Thread wake-up - ground loop
😱
Finally got it hooked up for music and I have a ground loop.
On the bench with a sig-gen and dummy load it is impeccable, so I let it soak test for a few days.
Now, hooking it up to my Yamaha receiver pre out I get hum whether the Yamaha is switched on or not.
Constant hum regardless of volume control.
Removed all other pre-amp inputs.
Yamaha runs on a groundless 2 wire mains connection.
Shorting out or opening up the ground lift circuit (diodes and 10R) makes little difference. As soon as the SECOND rca connection is made to the Yamaha, the hum starts.
I must confess that I don't know what to do next.
The SKA earthing is exactly as specified and I have ohmed it out - no unexpected chassis shorts anywhere!
I used to know this stuff but it is over 10 years since I used a soldering iron in anger ....
First thing, I guess, is to get my old NAD preamp down from the attic and try that ....
😱
Finally got it hooked up for music and I have a ground loop.
On the bench with a sig-gen and dummy load it is impeccable, so I let it soak test for a few days.
Now, hooking it up to my Yamaha receiver pre out I get hum whether the Yamaha is switched on or not.
Constant hum regardless of volume control.
Removed all other pre-amp inputs.
Yamaha runs on a groundless 2 wire mains connection.
Shorting out or opening up the ground lift circuit (diodes and 10R) makes little difference. As soon as the SECOND rca connection is made to the Yamaha, the hum starts.
I must confess that I don't know what to do next.
The SKA earthing is exactly as specified and I have ohmed it out - no unexpected chassis shorts anywhere!
I used to know this stuff but it is over 10 years since I used a soldering iron in anger ....
First thing, I guess, is to get my old NAD preamp down from the attic and try that ....
Hi - You're not alone I have exactly the same problem! I've been through just about every alternative earthing arrangement with Greg (who - it must be said - has to be one of THE most helpful people I've ever encountered) to no avail. My earthing is exactly as specified in the manual, and as you've discovered the ground lift diode arrangement hasn't made any difference. Managed to reduce the hum somewhat by joining together the two earth points between the green caps on both PSU boards. Also by re-routing the signal input leads it's reduced also. The amp is dead silent with no connections, and (usually) with one, but - like you - as soon as the second connection is made hummmmmm! It's so annoying as apart from that this is one of the best amps I've ever had the pleasure of listening to, let alone building.
My own theory is that the power amp is very sensitive to it's wiring arrangement. If i can't get it silent I think I'll have to try a totally different chassis layout with shorter PSU wiring runs.
Do let us know if you manage to clear the hum or not - it's got me pulling my hair out!
- John
My own theory is that the power amp is very sensitive to it's wiring arrangement. If i can't get it silent I think I'll have to try a totally different chassis layout with shorter PSU wiring runs.
Do let us know if you manage to clear the hum or not - it's got me pulling my hair out!
- John
Commisserations then, John!
Have a look at my layout in post #451.
Are you using a single trafo and dual psu boards?
The center two connections of the trafo output go to the earth-lift circuit, the other side of which is chassis. It should be clear from the photo.
Is your circuit like that?
Does Greg read this forum still or should I be posting this in "another place"?
I'll keep in touch.
Have a look at my layout in post #451.
Are you using a single trafo and dual psu boards?
The center two connections of the trafo output go to the earth-lift circuit, the other side of which is chassis. It should be clear from the photo.
Is your circuit like that?
Does Greg read this forum still or should I be posting this in "another place"?
I'll keep in touch.
It's exactly the same as your layout Cliff, but not quite as neat looking. Will post a picture shortly.
I think Greg hangs out at the other place - perhaps we should both be posting there
Greg reckons it's something very simple but I have my doubts, and I really can't see anything else that would explain the hum except the layout - I've followed his instructions to the letter.
- J
I think Greg hangs out at the other place - perhaps we should both be posting there
Greg reckons it's something very simple but I have my doubts, and I really can't see anything else that would explain the hum except the layout - I've followed his instructions to the letter.
- J
You say with signal on one channel its ok, but hums when both channels connected
Sounds like a signal ground loop between the channels, somewhere
Maybe a picture of amp layout would help
Sounds like a signal ground loop between the channels, somewhere
Maybe a picture of amp layout would help
OK, I see your very nicely bulit amp
I am sorry to say that in my early youth I made a similar layout with trafo at the back very close to inputs - and THAT is a NO NO
Or have I seen it wrong
BTW... I bet that if you place trafo outside of the box, hum will be gone
I am sorry to say that in my early youth I made a similar layout with trafo at the back very close to inputs - and THAT is a NO NO
Or have I seen it wrong
BTW... I bet that if you place trafo outside of the box, hum will be gone
This might work
Hi all,
I used to have similar problems with a different amp with balanced inputs. I found that disconnecting the ground connection on one input solved the problem. It would suggest that a ground loop of sorts was being created.
Perhaps the only caveat here would be that when using the amp in future, you would need to connect the grounded input first followed by the ungrounded input.
Hope this helps.
Ryan
Hi all,
I used to have similar problems with a different amp with balanced inputs. I found that disconnecting the ground connection on one input solved the problem. It would suggest that a ground loop of sorts was being created.
Perhaps the only caveat here would be that when using the amp in future, you would need to connect the grounded input first followed by the ungrounded input.
Hope this helps.
Ryan
Hi,
a stereo amp is TWO amps in one box.
The two input grounds ultimately connect to safety earth.
I would put in two separated audio grounds and connect each using a disconnecting network to keep the input grounds from completing the loop.
Bob Cordell described a different arrangement that appears to have merit. Go have a look at his suggestion in power supplies.
a stereo amp is TWO amps in one box.
The two input grounds ultimately connect to safety earth.
I would put in two separated audio grounds and connect each using a disconnecting network to keep the input grounds from completing the loop.
Bob Cordell described a different arrangement that appears to have merit. Go have a look at his suggestion in power supplies.
Hi AndrewAndrewT said:
Can you expand? I'm not using the ATI cases, but the Hexateq stereo chassis and intend to put 4 channels (2 psu's and 2 toroids) in the case. However I'm concerned about containing the two 0.45C/W heatsinks inside the case although I'm adament in using these chassis now that I have them.
This is the arrangement:
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and this is the chassis: http://www.hexateq-av.com/documents/Datasheet_stereo_enclosure.jpg
An externally hosted image should be here but it was not working when we last tested it.
Each amps will be driving a Linkwitz Orion so they won't be driven anywhere near their power rating.
Nice cases. I'd look at getting a local engineering company to mill slots or a big rectangular opening that you can fill with wire mesh above and below the heatsinks.
The enclosure already has some slots albeit in the wrong place for my ideal layout (as can be seen here).
It never occured to me to mod the chassis. I like the idea of large rectanglar cutouts and putting some mesh under it.
Ideally I'd like to not mod it at all when you see the cost of these things though
It never occured to me to mod the chassis. I like the idea of large rectanglar cutouts and putting some mesh under it.
Ideally I'd like to not mod it at all when you see the cost of these things though
There is guite a lot of metal in those chassis. If you attach the devices directly to the side panels and make sure that heat is transfered evenly to the rest of the panels (by using additional angles/brackets wherever needed), I think you should be fine with those amps, especially if they won't be driven anywhere near their power rating.
To avoid drilling too many holes in the sides, you can use copper sub-plate (heat spreader).
To avoid drilling too many holes in the sides, you can use copper sub-plate (heat spreader).
Hi V,
Amp Guru has revised the GB150 heatsink Rth s-a down to 0.8C/W for each channel with Iq=100mA and he quotes 50Cdeg temp rise. That is HOT. Even bigger when you go to Iq=150mA under Tweaking.
Your two channels on a single 0.45C/W sink are going to run a bit hot when exposed to a free air flow. Inside a case with those tiny vents in the top (are there any in the bottom?) the sinks are going to run much hotter (and cook the rest of the circuitry/transformer/capacitors).
My comment related specifically to that ATI case, so ignore it.
Amp Guru has revised the GB150 heatsink Rth s-a down to 0.8C/W for each channel with Iq=100mA and he quotes 50Cdeg temp rise. That is HOT. Even bigger when you go to Iq=150mA under Tweaking.
Your two channels on a single 0.45C/W sink are going to run a bit hot when exposed to a free air flow. Inside a case with those tiny vents in the top (are there any in the bottom?) the sinks are going to run much hotter (and cook the rest of the circuitry/transformer/capacitors).
My comment related specifically to that ATI case, so ignore it.
The same vents are on the bottom as well. There is enough height to fit taller heatsinks (100mm high) but I'm guessing its ventilations that's needed and not throwing more metal at the problem...
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
jacco vermeulen said:
Agreed.
But it seems SUCH a shame not to bond all that heatsink INSIDE to the natural (case) heatsing OUTSIDE 😱 😱
Funny thing,
if the heatsinks would be sawn in half and placed mirrored above the slots, they'd benefit from the chimney effect, have adequate ventilation and the space in the cases appears to would be used more efficiently.
Naaah, too Japanese.
if the heatsinks would be sawn in half and placed mirrored above the slots, they'd benefit from the chimney effect, have adequate ventilation and the space in the cases appears to would be used more efficiently.
Naaah, too Japanese.
Dear Vikash,
You can mount a subpanel to the sidewalls of the enclosure without any screws going through the exterior. Nothing is visible from the outside. The side panels would then act as heatsinks. It also means that there are fewer screws in the bottom panel.
That would also do the job.
Regards,
Richard Krol
Hexateq Audio Visual
You can mount a subpanel to the sidewalls of the enclosure without any screws going through the exterior. Nothing is visible from the outside. The side panels would then act as heatsinks. It also means that there are fewer screws in the bottom panel.
That would also do the job.
Regards,
Richard Krol
Hexateq Audio Visual
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