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.
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.
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
BE CAREFUL
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."
" 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."
Nuuk said:
carlosfm said: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.
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.
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.
roddyama said: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?
man this "you are under moderation" stuff is really annoying....
anyway i think i found my problem. i have a spst switch and i wired the "neutral" on to the switch instead of "hot". now i have 0.00v dc when the power plug is in and switch is off and +-22.9v dc when switch is on.
My remaining concern is that somehow I am not getting the 25/0.707 ~ +-35 v dc output as I should be getting. Does this have anything to do with the way I wired up the 2 bridges?
anyway i think i found my problem. i have a spst switch and i wired the "neutral" on to the switch instead of "hot". now i have 0.00v dc when the power plug is in and switch is off and +-22.9v dc when switch is on.
My remaining concern is that somehow I am not getting the 25/0.707 ~ +-35 v dc output as I should be getting. Does this have anything to do with the way I wired up the 2 bridges?
"...switch is off and +-22.9v dc when switch..." You mean +-22.9v AC, not DC. I'm assuming that's the transformer output measured where they connect to the bridge. If thats the case you should be getting about 33VDC on the output of the bridge minus 1 or 2 volt you'll drop across the bridge.rocktboy said:
On the output of the bridge, with out filter caps, you have full wave rectified AC. This will take the form of 120Hz half sinewave bumps with peaks of about 33V. If you measure this with a dc meter you should measure 33V X .707 ~ 23VDC.
Connect a PSU cap to the output of the bridge and let it charge and you should have your ~33VDC. During your test, you might want to connect a resistor across the cap so it will discharge. Maybe 1W 200ohm. It would be best if you had a variac to slowly raise to voltage.
Connect a PSU cap to the output of the bridge and let it charge and you should have your ~33VDC. During your test, you might want to connect a resistor across the cap so it will discharge. Maybe 1W 200ohm. It would be best if you had a variac to slowly raise to voltage.
rocktboy said:
If you have a centre-tapped transformer (25-0-25), use only one bridge.
rocktboy said:
That's why I use double switches, as I told on a previous note.
That way you disconnect the two wires, and you don't have to be worried about incorrect wiring on your electrical system.
In continental Europe it's worst still, as you can connect the mains plug to the plug on the wall in any position.
UK plugs are better, as they have a central ground pin and you can't reverse them.
Nuuk said:Am I missing something here? What's the problem? He should be getting ~23DC and he IS getting 22.9! I don't think that he need worry about 0.1DC.
I think he's confused because he's expecting to get 25V times 1.414 (35V), but of course he won't get that until he's connected the resevoir capacitors.
How are you getting on with your buffer problem?
Cheers,
Mark
mhennessy said:
I think he's confused because he's expecting to get 25V times 1.414 (35V), but of course he won't get that until he's connected the resevoir capacitors.
How are you getting on with your buffer problem?
Cheers,
Mark
what Mark said.....
the danger with gaincloning is that newbies like me who has absolutely zero knowledge in electronics will try to build one because it's simple and cheap enough.
i'll get it up and running this afternoon. thank you all for patiently answering my
type of questions......
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