STB + AV Receiver = Subwoofer Humming?

[hedgie]

Originally Posted by STurtle

Despite these being posted underneath a quote from me, I guess this was rather directed at neilboardman's added topic, rather than me? (Since I do not own a V+)


(Anyway, in my case it was only the power cables and the Video-RCA connection between STB and Receiver that produced the humming, adding the plastic TOSLINK or the VM-cable to the STB had no effect, nor any other wirings of other devices connected to the AV-Receiver. Clear case.)

I did reply to two posts individually, when this happens the forum glues the two replies together all on its own...

I have read the first post in more detail D'Oh..Sorry must spend more time reading and understanding less time typing !!

You state in your first post you have a Scientific Atlanta box, AFAIK this is called a V+ box, sorry if I have contributed to any confusion

Just to be clear;
-the hum is only from the cable box, no other sources?
-the hum will follow the cable box if it is swapped from one channel to another on the AV Amp.

These should eliminate you AV system from any suspicion ?

If all the cables are OK I am at a loss for an explanation short of a problem in the network or cable box. Sorry over to someone more qualified than me

[Misterguitar]

Originally Posted by hedgie

You state in your first post you have a Scientific Atlanta box, AFAIK this is called a V+ box, sorry if I have contributed to any confusion

A Scientific Atlanta 4200DVB is not a V+ box, it's a standard V box. The V+ is an 8300.

STurtle:
You could well have a faulty V box as it sounds like the ground for the audio is missing (could be dry joint or blown track on the SCART socket.) I used to work in the car audio repair trade and we used to get loads of stereos back for making an external amp 'Hum' just as you describe and it was usually an open circuit track on the PCB between the RCA sockets and the main ground in the circuit. Some manufacturers used fuse links to ground the RCA's so these would blow instead of a copper track.

[hedgie]

Originally Posted by Misterguitar

A Scientific Atlanta 4200DVB is not a V+ box, it's a standard V box. The V+ is an 8300.

I am a muppet

[STurtle]

Originally Posted by hedgie

Just to be clear;
-the hum is only from the cable box, no other sources?
-the hum will follow the cable box if it is swapped from one channel to another on the AV Amp.

Yes: If only the AV receiver, the speakers (unpowered) and the subwoofer are connected to each other and connected to the socket, the hum is audible.

No and Yes: The hum is heard already heard with the AV receiver in standby. It does not matter how the receiver is switched, it does not matter which cable is connected to where: Any cable, be it video from the Scart or one of the two analog Audio RCA connectors to any input port port on the AV receiver (video or audio) will cause the Subwoofer to start humming (unless the subwoofer has switched into standby itself).

Connecting the TV to the above changes the tone of the Hum somewhat, but without the TV, Av Receiver and Subwoofer alone produce no hum.

So this pretty much pinpoints to the STB.

---------- Post added at 20:40 ---------- Previous post was at 20:38 ----------

In reply to Misterguitar: This is very interesting. Thanks!

---------- Post added at 20:48 ---------- Previous post was at 20:40 ----------

However, how do I explain this to the VM Tech support?

I sort of expect them to say something like "Your STB box works with a plain Tele. Connecting it to a surround receiver is your problem!" Furthermore convincing them that something is their fault is usually very difficult, especially since I probably cannot show them my "fix", because I don't think VM appreciates me tinkering with their STB, faulty or not. Sure, it is just a grounding wire, but most people do have a healthy respect for electricity and would cringe seeing an extra cable leaving the lead (albeit I did it neatly, taking a proper three-wire plug and a spare C7 plug, separating the gound wire just 5cm before the case, including a pull-relief and fastening it around one of the STB's screws that hold the C8 socket). I doubt that communication with them will be easy...

Maybe I just stick with it and don't change my running system...?

[Feenix]

Originally Posted by Nedkelly

faulty isolater can do this i have seen it before or there might not be one the drop.

What he said^^ Try disconnecting the CATV feed (screw on F-connector) on the back of the STB. If the hum stops then this is the case and we need to visit to fix the fault.

[STurtle]

Originally Posted by Feenix

What he said^^ Try disconnecting the CATV feed (screw on F-connector) on the back of the STB. If the hum stops then this is the case and we need to visit to fix the fault.

I am not sure I understand?

I already wrote that the hum is entirely unaffected whether or not the cable that comes from the outside, from VirginMedia, is connected to the STB or not.

This cable is the only F-connector that I can see anywhere, so I am not sure what you are referring to. Could you please explain in more detail?


Also, as I had written before, the hum is produced by the STB already if it is only connected to a power supply and any single audio/video cable running from the STB to the receiver, connected anywhere, regardless of the state of either device (i.e. both in standby, except for the subwoofer itself.)

(Also, the STB is fairly hot at 48⁰C. I was told by VM phone support that this is normal for the ScientificAtlanta 4200DVB. However, the part of the NagraVision SmartCard that is inside the STB has turned to well-done brown color. There is nothing on top of it, it has about 5cm room to the next shelf above and to either side, and room temperature is at at 20⁰C. The STB is constantly burning 30W, regardless of standby.)

[Misterguitar]

Originally Posted by STurtle

---------- Post added at 20:40 ---------- Previous post was at 20:38 ----------

[/COLOR]In reply to Misterguitar: This is very interesting. Thanks!

---------- Post added at 20:48 ---------- Previous post was at 20:40 ----------

However, how do I explain this to the VM Tech support?

You have to convince them this 'Hum' is ONLY present when the V box is connected. Don't go mentioning the extra ground wire you've fitted though!

If they do agree to send an engineer then connect up another source to the amp like a VCR in the same way to prove to him (or her) that it is DEFINATELY the V box.

[neilboardman]

sorry I got the idea that you had a V+ box but my mistake but the advice I gave you will work on both boxes just so you know.

[Feenix]

Ah missed that bit, my bad.

[neilboardman]

what i said in my last post was complete crap, try a new scart lead, it sounds like its the scart lead, if not, then the best thing is to ring virgins faults line, it could just be a low signal, virgin will need to fix it.

[STurtle]

Originally Posted by neilboardman

what i said in my last post was complete crap, try a new scart lead, it sounds like its the scart lead, if not, then the best thing is to ring virgins faults line, it could just be a low signal, virgin will need to fix it.

I already get the hum by connecting the analogue audio out of the STB to the AV Receiver (i.e. the non-optical Cinch/RCA coaxial connection). Thus without any scart lead at all. However, for a different reason, I swapped the Scart-lead out to another cable, with exactly the same effect of obtaining the same hum.

Any electrical connection between STB and Receiver yields the hum.

[hedgie]

Originally Posted by STurtle

Any electrical connection between STB and Receiver yields the hum.

It seems that you have done all that could be reasonably expected to prove it is the VBox. Its call out time, I think.

If it was me, I would have a separate source on hand to demonstrate to the engineer that the same cables, and amplifier channel do not hum with other sources.

There can be no argument surely.

Hope you get it fixed,

[STurtle]

Originally Posted by hedgie

Its call out time, I think.

Well, I am still not sure it is worth the trouble. After all, I already fixed the hum myself - and why change a running system?

Worse, I am afraid that I get a different type of V-Box. This would mean mean at best that would I need to re-program my Harmony Universal Remote. Worse, the new box could lack the digital audio out, or have a different quirk that I might not be able to fix.

So unless there is some danger in damaging my other equipment with the extra grounding (or an unlikely health risk - well I did add an RCD), I will stick with the devil I know.

[scottjohnlucas]

Hi,

I am getting a Hum issue with my V+ HD Samsung 3110 box I had it installed on the 27th October and from then on I get a Hum through all speakers attached to my AV amp. Before reading the posts I had tried earthing the splitter box that Virgin had out in place and reduced the buzz by about 70% but I can still hear it and its driving me mad.

Has anyone called Virgin? If so have they sent a replacement box or replace cables? If so did this resolve the issue?

Regards Scott

[STurtle]

No, I took no further action since earthing the ScientificAtlanta. I am too scared that they will replace it by another model, which might have unknown consequences (e.g. missing digital out, different IR requiring me to reprogram my Harmony Universal Remote, etc.), especially since I am working during the day and could not explain anything to the engineer myself. Also, there is the pain in convincing the VirginMedia Telephone Support to send an actual Engineer - after all, that is the task of the Telephone Support Team, to reduce the number of call-outs.

So a lot of pain, but no possible gain (since there is no more hum after earthing).