Add RCA jacks and get better sound...

Monday 27th of February 2012
Clicks: 14711
Author: mikesnowdon

 

 
 



Earlier I had been looking at ways to improve the sound quality of the analogue audio output. I discovered which chip was responsible for audio duties. It's made by a company called Wolfson who have a great reputation in the audio world for making great sounding DAC chips. I contacted Wolfson with the part number and they got back to me saying that that particular chip was a one off they made for Microsoft, however it was 99% identical to the WM8521 chip and had identical pinout. They were also kind enough to send me a datasheet with pinout diagrams :)

What I wanted to do was take the audio signal straight off the pins of the DAC and wire it to phono connectors on the back of the console. By tracing the circuit from the relevant pins of the 8521 I found the coupling capacitors and lifted them to break the connection to the AV port. I soldered in some good quality Film capacitors and wired the output to the phono connectors. Ground connection from the phono's is taken directly to the Analogue ground pin on the DAC chip. I used the phono connectors out of the Microsoft adapter and mounted them on top of the AV port. Haven t wired in the Optical digital but can do so later if I wish.


Diagram:

a pic

WM8521 pinout:

a pic

WM8521 datasheet:

alldatasheet.com WM8521datasheet

Detail pics:

a pic

a pic

Info:

The points shown on the motherboard are the nearest available without soldering directly to the pins of the DAC chip. These points are on the input side of the coupling capacitors. The purpose of coupling capacitors is to prevent DC voltage getting into your preamp. They are otherwise known as 'DC blocking caps'. Because the audio signal passes through these cap's on its way to your amp, their quality matters. Microsoft has gone with the usual Tantalum types which are fine but not as good as Film type capacitors where quality audio is concerned. Film capacitors give the best sound quality. Unfortunately Film caps are usually physically big, so I have used 'Wima MKS2 4.7uF' Polyester Film Caps. You can use anything between 4.7uF and 10uF - voltage doesn't matter. But I recommend the Wima's as they are quite small in size as far as film caps go. I have used them in audio gear as a upgrade and they always bring the sound quality up a notch.

If you dont want to upgrade the coupling caps then take your signal off the other side of the existing caps. Simply solder to the AV connector side of the existing coupling capacitors. This is a convenient topside point to solder to and still has the benefit of bypassing the unnecessary filtering circuits etc....

....read on:

In my mod I lifted the tantalum caps to break the circuit to the av port. You dont need to do this but I did it to keep the audio signal as pure as possible. When you pass audio signals through many junctions, filters, components, connections etc it degrades in quality. The way I have done it above it comes right off the DAC via good quality caps and straight to the RCA phono sockets. In the existing scheme audio passes through various (unnecessary) components and connections before reaching your amp. There are filtering circuits on the 360 motherboard which aren't required, as the WM8521 already has them built in. See datasheet.

Last but not least, we now have proper RCA jacks on the back of our 360 so we can use a decent quality phono cable and get that delicate audio signal to our amp with as little degradation as possible. For cable I reccomend Canare LC-1 as a cost effective good quality cable. Their plugs are rather good too.

Blue Jeans Cable





Notice: The Tutorials have been done many times and were often successfull, however we cannot guarantee the success and so dont take any responsibility for any damages that might be caused by it, you do it on your own risk!!!


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