfsan

Hi:

Ok. You got single feed running to your STB. It is clear now you are suffering from the notorious 'ground loop', and your STB plays an important role in it. Do all of your components go into a 'surge protector' ? If not, get a new surge proctr., that might solve the issue.

One more suggestion, increase the volume in your STB to full, then control the volume only in your AVR, don't reduce the volume in your STB. Humming should go.

Please try reversing the 2 Pin Mains Plug of your STB.

Hi Vinod_David

Thank you for your suggestion and help.

I have set STB to about 80-85% of full range, and controlling the volume with AVR after that. What is observed earlier also, if I keep the STB volume low and increase the AVR volume more than -32 dB (reading on AVR), the humming becomes more audible. So your idea of keeping the STB volume high enough is good. Like basically you are keeping the signal strength high.

I thought that maybe the audio out cable from STB is to blame, as it is not a good shielded one. It is the stock cable (RED + WHITE) you get as freebie along with the product. But now I am not sure that changing the cable with solve the problem. What do you think?

Actually I do not have any surge protection / filters for all my AV equipment. Is this important? Can you suggest any known good makes? Any one from Hyderabad can suggest possible good sources?

Thanks again
Churfsan