Running two LM1875 mono amp from single psu

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Hi
I'm new to chip amps although ive built many car audio systems.
I've Wired two lm1875 mono amplifiers to a single power supply only to have the left amplifier have no output.
Ive checked the resistance of the input and the other wiring for good conductivity and still the left amp doesn't output.
Is it wired incorrectly?

IMG_20140519_232745.jpg
 
The power looks OK. (Except I would have installed a fuse and switch in the AC feed...covered for safety, of course)

If you are using a common ground source and a 4 wire feed (ipod or computer) and the "in" and "gnd" were reversed on the left channel amp connections then the left would provide no output.

Connect to one amp at a time to test.

Is the left amp the top or the bottom?

The top amp IC pins look a little bent. Might have shorted or twisted the copper pads on the bottom of the board.

Just a guess.

:)
 
Mains power and non insulated terminals combined with non-earthed metal work !!!
Or is that an earth tag attached to the transformer bolt?

You live very dangerously.

I hope we continue to hear from you.

That's the first thing I thought. I don't even see a grommet for the mains wire.

Sloppy, careless wiring like that has started a few car fires too, so the OP might not be as familiar with car audio systems as they claim.
 
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Yes, well, approximately 62% efficient amplifier, possibly 1a with 18+18vac = 36va. 36*0.62=22W. And, that LM1875 could be quite durable.
. . . 19W with 15+15vac 1A transformer.
. . . 17W with 14+14vac 1A transformer.
. . . 15W with 12+12vac 1A transformer.
*speaker load neither mentioned nor factored in to the above figures.
**ideal amplifier gain can differ depending on power voltage, so the datasheet component values may not (could not?) be ideal for all cases.
 
The power looks OK. (Except I would have installed a fuse and switch in the AC feed...covered for safety, of course)

If you are using a common ground source and a 4 wire feed (ipod or computer) and the "in" and "gnd" were reversed on the left channel amp connections then the left would provide no output.

Connect to one amp at a time to test.

Is the left amp the top or the bottom?

The top amp IC pins look a little bent. Might have shorted or twisted the copper pads on the bottom of the board.

Just a guess.

:)

The left channel is the bottom circuit board.

The audio input is left, right & one ground shared between the two circuit boards.

The input and ground are wired correctly and he input output wire were checked for continuity using a multimeter.

I could try checking each board seperatery although didn't as I assumed the two circuit boards were interacting with each other in some way.
 
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Mains power and non insulated terminals combined with non-earthed metal work !!!
Or is that an earth tag attached to the transformer bolt?

You live very dangerously.

I hope we continue to hear from you.

The earth has crimped end, which is bolted to the transformer bolted to the case.

The mains wires are heat shrunk although a fuse is yet to be added as I initially want to get it working.

Also the tape one the positive wires coming out of the transformer is temporary until it works, when it will be covered in heat shrink.

Thanks for the suggestion.
 
The power looks OK. (Except I would have installed a fuse and switch in the AC feed...covered for safety, of course)

If you are using a common ground source and a 4 wire feed (ipod or computer) and the "in" and "gnd" were reversed on the left channel amp connections then the left would provide no output.

Connect to one amp at a time to test.

Is the left amp the top or the bottom?

The top amp IC pins look a little bent. Might have shorted or twisted the copper pads on the bottom of the board.

Just a guess.

:)

The wires to the ice are a little twisted although they do not touch and that is the right channel, which works.
 
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The power looks OK. (Except I would have installed a fuse and switch in the AC feed...covered for safety, of course)

If you are using a common ground source and a 4 wire feed (ipod or computer) and the "in" and "gnd" were reversed on the left channel amp connections then the left would provide no output.

Connect to one amp at a time to test.

Is the left amp the top or the bottom?

The top amp IC pins look a little bent. Might have shorted or twisted the copper pads on the bottom of the board.

Just a guess.

:)

I changed the input and output around on the left channel and it works. It was so obvious but I just didn't see it. Thanks
 
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This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.