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Extreme Modifications to the Musical fidelity X-DAC V3.

By Alex Kethel (Rock Grotto forum member sandyK)

Discussion regarding these mods is here ( click this link )

PART 1

These modifications will take the sound quality of the X-DAC V3 up to, or better than, the sound from respected DVD players such as the Marantz SA-11. WARNING : Do not attempt these modifications unless you are an advanced hobbyist, or have a professional repairer perform them for you. The X-DAC V3 has very fine copper tracks and may be severely damaged if you are not experienced in these areas. Using the optional Musical Fidelity power supply instead of the supplied plugback, will make a worthwhile improvement to the X-DAC V3, The X-DAC V3 does not have any voltage regulators supplying the analogue section. A substantial improvement may be made by feeding the X-DAC V3 with well regulated + and - 15V DC from an outboard power supply.


STAGE 1. A 30 or 50VA Toroidal transformer with 15-0-15V AC windings may be used to feed a regulated power supply PCB using LM317 and LM337 voltage regulators. Silicon Chip magazine has designed a suitable power supply PCB.


Diagram 1


Jaycar Electronics stocks this kit for AU$17.95 as cat.KC5418 (diagram 1) Other suppliers will also have suitable modules available. Build the toroidal transformer, Regulator supply PCB and other components into a suitable enclosure.

 


Diagram 2


A male IEC chassis mounting fused mains socket should be used.Install a M205 500mA rated fuse. Make a suitable power supply lead with a 3 pin DIN plug fitted at the X-DAC end. The 0 Volts from the power supply connects to the center pin of the 3 pin DIN plug. Ensure that this plug's + and -15VDC polarities match the X-DAC 's PCB polarity markings. This is essential if the X-DAC bridge rectifier is removed and bypassed. The X-DAC V3 will perform better with this DC power supply than with the optional Musical Fidelity power supply, and may be used without modifying the X-DAC..

STAGE 2. Remove the circular bridge rectifier near the front panel and connect 2 wire links straight across where the bridge rectifier was previously. Double check with a Digital Volt Meter that the +VE marking for the bridge rectifier on the X-DAC PCB , will connect to the +VE supply from the DIN plug when inserted. The -VE supply from the DIN plug should also connect to the X-DAC PCB's -VE marking via the other fitted link. Remove the 2 x 2,200uF capacitors which are connected to the PCB traces from the bridge rectifier . Replace with 2 x 100uF 25V electrolytic capacitors.Ensure that the marked polarities of the new capacitors match the markings on the X-DAC PCB. Be very careful when replacing these capacitors, as they are glued to the PCB. Carefully remove the goo first ! The X-DAC will now have a full + and -15V regulated supply feeding the analogue section.There should be a further improvement in the perceived sound quality from the X-DAC.

Attached is a photo of my Regulated power supply (diagram 2). The selector switch is used to switch 2 SPDIF sources, and is not needed for this application.Note that ALL mains wiring, and the mains ON/OFF toggle switch is covered by heatshrink tubing for safety reasons.Mains earth from the IEC socket is connected to the aluminium base plate. IEC Fused Mains sockets vary in their number of connections and pin assignment.

A single pole mains switch could also be used.- connect one side of the transformer primary winding direct to the N terminal of the mains socket. The other side of the primary winding still goes to the switch contact.The other switch contact is connected to the fused side of the mains socket. All mains wiring must be in accordance with local standards. END -Part 1. (Part 2 will cover analogue I.C. replacement, as well as other component changes/additions.)

DISCLAIMER.
This information is given to stimulate interest in upgrading X-DAC V3. The author accepts no responsibility for any damage to equipment, or any injury or death, resulting from these suggested modifications.

 

Extreme Modifications to the Musical fidelity X-DAC V3.

By Alex Kethel (Rock Grotto forum member sandyK)

Discussion regarding these mods is here ( click this link )

Part 2

These modifications will take the sound quality of the X-DAC V3 up to, or better than, the sound from respected DVD players such as the Marantz SA-11. WARNING : Do not attempt these modifications unless you are an advanced hobbyist, or have a professional repairer perform them for you. The X-DAC V3 has very fine copper tracks and may be severely damaged if you are not experienced in these areas.

STAGE 3.


All components marked are replaced. The NE5532 I.Cs are replaced by OPA2134. The 100nF ceramic bypass capacitors (close to the I.C.s) are replaced by normal 100nF 63V polyester types. Do not replace the 2 ceramic bypass capacitors that are not marked. Other polyester capacitors around the NE5532s are replaced by polypropylene types of the same value if obtainable. The circular bridge rectifier near the front panel is removed, and 2 wire links fitted.


Photo 3

Be very careful removing these components, as the PCB is double sided, and many of the tracks around the I.Cs are very thin and easily broken.If in doubt, get an experienced person with the appropiate equipment to replace these components !After replacement, check the PCB carefully with a magnifying glass for any dry joints, or short circuits between tracks etc.

Check that the OPA2134 supply pin voltages are correct.(pin 8 = +15v, pin 4 = -15V - Pins1 and 7 should have low voltage readings ! ) If everything appears to be O.K. , audition the X-DAC again. There should be a further noticeable improvement in soundstage and resolution.

STAGE 4. To obtain maximum resolution, fit AD8066 SOIC modules in place of the output OPA2134 I.C.s SEE PHOTO 3. (again) Before fitting the AD8066 modules, the supply rails must be reduced to + and -12V. 78L12 and 79L12 voltage regulators are fitted under the PCB as shown:


The AD8066 should now be completely stable WITHOUT the need to fit ceramic 100nF capacitors adjacent to the supply pins. The conventional wisdom of fitting ceramic capacitors at this location when using these devices will cause a "hardening" of the sound.
Carefully check all work again as previously, and ensure that the supply pin voltages of the AD8066 are + and -12V. The output pins that connect to the output coupling capacitors should read only several millivolts. If all work has been performed correctly, the X-DAC V3 should now sound vastly improved, compared with the unmodified version.

I suggest that if connecting a DVD player with a switchmode power supply to the X-DAC V3, that the 4 high voltage diodes in a bridge rectifier configuration (e.g. 1N4007 etc)
near the mains input lead ,and connecting to the large high voltage electrolytic capacitor, be replaced by Vishay BYV26C (600V) diodes , which are fast, slow recovery types.
These diodes are available on order from RS Components. They work out at about 31 cents each (AU) when 50 purchased. Approx. 1 month delivery time is average. Fit a 100nF 630V polyester capacitor across this electrolytic capacitor. Sticking adhesive sound deadening foam inside the cover, but not directly over the transport mechanism when the cover is back on, as well as under the chassis to reduce vibration, will also help.


ONLY DO THESE MODIFICATIONS IF YOU ARE AN EXPERIENCED CONSTRUCTOR ! LETHAL VOLTAGES EXIST IN THIS AREA!!


The result is normally cleaner sounding audio, and a glossier, more 3 dimensional picture.
Replacing the diodes, and fitting the 100nF 630V capacitor to a DGTEC HD STB,also gave similar improvements to audio and video.

 

These mods were brought to you by Alex Kethel (Rock Grotto forum member sandyK) any questions please visit the forum.

Discussion regarding these mods is here ( click this link )

Many thanks Alex!


 
 
 
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