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Old 10th August 2009, 05:17 PM   #1
Jamh is offline Jamh  United States
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Default compact lm1875 amplifier

Finally got around building the briangt lm1875 amp and wanted to share its construction. What attracted me was the small size, but I am very pleased with the sound. I did a A/B comparison with a couple of amps and it may have come on top (class D, tube and LM38xx).

Parts can be ordered here (I deviated in the power supply somewhat):
http://www.chipamp.com/lm1875.shtml

Here you see the finished amp and power supply with a CD for a sense of scale.
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Old 10th August 2009, 05:20 PM   #2
Jamh is offline Jamh  United States
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The amp accepts two inputs that you can toggle between with a dip switch. One goes to my PC and the other to my IPOD. Volume is controlled by the computer/IPOD themselves.
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Old 10th August 2009, 05:24 PM   #3
Jamh is offline Jamh  United States
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Inside of the amp. Even with the small enclosure there is plenty of space to keep the signal away from the power cables. The heat sink is nicely oversized and only gets lukewarm to the touch.
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Old 10th August 2009, 05:29 PM   #4
Jamh is offline Jamh  United States
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The cramped inside of the power supply. The final power is +/- 26V to the amp. The transformer is a high quality one I pulled from a 60s dual amp (a $10 garage sale), same with the on/off switch. I was quite surprised at the components used in the dual, a couple of nice sterero pots, lots of quality resistors and caps too.

Notice the way the dual folks attached the tranny to the chassis with rubber to dampen vibrations.
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Old 10th August 2009, 05:38 PM   #5
Jamh is offline Jamh  United States
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Even with my noisy PC, this amp is dead quiet. With the computer volume turned all the way down, you can't tell if the amp is on or off with your ears next to the speakers. I opted for all the extra stuff such as the zobble and extra caps. Only the power supply's box is grounded to power. The amp's ground is the signal ground coming from the computer. Also the use of mini jacks helps with ground loops since only one ground signal is carried through.

I've had many difficulties cutting down the noise of my computer (it is a HTPC and connected to the Shaw cable). I can say with certainty that it is finally done.
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Old 24th August 2009, 07:06 PM   #6
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VERY nice.
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Old 24th August 2009, 07:15 PM   #7
Dr_EM is offline Dr_EM  United Kingdom
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Old 24th August 2009, 08:29 PM   #8
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Not here either. Probably some tuning?
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Old 24th August 2009, 10:04 PM   #9
PJPro is offline PJPro  England
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Fine for me.
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Old 25th August 2009, 12:50 AM   #10
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They didn't work for me the first time around. I just reloaded the page and now they're showing up. Cute amps!
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