DIY friendly S/PDIF out

[KlipschKid]

Originally Posted by Billyo

Does your mobo have a digital audio output plug? (like pictured in the ebay ad below)

If so, something like this is what I use flawlessly

MSI Motherboard S/PDIF-Out Connector JSP1 Audio cable | eBay

If you have a dmm, can you unplug this output panel, and measure the resistance between the gnd and spdif on the cable or the coax/rca socket. I'm curious to know if they have added any resistance or if it will measure an open circuit.

Thanks !

[Billyo]

Originally Posted by KlipschKid

If you have a dmm, can you unplug this output panel, and measure the resistance between the gnd and spdif on the cable or the coax/rca socket. I'm curious to know if they have added any resistance or if it will measure an open circuit.

Thanks !

I'd help you, except that I'd need to interrupt the wife's TV viewing for the evening, unplug everything, crack open the HTPC, do the measurement and then put it all back together again.

Why's it so important to know if there's any resistance?

[KlipschKid]

Hi,

If it's open circuit then the rca output is basically wire with an rca socket on the end. Convenient and functional. Flawless ? Well, don't use that word on this forum. I got blasted for simply saying good, even when I could prove it with a scope.

Anyway, if there are some resistors or a pulse transformer (fat chance) in there somewhere then it suddenly looks like someone did some design work. This is highly unlikely but you did use that word - flawless ;-)

BTW, it is likely you could better performance for similar money if you used some cat5 cable and a chassis-isolated 75 ohm BNC and 10 minutes to solder and fit. Or if the toslink is what you want, then a transmitter and the same cat5 cable wired differently.

And better still with more time, a scope, a pulse transformer and some resistors, but hey, suddenly that is very inconvenient eh ?

[KlipschKid]

Hi,

I've been playing with this :

USB to SPDIF coaxial I2S processor TE7022 24bit 96K board sc | eBay



and turned it into a nos dac :



diy friendly ? :-)

[redjr]

I'm always the skeptic.... And what percentage of audio quality improvement would you say you gained with this mod as opposed to simply using the original, unadulterated board?

[KlipschKid]

Hmm... well, the smps psu of my notebook has about 3mV noise. With the gyrator (5K, 22uF, MPS8099 NPN) and adp151 reg, this drips to 9uV (for the xo and te7022l), so that would be over 300%. :-)

Oh, plus it's now a usb nos dac, not just a usb receiver. Under the jungle of resistors is a tda1543.

[KlipschKid]

I was asked about the changes I made to the Tenor board so here goes.

I don't need spdif so I removed all the components to the right of C18. To get it to fit in a small box, I cut the right side of the PCB off. There's no opportunity for shorts so it's a safe thing to do, if done "gently".



I removed the 3.3V reg (U1) in the top corner because the AMS1117 is quite noisy. USB power is very noisy too so I added a gyrator (values above) which drops the voltage to 3.8V and cleans up the power, esp at higher frequencies.

Capacitance multiplier - Wikipedia, the free encyclopedia


I added an adp151 regulator after the gyrator (cap multiplier). It has a dropout of less than 200mV so it'll work with an input of 3.5V. It has just 9uV noise. This creates a very clean supply for the tenor and xo, and for the latter this is especially important to keep phase noise as low as possible.

The output pin is soldered onto the pcb first. This leaves 3 pins sitting up from the pcb. The centre is gnd and the other two are input and en, which need to be connected together. I find it is a little easier to solder the gnd pin if it is carefully bent away from the other two.



I also replaced C3 with a large value ultra-low ESR Cap to reduce noise/ripple. It's a Nichicon PLG 820uF.

I added an LED. There's already a pcb position and a suitable resistor to control current so that was a why not ?

Finally I replaced the xo with a Euroquartz X091. These are actually made by Mercury in Taiwan and are a bargain low phase noise xo.
Here's the phase noise plot :



Compare it to the Tent which costs far more and is at least -12dB better :



The rest of the stuff relates to the DAC. I'll post details if anyone's interested.

Here are some final shots. I hate hot glue, but it works.