OPA1612: Filter topology for high end audio high pass filter (20 Hz) OPA1612 OPA1656

Per-Anders Sjöström

Part Number: OPA1612
Other Parts Discussed in Thread: OPA1656

I'm up to, to design a 3rd or 4th order 20 Hz high pass filter with ultra low distortion. Does anybody know design advantages of choosing a certain topology? Sallen-Key, variable state, etc? The grey book is a fine old book with thousands of variants of filter but nowhere does it say pros and cons of each type. If I google I don't get much useful info. Opamps in mind is OP1612 or OPA1656.

Grey book: Active and passive analog filter design - an introduction by Lawrence P. Huelsman (extremely theoretical)

Active-Filter Cook book by Don Lancaster (very practical book)

6 months ago

0 Chris Featherstone 6 months ago

TI__Mastermind 20060 points

Hey Per-Anders,

Thank you for considering our audio amplifiers for you design. I don't have the books you mentioned but I do have a book called Small Signal Audio Design by Douglas Self. He discusses the Sallen and Key High Pass filter in this book and also the distortion. The OPA1656 has very good THD + N. Shameless plug I just highlighted the OPA1656 in my latest application note.

https://www.ti.com/lit/an/sboa580/sboa580.pdf?ts=1704273304457&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FOPA1632

The components surrounding the amplifier will contribute the most to the THD+N. Douglas Self discusses this in his book. A few years back one of our engineers, John Caldwell also discovered certain capacitor types causing THD issues in his design. He did some write ups on this you might find helpful.

https://e2e.ti.com/blogs_/archives/b/precisionhub/posts/stress-induced-outbursts-microphonics-in-ceramic-capacitors-part-1

https://e2e.ti.com/blogs_/archives/b/precisionhub/posts/stress-induced-outbursts-microphonics-in-ceramic-capacitors-part-2

In this article John discusses the Sallen-Key low pass and shows measurement results with different capacitor types.

https://www.edn.com/signal-distortion-from-high-k-ceramic-capacitors/

I hope this information is helpful. If you have further inquiries feel free to reach out. I will read the section in the book I have to see if there are any practical pieces of information I can share.

Best Regards,

Chris Featherstone

Audio

Audio forum

OPA1612: Filter topology for high end audio high pass filter (20 Hz) OPA1612 OPA1656