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Old 19th January 2013, 05:13 PM   #31
Mooly is online now Mooly  United Kingdom
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Does the hum appear if you just touch the Sonys "ground" part of the output lead (the outer) on to the corresponding "outer" part on the Arcams input sockets ? That doesn't read very well does it.

I'm wondering... is the Alpha 5 grounded via its mains lead or is it a two core double insulated product and is the Alpha 8 a three core mains lead with ground connected ?
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Old 19th January 2013, 09:33 PM   #32
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Originally Posted by Mooly View Post
Does the hum appear if you just touch the Sonys "ground" part of the output lead (the outer) on to the corresponding "outer" part on the Arcams input sockets ? That doesn't read very well does it.

I'm wondering... is the Alpha 5 grounded via its mains lead or is it a two core double insulated product and is the Alpha 8 a three core mains lead with ground connected ?
Interesting, many thanks, I'll investigate that tomorrow.

The Alpha 8 has a three core lead with the case grounded. The "ground" on the input sockets are not connected to the case (well, they are now at RF via the capacitors)!

I'll look at the 5 to see how that compares.
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Old 19th January 2013, 09:44 PM   #33
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What is the Sony model number and does it use a mains earth (not twin flex but 3 core mains lead)? Is the hum 50 or 100Hz?
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Old 20th January 2013, 09:08 AM   #34
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Originally Posted by Harleyjon View Post
What is the Sony model number and does it use a mains earth (not twin flex but 3 core mains lead)? Is the hum 50 or 100Hz?
It is a BDP-S185 and has a two core mains lead.

50 or 100 - Sorry to sound daft but I honestly don't know! It is 25 years plus since I used to play around with a little electronics so I'm not well tuned in. My guess is 50 Hz but I'll try to confirm.

Although interesting in terms of what on "earth" is going on here I don't actually need to connect the Blu-Ray player to the Arcam providing I can solve the next bit.....

More relevant is that I'm getting a similar problem connecting my TV via an optical to stereo phono adaptor . That has the inevitable plug in 5v power supply. Again, this was fine with the Arcam 5.

The whole installation is difficult to get to but I gong to haul the whole lot out today and rebuild bit by bit to try and be certain where the problem starts.

I will also double check the mains earthing etc.
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Old 20th January 2013, 01:49 PM   #35
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Ok Harleyjon, Mooley and others.....

If you can stand it, here is my latest update.

I have removed TV, HD recorder Blu-Ray and everything else from the area and checked mains leads.

With the Arcam Alpha 8 amplifier only there is the faintest hum from the right speaker only just as the Arcam chap described as "normal". This is down at a level you would only notice with an ear close to the speaker. It maybe increases very, very slightly at full volume. The amp uses a three core mains lead.

Adding the Arcam 8 CD player with decent quality audio leads makes no detectable difference. The CD player does not have an earth pin in its kettle type socket.

The moment I connect anything else, including an Arcam 7 Tuner, I get a noticeable hum from BOTH speakers. This is audible in a quiet room at normal listening distance. The tuner also is two core mains. Using my highest quality phono leads maybe reduces this very slightly but it is still unacceptable.

My powered optical to phono converter is slightly better providing I use a short, high quality phono lead but my Sony BluRay player is the worst. Both have two core mains.

So, at the moment it is only good with the CD player, borderline with the converter and unusable with the tuner and BluRay.

If I substitute the Arcam 5 amplifier everything is perfect!

Help!!!!

Thanks
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Old 20th January 2013, 02:04 PM   #36
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Many modern items (especially from Sony!) make a habit of injecting hum into their ground connection via the EMC suppression capacitors in the mains feed. I seem to recall the usual safety limit for this (to stop you dropping things on your foot when you get a sharp tingle) is 1mA. Sony equipment will happily inject several 100uA, which may be enough to generate audible hum. I first discovered this Sony 'feature' when my TV injected a serious tingle into the antenna wiring shared with my FM tuner.

Provided all audio signals are referred back via one path to one point this should not cause a problem. However, I guess your BluRay is also connected to the TV so that might introduce an alternative ground path. Does the hum go away when the HDMI/Scart is unplugged?
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Old 20th January 2013, 03:29 PM   #37
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Many modern items (especially from Sony!) make a habit of injecting hum into their ground connection via the EMC suppression capacitors in the mains feed. I seem to recall the usual safety limit for this (to stop you dropping things on your foot when you get a sharp tingle) is 1mA. Sony equipment will happily inject several 100uA, which may be enough to generate audible hum. I first discovered this Sony 'feature' when my TV injected a serious tingle into the antenna wiring shared with my FM tuner.

Provided all audio signals are referred back via one path to one point this should not cause a problem. However, I guess your BluRay is also connected to the TV so that might introduce an alternative ground path. Does the hum go away when the HDMI/Scart is unplugged?
Very interesting - thanks.

I thought I was imagining it with the tingle on the end of the leads!
Unfortunately I no longer have it connected as an easy solution was just to use the optical output from the TV (more chance of being in sync with the picture)! Now I've put everything back in the furniture it is not easy to get a connection to try it but I will do when I can.

Still doesn't explain why the Arcam Tuner should be nearly as bad though as that is the same generation as the amp and CD.
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Old 20th January 2013, 04:34 PM   #38
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It all sounds like a classic case of a ground loop and unfortunately there's not always an easy fix.

Lifting or breaking mains safety grounds isn't recommended for obvious reasons but there are workarounds,
Earthing (Grounding) Your Hi-Fi - Tricks and Techniques
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Old 21st January 2013, 03:38 PM   #39
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It all sounds like a classic case of a ground loop and unfortunately there's not always an easy fix.

Lifting or breaking mains safety grounds isn't recommended for obvious reasons but there are workarounds,
Earthing (Grounding) Your Hi-Fi - Tricks and Techniques
Thanks for that link.

The optical to stereo phone adaptor I'm using has the inevitable plug in (presumably switch mode) power supply.

Is there an easy way of getting it a better source of 5volts that won't create a ground loop? Apart from a battery obviously!
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Old 21st January 2013, 04:25 PM   #40
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You would need to be sure that this device really was the problem first but yes, there are easy ways to get 5 volts without a ground loop.

DIYing a small 5 volt PSU is easy.

If this SMPS is the problem (or a possible problem) you will be able to measure continuity from its mains plug earth pin to the ground on the 5 volt output. If there is no continuity then there's no ground loop via that route.
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