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Cheap as Chips OPA1688 Low-THD Muscle Amp
Cheap as Chips OPA1688 Low-THD Muscle Amp
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Old Yesterday, 07:53 AM   #91
Dibya is offline Dibya
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Shaq888 Good to see someone like me who is still using XP
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Old Yesterday, 08:14 AM   #92
Shaq888 is offline Shaq888  Ukraine
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I that case its not actually a choice. It comes as a device OS.
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Old Yesterday, 03:37 PM   #93
xrk971 is offline xrk971  United States
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Cheap as Chips OPA1688 Low-THD Muscle Amp
Here is a DIY'able single-layer board layout for a pair of paralleled buffers in SOIC8 that JPS64 made. It includes some nice low ESR caps (390uF 20v OSCON + 10uF X7R + 0.1uF X7R for both rails at the power supply pins) and also the option to cap-couple the input or output.

Cheap as Chips OPA1688 Low-THD Muscle Amp-opa1688-2parallel-buffer-copper-eetch-layer-png

Schematic (note, for balanced opamp inputs (w/ pot at full volume) use R104 & R105 = 1.72k, and R111 & R112 should be high quality metal thin film, or carbon film, but not thick film):
Cheap as Chips OPA1688 Low-THD Muscle Amp-opa1688-2parallel-buffer-schematic-png

Files below: schematic, copper etch layer, and placement guides for top and bottom.
Attached Images
File Type: png OPA1688-2Parallel-Buffer-Copper-Eetch-Layer.png (73.5 KB, 78 views)
File Type: png OPA1688-2Parallel-Buffer-Schematic.png (133.7 KB, 78 views)
Attached Files
File Type: pdf OPA1688_CMOY_ETCHED_SCH_00a.pdf (25.4 KB, 5 views)
File Type: pdf ETCHING_LAYER.pdf (42.2 KB, 4 views)
File Type: pdf PBA-TOP.pdf (12.1 KB, 6 views)
File Type: pdf PBA-BOT.pdf (10.6 KB, 4 views)
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Last edited by xrk971; Yesterday at 03:50 PM.
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Old Today, 02:48 AM   #94
Shaq888 is offline Shaq888  Ukraine
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I can see that due to limitation of a single layer layout it is a bit hard to optimize position of the "output stage" supply rail lines. Since this is essentially a class B stage, those rails will be carrying rectified load current, which will induce even harmonics in signal tracks. For circuit like that it can be easily a limiting factor if it's driving a low impedance load. Using a twisted pair of a hook up wire to bring supply to those opamps can help to avoid this problem.
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