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DC Coupled Soundcard DAC Mod

Started by Ken Morrow October 13, 2015
On 15/10/2015 21:52, Ken Morrow wrote:
> On Thu, 15 Oct 2015 14:38:58 +0100, Martin Brown > <|||newspam|||@nezumi.demon.co.uk> wrote: > > >> You put the unity gain buffer between the DC coupled output and the >> resistive load. The thing should not run hot if all you hang on the >> output is a scope probe. Something else is wrong. >> > > Yes, heating up just by changing the waveform with no significant > load is a mystery. It appears to be something happening within the > chip itself. > > The circuit diagram here appears to be of a similar device. > > http://www.electronics-diy.com/PCM2706_USB_Soundcard.php > > It would appear the if C9 was shorted, and a DC offset was present, > excess current would flow into R8.
The DC offset is already happily flowing down R5 & R6 which are across the chips outputs to ground. It would double the current and quadruple the power dissipation at a given output voltage but that is all. This chip can certainly drive a DC resistive load of 3k to ground - it is already doing so. I am a bit amazed that it will drive a pair of 8R headphones when AC coupled. It might be a better choice for you.
> > Perhaps the solution is to remove that resistor. > > Ken Morrow
The resistor on yours looked like 47k. That cannot be causing excess power dissipation sufficient to get the chip warm. -- Regards, Martin Brown