My MF A3-24 DAC takes feed from a Squeezebox Touch streamer, and it would sometimes make a rather loud pop corn noise when the s/pdif stream changes sample rate.
Much thanks to member georgehifi for his posts presenting the schematic diagrams. I realized the A3-24 has no hardware muting implementation, and its muting by the serial control bus is obviously in need of a helping hand. So I made a simple muting circuit and it serves well in silencing the pop noise.
The muting mod circuit takes Error output from the s/pdif receiver monitor(part of CS8420) and mutes the DAC chip PCM1738 immediately. The circuit also sustains the mute for a few hundred milliseconds after the Error condition has gone.
MF A3-24 seems to be a rarely mentioned DAC in the forum, but if you happen to have one, and it takes s/pdif feeds from a variable sample rate source, such as a network streamer or a USB-spdif interface device, the pop noise can be a nuisance, and this little mod may help.
Much thanks to member georgehifi for his posts presenting the schematic diagrams. I realized the A3-24 has no hardware muting implementation, and its muting by the serial control bus is obviously in need of a helping hand. So I made a simple muting circuit and it serves well in silencing the pop noise.
The muting mod circuit takes Error output from the s/pdif receiver monitor(part of CS8420) and mutes the DAC chip PCM1738 immediately. The circuit also sustains the mute for a few hundred milliseconds after the Error condition has gone.
MF A3-24 seems to be a rarely mentioned DAC in the forum, but if you happen to have one, and it takes s/pdif feeds from a variable sample rate source, such as a network streamer or a USB-spdif interface device, the pop noise can be a nuisance, and this little mod may help.
Attachments
I'm experimenting with a PCM1793 DAC right now. I connected the zero out pin to the mute pin to try to achieve the same result and have found it pop free as well. I see the PCM1738 has a separate left and right zero out pin so it's not quite as simple as my application.
I see PCM1793 and PCM1738 have similar zero detection in the datasheet. Never thought of using them to mute the chip itself. Not sure that would work for me in the case of the A3-24 DAC implementation, as I really wanted a muting coming straight from the very front end to reach the DAC chip immediately when there is an interruption to the s/pdif input, before the group delays of the sample rate converters. The CS8420, used as the front end receiver in the A3-24, is known to behave badly when there is an interruption to its s/pdif input and requires special care in application. What are you using as the front end?
I'm using a WM8804 in hardware mode for my front end. I've just begun testing live but no pops or bangs so far. My last DAC was awful! I have the mute pin of the DAC and all the flag pins of the WM8804 connected to a microcontroller just in case it doesn't work out.
- Status
- Not open for further replies.