LM3876 power supply

[!]

Originally Posted by happy hippy

When it comes to transformers, I'm not sure what I mean by parallel. What I want and need is 24-0-24. I know that there are differences between center-tapped and dual secondary, by for my purposes, they are alike, I think. At least, if I hook up the "center" wires together properly on a dual secondary, then it is for practical purposes, a 24-0-24. My son has offered to help me with that part of it. Whar I really need to know for CERTAIN is that the transformer I get is capable of being a 24-0-24. That means, to me, 48v even if someone else calls it a 24v. I'm 72 years old, and getting senile, according to some people :-), so I hope this is clear as to what I'm trying to do.

Thanx
THe Happy Hippy

AN-1224 will provide 24-0-24 AC output. It will work fine. Initially I was thinking you were building a two channel amp and was going to suggest 200VA, but for only one channel, 100VA will be ok.

Yes in one of the common LM3876 PSU designs used, including the one you posted, you could simply connect together separate secondary windings on these to create a center tapped secondary. Yes it is certain it is capable of 24-0-24 VAC output, which through a bridge rectified typical PSU circuit like you posted, would give roughly +33/0/-33 VDC output to the amp.

[AndrewT]

A dual secondary transformer has two secondary windings. They are isolated from each other.
You can use the windings to do different and independent jobs.
Or you can join the two windings together.

Here's the difficult bit and why I asked "parallel?"

You can join the two windings together and blow yourself up.

Or you can join them in parallel or in series.
Do you yet know the difference between series and parallel?

I want you to understand that working with mains is potentially lethal. You must be able to convince us that you know how to keep yourself alive, then we can lead you safely down the garden path.

So I set a test.
You explain to us what series windings means
and
explain what parallel windings means.

From your answer we can judge what level of assistance you require.

[!]

^ and use that light bulb current limiting circuit you often recommend (AC mains input to amp has an incandescent light bulb wired in series on the AC hot conductor).

[happy hippy]

Originally Posted by AndrewT

A dual secondary transformer has two secondary windings. They are isolated from each other.
You can use the windings to do different and independent jobs.
Or you can join the two windings together.

Here's the difficult bit and why I asked "parallel?"

You can join the two windings together and blow yourself up.

Or you can join them in parallel or in series.
Do you yet know the difference between series and parallel?

I want you to understand that working with mains is potentially lethal. You must be able to convince us that you know how to keep yourself alive, then we can lead you safely down the garden path.

So I set a test.
You explain to us what series windings means
and
explain what parallel windings means.

From your answer we can judge what level of assistance your require.

Problem is, I;m a functionalist. Thats the way my brain works. I know that I want 24-0-24. I now think that you call it series. But my son will be helping me with his oscilloscope, meters, etc., so I think I'll bo OK.

Thanks to all you guys for your assistance. I'm attaching the latest version of the schematic. This has on it changes we have discussed, and I also adde alpha-numeric designators on the resistors and caps. I think (and HOPE) everything's right this time.

Now one more question. I'm ready to put up the preamp schematic. Do I put it here, or start a new thread?

Thanx
The Happy Hippy

[AndrewT]

I was hoping for series saying something along the lines of the current through the first windings passes into the second winding.
Does that help confirm what you are thinking?

A dual secondary can be converted to a centre tapped secondary by joining the two windings together in series.
The voltage of the two windings adds up, when wired correctly to measure double the voltage.
That's where your ref. to 48Vac came from.
It is also the way you can check you have wired it.
You should be able to measure the two winding voltages at slightly more than 24Vac for each. maybe 25Vac to 26Vac each.
The series windings should then measure about 50Vac to 52Vac.

But before you plug anything into the mains build that bulb tester mentioned by !

[benb]

I was thinking you would say something about the primary - the schematics posted, such as in #44, don't show the primary the way it's shown on that transformer's datasheet. Connecting it wrong can make the bulb tester glow at full brightness, but at least that's better than wondering why the fuse blows every time the unit is turned on.

[!]

Originally Posted by happy hippy

Now one more question. I'm ready to put up the preamp schematic. Do I put it here, or start a new thread?

Thanx
The Happy Hippy

New thread (it is not a power supply + wrong sub-forum)

[happy hippy]

OK the preamps now posted under the chip-amp subforum.

Thanx
The Happy Hippy

[aymantn]

Originally Posted by happy hippy

Here's the modified revision of the revised modification of the....oh never mind.

Thank you very much.