Thanks AndrewT, I've ordered one of these:
http://www.ebay.co.uk/itm/GOLD-PLAT...700?pt=LH_DefaultDomain_3&hash=item416fb812fc
http://www.ebay.co.uk/itm/GOLD-PLAT...700?pt=LH_DefaultDomain_3&hash=item416fb812fc
That one fits between the TV and the rest of the Audio system.
You may need the other type that goes between the cable and the TV.
You may need the other type that goes between the cable and the TV.
Well it's on its way, so I'll try the audio one first. I'm reluctant to put anything on the coax, as it's a long cable and the signal is probably at the limit. Further attenuation may cause more dropouts.
" I've ordered one of these:"
In general, the transformers in those are so small than they have no bass.
In general, the transformers in those are so small than they have no bass.
This problem is apparently pervasive, and almost always has once cause. I've read about cable TV hum problems and The Solution as long as two decades ago on Usenet.
The problem is the cable for Cable TV is grounded at the telephone pole, which is different enough from ground in the house to cause lots of hum in audio. I just read a forum post on this that said "the problem is often with the cable company." No, the company is doing things right by grounding at the telephone pole, where lightning often strikes.
It's in this RF path, between the cable box and the TV, that you need an isolation transformer. The good news is this is a really inexpensive transformer.
I see Jensen makes a $70 one, but it seems Jensen is expensive on principle (okay, their main product, audio signal transformers, are surely worth the price, but you can fix THIS problem on the RF side with a much cheaper device).
This looks like it'll do, at just under $10, and as it says it is made precisely to solve this problem:
Parts Express Cable Television Isolation Transformer
If that's too much, get two 75-to-300 ohm transformers (at $1 to $3 each), connect the 300 ohm ends (the two wires with spade lug connectors coming out) together, then add another cable between those two and your TV. I'm not sure how this might affect digital TV (who knows, it might improve reception), but those things worked fine back in the analog TV days.
I would not have mentioned the audio side (unless the TV itself is later demonstrated to be "broken" as far as hum/grounding). Just isolate the ground connection to the TV cable. This hum problem happens virtually every time an audio device with audio grounded to the power outlet is connected to a cable-TV-connected TV.
"I'm open to suggestions, but can't afford much more than about £20 ($30)."
That inexpensive one would probably work on the audio output of the TV, you may not notice the bass loss like you would on music.
The RF side solution should work too.
That inexpensive one would probably work on the audio output of the TV, you may not notice the bass loss like you would on music.
The RF side solution should work too.
Thanks benb, but that transformer says that it interferes with digital cable. I'll look out for something similar that doesn't though (if it exists).
I'm not sure about my cable being grounded at the telephone pole. It's fibre to the street box, then coax underground to the front wall of my house. Then it goes into a small, plastic box. It never goes near the telephone pole. Anyway, wherever it's grounded it's obviously different enough.
Thanks djk. If the cheap one doesn't work, the Behringer should - it's designed for musicians after all!
I'm not sure about my cable being grounded at the telephone pole. It's fibre to the street box, then coax underground to the front wall of my house. Then it goes into a small, plastic box. It never goes near the telephone pole. Anyway, wherever it's grounded it's obviously different enough.
Thanks djk. If the cheap one doesn't work, the Behringer should - it's designed for musicians after all!
Update: the cheap transformer has eliminated 90% of the hum and about 70% of the bass.
The search for a solution goes on...
The search for a solution goes on...
Try to find out WHY the bass has been attenuated.
This could be simple RC time constants building up against you, or it could be lack of LF capability in the transformer.
That analysis might find a cheap solution, or point to a very expensive transformer.
There is no advantage in jumping to the conclusion
"that cheap transformer is no good".
This could be simple RC time constants building up against you, or it could be lack of LF capability in the transformer.
That analysis might find a cheap solution, or point to a very expensive transformer.
There is no advantage in jumping to the conclusion
"that cheap transformer is no good".
The bass is less of a problem than the still existing hum, to be honest, as I can turn up the sub to compensate.
I'm not sure how to do what you suggest.
I'm not sure how to do what you suggest.
Draw out the TV to Input circuit.
Assign values to the various components and see if there are any high pass filters in there that could be adjusted.
Assign values to the various components and see if there are any high pass filters in there that could be adjusted.
I'm afraid I'm not an electronic engineer and I don't know what you mean by "TV to input". There's just a mini jack to phono lead (now with transformer).
I wonder if this would work: http://cpc.farnell.com/vision/v5-025/galvanic-isolator-2-3ghz/dp/AP02680?ost=galvanic+isolator
"it's designed for musicians after all!"
It may not be much better.
In the USA I would consider the Edcor product.
The transformer without the box is under $10.
There is probably something similar in the UK.
It may not be much better.
In the USA I would consider the Edcor product.
The transformer without the box is under $10.
There is probably something similar in the UK.
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Ground loops in connected equipment is usually down to too many earths connected to the zero volt lines.
There should be no more than one connecting to the zero volt line to earth.
You don't need to disconnect earth from any chassis as that is unsafe but you can disconnect zero volts from earth in equipment until there is only one left.
That's the strategy I have used with any amps I design and it works well.
Alternatively you can buy a ground loop breaker.
There should be no more than one connecting to the zero volt line to earth.
You don't need to disconnect earth from any chassis as that is unsafe but you can disconnect zero volts from earth in equipment until there is only one left.
That's the strategy I have used with any amps I design and it works well.
Alternatively you can buy a ground loop breaker.
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