Afternoon all. Can I pick your collective brains please?
Music System: CDX/XPS, 82, 2 x HiCap, 2 x 135, Epos 30's
AV System: Sony DVD, TV and VCR, Pace Satellite all connected to a Yamaha AV processor.
Left and right front line out's from the AV processor are fed the 82.
The problem is a mainslike hum when it is all connected together. This all started when the CDX was introduced to the system late last year. When listening to the AV system I have to disconnect the CD input from the 82 to eliminate the hum.
I've been chatting to Mark Raggart in the Naim service department who has been really helpful suggesting a few solutions.
1) Try to link the ground of the two systems. I ran a wire between the 82 ground binding post and one of the AV processor's speaker ground posts. No effect.
2) See if one of the aerials was causing the problem. Bingo! Unplug the satellite aerial and it all goes quiet. Naim have a small in-line hi-pass filter (single capacitor) for normal co-ax cables in response to others who have had this issue. Mark gave me the value of capacitance used and I knocked up a box with appropriate connectors for the satellite cable. No effect.
3) Replace the link between signal and chassis ground on the CDX output DIN plug with a 28 Ohm (I think) resistor.
Looks like I'll have to try #3 (I'll check the resistor value first with Naim, don't worry!), but before I start doing some DIY on my CDX I wondered if any of you had come accross a similar problem and had managed to solve it.
Any input much appreciated.
Posted on: 06 June 2001 by Andrew L. Weekes
quote:
Mark gave me the value of capacitance used and I knocked up a box with appropriate connectors for the satellite cable. No effect.
Does the buzz appear when you make the center coaxial connection, or the outer braid?
My suspicion is that the braid is the thing you need to capacitively couple, as this is producing a second DC path to ground and thereby giving you a ground loop, along with it's associated buzz.
Try a simple test to prove the above and then try the capacitor in series with the braid.
I assume this aerial is not to a dish (and it's LNB) as if this is the case, the DC block cannot be used, since DC is passed up the coaxial cable to power the LNB and possbibly provide switching functions for different bands.
Andy.
Andrew L. Weekes
Posted on: 06 June 2001 by Duncan Fullerton
Thanks Andy, I'll try that. Thank God I'm in IT and not an electronics person ... the cable does indeed go to a dish, but it is communal and therefore I'm just plugging into a splitter box. As the signel is still getting through, I'm presuming that the LNB is powered from elsewhere. Is that possible?
Posted on: 06 June 2001 by Andrew L. Weekes
Duncan,
I think it's highly likely the DC feed to the LNB comes from elsewhere, so you're in with a good chance.
It's also likely the DC feed is blocked already by a capacitor in the splitter box in series with the centre conductor.
Andy.
Andrew L. Weekes
Posted on: 06 June 2001 by Mike Hanson
I bought a little box called "MAGIC". It stands for "Mondial Antenna Ground Isolation Circuit", or something like that. It breaks the ground on the incoming cable so that it doesn't interfere with the one on your CDX. For more info, check out
www.mondialdesigns.com. Position your mouse cursor over "Mondial", then "Acurus", then "Accessories", then "Magic Box".
Apparently there's a cheaper one that Radio Shack sells, but when I asked them about it they looked at me dumbfoundedly.
-=> Mike Hanson <=-
Posted on: 06 June 2001 by Andrew L. Weekes
To be fair, it does a little more than just provide ground isolation, but I'd stick with your capacitors, Duncan!
If it affects signal quality, go to http://www.rsgb.org/shop/acatalog/index.html.
Type in 'braid breaker' (without quotes) in the search box and select 'Filter 1' from the list.
Braid breaker is yours for 10UKP, not sure of it's upper frequency charactersitics though, may be worth checking first, if your experiment proves it works.
http://www.nevada.co.uk/ sell them as well, you may be able to get specs here as to it's suitability.
A.
P.S. Just found AKD's website (the manufacturer of the BB1)at www.akdinfo.com. Webiste's naff, but they do have email for questions.
Andrew L. Weekes
[This message was edited by Andrew L. Weekes on WEDNESDAY 06 June 2001 at 16:49.]
Posted on: 07 June 2001 by Duncan Fullerton
It better not be the 135's, they were all re-capped a couple of years ago. Talking of which, does anyone know the recommeded "service interval" for 135's/HiCap's etc.?
Posted on: 07 June 2001 by Andrew L. Weekes
Don't worry.
I believe the recommended interval is 8-10 years.
Most capacitors have a life quoted in tens of thousands of hours at the rated voltage and ripple current.
Modern capacitors can have up to 30,000 hours or so giving 3.5 years of life.
Add the derating factor of lower applied voltage, the fact that ripple currents are unlikely to be anywhere near maximum, whether in use or not, for most users and ten years sounds reasonable.
Andy.
Andrew L. Weekes
Posted on: 11 June 2001 by Simon Anthony
I have searched the Radio Shack web site and asked at a number of their stores, but have not been able to find an antenna ground isolator like Mike Hanson's $100 MAGIC box.
However, there is another approach. They do have a Ground Loop Isolator. This is RCA to RCA with a 3K ohm 1:1 transformer in the middle. Catalog number: 27-054 and $14.99. Appears to be available in stores and on the web.
To use one with a VCR or A/V amp, you would need to change the RCA plugs to a DIN connector at one end or use an RCA to DIN adapter.
No idea of the quality of the wire, transformer or plugs, but avoiding the hum has to be worth while.
Simon
Posted on: 11 June 2001 by Andrew L. Weekes
I'm guessing from your description this is intended for the audio, rather than the RF leads. If this is the case use it for the audio out of the video kit, rather than the audio from any primary source.
This should cure the ground loop, with minor degradation to the video sound only.
A.
Andrew L. Weekes
Posted on: 11 June 2001 by Mike Hanson
That does make more sense, Andrew. Actually, two will be required, one for each channel of the video's audio output connectors. Back in my apartment, I had the TV and VCR as separate inputs on my pre-amp (for the shortest signal path), so I would have needed four of them. At $15 each, this comes to $60. For those with two VCRs and a TV (or TV, VCR and satellite tuner), this could be $90+. All of a sudden the $100 MAGIC box doesn't seem so expensive.
-=> Mike Hanson <=-
Posted on: 12 June 2001 by Simon Anthony
Yes, it must have two transformers as it is a stereo unit with two RCA plugs at each end. So, Mike, you would only need two.
I would rather have something that works on VHF/UHF than this, but I have not found anything else.
The RS web site has additional detail that suggests it has a flat audio frequency response. Still that's not a guide to how much damage it might do to the music.
Simon
Posted on: 12 June 2001 by Mike Hanson
When I'm watching TV, I don't tend to listen critically to the audio. I smile if it goes boom, boom, crash, bang, kablooey, and as long as it thunders out and fills the room with sound, that's all that matters. Besides, the quality of the audio signal from most video sources is already laughable compared to a good Naim system, so adding this extra level of filtration shouldn't make much of a difference. That's why I strongly suggest you connect this little doohickey to your video's audio feed, and definitely leave it out of your Naim CD signal chain.
-=> Mike Hanson <=-
