| atenolol50 |
hi,
i'm having a bit of a situation over here.
-35v DC at the output.
i'm using the schematic from brianGT for LM3875.
i'm able to get +/-36V at the V+ and V- resp. measured at pins 1 and 4.
the NFB resistor is also in place between pins 3 and 8.
need troubleshooting tips.
thanks. |
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| scone |
| It sounds like you have a short between -V and your output, I would check the solder connections. Check the voltage on your chassis too... |
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| Mattyo5 |
I had that, turned out my feedback resistor's paint had chipped off and was bridging my -V rail and the output. yikes!
i'd check on something like that in this case
-Matthew K. Olson |
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| Enrico |
Hello Atenolol50,
During testing of my LM 3886 gainclone (gainclone with smd parts by Per-Anders), the voltage at the speaker output is 36V. But after replacing the LM3886 IC, the voltage at the output becomes 0V. Now my gainclone is already playing music. :-)
By the way, I am also from Singapore. If your are free, you can contact me.
cheers,
Enrico
Address:
Blk 231 Ang Mo Kio Ave.3, #11-1226, Singapore
Tel. No.: 64514239 |
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| atenolol50 |
its kinda strange.
when i got -36v i thought my chip was broken so desoldered and replaced it.
i got a -15mv reading, was happy and went on redo the other channel and hooked both of them up.
the 2nd channel still gave me -36v, went back to check the first, but its back to -36v too.
are my chips damaged? |
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| Reklats |
I was building a p2p lm3875 amp a while ago, and the first indication that I'd done something wrong was -36 volts on the output. It turned out I'd forgotten to connect the inv. input. (I was rushing)
Double check your p2p wiring. A lot. |
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| Sheldon |
| quote: | Originally posted by atenolol50
its kinda strange.
when i got -36v i thought my chip was broken so desoldered and replaced it.
i got a -15mv reading, was happy and went on redo the other channel and hooked both of them up.
the 2nd channel still gave me -36v, went back to check the first, but its back to -36v too.
are my chips damaged? |
The chips are pretty tough, so most likely its a wiring error /bad joint somewhere. It is possible to cook them by reversing the polarity of the power supply, but I'm not revealing how I know this. |
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| pinkmouse |
With the LMs, if they look ok, they usually are, the internal protection is pretty good.
It's when they look like this, you know you might need to replace them. |
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