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Old 10th May 2006, 08:48 PM   #1
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Default How to wire toroid and line cord?

The attached file shows the wiring diagram for the Avel Lindberg Y236750 330VA toroid, and a sketch of a power cord. I need guidance on wiring these to a BrianGT LM3875 gainclone kit.

Am using 2 amp boards and one rectifier board.

I do have 2 rectifier boards but populated only one with all the 8 rectifiers. I was going to not use the extra one.

1) Did I need to use all 8 rectifiers since I am only using 1 rectifier board for two amp channels?

2) What do the dots on the diagram for the toroid represent?

3) How to wire the primary of the toroid to the line cord?

4) How to wire the secondary of the torid to the rectifier board points V- PG+ PG- V+.

5) Do I fuse the primary, one secondary, or two secondaries, or primary and one secondaryˇ? What fuse ratings?

6) For wiring from the rectifeir board to the amp boards, is 16 guage stranded wire a good choice?
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Old 11th May 2006, 01:25 AM   #2
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First off, it sounds like you may be new to electronics. Be CAREFULL!!

PLEASE get an experienced freind to help you through this.
You'll still feel the rewards of building your own and will be around to send us pictures of it.

You will need all 8 diodes in the rectifier circuit.
The dots represent phase for parrallel and series wiring.
The intructions for wiring the toroid are here:

http://www.partsexpress.com/pdf/avelspecs.pdf

The primary should be wired as in the first picture. Reffer to BrianGT's instruction sheet for the secondaries.

The fuse goes between the black wire of the power cord and the transformer.

There should also be a switch on that leg also.

PLEASE PLEASE get some one to walk you through this. These voltages can kill.
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Old 11th May 2006, 01:42 AM   #3
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Default How about the wiring of the power cord?

Hey that diagram is excellent for wiring the primary!

Now the line cord has a male plug on one end, female on tyhe other - like a computer cable, so I cant tell what color each contact is.

I understand the ground prong is the separate, round prong, and am I right is should be connected to the aluminum enclosure?

Referring to the attached diagram, which power cable contact is black? Is the black one the neutral and the other (is it white) the live wire?

Since this is a 330 VA toroid, is a 2.5 amp fuse appropriate:

2.5 amp x 120 vac = 300 watts?

Fast blow or slow blow?
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Old 11th May 2006, 01:55 AM   #4
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"Now the line cord has a male plug on one end, female on tyhe other - like a computer cable, so I cant tell what color each contact is."


AGAIN! If your knowledge is that limited, get someone with experience in electronics.

No reflection on your ability, but that question tells me you should not go any further without help.

PLEASE!!!!
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Old 11th May 2006, 03:48 AM   #5
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Default It is a reasonable question

Thank you for your concerns for safety. Please know that I fully understand the safety issues, and for this reason I am very careful to get the grounding correct.

You advised to place the fuse in series with the hot (black) lead. Since I am using a computer type cable with male plug (wall side) on one end and female (amplifier side) on the other I do not have exposed wires and do not know ac wiring standards so do not know which is hot (black).

Can someone kindly look at the attached diagram and advise which is hot? Else I will carefully measure it with a meter to see which side is neutral ralative to ground and assume that is white and the other, at 120 volts relative to ground, is black and therefore hot.

I understand the ac safety ground is the separate, round prong, and am I right it should be connected to the aluminum enclosure? The briangt documentation seems to indicate this is the "central ground" and I am looking for clarification to be sure it is meant to be tied to the aluminum chassis.


Since this is a 330 VA toroid, is a 2.5 amp fuse appropriate:

2.5 amp x 120 vac = 300 watts?

Fast blow or slow blow?

Still looking for an answer to my above question about the rating for a fuse on the primary. 2.5 amp fuses are not as common as 2 amp so I might be stuck using a 2 amp fuse, meaning I am limited to 240 watts on a 330 watt system. I am hoping fo some comments on this.

Any input is most welcome, and please know that I will not attempt any testing under power until all is sorted through. I have some circuit desing background, am and Industrial Engineer, and am simply not knowledgeable on home wiring standards as an electrcian would be.
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Old 11th May 2006, 04:40 AM   #6
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Do you have a voltmeter??

There are two ways to do this. The first is by a voltmeter. Turn meter to AC volts between ground and the two prongs while the "convenience cord" is plugged into the wall. Only one of these will have ~115 VAC. That's the hot. The other prong is neutral.

The other solution is to just cut the female end off and wire directly with a proper bulkhead stress relief in the bulkhead. When you strip the wire, you will find a green wire, a white wire and the black HOT wire.

It would be reasonable to assume that a soldered connection of the power input cable (black-->fuse-->switch-->tranny & white-->tranny is better than an IEC socket.

Avoid hazardous shocks. Don't test while showering or bathing. Remove all bling-bling from hands.
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Old 11th May 2006, 05:26 AM   #7
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If the outlet is wired correctly, A will be hot and B will be neutral. The shorter slot in the outlet is hot and the longer one is netrual.
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Old 11th May 2006, 03:41 PM   #8
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Default Great! How about coments on the fuse...

Thanks for the helpful information! I will test to confirm A is indeed hot. The AC neutral and AC hot male plugs are both same length and width! But since it is polarized, not a problem.

Now, how about the fuse - is my logic correct - use a 2.5 amp if available, otherwise use a 2 amp, and 2 x 120v = 240 watts, so the 330VA toroid will only be able to be driven wellbelow its capacity. Is that correct?

Since this is a 330 VA toroid, is a 2.5 amp fuse appropriate:

2.5 amp x 120 vac = 300 watts?

Fast blow or slow blow? I assume fast blow, but in the case of using a 2 amp fuse perhaps slow blow might be better??? Any electrical engineers out there?
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Old 11th May 2006, 03:50 PM   #9
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Both are a little light. Choose slow blow because of inrush current to the toroid. I don't think there is any issue with 4A or 5A. If there's a wiring mistake, they'll blow just fine and do what they're supposed to do. That is protect the line side of the device... cord, plug, and receptacle. If it's an issue, start with a 3A but my bet is that it will blow occasionally.

EDIT: I'm not an EE but I have blown 3A on 330VA Avels. 4A fixes it. No calculations were necessary.
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Old 11th May 2006, 04:27 PM   #10
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But a 3 amp fuse on 120 volts protects for 360 watts, 30 watts over the toroid rating. And if it is slow blow type fuse, arent we asking for trouble?

Does the fact that this is AC affect the thinking? The 120vac is measured as rms, isnt it, so an average, not a peak voltage...
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