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Old 8th February 2009, 09:54 PM   #1
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Default LM3886 Problems

Before I get some well-earned "you should have known betters" from the group, I am aware that I did try to shortcut the process and am now paying the price. I had built an LM375 kit a while ago and had zero problems -- and now suffered from the arrogance of the lucky I guess!

I assembled a set of BrianGT LM3886 boards and a single power supply. When I wired everything up, I hooked the amp up to some old speakers and got a big turn-on thump and low output (music) level coming out of the speakers.

I couldn't figure out what was wrong so I tried to verify all the wiring. I wasn't clear from what I read on Brian's website how to wire the transformer so I found a thread regarding the wiring of a AVEL transformer into a BrianGT power supply board. I determined that I had swapped the orange and yellow wires on the AC2 connection.

I swapped the wires around and fired the amp up again -- this time nothing coming out of the speakers (no thump, no hum, no music, nothing). So I did what I should have done in the first place and followed Brian's direction. I measured the output of the transfomer and it is correct as is the output from the power supply board. What I do have is a significant amount of DC on the binding posts (440mV).

Any idea on what my next steps should be? Have I fried the ICs?

Thanks in advance.
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Old 9th February 2009, 08:02 AM   #2
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Just swapping the Orange and Yellow wires with each other, will have no effect! If you now have the correct voltage readings from the rectifier board, you would have had the same readings before the swap.
The problem must have been on the Amp boards (or the connection to them).
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Old 9th February 2009, 08:09 AM   #3
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Are you aware of the mute pin? It is not present on the LM3875, but needs a resistor to V- on the LM3886.
If you've always done it like that, then it's probably wrong. (Henry Ford)
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