Just last week I purchased a Topping TP20 mk2. I have been very happy with the amp, until last night when a "shocking" truth became apparent. I was switching the inputs from my CD player (NAD C541) to my television, both of which are not grounded to earth. The TV and CD player have separate interconnects, so I was switching them at the input to the amp, and not from source to source. My system is setup on a bottom shelf, so I was on my knees with my arms behind the equipment. My left forearm was in contact with the grounded chassis of my tube amp and my right hand was switching the connectors. As I removed the second connector, I felt a little tickle of the electrical sort.
Not a full 120 or anything, but something was definitely there. I got out my meter and read 43 vac between the grounded chassis of the tube amp and the ungrounded chassis of the Topping amp. After that, I unplugged the power from the Topping and measured nothing between it and earth. Then I measured from the DC negative of the power supply, an external switcher rated at 14vdc and 4A, and read the 43 volts again. I also measured the same from between the positive center pin and earth. Between the two pins I measured 0vac and 14.1vdc.
So this morning I called up parts express, who I ordered the amp from, and they will be sending a replacement soon. But, knowing little of SMPS's and how they work, I decided to do some testing when I got home from work today. First off, the grounded switching power supply for my notebook computer: 0vac between either pole and ground. Next up, an ungrounded switching wallwart to a digital picture frame: 25vac between each pole and ground.
Now I'm wondering if this is okay or not. So here's my questions for those of you who would be kind enough to help me out:
1. Is this a normal meathod of operation for ungrounded supplies?
2. Will this hurt my other ungrounded equipment by having 43vac on the 0vdc common?
3. Is it best to use a grounded PS with all amps?
Thanks in advance,
Phil
Not a full 120 or anything, but something was definitely there. I got out my meter and read 43 vac between the grounded chassis of the tube amp and the ungrounded chassis of the Topping amp. After that, I unplugged the power from the Topping and measured nothing between it and earth. Then I measured from the DC negative of the power supply, an external switcher rated at 14vdc and 4A, and read the 43 volts again. I also measured the same from between the positive center pin and earth. Between the two pins I measured 0vac and 14.1vdc.So this morning I called up parts express, who I ordered the amp from, and they will be sending a replacement soon. But, knowing little of SMPS's and how they work, I decided to do some testing when I got home from work today. First off, the grounded switching power supply for my notebook computer: 0vac between either pole and ground. Next up, an ungrounded switching wallwart to a digital picture frame: 25vac between each pole and ground.
Now I'm wondering if this is okay or not. So here's my questions for those of you who would be kind enough to help me out:
1. Is this a normal meathod of operation for ungrounded supplies?
2. Will this hurt my other ungrounded equipment by having 43vac on the 0vdc common?
3. Is it best to use a grounded PS with all amps?
Thanks in advance,
Phil
There's a good article on DIYAUDIO:
http://www.diyaudio.com/forums/diya...udio-component-grounding-interconnection.html
This piece on Rane's website is often referred to:
Grounding and Shielding Audio Devices
and one by Rod Elliott:
Earthing (Grounding) Your Hi-Fi - Tricks and Techniques
http://www.diyaudio.com/forums/diya...udio-component-grounding-interconnection.html
This piece on Rane's website is often referred to:
Grounding and Shielding Audio Devices
and one by Rod Elliott:
Earthing (Grounding) Your Hi-Fi - Tricks and Techniques
you were probably feeling the ~60vac present due to the X caps pulling the "ground" to half way between "hot" and "neutral"
Generally the capacitors are rather small value, which is why your 1Mohm meter pulls it down from 60vac to 43vac. you should be able to measure the current with an ac amp meter from chassis to ground, let us know what it is.
Generally the capacitors are rather small value, which is why your 1Mohm meter pulls it down from 60vac to 43vac. you should be able to measure the current with an ac amp meter from chassis to ground, let us know what it is.
Yes, this sounds like mains filter capacitor current. It won't harm you, but it can make you jump. It is an unfortunate side effect of the modern habit of making consumer electronics which doesn't need a ground connection. I discovered this a few years ago when unplugging the aerial cable from my homemade FM tuner (properly grounded, like all good DIY stuff) and discovered that the cable was 'live' thanks to my Sony TV set - they shared a cable from the aerials in the loft.
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