Quad 33/303 baffling hum

[Jez1234]

Sounds like classic ground loop problems. It can be difficult to advise without being there and there can be combinations of equipment which when all plugged into the mains, whether switched on or not, will cause this problem. Sometimes the solution is an easy one which I've used myself many times but I have a feeling there could be legal repercussions if I made it clear so I won't.

It has been known to help matters if all equipment is plugged into one multiway block with as many sockets as you need.

[PaulR]

It is all effectively connected to one plug. The CD player, record deck and tuner are connected to a multi socket which is connected to one of the switched power outputs on the 33. The 303 is connected to the other switched output. Everything else is connected to another multi socket and thence with a single lead to the mains socket.

The hum is only caused by the TV and tuner whether they are plugged in or not, and whether or not their output is selected. It stops for either if its aerial is unplugged. I am wondering if something to try would be to disconnect the screen from the aerial sockets on the wall.

I have had several different amps and tuners in the same position with no problem - it seems to be something particular to the 33. After I had bought the 33/303 a friend gave me theirs which they were replacing. I have passed it on to my son but I did try the 33 in place of mine and the hum was still there so it isn't just with my example.

Edit - It is worse in the left channel. Curiouser and curiouser!

[Jez1234]

There will no doubt be an earth connection to the screen of the aerial leads. I'd still plug everything into one multiway and not use the switched outputs of the 33, convenient or not.

[PaulR]

I will try it independently of the 33 output tomorrow

[audiomm]

As the Aerial connection is the culprit, what exactly is the Aerial arrangement? Is the TV aerial also being used for FM via a splitter?
You might be interested in how I sorted mine.
I initially had a hum loop with my Quad setup when I connected the TV audio output directly to the 44 Control Unit. Simple fix for me was to use a small (& cheap) D/A converter with optical input and RCA's out, so TV was connected to the DAC by optical cable and the output via the RCA's to the 44 - hence the earthing 'chain' was broken and the hum disappeared
And my FM4 Tuner is fed from separate external 5 element FM Aerial (I'm 85kms away from the stations I want to listen to) so hum free listening was a must..
Mike

[samjmann]

Have you removed the aerial from the TV and tuner? I've known odd things from aerial distribution systems and grounded wall plates in blocks of flats etc. Virgin media wall plates are normally grounded as well. I had to fit an isolated wall plate to a FM input on a high end system once. It had hummed since new. About 25years!!! SJM.

[Jez1234]

The shared earth return from the 33, often quite thin cable to the 33's mini Bulgin, will be exacerbating "ground bounce" of any other ground loops which find their way back to the 13A socket, especially if some items run from the 33's outlets and others are plugged into their own sockets, hence the recommendation to fit each item with it's own 13A plug and put them all in one decent quality multi block (Olsen are good) with a short thick cable from it to the 13A socket. If everything's plugged into this at least everything's floating at the same "ground reference" and the shared earth is via a metre or less 13A+ thick cable. It also removes the behind the wall earth loop bit due to the resistance of the earth connections and wiring from socket to socket of the ring main
(to be pedantic, you could even run an extension cable from the TV to another socket on this multiway). All this can help in troublesome cases. A loops a loop though and you may have to break a loop somewhere.... diode protected ground lifts, which reconnect ground via rectifiers (a few in series x2 back to back to allow things to float by a few V) capable of blowing the mains fuse if an ungrounded chassis should become connected to live, are the safe way to do this of course....

If earthed aerial leads prove a big issue then I guess some sort of "un-balun" 1:1 ferrite transformer will be available to act as a braid breaker.

[PaulR]

Thank for all the suggestions.

A quick explanation of the rather eccentric setup here - which is partly due to the aerial wiring inherited when we bought the house.

There are two downstairs living rooms each with hi-fi and TV set.

For the TV there is one aerial which feeds into the back room via a signal amplifier. There is a long cable from this into the front room which is used for TV only. There is an FM aerial on the roof which also feeds into the signal amplifier but this is only used for the back room tuner.

There is a separate FM aerial for the front room. This feeds into a double wall socket which also carries the TV feed from the back room. This is rather complex in a way but it has worked for the last 20 odd years with no problems. I have had very similar set ups in the same position with no problems. In fact the hi-fi in the back room consists of a Leal Delta 30 and matching tuner powered through it with no hum at all.

I tried connecting all the equipment directly to the mains. Admittedly there are too many plugs for one multiway I have but it made no difference. The tuner was still not earthed though, as it only has two wires leading to the Bulgin plug

If I connect the earth screw on the 33 to the screen of the aerial cable then the hum almost completely disappears. I suspect that the screens are connected together in the front room wall socket.

Like the hum, I have gone round and round in circles thinking about this! If it was just caused by the aerial connection to the tuner I would say it is because of the fact that it is only grounded through the 5pin DIN plug but it still hums if the tuner is completely disconnected but the TV (which is powered via an external supply plugged into the same multi block) has its aerial plugged in.

I would prefer not to have the tuner plugged straight into the mains as Quad in their wisdom didn't fit a power switch to it. Is there any objection to leaving the aerial lead permanently grounded to the 33? That seems to be the simplest solution.

I almost wish I hadn't bought the Quad stuff and left the Technics amp that was previously there but I have always wanted some since I saw it in hi-fi shops many years ago.

[Jez1234]

As I said you could use a "braid breaking" ferrite transformer to isolate the aerial from ground.

[PaulR]

Is this the sort of thing?

https://www.amazon.co.uk/Isolator-El...096VLG1RN?th=1

[Jez1234]

It's certainly the sort of thing yes but ideally you want the correct plugs and sockets on it.

You may have to make something yourself or use/make Belling Lee 75R to F or N type or PL/SO259 etc.

[PaulR]

I have some plugs to make up the leads but these are a little cheaper with postage so I might go for them

https://www.amazon.de/-/en/Wentronic...6G52S%3Fth%3D1

[Radio Wrangler]

AKD and a few other firms made Belling Lee connectored braid breakers suited to UK VHF/UHF radio and TV which were marketed to radio amateurs suffering problems with home and neighbour's broadcast receivers.

Stick a post in the wanted section, there are likely to be people who still have one salted away for a rainy day. DIY instructions were common in amateur radio magazines and handbooks.

David

[PaulR]

Thanks David. I had already sent off for the Amazon ones. I will report back when they arrive

[PaulR]

The Mantelstromfilters (great term) arrived yesterday and have cured the hum.

Thanks for the input, all.

[fetteler]

Result!

Now you can really enjoy the Quad setup and I reckon any pangs of regret at ditching the Technics will fade away rather quickly

Steve.

[PaulR]

Thanks Steve