Author Topic: Opamps for audio: What's the voltage noise king these days (late 2024)?  (Read 1074 times)

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Offline cvancTopic starter

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Has anyone gone past the LT1115?  AFAIK that's still the quietest when discussing voltage noise?  Thanks.

www.analog.com/media/en/technical-documentation/data-sheets/lt1115fa.pdf
 

Offline Someone

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Re: Opamps for audio: What's the voltage noise king these days (late 2024)?
« Reply #1 on: September 26, 2024, 08:18:33 am »
If only there was a carefully curated list of parts with their relevant parameters that could be searched and sorted to find out such information.....
 

Offline David Hess

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Re: Opamps for audio: What's the voltage noise king these days (late 2024)?
« Reply #2 on: September 27, 2024, 11:38:14 am »
The comparable Texas Instruments part is the OPA1611/OPA1612.

For not quite as low noise but more useful higher source resistance, a JFET part like the OPA1641 or OPA1655 is better, or the CMOS OPA1677.

If you really need lower input voltage noise at any cost, then a discrete input stage or multiple operational amplifiers in parallel is still required.
 

Online magic

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Re: Opamps for audio: What's the voltage noise king these days (late 2024)?
« Reply #3 on: September 27, 2024, 11:46:12 am »
ADA4898 is supposed to come very close at a much higher speed.
 

Offline David Hess

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Re: Opamps for audio: What's the voltage noise king these days (late 2024)?
« Reply #4 on: September 27, 2024, 10:05:07 pm »
The ADA4898 achieves lower noise by not having input bias current cancellation, which should not be required in an audio application anyway, but is also a 2-stage design so I would expect higher distortion which seems to be born out in the specifications.  I guess they try to make up for that with a more linear input stage.
 

Online magic

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Re: Opamps for audio: What's the voltage noise king these days (late 2024)?
« Reply #5 on: September 28, 2024, 05:30:41 am »
For the record, everybody except Douglas Self calls this a single stage design.

Distortion is only speced above 100kHz, but the slopes are increasing so it should be better below 100kHz.

This seems related to AD797, which has the same voltage noise except near 20Hz, and has been tested by Samuel Groner to be one of the lowest distortion opamps out there. In particular, it is essentially unaffected by 600Ω loading and apparently drives 200Ω better than TI's OPA211 (industrial version of OPA1611) drives 600Ω.
 

Offline David Hess

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Re: Opamps for audio: What's the voltage noise king these days (late 2024)?
« Reply #6 on: September 29, 2024, 11:30:10 am »
Distortion is only speced above 100kHz, but the slopes are increasing so it should be better below 100kHz.

Do not underestimate marketing.  If the slope changed below 100 kHz and distortion increased, they could leave it out of the datasheet.  The only way to really know is to test it.
 

Offline 0xFFF0

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Re: Opamps for audio: What's the voltage noise king these days (late 2024)?
« Reply #7 on: September 29, 2024, 01:04:01 pm »
 

Offline MasterT

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Re: Opamps for audio: What's the voltage noise king these days (late 2024)?
« Reply #8 on: September 29, 2024, 02:35:14 pm »
I come accross this thread:
https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/421088/op-amp-dirty-little-noise-secrets
 And indeed LT1028 chart shows :
2386485-0
 Same time LT1115 DS hide this misbehavior , but comparing Gain-Phase charts of both LT products:
2386489-1 it's obvious that LT1115 'd have same abnormal noise hump at 400 kHz.
 

Edit: picture 1 & 2 swapped, can't get it right.
« Last Edit: September 29, 2024, 02:36:49 pm by MasterT »
 


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