Building the $99 ES9018 DAC Board (Part II)
You can read part I here: [link]
You can also read another build log here: [link]
VERSIONS OF DIYINHK BOARDS
I have been able to identify 5 different versions. My board is V2. Each version has a new input pin configuration and/or other enhancements.
V1: Hardwired for I2S plus additional SPDIF iputs
V2 (my board). Access to all the inputs (must cut the shorting trace for I2S), more chip bypass.
V4. Introduces a contiguous ground plane (big deal) and other enhancements:
Another V4 board [link]:
V5. Separates AVCC-L and AVCC-R:
SEPARATING AVCC-R AND AVCC-L (IN EARLIER VERSIONS OF THE BOARD)
Easy mod to separate the power connections for AVCC for the right side and the left side.
The board neatly connects the left and right side AVCC pins as shown in this photo [link] of V4 of the board, showing the main trace for AVCC that is under the DAC chip. On the other side of the board are bridges from the main trace to the individual AVCC pins. Cutting those bridges effectively separates AVCC-R from AVCC-L.
Here is a photo of V2. It seems that the bridge pattern matches the AVCC trace of the V4 board. I’ve measured the connections of all the bridges and they connect to AVCC.
Here is an overlay of the V2 board traces on the V4 front side photo. Seems like a workable solution. You can also see that each of the 8 AVCC pins has its own bypass capacitor. Hmmm, since there are 8 internal DACs in this chip, this means each internal DAC has its own supply pin.
Connecting the AVCC-R traces together:
And cut the bridges:
Measurements confirm that the AVCC-R and AVCC-L are no longer connected. This mod should work at least in V2 and V4 boards.
Separately powering AVCC-L and AVCC-R has audible advantages as reported by diyinhk [link]:
Separating the ES9018 AVCC_R/L power supplies provide a much more 3D sound stage. The location of every instrumentals is much much more clear
It’s like listening the differences between an upright piano and a grand piano.
This is really a breakthrough even after many layout improvements since the first version. I finally know why many diy’ers want dual mono config or at least a seperate AVCC_R/L power supply.
One option is to use TPA’s AVCC which is a dual shunt regulator board. A diyer just did that [link]:
Since I updated the AVCC board in my BII DAC [link], I also have the older version to use.
ESS OPAMP BUFFER
Another option is to use the ESS opamp buffer as specified in the ESS documentation [link].
ESS specifies a single buffer for both channels, but this was for their original ES9018 evaluation board with a 40 MHz clock and 3.3V supply. If one uses a faster clock and increase the operating voltage a bit above the 3.3V, then the power requirement would be higher as shown in this graph:
Notice that if the clock frequency is 100 MHz, then the current requirement for AVCC at 3,3V is beyond 50 mA. Most opamps max out around 50 mA, thus using two opamp buffers makes a lot sense.
After upgrading my Buffalo II with the AVCC 2.1, the original AVCC v1 became available. No reason not to reuse it.
Removing AVCC module from BII: It wasn’t easy to desolder it from the BII (I had soldered the module to the pins rather than using the pin header for plug-in). Luckily the two “IN” connectors are tied together so connecting the input on one side is sufficient.
With cat-5 cables making 4 connectors, it can fit on the board connecting GND and AVCC L and AVCC R
Connecting to AVCC L pin and AVCC R pin (after separating AVCC) and ground pads
The input to AVCC needs to be 5V (5.5V is maximum for this version of the AVCC board). It can be fed externally without connecting FB3. This way the AVCC/2 offset voltage used by the opamps can be generated without any modifications. For ultra-accuracy, the AVCC/2 offset voltage can be separated between L and R by using a similar resistor divider (externally implemented) for the other channel and by cutting the AVCC/2 offset line between L and R channels
I also tested it to ensure good working condition:
It is designed for 3.5V output. The output would settle to about 3.51V because the reference voltage is based on an LED and LEDs have a negative temperature coefficient, so as it warms up, its forward voltage decreases slightly.
This module has “uneven” LED brightness. It was like this since day one [link], but TPA assured me that it is of no consequence. I tested it with a 70 ohm load (drawing 50 mA per side) and measure the output with my rudimentary mini scope. The output looks clean.