The three places where tweaks to an inexpensive player can make the most difference are the power supply, the power supply, and the power supply. Okay, that may be a slight overstatement, but it's a fact that the power in your home is often corrupted by air conditioners, dimmer switches, halogen lights, and other noisy appliances—yours and your neighbors'. Cleaning up and filtering out this noise on the line will help any player perform better.

Essentially all low-cost DVD players these days use a switching power supply. It converts the line's ac voltage to dc, at, for instance, the 3.3, 5, and 12 volts needed by chips, motors, and other internal components. Switching power supplies use switching transistors and other devices to, in effect, chop the 50- or 60-hertz line frequency into an ac signal at tens or hundreds of kilohertz. The advantage of this higher frequency signal is that it can be filtered, and its voltage changed, with small and light capacitors and transformers. The high-frequency transformer also easily provides multiple output voltages and isolates the dc from the input voltage.

The supply consists of a power-input receptacle, a bridge rectifier to convert ac to dc, capacitors for smoothing the resulting pulsed dc waveform and for storing the energy needed by the other sections, MOSFET transistors to chop up the dc into the high-frequency ac, and the high-frequency transformer with multiple secondaries to produce the various desired voltages. For each secondary coil, there are rectifiers and filter capacitors to yield the desired dc output. Besides being smaller and lighter, switching power supplies are typically more efficient than other types. The tradeoff is that they tend to generate more high-frequency noise on the power line. Sufficient filtering becomes important—especially in audio circuits.

Before you begin, a few words of caution. You will be playing with a system that runs on real ac current, so make sure the unit is unplugged while you are working on it. If you are new to the world of building and troubleshooting electronics, read this excellent guide before proceeding: http://repairfaq.ece.drexel.edu/REPAIR/F_appfaq2.html. Be careful and patient. Oh, yeah, this will definitely void your warranty, too.

To open the Toshiba SD4960, remove the three screws on the back panel; then slide off the lid. Snap off the front panel, being careful not to break the fragile plastic clips that hold it in place. Unplug the ribbon cables where they attach to the main printed-circuit board and unplug the wire running from the electrical cord to the board. Unscrew the board, and lift it gently out of the case.

On the board (See photo, "Inside the Toshiba SD4960"), you will notice lots of insectlike components, their bent leads splayed like little legs on the surface of the board. You will be leaving these surface-mount parts alone. They are too small to fuss with, and their would-be replacement parts too big to fit in their place. Also, they have been machine-soldered to the top of the board and would be hard for you to remove and replace without damaging other circuitry.

Starting with the power supply section (indicated in yellow), first identify all of its capacitors and their values. You should replace all of these capacitors with higher-quality capacitors with the same voltage value but about 20 percent more capacitance. (See table, "Replacement Parts Selection.") There are various measures of a capacitor's quality; one is ESR, or Equivalent Series Resistance. A low ESR means low resistive losses inside the device, and therefore better ability to deliver power to the sort of fast-changing loads presented by the clock and other high-frequency digital circuitry. There will also be one relatively large capacitor just after the rectifier or diode bridge (indicated in pink); you can double the capacitance value of this one, from 82 microfarads (µF) to about 180 µF, or whatever you can fit in the available space.

Basically, by using better-quality parts, like Sanyo Oscon, Panasonic FC, or Nichicon UHE or FG/KZ capacitors, and increasing their values, you will improve the power delivery to the other circuits. That in turn will increase the dynamic range and enhance the all-important bass performance. Besides low ESR, such high-end capacitors have tighter tolerances and use better materials (the Nichicon leads, for example, are copper, not steel).

The one constraint you'll face in replacing capacitors is the space on the board—capacitors with larger values are bigger, so make sure you have enough real estate for them. And don't forget to note the polarity of the capacitors you are removing so you know which way to solder in the new ones. Polarity is usually indicated on the board, but go slow and be cautious.

To take your upgrade a step further, replace the diode rectifier bridge with "soft" recovery FREDs (fast recovery epitaxial diodes) or Schottky diodes. These fast-action diodes have what is known as soft recovery. What that means is that when the voltage across them changes polarity, causing them to go from forward- to reverse-biased, the plot of current versus time slopes smoothly back toward zero current, rather than overshooting the zero axis and wobbling briefly around it, or "ringing." Basically, the lack of ringing means less noise.

Buy replacement diodes with higher amperage ratings than the original ones. The original diodes are designed to tolerate high-peak surge currents, which occur when the power-supply capacitors are charging (and don't forget, you added more capacitance!). Chances are, your replacement diodes aren't designed for high current surges; in my case, replacing the specced 1-ampere 600-volt diodes with the same value FREDs smoked them. So I used 4-A 600-V diodes and they worked fine.

You may have to be a bit creative with the installation of these replacements, because diodes with this increased rating are usually only available in a TO-220 type package instead of the original DO-41 package. Note that the TO-220 package has a metal tab at the top; this tab is generally connected to the cathode and should therefore be insulated with heat-shrink tubing to avoid any shock hazard.

Again, be very, very careful of the orientation of these diodes. By putting a faster, soft-recovery rectifier in the power supply, you will allow the power supply to respond more rapidly to the demands of the downstream circuitry with less switching noise.

Taking the modification yet further, you can also replace both of the X-rated capacitors (indicated in orange)around the transformer with 0.47 µF 600-V Auricaps. These will set you back about $13 apiece. X-rated capacitors are standard components that meet Underwriters Laboratories Inc. (UL) standards for use on ac mains lines. These capacitors are designed to be self-extinguishing in the event of a big surge on the power line. They're potted in fire-retardant compositions, and are designed to fail open, rather than closed, so components up- and downstream will be protected. Auricap capacitors, a brand of high-end capacitor favored by audiophiles, are not rated against UL standards for ac current.

While this tweak is widely used in audio modification circles and no problems have ever been reported on the audio tweak Web sites (as far as I know), it could potentially lead to damage in other parts of the system, so you might say it's risky. But, to my ears anyway, it does noticeably improve audio quality. If you're squeamish about replacing the X-rated capacitors, you might try a compromise, such as replacing the stock X-rated capacitors with a good-quality safety-rated polypropylene capacitor, such as the MKP series from Illinois Capacitor (part number 474MKP275K).