mods for the MF X-DAC V3 [not definative]

Discussion in 'DIY Discussion' started by zanash, Apr 28, 2006.

  1. zanash

    zanash

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    MF –x dacv3 mods

    The aim was to try and improve the unit but on a strictly limited budget of about £50 for parts. The unit on initial listen sounded thin, closed in and a little congested, with fair imaging and good bass. After each mod the unit was hooked back into my system and the changes where evaluated ..fortunately there were no retrograde steps but a couple of the mods provided very little obvious improment though these were left in rather than removed.

    The case

    The case rings badly, with the ends removed hold by a corner and tap it with a screw driver. As all components are microphonic any ringing will effect the performance of the unit. The case front and back need to be damped , I use bitumen damping sheet and covered the internal flat surfaces, but with enough room to spare for the pcb to fit and the end plates.

    The sockets

    These should all be swapped for high quality parts, ie Teflon insulated types. My preferred type are the ones you can bolt onto the back plate.

    The wire

    For me this plays a big part in the sound of the unit so I’ve gone for the best at any price. Pure silver in ptfe sleeve, two cores are tightly twisted and connected from the pcb to the sockets on all the external connections.

    The Input

    These appear fitted with pulse transformers and on the whole is ok you could check the output impedance of the transport and match that with the receiver chips but that’s definitely icing on the cake. There are a series of disc caps …I hate disc caps these can be swapped for higher grade types, but its debatable if there any sonic advantage.

    The two reciver chips should be covered in copper foil and grounded to the ground plane close by. The copper foil must be cut so that it is clear of the pins other wise you will cause a short. Once completed the chips should be covered with a piece of bitumen damping material.

    The mains

    The xdacv3 has an external psu that provides the 24v ac that this unit runs off, making a better unit or using the x-pusv3 will of course give you big gains even if you don’t do any other mods. All the diodes should be replaced that includes the two descrete diodes and the diode bridge. The diodes that I used here are Schottky 11DQ10’s these are just superb and offer the best bang for buck of all the mods carried out. It easy to build a little bridge to fit the position of the round rectifier bridge removed, though mind did look like a drunk spider but worked just fine.
    Without wholesale curcuit changes I left the voltage regulators to do there job, I’ve always found that it’s a big job to rebuild the curcuit board if you change these and in this instance was not pat of my remit, though big gains can be had but using different devices. Once the ac has been converted to dc and the correct voltage established the next area of modding is the capacitors. I’m of he school that thinks many small caps are better than one big one, so I swapped the single large supply caps with stacks of three caps each with better spec and a slightly higher total capacitance. The type of caps you can use here include Panasonic fc or the more exotic types, I’m not certain I would use oscons, but elna silmics or stargets would go well. All you need do is make certain that there is enough room for your choice of cap.

    The dac

    Here I include the square silver box which is the crystal. I was surprised at how much the sound changed by just adding a sheet of damping to the top and side of the case. Other than that I left it alone [again not part of the original remit].
    I placed foil and damping on the dac chip and other two chips, which again provided some sonic gains. But again efforts were concentrated but to the restrictions previously mentioned.
    There are a series of caps that supply the dac chips I removed them all and replaced with stargets, but oscons would work very well here. My choice was what I had to hand rather than any great need to use stargets. The stargets sounded pretty good over the old caps. A word of warning here the caps feed the dac chip by the thinnest pcb traces you can imagine …and yes I managed to lift one but saw it in time. It was super glued back down, the resist was scraped off and the caps leg soldered to the trace with out ill effect. …phew.

    The output stages

    The dac feed six sets of opamps with there associated power supply network and filters. As I didn’t have a huge budget to work with I concentrated on the final opamp a pedestrian ne5532 of staid performance. This was removed a good quality socket fitted and a opa2604 fitted, this is not the best opamp but is very good for the cost better ones can be found ! Wow huge jump in performance just think what a top opam could do. The signal path was followed and the resistor r206andr106 were swapped for dale/vishay’s again this was a good move great bang for buck ! Now why would you add muting restistors to a dac ? who knows unless the dacs been coppied and paste straight out of a cdp design . These were removed to an opening up of the sound. Finally in the signal path were a pair of rather nondescript bipolars ….yuck I replaced these with silmics , but you need to make certain that the orintaion is correct the positve side must be towards the opamps and the negative to the output. Wow gone was the congestion that had been present. You could use film caps here but I had none of a sufficient size to work …even stacking wima 1uf film caps would have used too much space. Though these have work very sweetly in other dacs.

    Bypassing

    All the electrolytic caps were bypased using 1uf 63v wima film caps on the base of the pcb.This had the effect of really opening up the sound.

    Final sound ….

    This is so far removed from the original as to be astonishing, one wonders why they fitted all the cheap components to start with. The units is now fast and articulate with a very wide sound stage and pin point imaging a complete revalation. The owner seems particularly happy with these mods…so that’s a great sucsees all round.

    A final note

    These mods are not cast in stone, and are mean more as pointers as there are many more things that can be done. ie the output stages [you have four other opamps to swap and loads of resistors that can be uprated] but for this unit the budget limit was reached.

    ……happy modding
     
    Last edited by a moderator: Apr 28, 2006
    zanash, Apr 28, 2006
    #1
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