TL972: TL972 with audio application

Hirotaka Matsumoto

Part Number: TL972
Other Parts Discussed in Thread: RC4580

Hi all

Would you mind if we ask TL972?

Please refer to the attachment file?
20171026_TL972.pdf
In the first place, should we confirm this query at Audio forum?

Kind regards,

Hirotaka Matsumoto

over 6 years ago

0 José Luis over 6 years ago

TI__Mastermind 20085 points

Hi Matsumoto-san,

One of my colleagues will be responding soon with further information.

Best Regards
José Luis Figueroa
Audio Applications Engineer

0 Hirotaka Matsumoto over 6 years ago in reply to José Luis

Guru 27525 points

Jose san

Thank you for your reply!

OK, we are waiting for your reply.

Kind regards,

Hirotaka Matsumoto

0 Hirotaka Matsumoto over 6 years ago in reply to Hirotaka Matsumoto

Guru 27525 points

Jose san

Could you let us know your circumstance?

Kind regards,

Hirotaka Matsumoto

0 Hirotaka Matsumoto over 6 years ago in reply to Hirotaka Matsumoto

Guru 27525 points

Hi team

We guess that your team is so busy, however could you give us the reply?

Kind regards,

Hirotaka Matsumoto

0 Ivan Salazar over 6 years ago in reply to Hirotaka Matsumoto

TI__Guru* 95355 points

Hi Matsumoto-san,

I apologize for the delayed response.
We're not very involved on TL972 as it is more like a general purpose OpAmp. With higher R2 the noise is gone? Or is it just reduced?
This is intended for an inverting configuration, right?

Best regards,
-Ivan Salazar
Applications Engineer - Low Power Audio & Actuators

0 Hirotaka Matsumoto over 6 years ago in reply to Ivan Salazar

Guru 27525 points

Ivan san

Thank you so much for your reply!
And we were sorry to rush you.

With higher R2 the noise is gone? Or is it just reduced?
->As our customer's recognition, the noise is gone.(However, they might just not hear as the noise.)

This is intended for an inverting configuration, right?
->Yes, it is inverting configuration.

Kind regards,

Hirotaka Matsumoto

0 Ivan Salazar over 6 years ago in reply to Hirotaka Matsumoto

TI__Guru* 95355 points

Matsumoto-san,

When customer tried with higher R2, did they increased the value of R1 as well in order to obtain the same gain level?
Perhaps something is driving the TL972 into instability.
Is my understanding correct that there is an additional stage at the output of TL972? If that is the case, have you tried to disconnect TL972 output and check if the noise is still there?

Best regards,
-Ivan Salazar
Applications Engineer - Low Power Audio & Actuators

0 Hirotaka Matsumoto over 6 years ago in reply to Ivan Salazar

Guru 27525 points

Ivan san

Thank you for your support always!
Our customer confirms these, so we will feed back soon.

Kind regards,

Hirotaka Matsumoto

0 Hirotaka Matsumoto over 6 years ago in reply to Hirotaka Matsumoto

Guru 27525 points

Ivan san

We will attach the file as below.(Please refer to P3 to P5)
20171115_TL972.pdf

We appreciate your help always!

Kind regards

Hirotaka Matsumoto

0 Ron Michallick over 6 years ago in reply to Hirotaka Matsumoto

TI__Guru*** 140136 points

Hirotaka-san,

I will be supporting this thread now.
I have only one question, Is it just one sample of TL972 that does or do many or all TL972 do this?

This looks like popcorn noise which is a rare occurrence.
It is also called burst noise, impulse noise, bi-stable noise, or random telegraph signal (RTS) noise.

0 Ron Michallick over 6 years ago in reply to Ron Michallick

TI__Guru*** 140136 points

Hirotaka-san,

If all TL972 do this, then check your power supplies for this same noise. Alos check for strong electromagnetic noise sources. Try using a faraday cage , batteries, and fully shielded cables. I often use a metal paint can for a faraday cage. (be sure lid is good electrical connection)

0 Hirotaka Matsumoto over 6 years ago in reply to Ron Michallick

Guru 27525 points

Ron san

Thank you for your reply.

If all TL972 do this, then check your power supplies for this same noise.
->Yes, all TL972 do this. And then, our customer uses power source with battery or stabilized power supply. The result was the same.
   And, our customer uses shielded cables. The result was the same.
   As our customer's suggestion, it seems that TL972 emits the noise.
   If you have some additional advice, could you give us?

Kind regards,

Hirotaka Matsumoto

0 Ron Michallick over 6 years ago in reply to Hirotaka Matsumoto

TI__Guru*** 140136 points

Hirotaka-san,

I strongly believe that the power source wiring (even when using batteries) is not inside a faraday cage. The signal capture is likely a nearby cell phone. I was able to replicate a similar signal by putting TL972 amplifier in the cage and having power source outside cage.

Here is a 100 dB gain output with cell phone close to power leads.

Due to the schematic differences between 972 and 4580, 4580 should have better power supply EMI rejection.

I saw greatly reduced output signal when doing the same test with Texas Instruments RC4580

0 Hirotaka Matsumoto over 6 years ago in reply to Ron Michallick

Guru 27525 points

Ron san

Thank you so much for your reply!
We told our customer to confirm with the cage.
We will feed back you as soon as we can.

Kind regards,

Hirotaka Matsumoto

0 Hirotaka Matsumoto over 6 years ago in reply to Ron Michallick

Guru 27525 points

Ron san

Thank you so much for your support!
Our customer could confirm your saying.

Kind regards,

Hirotaka Matsumoto

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TL972: TL972 with audio application