I recently designed and made a digital/analogue preamplifier.
It supports multiple SPDIF sources (USB via a PCM2707, TOSLINK, Regular SPDIF). These are switched and converted to I2S by a CS8416, and then fed into a PCM5102 DAC.
The output from the DAC, along with several analogue inputs, are switched by relays and summed and buffered by a pair of LME49710 opamps.
This signal is then fed into a PGA2311 voltage control chip.
This all works well. However, I seem to be having a slight issue with noise being introduced by the DAC.
When there is no SPDIF signal being fed into the CS8416 (thus no I2S data going into the DAC), there is a small amount of noise on the output - as recorded in the attached file.
Once valid SPDIF/I2S data is played, this noise disappears. Even if the data is silence (for example a muted youtube video), it still disappears.
As soon as SPDIF data stops coming (and thus I2S data stops being generated), the noise returns.
I suspect the issue is something to do with the internal analogue muting in the PCM5102? I have tried replacing the PCM5102, however this does not fix the problem at all.
I'd very much appreciate any thoughts on the matter, and am happy to answer any questions you may have.
Many thanks,
Andy
Note - the forum won't let me upload an MP3 of the background noise as an attachment, so I've had to .zip it. Sorry!
It supports multiple SPDIF sources (USB via a PCM2707, TOSLINK, Regular SPDIF). These are switched and converted to I2S by a CS8416, and then fed into a PCM5102 DAC.
The output from the DAC, along with several analogue inputs, are switched by relays and summed and buffered by a pair of LME49710 opamps.
This signal is then fed into a PGA2311 voltage control chip.
This all works well. However, I seem to be having a slight issue with noise being introduced by the DAC.
When there is no SPDIF signal being fed into the CS8416 (thus no I2S data going into the DAC), there is a small amount of noise on the output - as recorded in the attached file.
Once valid SPDIF/I2S data is played, this noise disappears. Even if the data is silence (for example a muted youtube video), it still disappears.
As soon as SPDIF data stops coming (and thus I2S data stops being generated), the noise returns.
I suspect the issue is something to do with the internal analogue muting in the PCM5102? I have tried replacing the PCM5102, however this does not fix the problem at all.
I'd very much appreciate any thoughts on the matter, and am happy to answer any questions you may have.
Many thanks,
Andy
Note - the forum won't let me upload an MP3 of the background noise as an attachment, so I've had to .zip it. Sorry!
Attachments
I experience this problem. For me, it is the I2S signal into the DAC. With not playing music, there is noise. With music playing and digital volume is 0 (-140dB), there is not noise. With I2S disconnected, there is not noise.
Maybe you can investigate the signal into the DAC ?
Also, you use the PLL in PCM5102 and not the sclk/mclk ? Maybe you can try mclk input to PCM5102 ?
Maybe the PCM5102 expert can help....
Maybe you can investigate the signal into the DAC ?
Also, you use the PLL in PCM5102 and not the sclk/mclk ? Maybe you can try mclk input to PCM5102 ?
Maybe the PCM5102 expert can help....
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