First diy project need help with LM3886

[M D]

Hi everybody,

I bought the stereo kit LM3886 from chipamp.com. I have been having a couple of problems.

The first problem is my output secondary voltage when I put one lead on one of the output secondary wires and one lead on the ground connection gives me a reading of 40.9 volts. The model is the AN-3225 its output voltage should be 25.

The second problem is when I attached my power supply volt, it did not convert the ac to dc, and instead it ran ac out to the v+ terminal. I am not sure how to fix this issue.

Any help is much appreciated. Sorry I don't understand too much about all of this stuff yet, but I have been trying to read and learn how all the circuits function.

Thanks

[AndrewT]

Did you connect AC power to the amplifier?

[GloBug]

I was wondering that too.

Assuming nothing is burned out it sounds like you need to double check the wiring on your transformer and check your diodes. Most voltmeters have a setting for diodes.

I would disconnect the transformer from the project and test the voltage of each secondary.
You should read ~25 from blue to green. Make sure your wired for 120V not 220V.
http://www.antekinc.com/pdf/AN-3225.pdf

You can also check your diodes with an ohm meter if it does not have the diode function.
How to Test Diodes with a Voltmeter | eHow.com

report back or go from there.

[M D]

Thank you for your responses guys they were helpful. I did have my transformer wiring wrong. I fixed it, and it is now outputting the correct voltages.

I attached the ac power to the power supply because I wanted to test the dc voltage before I connected to the amp boards.

The power supply pg+ and pg- were not attached to the star ground. Should I do that for the DC test?

The diodes I think are gone. I tested one of the smaller diodes and it was working fine. But the ones with the steel backing would flow electricity both ways (although one way more strongly than the other).

I fired up the power board again to see if I would get DC, and I got very minimal dc 0.05 or so, and I tested and AC was around 47 volts when compared to ground.

I think I have to reorder a new power supply board and components set.

[GloBug]

That's a shame, it happens.

[M D]

I checked my diodes a second time, and I think they are actually ok. The meter was just going to a high number and then saying .0L at the end.

Any other ideas on why I am getting AC on the output?

[gootee]

The .0L usually means "off-scale high", i.e. very high resistance, i.e. not conducting in that direction. Do you have separate diodes with two leads each or a bridge rectifier with four leads? When using an ohmeter with separate diodes, one direction should not conduct (should be off-scale high) and the other direction (reversing the meter leads) should have some ohms reading that is not off-scale-high.

Can you give the model number of the diodes?

P.S. You should be using a bulb tester, so things can't be destroyed as easily.

[M D]

It's the lm3886 kit from Chipamp.com the diodes are the MUR860. Is the power supply board supposed to be attached to the earth ground while you are testing the output voltage?

[gootee]

Originally Posted by M D

It's the lm3886 kit from Chipamp.com the diodes are the MUR860. Is the power supply board supposed to be attached to the earth ground while you are testing the output voltage?

Earth ground is for safety. So yes, it should always be connected when power is applied. But it shouldn't affect your measurements at all, either way. You should be measuring with respect to the circuit's ground rail, not the earth ground. There is nothing special about "ground". It's just a place in a circuit that we call "zero volts".

[M D]

I am currently testing dc offset through my binding posts, I have a potentiometer linked in. And the one side tests -5mv to -75mv and the other side tests +16mv to +18mv without much variation. Is this normal to have such little variation in the mv on the other side?