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Opamp + volume control question.
Opamp + volume control question.
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Old 5th August 2019, 06:14 PM   #11
analog_sa is offline analog_sa  Europe
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Opamp + volume control question.
Originally Posted by Kay Pirinha View Post
What is meant with 'better'?
This is often a hard question, but luckily not this time

Around 1985 i wanted to design a phono pre using opamps which will beat my factory made discrete phono. Turned out to be a really frustrating exercise. The best opamps i could get at the time were 5534 and after months of frustration i conducted a simple experiment.

Set up a 5534 as a non inverting amp for a gain of around 10 into a high impedance load. A fixed attenuator at input adjusted the overall gain for unity. This made it possible to evaluate the opamp against a bypass. And it sounded nothing like the bypass. A bit of research led me to the inverting mode and a bit more research led to setting the impedances on both inputs to be equal. And voila it sounded good. Not quite like the bypass but very close.

Today there are much better opamps and the differences are not so dramatic but even so the inverting topology often sounds a bit better. Unsurpsingly, many are unconvinced or unwilling/uninterested to listen.
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Old 5th August 2019, 10:06 PM   #12
BesPav is offline BesPav  Russian Federation
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Originally Posted by Kay Pirinha View Post
Why should an inverting opamp stage tend to sound better than an non inverting one?

Because common mode error are nonlinear with common mode itself.

Originally Posted by analog_sa View Post
a bit more research led to setting the impedances on both inputs to be equal

Clearly! Input bias currents must provide equal bias voltages at both inputs.
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