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Chip Amps Amplifiers based on integrated circuits

Running two LM1875 mono amp from single psu
Running two LM1875 mono amp from single psu
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Old 25th May 2014, 06:54 PM   #11
danielwritesbac is offline danielwritesbac  United States
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A 2 ampere transformer could do the job for a pair of LM1875 chips.

The transformer in the photo looks too small; however, if it is a 1 ampere transformer, just buy another and make monobloc amplifiers (one transformer per each chip).
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Old 27th May 2014, 01:14 AM   #12
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by danielwritesbac View Post
The transformer in the photo looks too small; however, if it is
a 1 ampere transformer, just buy another and make monobloc
amplifiers (one transformer per each chip).
Hi,

Whatever it is, two will be twice as good as one at that size

rgds, sreten.
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Old 2nd June 2014, 09:08 AM   #13
danielwritesbac is offline danielwritesbac  United States
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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.
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Old 2nd June 2014, 01:14 PM   #14
si82 is offline si82  United Kingdom
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Quote:
Originally Posted by DUG View Post
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.

Last edited by si82; 2nd June 2014 at 01:38 PM.
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Old 2nd June 2014, 01:17 PM   #15
si82 is offline si82  United Kingdom
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Quote:
Originally Posted by KatieandDad View Post
I can't see any insulation between the boards and the chassis.
The bottom of the circuit boards have an insulating double sided sponge although I have not stuck them down yet as I want to get them working and fused first.

Thanks for the suggestion.
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Old 2nd June 2014, 01:22 PM   #16
si82 is offline si82  United Kingdom
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Quote:
Originally Posted by AndrewT View Post
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.
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Old 2nd June 2014, 01:23 PM   #17
si82 is offline si82  United Kingdom
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Quote:
Originally Posted by DUG View Post
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.

Last edited by si82; 2nd June 2014 at 01:39 PM.
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Old 2nd June 2014, 01:28 PM   #18
si82 is offline si82  United Kingdom
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Quote:
Originally Posted by DUG View Post
I missed that.



That looks like a definite problem.
If you try turning a piece of paper with three distinct marks through 180 degrees you will see it is correctly wired on the power supply side.
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Old 2nd June 2014, 02:06 PM   #19
Mark Whitney is online now Mark Whitney  Netherlands
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Power connections are correct its the input and output connections on one board that are switched (not the polarity but the location). Place the boards next to each other to see the problem.
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Old 2nd June 2014, 03:29 PM   #20
si82 is offline si82  United Kingdom
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Quote:
Originally Posted by DUG View Post
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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