Here are a few thoughts on cd mods, all of which have made a sonic difference to the players I've moded. So what am I missing, I'm not intrested in gutting and redesigning the players just squeezing the best from the original design concept. Generic CDP mods I prefer to try and get the best from the circuits as they stand rather than rip out and replace. The designer must have had some design aim in mind when he produced the design….? Case work The thin pressed steel case work will need damping ……foamed butyl rubber sheet or bitumen damping panels as used in the motor trade work really well. The lid and base will need damping as well don't forget. The transport and draw can be treated in a similar way. But don't foul the workings with too much. A blue led shone onto the disc also has an effect [do't ask why as I don't know]. A green poster paint pen like the Posca pens by Uni can be used to put a green ring round the edge of cd's [including the inner hole]. If the case work is sprayed green on the inside [big job to remove all the working and mask up] this will help cut down the stray infra red scatter from the laser. The green shade depends on the freq. of the laser so a bit of trail and error is normally involved. Try getting two identical cd's and paint the edges of one…..when dry do a bit of DBT. I find that the green one often sounds more relaxing [but not always]. PSU Decent mains cable from inlet to board Check the thermal compound on the regulators, and upgrade to a silver based compound . Replace diodes with schottky types of suitable rating. As these work on a different principle to the normal diodes they have none of the draw backs like reverse current generation and rf production. In effect they are much quieter and I've found pound for pond one the single best upgrade you can make Replace the resovoir caps with audiophile types and then bypass them with values of 10% ie if a1000uf with100uf, 10uf, 1uf, the theory being that smaller caps respond faster to transient power demands. Making for a faster and more detailed sounding player. Look at the quality of the power supply wires to the various parts use a high quality Teflon insulation , and route to cross the unit at right angles to other cabling. Output stages First look to remove any muting transistors, just snip them off the board. These things are switched on when you press next track or the skip buttons, and reduce the slight popping noise created by diverting part or all the output to ground and thus muting the player. But as the transistor never actually switches off a small amount of output is constantly drained to ground, never a good idea. The difference after removal is considerable in the scale of tweaks. Opamps ….there are any number on the market ranging from a few pounds to tens of pounds [more expensive is not always better] its often a matter of personal taste, my low cost fav is the Bur Brown opa2604, 604 for the mono. Remove the original opamp, solder in a high quality socket I use ones with Berylium Copper legs. This allows for easy swapping, even with the extra connections this set up sounds better than the original in all the players that I've made the change. As most opamps work at such low level, the can be actually operating in class B or C. Its worth putting a constant load on the out put to raise the operation into class A. There are lots of web site that give you the instructions in how to do this. But remember that in class A 50% of the output is going to be heat ! so you need to address that problem and add a heat sink to the opamp. Signal path The replacement of the resistors in and around the signal path will also remove a veil from the sound…..as a minimum use Holco's precision metal film [0.01% tolerance ] but there are a lot of expensive good ones about ie Vishay bulk foils or Audio Note Tantalum's etc. Relace the copper tracks on the pcb with silver wire…[hard work ! not to be attempted unless really confident]. Clock Replace the following with its own power supply Trichord research clock 4 or similar. Consider Non 0versampling [this of course is specific to the dac in the machine] RF / EMI Copper foil shield all ic's, bundle and wrap all cables in foil, this must then be grounded to a convenient point on the case work. Cut the foil to size and stick to the top of all the IC's use a small wire and solder the foil to the ground leg of each IC. Look to make a copper sheet screen to shield the psu from the drive and the drive from the output stages. Shorting plug Build a shorting plug for the digital out put [URL]http://diyparadise.com/75ohmtweak.htm[/URL] Cd output This can be high and might be the cause overloading of the input stages of the pre amp…simply use a plug in attenuation or add the appropriate resistors to the IC plug. Tubes [for player like the jolida xxx's] I like svetlanas for me they give an velvety inky black silence and a smooth warm in there presentation, but these are a very personal choice. Dislikes and Don'ts I'm not a great fan of black gates…..they take years to burn in so you will never get their full benefit, there cost is prohibitive to. I like Elna Stargets….they are cheaper and give an honest performance straight from the box. Replace all the caps [not already swapped ] with oscons [sg?] the copper legged ones. Don't use any ferrite beads ….they will squash the dynamics of the system. I don't remember posting any comments about them! Out of box things to do Make or buy a decent shielded Mains lead ….these act as filters removing grunge and cack before it gets to the player. Look to use a mains conditioner beyond the power cable, and use decent wall plugs. Don't neglect to clean all metal metal contacts. Metal oxides act as diodes. Feet ………well a simple three point system of cones will be effective there are many on the market to suit all pockets but if you are like me I prefer the DIY approach, I'd try some domed hard wood cupboard door knobs approx 10mm dia. For me these work as well as anything. The support should be a vibration absorbing sandwich on a sand box. I use 2 x 5mm MDF separated with a sheet of foamed butyl rubber….kills vibration by an average of 20% more for high freq's . The sand box is a box full of sand [oven dried ] with a sheet of mdf sitting on the levelled sand but clear of the sides of the box by a few mm. Build the best IC you can for me at the moment this is a simple twisted pair of solid silver 4n wire in a Teflon sleeve with bullet plugs, fabulously revealing but not as over bright as you might expect. In my opinion you can achieve a lot by cleaning the pins of the mains plug so they shine, use duraglit or other metal polish, don't forget the fuse ends and the holder. In the uk the fuse is in the wall plug , the fuse has copper caps but they are covered in soft solder [tin and lead] once removed the difference is clearly audible. Also if the cdp has valve output stage, clean the pins on the valves.
