alternative to AD8608 op amp for active filter design - ADAU1701

SigmaDSP & SigmaStudio I_love_dsp Apr 10, 2022 00:00 4 replies Original on forum ↗

I_love_dsp Question

Apr 10, 2022 00:00

Hi all,

I've been looking to implement an active reconstruction filter on the DAC output of my custom ADAU1701 however the op-amp recommended in the datasheet seems to be end of life and highly priced at the moment (at least via lcsc). Is anyone able to offer any suggestions to an alternative op-amp and accompanying circuitry or can I simply replace the op-amp in the datasheet's circuit with a similarly speced one e.g the LTC728?

Thanks in advance,

Regards

Audio Signal Processors

Operational Amplifiers (Op Amps)

reconstruction filter

amplifiers

ad8608

SigmaDSP Audio Processors

Low Input Bias Current Op Amps (≤100 pA)

adau1701

dac

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KJBob Reply

Apr 10, 2022 00:00

Hello,

This single-stage, two-pole Sallen and Key lowpass filter is not particularly fussy to implement. As long as the op-amp specs are "good enough," the filter's operation is determined by the external R's and C's, not the op-amp itself. Thus, a substitute op-amp with suitable specs should work fine. Comparing the two data sheets, the LTC728 has slightly more noise while its other major specs are comparable to the AD860x. Thus it looks like a good choice.

Best regards,

Bob

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Brewster Reply

Apr 11, 2022 00:00

The 1701 performance is much lower than typical audio op-amps. ADI does make some great high performance op-amps but they would be overkill; unfortunately mid performance low cost "commodity" audio op-amps isn't something ADI seems to make. Use a 5532.

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I_love_dsp Reply

Apr 11, 2022 00:00

Thanks for the suggestion, I'll definitely consider this op-amp

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I_love_dsp Reply

Apr 11, 2022 00:00

Thanks for clarifying that, I'll check out a few more alternatives based on this response

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