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Old 10th July 2003, 12:29 AM   #1
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Question about to turn it on.....some final concerns

Hi All,
I am about to connect the power supply to the amplifier section (28mv dc offset on both channels when powered by a lab power supply, checks out okay) and I have some final concerns here.

I checked both channels of the dc output of the bridges and found them to be +- 24 volts, as expected.

But the interesting thing is when the power plug is in but the switch is off, the positive rail is at about 0.9v dc, and the negative rail is at about -0.9v dc. And when I unplug the power cord it reads 0.00v dc. It is the same for both channels. Do I have a problem here? Because of this I am not sure if everything is in order here and I don't want to connect the power supply to the gain clone yet

Any and all suggestions are appreciated.
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Old 10th July 2003, 05:10 AM   #2
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Your problem is most likely in your house wiring. Somewhere in your house the hot and neutral are swapped and some appliance is feeding voltage back on the neutral. 1v isn't a big deal, and I wouldn't get too concerned, but you might what to go through your house wiring and find where the cross is. Check the recepticle for voltage from neutral to ground. if your seeing .9v at the secondaries, you should see 4 or 5vac across N and G.

BE CAREFUL
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Old 10th July 2003, 08:14 AM   #3
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A friend of mine had a similar situation (he has 0.12V with the switch turned off) after completing his PSU and contacted the supplier of the IEC switch that he was using. He got the following reply:

" This is probably a capacitive effect due to leads being close together and is normal, it would not be noticed if a analogue meter was used."
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Old 10th July 2003, 09:38 AM   #4
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Nuuk,

That's normal, forget it.
The answer from that supplier seams correct to me.

You can do an experience: disconnect the PSU and measure DC offset on your GC.
Sometimes the is something there, even without power.
Forget it.

Just put your helmet on and switch it on!
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Old 10th July 2003, 12:01 PM   #5
Nuuk is offline Nuuk  United Kingdom
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Quote:
Just put your helmet on and switch it on!
Thanks Carlos, that's about the advice that I gave!
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Old 10th July 2003, 03:37 PM   #6
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Talking Aham...

rocktboy,

So...?
So much time to turn it on...
Or did you blow your house?
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Old 10th July 2003, 04:33 PM   #7
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Quote:
Originally posted by Nuuk
" This is probably a capacitive effect due to leads being close together and is normal, it would not be noticed if a analogue meter was used."
Quote:
Originally posted by carlosfm
Nuuk,

Just put your helmet on and switch it on!
If it were a "capacitive effect" it wouldn't go to 0V when it was unpluged. I assume you guys know the domestic power feeds in the US are different then in Europe. The grounding in the US, paticularly in older homes, can be quite messy.

I'm not setting off the fire alarms here, but you should never take the banzai approach to AC power.
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Old 10th July 2003, 04:44 PM   #8
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Well then...
Just got to my mind that maby you're not using a proper switch for mains.
You can try another type of switch.
Oh, and I always use double switches to disconnect the two wires.
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Old 10th July 2003, 04:59 PM   #9
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Hi Carlos,

We typically use a single pole switch in the US as well. The problem with US power feeds is that there are 3 wires (Hot 117VAC, Neutral 0V and Ground). The neutral is bonded to ground at the feed to the home. It is also the third prong on the recepticle. In old US homes the owner can install a recepticle and cross the hot and neutral (easy to do) and it will still work fine in most situations, but it can be trouble if you assumes the neutral is bonded to ground and it turns out to be hot.
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Old 10th July 2003, 05:24 PM   #10
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Quote:
Originally posted by roddyama
Your problem is most likely in your house wiring. Somewhere in your house the hot and neutral are swapped and some appliance is feeding voltage back on the neutral. 1v isn't a big deal, and I wouldn't get too concerned, but you might what to go through your house wiring and find where the cross is. Check the recepticle for voltage from neutral to ground. if your seeing .9v at the secondaries, you should see 4 or 5vac across N and G.

BE CAREFUL

I am actually doing this in the electronics lab at work. the neutral to ground reads about 0.5v ac, and I think that's normal.....

Let me describe my torroidal and bridge wiring and see if you guys and spot some serious flaws:

I have a single 25v 0v 25v secondary so I hooked the two 25v wires to the two ac in's on the first bridge. I simply did the same thing to the second bridge (so in effect the 2 bridges are in parallel?) so I have 2 channels of +-V dc. And the 0v wire goes to the power star ground. Anything wrong with what I am doing?
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