Hey guys got a very good sounding dac it uses these LT1819 for the balanced or single ended output buffer. Is there anything better??
(Note these run on +-5v rails, +- 6v max)
https://www.analog.com/media/en/technical-documentation/data-sheets/18189fb.pdf
Cheers George
(Note these run on +-5v rails, +- 6v max)
https://www.analog.com/media/en/technical-documentation/data-sheets/18189fb.pdf
Cheers George
Hi George - I'd take a look at ADA4898-2 primarily because its much lower noise.
https://www.analog.com/media/en/technical-documentation/data-sheets/ADA4898-1_4898-2.pdf
Bandwidth and slew rate are lower but I doubt they're called for in a DAC assuming there's some filtering prior to the output buffer.
https://www.analog.com/media/en/technical-documentation/data-sheets/ADA4898-1_4898-2.pdf
Bandwidth and slew rate are lower but I doubt they're called for in a DAC assuming there's some filtering prior to the output buffer.
Thanks, abraxalito.
Hmmm, the LT has an input impedance of 5mohm (fet input?) where the ADA is only 5kohm (bi-polar input?), which says to me the if the stage before is as I suspect the discrete R2R ladder dac resistors they'd prefer the higher fet input load??
Cheers George
Hmmm, the LT has an input impedance of 5mohm (fet input?) where the ADA is only 5kohm (bi-polar input?), which says to me the if the stage before is as I suspect the discrete R2R ladder dac resistors they'd prefer the higher fet input load??
Cheers George
Attachments
So do you think neither will have any loading effect on the output of the R2R ladder stage, as I worry about reducing dynamic swing of the ladder stage. As it is now this dac kicks some seriouse **** in dynamic ablity, hate to loose even a little of that.
Oh also it's all direct coupled, at the moment geting around 10mv dc offset on both channels , do you think this will be better or worse with the ADA's
Cheers George
Oh also it's all direct coupled, at the moment geting around 10mv dc offset on both channels , do you think this will be better or worse with the ADA's
Cheers George
Now I've seen the picture of the PCB it looks like that buffer is fed direct from the R2R ladder. Which means current noise is more of an issue than voltage noise and the ADA4898-2 has higher current noise than the LT1819. So I need to look for a lower current noise solution. Off the top of my head I would try OPA2210 as I recall that's pretty good current noise-wise.
I will look into the offset issue and get back to you on it.
I will look into the offset issue and get back to you on it.
I would think that the OPA2210 was specifically selected for its very high bandwidth and slew rate in this position. A resistor ladder DAC is not exactly the nicest place to be for an opamp.
Mind you, if you have a high-spec ADC or audio analyzer at hand, I might toss an OPA1656 at it and see what that does in terms of IMD(f) and THD(f). Not quite as low in voltage noise as the OPA2210, with a fair bit of 1/f (though current noise is negligible), but roughly 3 times as fast.
Mind you, if you have a high-spec ADC or audio analyzer at hand, I might toss an OPA1656 at it and see what that does in terms of IMD(f) and THD(f). Not quite as low in voltage noise as the OPA2210, with a fair bit of 1/f (though current noise is negligible), but roughly 3 times as fast.
Just found a little more on these LT1819's if you gfuys see any extra you can comment on.
https://www.analog.com/en/resources...rocess-large-signals-with-low-distortion.html
Cheers George
https://www.analog.com/en/resources...rocess-large-signals-with-low-distortion.html
Cheers George