I'm currently building up this dual PCM1794 DAC board and found a major issue. There appears to be 5v on both the analog differential outputs.
I soldered the PCM1794 myself using a Flux pen and the drag soldering method. The overall soldering quality looks very good with no bridges, good connections to the pads.
Upon first powering up the board I had no 3.3v, it was drawing quite high current, around 200MA. I replaced the 3.3v TO220 regulator with an ASM1117 3.3v, that's all I had. That fix that problem. When I tried putting an test tone though the DAC board I just get 5v on all the analog audio outputs when testing with my oscilloscope, I don't think this is normal.
The other IC on the board is an Cirrus Logic 8416, that's working I'm getting the SCK, BCK, LR and DT just fine. The board draws draws more power when you plug an input into it.
I really hope I haven't killed two PCM1794, there not exactly cheap!!
That black wire joins analog ground with digital ground.
I soldered the PCM1794 myself using a Flux pen and the drag soldering method. The overall soldering quality looks very good with no bridges, good connections to the pads.
Upon first powering up the board I had no 3.3v, it was drawing quite high current, around 200MA. I replaced the 3.3v TO220 regulator with an ASM1117 3.3v, that's all I had. That fix that problem. When I tried putting an test tone though the DAC board I just get 5v on all the analog audio outputs when testing with my oscilloscope, I don't think this is normal.
The other IC on the board is an Cirrus Logic 8416, that's working I'm getting the SCK, BCK, LR and DT just fine. The board draws draws more power when you plug an input into it.
I really hope I haven't killed two PCM1794, there not exactly cheap!!
That black wire joins analog ground with digital ground.
Nevermind, I found an interesting explanation here: The COD - Current Ouput DAC 🙂 The PCM179x series is a current output DAC, so without a load, anything is possible (ie. 5V output).
Also, make sure you're using 32bit frames, not 16bit.
PS: It turns out that my DAC wasn't working because of something else: the floating MUTE pin, that needed to be tied to GND.
Also, make sure you're using 32bit frames, not 16bit.
PS: It turns out that my DAC wasn't working because of something else: the floating MUTE pin, that needed to be tied to GND.
Hi,
The TI PCM-DACs are current sourcing DACs with current outputs, hence requiring a curent path to close the current loop.
For a test You can generate a output voltage by connecting a small valued resistor to gnd.
As the signal current of (+-3.9mApp) is offset by the centre current (-6.2mA), the current swings between -2.3mA and 10.1mA.
So a 33Ohm or smaller resistor should suffice (due to internal protection diodes voltage levels >300mV start getting distorted .... voltage should remain <600mV, below the diodes get into full conduction).
With the 33Ohms the voltage should swing between 76mV and 333mV, resp. 205mV +-128mV.
If left open the voltage must go through the roof as the current ´sees´ only the 10Meg internal impedance of the multimeter.
In other words. Without a decent IV-converter connected to the DACs output the thingie can´t work as supposed.
jauu
Calvin
The TI PCM-DACs are current sourcing DACs with current outputs, hence requiring a curent path to close the current loop.
For a test You can generate a output voltage by connecting a small valued resistor to gnd.
As the signal current of (+-3.9mApp) is offset by the centre current (-6.2mA), the current swings between -2.3mA and 10.1mA.
So a 33Ohm or smaller resistor should suffice (due to internal protection diodes voltage levels >300mV start getting distorted .... voltage should remain <600mV, below the diodes get into full conduction).
With the 33Ohms the voltage should swing between 76mV and 333mV, resp. 205mV +-128mV.
If left open the voltage must go through the roof as the current ´sees´ only the 10Meg internal impedance of the multimeter.
In other words. Without a decent IV-converter connected to the DACs output the thingie can´t work as supposed.
jauu
Calvin
- Status
- Not open for further replies.