September 18, 2001

Welcome to my Simple Mods for CD Players page.  Here are a few quick tricks, along the lines of improving mechanical integrity and enhancing immunity from both generating and being susceptible to EMI and RFI that are guaranteed to improve the sound of your CD player (and system) with no soldering required.  I have personally applied these techniques to a Rotel 930, a Cambridge CD4SE, a Marantz CD-67SE, and a Sony CDP-445 carousel with almost uniformly noticeable results.  The one exception may be the Rotel, for amazingly--especially at its price point--it already incorporates one of the mods internally.

Stage One--Mechanical Integrity

This has been mentioned in the past--I first discovered a treatment of it on Thorsten's TNT Audio page some time ago, but only recently tried it (after the warranty periods were out on some of my players, gutless SOB that I am). Basically, you go to a car stereo shop and buy a smallish sheet--usually in a roll--of sound absorbing material. I went out in search of DynaMat--the original, as it were--but as the store I happened into only had StingRay, that's what I got. I paid too much ($30 for a roughly 44" x 19" roll), but I ended up treating four players, so it was a bargain if you ask me. What I didn't want was the stuff to fall down inside the player some day from adhesive failure, so I opted for a name brand. I suggest you do the same. Get relatively thin stuff--around a sixteenth of an inch or so--as it has to go on some side panels that are only a sixteenth of an inch from the cover when reassembled.

NOTE--the good stuff does NOT need to be applied with heat--in fact, it causes bubbles (trust me on this one).

The primary place for this stuff is inside the cover, but I found locations on the player chassis themselves in some cases. I'll give more specific details as I add to the page. Just be sure to watch out for interference with chassis metal, both on the front and rear as well as the sides, as once this stuff is on, it's ON. Don't sweat covering EVERY square inch--often just a patch in the center of a large area will dampen it sufficiently. Place as large a swatch as possible on the inside top of the cover, though, and some on the inside of the cover sides as well. If you can, get crazy and add it to the undersides of any crossbraces (like in the Marantz CD-67SE--very effective), and open spaces of the main chassis (like in the CD4SE--lots of open space in there!). You'll be amazed at just how dead this stuff makes bare sheet metal.

CAUTION--Fucking Sony sheet metal WILL cut your fingers (excuse my explicitness).  Be careful.

The primary effect this addition has is to deaden the enclosure and make the player more immune to vibration, whatever the source. Mechanical integrity is your friend, despite what they say about digital equipment theory.

Stage Two--EMI/RFI Suppression

There has been a lot of speculation about just how much of the so-called digititis that plagues many popular CD players (in systems) is actually caused by both conductive and susceptive electro-magnetic interference (EMI), as well as radio frequency interference (RFI). The fix is pretty simple, short of covering all the chips on the PC board with copper shielding--put a ferrite choke on the AC power cord. I use Radio Shack square yoke-type chokes on AC power cords, and cylindrical clamp-type chokes on small-diameter cables, such as small coax, etc. The basic idea is to get as many passes (wraps) through the choke as you can--5 is usually enough but 6 is better, etc. Interestingly, the Rotel 930 has a big mother of a choke wrapped around their AC power cord inside the box, which absolutely amazed me. But the other cheap-ass manufacturers would rather quote great specs than spend another couple of bucks and provide protection against near-field EMI/RFI. Go figure.

The problem is that CD players are not only affected by EMI/RFI (which can modulate the output signal at both the digital and analog stages, thus increasing jitter and graininess in the sound), but they can generate it, too. This can affect other equipment in your system, as not only the AC line (which is common to all the equipment), but the air itself can becomes a channel for interference unless adequately filtered and/or suppressed at the source/destination. Thus the choke--it has to be at the point of entry/exit on the equipment (right at the unit, as close to it as possible). You will hear the result of this change as smoother sound, especially at higher volumes.

Another area of potential interference is from power supply rectifier diodes themselves. A semi-cure for this is to place parallel bypass (or "snubber") caps across each diode. I use commonly available .01 mfd @ 500vdc ceramic caps sold at Radio Shack. This working voltage is adequate for use in solid-state equipment, but I have also successfully used them to bypass 1N4007-class diodes in tube equipment as well, which have a rating of 1 Ampere at 1000 PIV (peak inverse volts). Interestingly, this approach is mandated by the EC in modern designs sold in Europe to minimize interference to local Television reception, but my Audio Note OTO SE Phono does not have it. Perhaps it preceded the EC regulation. The US has no such requirement, however, so you have to do it yourself. Always use a heat sink when soldering a diode, by the way.

That's it for now. Try these changes and see what you think--they may well improve the sound of your player at little to no cost.
 

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