ATDAC-92

We have been asked many times about the multi channel DAC, more advanced than very simple ATDAC-91, but cheaper than ATDAC-9, for multi channel (5.1-7.1) and multi-band applications.

Also some people asks about more then 8 channels - to build multi-channel and multi-band system, for example - 7.1 home cinema system with multi-band front and center speakers and DBA (Double Bass Array sub woofer).

As a result, ATDAC-92 was designed.

The basic version is 8-channel, supporting PCM from 44.1

up to 192kHz, bit depth - up to 32 bits.

There is no DSD support, because there is no way to do digital crossover without converting DSD to PCM, and so no sense to the back conversion to DSD.

The USB input (XMOS) has the main features of the xV / xVM USB interfaces, as:

- UAC2 asynchronous operation,

- powering of the USB part from the PC,

- full galvanic isolation of the DAC from the USB part,

- clocking from an oscillator located near the DAC chip,

- Clock Monitor, which allows the PC "not to notice" the absence of the clock from the DAC, for example, if the DAC is powered off.

The DAC is based on the AK4458 chip and LM49723 based Low Pass Fillter/Output Buffer.

ATDAC-92 is powered from two power sources (not included):

1) + 5-7VDC, up to 50mA to supply the digital circuits.

2) +/- (15-20) VDC, up to 30-40mA on the minus and up to 60-70mA on the positive power supply.

As you can see, the power consumption is not exceeds 2 watts in the worst case.

The LM317 / LM337 (TO-220) voltage regulators  can be installed without the heat sinks (just 16 channel version can require).

ATDAC-92 can be extended to 16 channels, with a daughter board.

The maximum sampling rate at 16ch configuration is 96 kHz (the restriction is caused by a limited band pass of the USB stack in XMOS and it's the driver).

The nominal output voltage (0dBFs) is 2.3Vrms.

Both the 8-channel and 16-channel versions can be supplemented with a small CPU daughter board (under development now) to extend the functionality:

- volume control (digital), with indication,

- 7-segment LED display, volume and sample rate indication,

- DAC digital filters switching, with indication,

- control of (external) mute relays.

Functional diagram:

ATDAC-92L - light version.

ATDAC-92L was designed as a part of  DMCS project, which will be presented soon.

ATDAC-92AU - automotive!

In addition,the special automotive version was designed.

Differences from the regular ATDAC-92:

• built-in 2-step converter for power supply from the vehicle’s on-board network, 12V, with additional filter and protection.

• 2-step converter allows you to work in a wide range of supply voltages, often possible in a car - theoretically from 4.8 to 20V.

• There is no connection of "daughter cards".

• The USB part is powered not from the USB bus but from the DAC. (so-called "SELF POWER" instead of "BUS POWER").

Why self, despite the fact that it increases the device cost?

The current consumed from the USB port is quite large in the case of bus power. For example, for fully USB-powered DACs and transports (ATDAC-8A / AM / AX, xV / xVM), it can reach the limit for USB 500mA.

OK, USB port in Car-PC can supply this current, the problem is in the cable - those who do not know Ohm’s law can no longer read, but those who know, should understand what will happen if a device with a large current is connected via  5-meter cable, especially if this cable equipped  with thin wires.

And, If at home, a DAC can be placed near PC, on a 15-50cm cord, then for automotive use case, I would be good to use a longer cord. What if the Car-PC located in the front, and the DAC with amplifiers in the trunk?

In the case of self power, the 5v bus on USB is only a signal and not a power supply, the current through it is less then 1mA, and this current will not limit the length of the cable. It is needed only for signaling the USB interface that the device is  connect to the USB port.

Block diagram of the device:

The device consists of three parts, galvanically isolated from each other:

1) On-board power, filter, protection, primary regulator

2) USB transport (XMOS XUF208)

3) DAC, based on AK4458 with output filters (OPA1662 or LME49723).

To have analog part isolated from USB (Car-PC) and also from the main 12V bus is useful for eliminating any "ground loops" when connecting to amplifiers (And if a pseudo-balance connection is used, then it will be just great!)

Output voltage - 2.3 Vms.

Supported formats: PCM 44.1-192kHz, 32 bits.

It is possible to remotely turn on / off the power of the entire device (in the off state, consumption is micro amperes). In the current version, by default, the device is turned on, to turn it off, you need to close the control signal to the ground (everything in the 12v car potential).

The measurements are mostly the same as with regular ATDAC-92 version, but you can see the exact 92AU one: