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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 Today, 06:11 AM   #41
tomchr is online now tomchr  Canada
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Originally Posted by xrk971 View Post
The graph is unusual too (I have never simulated anything that has zero features before)
Not to burst your bubble too much, but THD is one of those things that is often not covered well in the simulation models. Your sim shows that you didn't make any obvious mistakes. I highly doubt measurements of the circuit will come even remotely close to the simulated values.

Regardless, it should still be a pretty nice amp. Watch the power dissipation in those itty-bitty packages, though.

Modulus-686: 240W/8Ω @ <0.00025% THD. Modulus-86: 40W/8Ω @ 0.000054% THD. DG300B & Other Tube Circuits.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old Today, 06:19 AM   #42
Shaq888 is offline Shaq888  Ukraine
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Originally Posted by xrk971 View Post
Here is an interesting surprise, I replaced the LME47720, the supposedly "king of the low THD" opamps in TI's arsenal, with the lowly OPA1688 (which is also serving as the buffer).
Simulations of THD, while using only basic functional opamp models, make no sense. It will no produce any meaningful result. Those models are made from a bunch of controlled voltage and current sources. The only nonlinear effect they usually take into account is supply rail clipping. There are transistor level models of opamps, but the one you have is not one of them.
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