Paralleling DACs to get more current works fine until we get bored with soldering so many chips down to the PCB. I've also been wondering if more juice can be had without tying up so much PCB real-estate. So I've been looking for DACs which deliver more current, and in particular, more output current in relation to supply current. In Celibidache I'm using 20 TDA1387s and the supply current is 110mA @5V to deliver 20mA output swing, per channel. Hence 5.5mA per 1mA output current but in its favour there are two independent channels.
Communications DACs are quite a long way from the world of audio DACs but I've long suspected they might turn out to work fine reproducing audio. Their THD specs tend to be poorer without a doubt as they don't use DEM methods to improve DNL/INL. (There are one or two recent designs that incorporate self-calibration though.) Recent designs tend to be more expensive and in much trickier to use (higher pin-density) packages so I tend to favour older models in SOP28 and the like. Things that appeal to me about comms DACs are - they're stripped down to bare essentials converters, no fancy features like digital filters or sample rate converters on-chip. They are cheap when bought recycled (under $1 a piece typically) and they go up to insanely high sample rates. This latter aspect gives me confidence that we can run them heavily oversampled if need be without loss of significant performance as even 32X OS is off to the far-left of the spec graphs of these devices. Their extreme speed capability means they're always parallel-input this is a minor inconvenience in terms of an extra logic overhead.
I have a short tube of AD9764 in my possession - this chip delivers 20mA balanced output swing for a supply current of under 30mA, depending on sample rate. Better than 1.5mA of supply per 1mA output current. Here are its lack-lustre characteristics - bear in mind this is a 14bit part :
and here's its block diagram :
Its a multiplying DAC so its reference input can be varied (over a 10:1 range) to create a rudimentary volume control for the first 20dB.
The output noise spec is 50pA/rtHz which translates to 2.5nV/rtHz in a 50R resistor, giving a dynamic range of 120dB, assuming no intrusive 1/f noise. This is rather a lot better than even TDA1541 (110dB) and it has a high Zout (100k) and a wide compliance range of over 1V. So relatively tolerant of I/V stages. We just need to find ways to improve the resolution from 14bits and perhaps to smooth out the INL/DNL somehow.
Communications DACs are quite a long way from the world of audio DACs but I've long suspected they might turn out to work fine reproducing audio. Their THD specs tend to be poorer without a doubt as they don't use DEM methods to improve DNL/INL. (There are one or two recent designs that incorporate self-calibration though.) Recent designs tend to be more expensive and in much trickier to use (higher pin-density) packages so I tend to favour older models in SOP28 and the like. Things that appeal to me about comms DACs are - they're stripped down to bare essentials converters, no fancy features like digital filters or sample rate converters on-chip. They are cheap when bought recycled (under $1 a piece typically) and they go up to insanely high sample rates. This latter aspect gives me confidence that we can run them heavily oversampled if need be without loss of significant performance as even 32X OS is off to the far-left of the spec graphs of these devices. Their extreme speed capability means they're always parallel-input this is a minor inconvenience in terms of an extra logic overhead.
I have a short tube of AD9764 in my possession - this chip delivers 20mA balanced output swing for a supply current of under 30mA, depending on sample rate. Better than 1.5mA of supply per 1mA output current. Here are its lack-lustre characteristics - bear in mind this is a 14bit part :
and here's its block diagram :
Its a multiplying DAC so its reference input can be varied (over a 10:1 range) to create a rudimentary volume control for the first 20dB.
The output noise spec is 50pA/rtHz which translates to 2.5nV/rtHz in a 50R resistor, giving a dynamic range of 120dB, assuming no intrusive 1/f noise. This is rather a lot better than even TDA1541 (110dB) and it has a high Zout (100k) and a wide compliance range of over 1V. So relatively tolerant of I/V stages. We just need to find ways to improve the resolution from 14bits and perhaps to smooth out the INL/DNL somehow.