Chip amp power supply- a beginners guide

[Nuuk]

Following on from some of the discussion on this forum about building chip amp power supplies, I am pleased to announce the addition of another page to the Gainclone section at Decibel Dungeon. I hope that it will answer many of the typical power supply questions that regularly crop up here.

I have tried to explain things both simply and comprehensively but most importantly, I have focussed on the safety aspects of building a mains fed power supply. I sincerely hope that all chip amp builders will make use of this resource and that it will keep them, and their property safe.

If you think that there is anything to add to the guide, or anything that isn't explained clearly enough, please use this thread to point that out, and I will make the necessary amendments.

A big thank you to AndrewT who took time off from his dancing) to proof-read the guide, and suggest corrections and additions.

You can find the guide here .

[kanifee]

WOW! great tut nuuk, it really helped me with discrete diodes and bridge rectifiers. best of it is its rite in time for me to build my PSU for my bridged gainclone. One question i think i always get mixed with, a transformer wired with twin secondary's has a positive and negative rail, when its wired as a center tapped trafo does it still have a positive and negative rail along with a ground or is a say +25 0v(ground) +25. i only ask as buiding my bridged lm3886 i need to fit the terminals and noticed the LM3886 has +v +v -v and ground pins. my first thought was, +v -v and ground were what i used to connect to the psu but now im questioning my self. admitidly i should post this in the chip amp section but the problem has just arised and reading this tut i feel more \might ask similerl so it seems like the rite place.

Once again great tut!

[Nuuk]

No transformer has positive or negative outputs. It is all AC until after the bridge rectifier(s).

If you have a centre-tapped traffo, you can (only) feed one bridge and you get a single positive and a single negative rail out of that. By referencing those rails to the centre tap you get your +/- voltages.

If your transformer has twin secondary windings, you can use two bridges, have two sets of positive/minus rails, and the zero volt rail is the junction between the negative or one, and the positive of the other (as in the diagram below)

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[Greg Erskine]

Nice work Nuuk, that must have taken some effort.

BTW: Rod Elliott has 2 t's

regards

[Redshift187]

Just in time for me too as I'm starting my PSU today or tomorrow.

The only thing that didn't make sense is use of the lightbulb protection... specifically, wouldn't you test with the 40W, then the 60W, then the 100W, THEN use the bulb bypass switch?

[Nuuk]

BTW: Rod Elliott has 2 t's

Better change that then Greg. I don't want to upset Rod!

The only thing that didn't make sense is use of the light bulb protection... specifically, wouldn't you test with the 40W, then the 60W, then the 100W, THEN use the bulb bypass switch?

I'll let Andrew answer that one Redshift, and then update the guide if necessary.

[kanifee]

one more thing about cap orientation on these + and minus rails of the psu, on the plus side obviously the positive pin of the cap is on th e positive rail and negative on the ground, on the negative rail is this the same case or does the negative leg go on the -v rail and positive leg on the ground like this?



or am i just being silly!

[Nuuk]

Think of the voltage rails being rungs of a ladder.

The positive rail is the highest, the zero volt rail is in the middle, and the negative voltage is the lowest rung.

And the rule is, the positive side of the cap always goes to the higher rung of the ladder.

Another way to think of it is 0 is higher than any minus figure.

So yes, your diagram is correct (and it wasn't a silly question).

[kanifee]

Great analogy, itj ust seemed a little daft when i went over it in my head but the way you put it across was spot on!!!

[!]

Nice job on the article but I would have to disagree with the following sentence in it, or possibly only the way it is worded:

I suggest the following arrangement. About 10-100 uF after the bridge rectifier, and 1000 uF on each pin of the chip amp

Generally the most capacitance should come immediately after the bridge rectifier with the 10-100uF on each power pin of the chip amp. Whether or not this has as much *magic* depends a lot on the source and speakers. When either of those color the sound it can mean doing odder things to the amp but I would rather have a tonnally & detail accurate amp and replace the parts with a problem instead.