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AK4493 DAC
AK4493 DAC
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Old 16th February 2019, 08:09 AM   #21
hidjedewitje is offline hidjedewitje  Netherlands
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Quote:
Originally Posted by sesebe View Post
It is forbidden to put a capacitor from the output of a voltage amplifier to ground if you do not want problems.
I don't quite follow you there. Why is a capacitor to ground forbidden?

Is it because of the phase shift caused at higher frequencies and possibly creating 360 degrees?

Or is it perhaps the inrush current?
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Old 16th February 2019, 09:01 AM   #22
chris719 is online now chris719  United States
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Originally Posted by sesebe View Post
With a very large cap the current limitation of the op-amp will limit the voltage excursion to a level that can't generate oscillation but the problem remain and the noise problem that is mentioned above is a good example.
A L-C filter will have an effect in a much wider band than any shunt or LDO regulator.



If you know something more please do a demonstration (mathematically).
I am not saying it is a good idea. It's used by a lot of people following the ESS app note, for example, without noise problems to my knowledge. I don't really have the time or interest to investigate it mathematically as I wouldn't do it in the first place.
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Old 16th February 2019, 09:14 AM   #23
hidjedewitje is offline hidjedewitje  Netherlands
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Originally Posted by chris719 View Post
I am not saying it is a good idea. It's used by a lot of people following the ESS app note, for example, without noise problems to my knowledge. I don't really have the time or interest to investigate it mathematically as I wouldn't do it in the first place.
How would you solve this problem then? I'll look into it myself then when I get the time!
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Old 16th February 2019, 09:21 AM   #24
chris719 is online now chris719  United States
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Originally Posted by hidjedewitje View Post
How would you solve this problem then? I'll look into it myself then when I get the time!
I'd use an LT3042 and be done with it .
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Old 16th February 2019, 12:54 PM   #25
sesebe is offline sesebe  Romania
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Quote:
Originally Posted by hidjedewitje View Post
I don't quite follow you there. Why is a capacitor to ground forbidden?

Is it because of the phase shift caused at higher frequencies and possibly creating 360 degrees?

Or is it perhaps the inrush current?
What you want to obtain punting a big capacitor at the output of an operational amplifier?

Can you explain?

A capacitor to ground it is used to filter the noise BUT the opamp it is put there to generate a CORRECTED signal that not need a capacitor to shunt to ground the noise. Finally the capacitor will shunt to ground most of the noise and the opamp will try to adjust the same thing.
Every body will try to do the same thing BUT their actions will be in opposite directions and will be neck to neck.

Anyhow, audiophile is a serious illness that likes to complicate unnecessarily.
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Old 16th February 2019, 01:10 PM   #26
hidjedewitje is offline hidjedewitje  Netherlands
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Quote:
Originally Posted by sesebe View Post
What you want to obtain punting a big capacitor at the output of an operational amplifier?

Can you explain?

A capacitor to ground it is used to filter the noise BUT the opamp it is put there to generate a CORRECTED signal that not need a capacitor to shunt to ground the noise. Finally the capacitor will shunt to ground most of the noise and the opamp will try to adjust the same thing.
Every body will try to do the same thing BUT their actions will be in opposite directions and will be neck to neck.

Anyhow, audiophile is a serious illness that likes to complicate unnecessarily.
Well the datasheet of the AK4493 states that a high capacitance on the VREF pin is recommended. I wanted to use a very stable voltage reference and came across the LTC6655 5V reference.

The LTC6655 doesn't like high currents or high capacitors. Diyaudio user Thorb showed me that manufacturers sometimes buffer the voltage reference. So I started looking for buffers. I am most comfortable with using opamps so I started looking there.

Now I am getting feedback that opamps are not recommended for this application. I do not understand why exactly.
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Old 16th February 2019, 01:56 PM   #27
sesebe is offline sesebe  Romania
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Try with a resistor of 0.5-1ohm (maybe more) between LTC6655 output and capacitor.
The LTC will be harpy with this. I do not know about the DAC.
Personally I will use only a LC filter without the LTC.
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