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Why does my tuner cause hum?

W

Wiz

Active Member
I've just got my Cambridge A50/P50 amps back from th eengineers and they're making some great music, but when I plug in my Luxman tuner there's a distinct hum through the speakers. It doesn't increase with volume, just stays at the same level. Can anyone suggest why this might be? Any ideas appreciated.:confused:
 
Your tuner probably has just a two pin cable with no earth,or it could be an rf problem,try pluging your tuner into a different socket to see if that makes any difference.
 
Thanks Stevie. I get the same result when I plud nito the aux socket. Will check the cable, though it is a 3 pin plug
 
If you use some CableTV service (or shared flatblock antenna) for your FM antenna it could well be the cause. They often boost the signal by applying some voltage to both signal and earth wires.

Solution - get an isolator - there seem to be two sorts, capacitve and transformer-based usually built into a small tube with a F type aerial connector at each end.
Nigel
 
I would also check for DC (or measurable AC with no signal) on RCA output's, assuming it is only the one source causing the issue. Could be your previous pre-amp had more input filtering?
 
I would agree with Uncle Nigel. The tuner is probably being earthed by the shield in the antenna cable. This is commonly a problem in flats, where someone else's tuner or TV is connecting the shield to mains earth. If the hum stops when the antenna cable is pulled out of the tuner, then it is definitely this. You are lucky that you had noticed the hum. Sometimes, there is no audible hum, but the sound quality of the whole system is degraded by this earth loop.

An easy fix is to just connect the centre cable of the coax. Or else get an isolator.

Andy
 
Sawing the earth pin off the power lead is not recommended. I did this with my Nakamichi 500 to remove an earth loop, meaning the cassette deck was only earthed through the RCA shield. I was 18, and it worked just fine as a solution, but was VERY VERY BAD, from a safety standpoint.
 
That sounds possible - I'm only using a bit of wire for an aerial as I've got a pretty strong signal, and haven't got round to doing anything else, so it can't be can't be cable or shared antenna. Sorry I'm thick as regards the technical stuff - how do I check for DC on the output's, and what if anything do I do about it? Thanks for all this advice. Th esound quality by the way is really good, more dynamic and deeper bass than with my old MF amp, although stereo is too noisy so I use mono which I don't mind for radio really. But with the hum in th ebackgroud spoken word stuff in particular isis just too irritating.
 
IIRC , it will have been a requirement on importing that receiver that it be fitted with a 3 pin plug for British conditions, including an earth to the chassis.

Over here, the neutral line is returned to earth at the bus rail on your power distribution board. Removing the neutral link at the power board is very dangerous. In the case of a two pin power connector, we would normally assume the chassis of the equipment is double insulated, preventing a path to earth through the user, if the chassis goes live. The instant the chassis goes live, the main fuse or breaker would pop, since it would be a short circuit- supply to earth.

Your problem is too many earths , with the earth potential not being the same for both devices. A hum loop is caused by a circulating current in the earth return BETWEEN the two devices.

You have to lose an earth somewhere..My only recommendation at this point is to get an electrician to meter out the tuner power connections to find how the earth is connected, and whether it is in fact , double insulated.
 
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