Chip amp power supply- a beginners guide

[kanifee]

How do you mesure to ensure the rectifier is ok, do you mesure from each dc out point to the ground of the transformer?

[!]

Originally posted by kanifee
How do you mesure to ensure the rectifier is ok, do you mesure from each dc out point to the ground of the transformer?

A bridge rectifier is just 4 standard (for this purpose) diodes, you can use the diode test on any multimeter.

[lanchile07]

Great job Nuuk!.
Your help is more than appreciate in this forum.
thank you.

[Nuuk]

Originally posted by !
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:



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.

The guide is meant to be a 'how-to' rather than a 'recipe' for want of a better word. My advice (to beginners) is always to go with the most basic of GC's to begin with. And the 'accepted' circuits did use a small amount of capacitance after the bridge, and 1000 uF on each voltage supply pin of the chip. I agree a lot depend son what loudspeakers the GC in question will be used with.

So that's not 'set in stone', and everybody is welcome to try their own 'recipe' for the best sound in their system. But adding yet more variations to a beginner's guide can just make the whole process seem even more daunting!

[Nuuk]

Thanks for the positive comments guys. If the guide helps just one person get started with a GC, and they get the same thrill that I got on hearing my first GC, it will have been worth the effort.

[Nuuk]

Originally posted by kanifee
How do you mesure to ensure the rectifier is ok, do you mesure from each dc out point to the ground of the transformer?

Kanifee, I presume that you are asking about checking that you have the correct voltages rather than checking the bridge rectifier is OK (although one depends on the other).

So yes, you measure voltages between two points where you have different voltages. Where you measure the output of the bridge rectifier depends on if you have one or two or them coming off the same transformer.

If you have a centre tapped transformer with a single bridge, you would measure from the + leg of the bridge to the centre-tap of the transformer to get your positive rail voltage, and from the - leg of the bridge to the centre-tap, for the negative voltage.


With twin bridges, you just measure from the + leg to the - leg on each bridge. Then at the point where you join the bridges together (where ever you do that) you can check the voltages from the + leg, and the - leg, the point where the join is made.

[kanifee]

quick q then, i have a transformer of 15-0-15, what should be my voltage from the rectifier bridge?

[Nuuk]

Originally posted by kanifee
quick q then, i have a transformer of 15-0-15, what should be my voltage from the rectifier bridge?

Looking at the table in the guide (hint ) it will be around 21 volts.

[!]

Originally posted by Nuuk



Looking at the table in the guide (hint ) it will be around 21 volts.

The table could include the bridge rectifier loss.

(VAC * 1.41) - (2 * Diode Forward Drop) = DC Output @ rated transformer load.

Of course the remaining question is whether silicon or schottky diodes are used since the former has about half the drop of the latter though it's typically under 1V difference either way, and that (most?) people would probably be measuring their supply voltage while it is lightly loaded or not loaded at all (to confirm proper operation before powering the amp with it) instead of at the transformer rated load so the voltage will be a little higher.

[Nuuk]

Again, I don't want to go into so much detail it looks like a University degree course. However, it is important to stress that a load must be connected to the bridge when taking the measurements. Hence the following quote from the section on testing!

You will need to have your reservoir capacitor connected on the output of the bridge rectifier to provide a load. If you don't you will not measure the correct voltage!