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OPA172: Single-Supply, Electret Microphone Pre-Amplifier for OPA172 how to impore gain

Lawrence He
Genius 3280 points
Part Number: OPA172
Other Parts Discussed in Thread: TINA-TI

Dear

our client design opa172 as attached, and lastet question we got  the answer from Ronald Michallick as below link:

https://e2e.ti.com/support/amplifiers/etc_amplifiers__other_linear/f/18/p/673295/2477893#2477893

8156.opa172.pdf

Assuming headphone is a 32 ohm load. there will be more voltage loss across R70 and C73. Xc=1/(6.28*2.2uF*1kHz)= 72 ohms.
Headphone voltage will be 3Vpp * 32 ohms / ( 32 ohms + 50 ohms + 72i ohms)
3Vpp * 32 ohms / ( 82 ohms + 72i ohms)
3Vpp * 32 ohms / sqrt ( 82^2+ 72^2) ohms
0.88Vpp ; this is close to actual green signal, so problem identified.

so OPA172 is correct soultion? and  how to enhance gain ,we cannot assign customer use low resisger headphone to test.

If any suggestion, Please advise me.

Thanks,

Best regards,

Lawrence.

TI Designs – Precision: Verified Design
Single-Supply, Electret Microphone Pre-Amplifier
Reference Design

  • 0
    Guru 140200 points
    Hi Lawrence,

    a TINA-TI simulation shows that you cannot get out more than 2Vpp undistorted output signal when directly driving a 32R load (R70=0). More is not possible, because the OPA172 is not a headphone amplifier but an OPAmp designed for driving >600R loads. Or by other words, this is not a question of gain but an output strength issue of OPA172.

    Kai