ADC AK5572 v1.2 available

14.8K

ADC AK5572 boards are available again, in slightly modified version 1.2. Despite a rather long list of changes there are no differences in performance and no major changes in functionality.

Note that there is also v1.3 now. It is the same as v1.2 except the PCB is green.

Changes are:

• XLR-connectors now fit completely on PCB
• Default maximum input signal is now 4 Vrms (instead of 3.6 Vrms) to align with other boards
  • 4 Vrms possible in single-ended signal as well; in v1.1 input protection clipping prevented this
• No reset button, just header
• Screw terminal for supplies
• Changes in default component population and settings
  • Input AC-coupling is now optional and uses bipolar electrolytics
  • Jumper header is unpopulated by default
  • ADC is I2S Slave without any jumper (opposite in v1.1)
  • Digital high-pass filter is enabled without any jumper (opposite in v1.1)
  • 32-bit I2S option removed from header and now set by 0R resistor
• Possibility to configure input buffers as instrumentation amplifier and use bottom side trimmer to adjust gain
• Wee DAC headers added at edges so that Wee DAC power supply board can be used
• Changes in input protection

Despite this list, for majority of users using the board remains exactly the same. Old feature list from v1.1 still holds:

• Up to 768 kHz / 32-bit audio
• Very high (measured) performance, typically:
  • 121 dBA dynamic range / SNR (124 dBA in mono mode)
  • -113 dB THD+N (-1 dBFS, 1 kHz)
  • -117 dB THD (-8 dBFS, 1 kHz)
  • -130 dB crosstalk (10 kHz)
• Balanced differential input
• Stereo or mono operation
• I2S output; Master or Slave
• HW configurable (supports I2C as well)

This post focuses on differences between v1.2 and v1.1. For basic information refer to the original ADC AK5572 v1.1 post.

Design

Here are some of the changes explained in more detail and what it means.

PCB

Board dimensions are the same (5x10cm, 4 layers) and major blocks are almost unchanged. Main difference is that now XLR connectors fit completely onboard and are populated by default.

Edit 02/02/2021. There is also a version 1.3 which is the same as v1.2 except the PCB is green and there are some minor changes in manufacturing the board. Everything here holds also for the v1.3.

Input circuit

AC-coupling capacitors are not populated by default but shorted with shorting links on bottom side. If capacitors are soldered, these links must be cut with a knife. When capacitors are in place, they can be shorted with jumper links on 2×2 header. Capacitors are now 10u bipolar electrolytics as opposed to 1u plastic caps in v1.1. Lower 1u capacitor caused odd low frequency noise behaviour on some boards. If you’ve got your v1.1 ADC with 1u cap don’t worry, then I didn’t see any issues with your board. As a workaround some boards were shipped with 33u through-hole bipolar electrolytic. In most cases AC-coupling caps are not needed (hence not populated by default) as digital high-pass filter takes care of small DC.

Input buffers are still the same by default. However, now there is a possibility to use them in instrumentation amplifier configuration. Furthermore, bottom side trimmer potentiometer can be used to adjust gain. This is all really for people who need this customisation, normally it is not used or needed. They are mostly for professional/studio use where gains may need to be trimmed. There is still a limitation that this gain control mostly allows increasing gain and supporting very high signal level (where attenuation is needed) with adjustable gain may not be suitable. This was more of a proof of concept to see if such trimmer configuration impacts audio performance – luckily not.

Differential amplifier stage is the same but gain is now 0.5. As ADC input range is 2 Vrms (1 Vrms per input), this gives 4 Vrms input range to this whole circuit.

There are changes in input protection. Major outcome of this is that 4 Vrms single-ended signal can now be used for maximum ADC input. In v1.1 max 2 Vrms single-ended signal was usable. Input protection is still not as robust as I want so there will still be some changes in future revisions. It doesn’t matter in normal audio use but I’d like the input to withstand almost whatever is thrown at it.

This is an evolving design and gain trimming and input protection will likely see more changes in the future.

Configuration pinheader

Large pinheader with jumper links to change settings is not populated by default now. This along with some other changes (especially use of Shorts instead of 0R resistors) saves time in assembly. To offer better default settings without the header, HPF and Master/Slave settings were inverted. The same settings are still available when the header is soldered and jumper links used. Except 32-bit I2S setting that was removed due to space constraints, and moved to be a resistor setting. After all, it doesn’t matter if I2S is 24-bit or 32-bit; there is no more information.

Settings are now as follows.

Clock configuration

CS3	CS2	CS1	CS0	Sample rate
open	close	close	open	768 kHz
open	close	close	close	384 kHz
close	close	close	close	192 kHz
close	close	open	open	96 kHz
close	open	open	close	48 kHz

When in I2S Slave mode (default), it is recommended to keep all CSx links open for automatic clock setting.

Digital filter

SD	Slo	Filter roll-off type
open	open	Sharp (default)
open	close	Slow
close	open	Short Delay Sharp
close	close	Short Delay Slow

Other settings

Jumper	Open	Close
HPF	Digital HPF enabled (default)	HPF disabled
Sla	I2S Slave (default)	ADC is I2S Master

In addition, support for Wee DAC edge headers was added. There is not really an application for that yet except that the PSU baseboard could be used as a power supply for the ADC.

Dual mono operation

Mono operation is still available for creating a dual mono ADC. It improves SNR and DR by 3 dB but comes at a cost as mono board costs almost the same as a stereo board. There is not really improvement in crosstalk as it’s already almost unmeasurable in stereo board due to completely separate circuits for channel 1 and 2. However, dual mono always remains as an interesting design philosophy in my opinion.

Measurements

Audio performance is on par with version 1.1. Based on a test batch of 7 boards there are no statistically significant differences.

Input level

By default the maximum input level that gives 0 dBFS digital signal is 4.0 Vrms. This aligns with other nihtila.com boards that use 4 Vrms level in balanced connections. In v1.1 maximum input level was 3.6 Vrms.

Another difference is that now input works as “true differential” in a way that one can get the maximum level with single-ended signal as well. So the ADC happily takes in 4 Vrms single-ended input signal. In v1.1 this was limited to 2 Vrms due to input protection clamps.

Power consumption

Power consumption figures are slightly changed, typical figures for stereo board being:

• 5VD: 12mA
• 15VA: 95mA
• -15VA: 57mA

This means that the board does get significantly warm.