Let's rewind a bit...
If you connect just the amp and 'nowt else but a pair of speakers and using the battery powered CD portable as a source does it hum. At all ? Left ? Right ? Both ?
If it does then that is problem number 1. (and from what I remember you saying somewhere, Arcam implied that was normal and might be tweakable by rotating the tranny ?). If you can't get it right at this stage (just the amp) or the hum is unacceptable then it seems like a design fault to me.
As to cutting the earth in other equipment to overcome any external ground loop issues... well from a safety perspective we can't recommend that for obvious reasons. The earth connection is there to protect you in the event of a fault. There are ways to retain the safety earth and still "isolate" it from the circuitry using a diode bridge.
Just because there might be a ground loop issue doesn't mean you can't sell the amp because it would happen with any new similar model. It's not faulty as such.
I had the same issue with my Pure DRX 701 tuner and it is annoying. When the 3 core mains lead was plugged in a steady pure 50 hz hum appeared on any input.
If you connect just the amp and 'nowt else but a pair of speakers and using the battery powered CD portable as a source does it hum. At all ? Left ? Right ? Both ?
If it does then that is problem number 1. (and from what I remember you saying somewhere, Arcam implied that was normal and might be tweakable by rotating the tranny ?). If you can't get it right at this stage (just the amp) or the hum is unacceptable then it seems like a design fault to me.
As to cutting the earth in other equipment to overcome any external ground loop issues... well from a safety perspective we can't recommend that for obvious reasons. The earth connection is there to protect you in the event of a fault. There are ways to retain the safety earth and still "isolate" it from the circuitry using a diode bridge.
Just because there might be a ground loop issue doesn't mean you can't sell the amp because it would happen with any new similar model. It's not faulty as such.
I had the same issue with my Pure DRX 701 tuner and it is annoying. When the 3 core mains lead was plugged in a steady pure 50 hz hum appeared on any input.
OK, currently it is in my workroom set up exactly like that.
Since we last spoke I have had it apart, re-soldered the earths on all the phono and speaker sockets, the mains socket and cleaned the PCB earthing point that bolts to the case.
It current has a pair of speakers from a mid price Technics midi system single wired with bog standard cable.
If I put my ear against each speaker I can hear a very small amount of hiss from both and a tiny amount of hum from the right only. This wouldn't be noticeable at any normal listening distance.
Yes, you remember Arcam's comments correctly. As the transformer is so firmly stuck down I'm not going to try rotating it for now. If that remains the only problem I'll consider it but it hardly seems worth the trouble.
I'm using a decent (i.e very expensive in its day) Technics battery powered CD player's line output connected with its supplied 3.5mm jack to phono lead.
This causes no discernable increase in hum and, I have to say, like that it sounds lovely!
I'm next going to bring my Arcam Tuner upstairs and connect that.
Watch this space!!
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Progress!!!
Although heaven knows why!
Connecting the Arcam 7 tuner in my workroom no longer creates immediate hum on all inputs as it used to do downstairs. Previously this was regardless of volume setting and was enough to make the system unusable.
Now I get a slight hum only when the tuner input is selected and this is directly proportional to the volume setting. I would say this is about the amount I would have expected from a turntable, no more.
Interestingly I get this whether the tuner is turned on on not.
No noticeable difference when connecting the aerial.
Sounds good through the cheap speakers.
Currently the tuner is sitting on top of the amplifier. Downstairs the amp was on a shelf about a foot above the tuner.
What next, apart from supper?!?
I really am grateful for your help.
Although heaven knows why!
Connecting the Arcam 7 tuner in my workroom no longer creates immediate hum on all inputs as it used to do downstairs. Previously this was regardless of volume setting and was enough to make the system unusable.
Now I get a slight hum only when the tuner input is selected and this is directly proportional to the volume setting. I would say this is about the amount I would have expected from a turntable, no more.
Interestingly I get this whether the tuner is turned on on not.
No noticeable difference when connecting the aerial.
Sounds good through the cheap speakers.
Currently the tuner is sitting on top of the amplifier. Downstairs the amp was on a shelf about a foot above the tuner.
What next, apart from supper?!?
I really am grateful for your help.
So it hums when tuner input is selected and the tuner being on or off makes no difference. And the hum level is affected by the volume control setting.
Exactly.
Hum stops as soon as I pull the mains plug out of the tuner!
As I say, this is very different to the effect I was getting downstairs where I had hum on all inputs the moment the tuner was connected
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The tuner doesn't have a mains earth connection.
All the Arcam units have a kettle type socket on the back panel but only the amplifier one has an earth pin.
Despite this, I've just done as you suggest in case the presence of an earth wire in the lead affected it - it doesn't. No hum.
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Fair enough 
Next guess is that the tuner doesn't actually have a true mains switch but simply switches either the secondaries or operates directly on the low voltage PSU in some way. In other words the transformer is always on.
If so then its looking like we are back to design issues I'm afraid.
Next guess is that the tuner doesn't actually have a true mains switch but simply switches either the secondaries or operates directly on the low voltage PSU in some way. In other words the transformer is always on.
If so then its looking like we are back to design issues I'm afraid.
Yes, it is. I think it is because the memory is only backed up by a capacitor. Confusingly the front panel switch is identical to the amplifier externally but that does have a double pole mains switch.
Yes, but the Arcam tuner wasn't the only (or even the worst) offender. Downstairs the Arcam CD player was the only item that didn't create permanent hum on all inputs.
Supper's ready! After that I'll check back and, unless you think differently, bring things downstairs.
It maybe I've fixed a dry joint or something in the amp but somehow I doubt it!
Back soon!
You have to stay logical. With it set up as it is now the tuner causes hum. That has to be a problem (and maybe it is one we can't resolve, I don't know). Also, another thought. 50hz hum is... well 50hz... and if your main speakers are bigger and better
then they will reproduce the hum bigger and hmmm ! better.If you have another amp (the other Arcam ?) and you substitute just the amp in your test room set up does the hum problem remain ? In other words, do the two perform identically in that very specific test set up or is one worse than the other in that set up with regard to hum.
Point taken but unfortunately that post crossed with taking things downstairs!
However I can come back to it another day.......
Anyway.......
Better but not perfect!!!!!!
Downstairs, connecting the tuner introduces a little non volume dependant hum on all inputs. Upstairs it didn't. However you really have to listen for it now, before it was unusable. I will shortly experiment with aerials as obviously that it different to upstairs.
However, connecting my Freeview hard disk recorder (so that I have digital radio) produces too much hum on all inputs to use. Nevertheless still not anything like as bad as it was before.
Putting an eBay £3.99 ground loop isolator in the signal lead cures it! What are these things, other than a mysterious black tube half way along a cheap and nasty phono lead?
So, It is substantially better than a few days ago but I have no real idea why.
My main speakers are Castle Kendals, bi-wired with reasonable cable. However, I'm beginning to wonder if this is a good idea as it means running the tweeters from the switched speaker jacks on the amplifier. Having looked at the naff switch and having had to resort to contact cleaner to get it to work...........
However I can come back to it another day.......
Anyway.......
Better but not perfect!!!!!!
Downstairs, connecting the tuner introduces a little non volume dependant hum on all inputs. Upstairs it didn't. However you really have to listen for it now, before it was unusable. I will shortly experiment with aerials as obviously that it different to upstairs.
However, connecting my Freeview hard disk recorder (so that I have digital radio) produces too much hum on all inputs to use. Nevertheless still not anything like as bad as it was before.
Putting an eBay £3.99 ground loop isolator in the signal lead cures it! What are these things, other than a mysterious black tube half way along a cheap and nasty phono lead?
So, It is substantially better than a few days ago but I have no real idea why.
My main speakers are Castle Kendals, bi-wired with reasonable cable. However, I'm beginning to wonder if this is a good idea as it means running the tweeters from the switched speaker jacks on the amplifier. Having looked at the naff switch and having had to resort to contact cleaner to get it to work...........
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It may be better because the load onthe mains in lower so there are fewer harmonics in the hum, which makes it less audible.
The cheap ground loop isolators usually contain coupling caps. More expensive ones have a coupling transformer.
If you get hum downstairs but not upstairs either you have a strong mains magnetic field, or voltage direr rentals between the mains connections.
Fields are generated by high currents flowing through cables the longer the cables the worse and if the form a coil they will be much worse.
Differentials are caused by resistance between different ground returns. This is reduced by reducing the distance between mains connections. So if you can get all the sources and amplifiers on one distribution block that may help.
Regards,
Andrew
The cheap ground loop isolators usually contain coupling caps. More expensive ones have a coupling transformer.
If you get hum downstairs but not upstairs either you have a strong mains magnetic field, or voltage direr rentals between the mains connections.
Fields are generated by high currents flowing through cables the longer the cables the worse and if the form a coil they will be much worse.
Differentials are caused by resistance between different ground returns. This is reduced by reducing the distance between mains connections. So if you can get all the sources and amplifiers on one distribution block that may help.
Regards,
Andrew
Thanks.
The house has two ring mains, one up and one down.
Previously, when the problem was really bad, I removed everything (TV, Blu Ray etc etc) from near the downstairs installation then rebuilt starting with the Arcam stuff. Then, any connection to the tuner (or anything apart from the CD player) made it unusable. It really was that bad.
I understand the concept (I think) but in this case the amplifier is the only item with a mains earth connection. None of the other devices, including the TV and aerial amplifiers do.
Something has clearly changed for the better. Perhaps it was a dodgy ground connection in the amplifier? If so, maybe the tuner has a similar problem - they are both from the same series?
Downstairs the aerial has been through two amplified splitters (horrible I know!!) is it worth isolating? Upstairs has only been through one. I have read that two 10 nF capacitors are all that is needed?
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Thanks.
The plugs had been in and out dozens of time in all this but I did also carefully clean the outers of the amp's phono sockets at the same time as re-soldering the ground connections today.
Previously I had tried using different inputs and cables, for example plugging the problem tuner into the "good" cd sockets but to no avail.
I will investigate better / more direct or, if all else fails, an isolator in the aerial feed tomorrow.
Any views on the wisdom (or otherwise) of using the switched speaker outputs for bi-wiring?
OK, latest update for Mooly, gfiandy and anybody else who can still stand this!!!
I have now done as you suggest.
Upstairs in my workroom the tuner gives the same volume dependant hum with the "perfect" Alpha 5 as it does with the "suspect" 8.
However, what it does NOT do is give the non volume related hum (ground loop ??) on all inputs that I get downstairs when connected to the 8.
So, something downstairs is causing a slight ground loop effect which the 8 is sensitive to and the 5 is not.
As mentioned, this is nothing like as bad as it was a few days ago. Unless something external has magically and coincidentally changed, re-soldering and cleaning ground connections has given a 75% improvement.
What next?
Thanks again!
I suspect you are never going to be happy with any of this kit tbh...
A tuner should not add or produce any audible hum on its audio output. We've established the Arcan tuner has no mains earth so it seems we have a design issue.
What would I do now. I would scope the tuner output with it just in standby and see if any measurable signal is present. There should be none of course.
I suspect you may well be right!
However, at least for the time being I've got to a point where the three items are connected up in my living room and are perfectly useable. The volume has to be turned well above my normal listening level before the hum is detectable even three feet from the speakers. A few days ago the setup was impossible.
I will do this although probably not for a day or two as it has all taken up too much time recently. Frustratingly the tuner's reception and sound quality seem excellent.
I would still like to know why there remains this incredible sensitivity to ground loop issues. The £3.99 isolator has provided an acceptable quick work around for the Freeview box but obviously is an aspirin for a broken leg!
Meanwhile the NAD 7240 receiver in my office has suddenly produced a strong warm smell then stopped working!!!! I expect I'll be starting a thread about that when I get time!
Thanks again for all your help.
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