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Dogue 24th January 2012 05:53 PM

Beginner LM3886 Chip Amp Build Questions
I'm building a mono LM3886 amplifier and have a few questions. While I've built lots of electronic circuits, this is the first AC build, and so I want to be absolutely sure I'm doing everything correctly.

My transformer is an Avel Lindberg Y236652 250VA 25V+25V Toroidal (Avel Y236652 250VA 25V+25V Toroidal Transformer 122-625). The power supply board uses terminal blocks with two terminals each for AC1 and AC2. Does it matter to which of the two terminals on each block I wire the secondary 0V and to which I wire the secondary 25V?

Also, how should I wire the transformer primaries? There are four wires, marked:


Finally, I presume that the AC hot should go to the lower of the two fuse holder terminals, and then the upper of the two fuse holder terminals should go to one of the transformer primaries?

Sorry for the beginner questions; I've searched and haven't found exact answers in text or picture and want to be certain I am doing the right thing.


jcx 24th January 2012 06:09 PM

Transformers and Power Converters From Avel Lindberg, Inc.

the site sucks - "haz certification" is meaningless - they should spell out meets EN 60650 double/reinforced insulation for for 240 VAC overvoltage category (II?), passes 4kV HiPot... somewhere easily found on the site

ask them, I'd use 3-pin plug, "protective earth" safety gnded chassis with this xfmr without further info

AndrewT 24th January 2012 06:14 PM

Primary first.
Build and learn to use a bulb tester.
That will prevent you from blowing up your mains powered equipment.
Test every intermediate stage of the mains power build, before trying to power up the whole thing.

Attach each transformer wire end (tail) to a separate terminal of an insulated terminal strip. This is to avoid accidental shorting and to prevent you killing yourself.

You can wire up one primary. To do this you must identify clearly which two ends are parts of one primary winding. Use an ohmmeter. Check for isolation between the two primary windings.

Plug in the bulb tester and check it works. It should not light up.
Plug a heating appliance to the bulb tester. Switch on. The bulb should light up telling you you are drawing excessive current from the mains. That is what the bulb tester does. It measures the current draw and compares that to what is needed to make the filament glow orange hot.
If the current draw is <<<hot current then the bulb stays cold and appears to be off.
if the current draw is <<hot current then the bulb glows dimly.
if the current draw is <hot current then the bulb lights up but not at full brightness.
if the current draw is >hot current then the bulb lights up fully and limits the voltage supplied to the DUT (Device Under Test). Learn to interpret these clues to bulb tester operation.

Now on your 110/120Vac mains system, you can wire up just one primary and test it through the bulb. Neither you nor the transformer nor the bulb will come to any harm by testing just one primary winding.

Unplug from the mains.
Wire the second primary in parallel with the first. Do you know the difference between parallel and series?

Plug in both connected primaries to the bulb tester. Does the bulb light or stay off?

If the bulb lights you have mis-wired the primary winding out of phase. You must swap around the two ends you last connected in parallel. The original two ends stay where they were.

If the bulb stays off, you have wired the two primaries in phase. We have passed the first assembly successfully and not even a fuse blown.

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