Decibel Dungeon

Upgrading equipment power supplies.

Although I don't intend (at present) to include details of specific equipment upgrades, I thought some suggestions for modifying equipment power supplies would be useful as these suggestions apply to nearly all types of hi-fi equipment. Click HERE for an article by Nelson Pass on the importance of a good power supply for amplifiers.
The power supply to any piece of hi-fi is very important and improvements will benefit sound quality. Here is a list of suggestions, not necessarily in order of importance:
Experiment with the mains lead. See the hi-fi cabling section for further details.
Replace fuses with circuit breakers. Make sure that you use circuit breakers with the correct rating. The fuse carrier(s) should be removed and replaced with insulated wire links.

TIP - you can get circuit breakers that also function as an on/off switch.

Use a higher rated transformer. Look at the VA rating of the existing transformer. Usually a higher rated model will give better results, especially if you have made other modifications to the power supply section. If the new transformer is too large to fit in the original case, put it in a separate housing. This will probably involve moving other items like the power switch and fuses/circuit breakers. Even if you don't get a larger transformer, removing it to a separate housing is held to be beneficial because the transformers introduce mechanical vibration and have a magnetic field.
Insert some resistance between the secondary outputs of the transformer and the rectifier bridge. The resistors should be rated at 5 amps or more. Try 10 ohms for preamps and 0.1 ohms for power amps.
Replace the diodes in the rectifier bridge with better quality items like the ultra-fast, soft recovery diodes, eg Schottky BYV79E-. Alternatively, solder some 100n polypropylene capacitors across each diode.
Replace the smoothing capacitors with something like Aerovox equivalents. Bypass these with smaller value capacitors of the best quality you can afford. BYPASS - Add one or more (smaller value) capacitors in parallel with a large value capacitor.
Replace the standard voltage regulators. Ask specialist component suppliers what they recommend.
The above suggestions apply to virtually all mains powered hi-fi equipment. Some may argue that you should modify the power supply before you do anything to the rest of the equipment. Because these modifications involve parts of the equipment carrying mains voltages, you are advised either not to do them unless you are qualified to do so, or to have your work checked by someone who is qualified BEFORE you reconnect the equipment to the mains supply.
If you would like to replace a power supply with something better, you can do a lot worse than take a look at this DIY PSU design by Dejan Veselinovic. He even provides the circuit board!

For an in depth discussion on power suppliers for power amplifiers, go to the TNT Audio site.
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Upgrading amplifiers

Amplifier upgrades can be divided into two categories: those to the pre-amp section and those to the power-amp.

The pre-amp section

Here are a list of modifications that you can make to the pre-amp sections of amplifiers (or separate pre-amplifiers):
  • Modify the power supply (see above).
  • Replace the input sockets. Whether this will improve sound quality depends on the type and quality of the existing sockets. If your equipment has the older style DIN sockets, then it is worth replacing them with the phono type (or even XLO) as it will make it much easier to try different interconnects. I personally don't think that having gold-plated plugs or sockets makes much difference. My preference is for nickel-plated items which I clean about twice a year.
  • Replace any internal wiring. Again, I'm not sure how much improvement this will make but it is not a difficult job and may be worth a try. Some audiophiles even replace the wire links on a PCB with exotic alternatives like silver or silver-plated wire.
  • Clean all the switches with contact cleaner. Whether it is worthwhile replacing them is another contentious issue. Some people swear that one type of switch is better than another but I have my doubts.
  • If the pre-amp is an active model, investigate whether you can replace some of the electronic components in the circuit. Items like op-amps, transistors, capacitors and resistors can usually be improved upon.
  • One area ripe for improvement is likely to be the volume control. On most commercially produced equipment, this will probably be a cheap potentiometer. The 'pots' do the job, ie allow you to adjust the volume, but they don't perform very well in other areas. The possibilities for improvement include a better quality 'pot' or, better still, a stepped attenuator. Stepped attenuators outperform 'pots' as regards channel matching and separation but are physically larger than 'pots' and may not fit in place of the original 'pot'. There are several sources of stepped attenuators but if you do want to try one, they are quite easy to build for yourself. The hardest part of the job is working out the values of the resistors so I hope to include some suggestions here in the near future.

The power-amp section

Most of the component modifications listed for the pre-amp section also apply to the power-amp. The power supply is very important. Refer to my comments on isolating the two sections of a power-amp.
Loudspeaker terminals are one item worth paying attention to. If your amplifier has those nasty little spring clip sockets, it would be a good idea to replace them with something that allows you to use 'speaker plugs or some other terminal which gives a better contact and allows the use of larger conductors. There are a variety of suitable plugs and sockets for connecting 'speaker leads to an amplifier although I am still using the type which accept a banana plug. They work well-enough and I have replaced the wire which runs from PCB to the back of the terminals with something more substantial.
Of all the electronic components which you can replace in a power amplifier, perhaps the most important are those in the feed back loop. These should be replaced with the best you can afford as they are likely to have most impact on the sound quality. If you can't identify them yourself, it should not be too hard to find someone who can although you will need to be able to send them a copy of the circuit diagram.
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Upgrading CD players

Despite the fact that CD's were launched with the promise of perfect sound, it wasn't long before we all found out that the product fell way short of the advertising hype. In fact, nearly any commercially available CD player, particularly models from the budget end of the market, respond quite well to some modification.
I should issue a caution here before you open up your CD player and 'dive' in with a hot soldering iron. Most CD players (and other digital equipment) use a high percentage of surface-mount (SM)components which allows the designer to pack everything into a very small space. There are advantages in doing this including keeping tracks as short as possible which minimises their tendency to pick up RFI. In addition using SM components helps keep production costs down. (The components are soldered onto the PCB's using computer-controlled equipment) SURFACE-MOUNT components are designed to be more compact than their non SM equivalents. Instead of sitting on the top of the PCB with their legs soldered to the tracks on the opposite side of the board, SM components sit on tracks on the top side of the PCB. This makes it easier to solder them into position using mass-production techniques but more awkward using a soldering iron.
The disadvantage for the DIYer is that this makes it very difficult to modify the circuits. Some of the SM components are so small that you need a magnifying glass to see them, never mind identify what they are. So, be warned, modifying a CD player is much more demanding than working on analogue equipment like amplifiers. It's not impossible though but you should practise your soldering skills on a similar piece of defunct equipment before you start on anything important.
There are four main areas to look at when modifying a CD player: the power supply, the transport, the DAC and the analogue output stage. In addition, an upgrade to the system clock is recommended.

The power supply

All the points raised in the Upgrading power supplies section apply equally well to CD players. You should be very careful with CD players as their circuits are much less tolerant of any changes in voltage supply. In addition, CD players contain sensitive circuitry which may be affected by parts of the power supply circuit so you can't just run power lines anywhere. If you are not experienced with digital electronics, seek guidance from someone who is.
It can be particularly beneficial to move the power supply transformer from inside a CD player (or DAC) to a separate enclosure. Close examination of a CD player with a stethoscope (like doctors use) will reveal just how much mechanical vibration is caused by the transformer.
One upgrade often suggested for CD players is to give each part of the CD player its own power supply. With the help of a circuit diagram, you will need to identify the tracks connecting the power supply to each section. Then, being careful to supply exactly the same voltages, build a separate supply for each section.

The transport

Some people are amazed when it is suggested that the transport can have any effect on the sound quality of a CD player. In theory, all it does is retrieve digital information, ie ones and zeroes and surely they are either right or wrong. It should be realized though, that not all the information coming off the disc is correct, that's why the transport has a facility for correcting errors. It was this error correction which was though would provide 'perfect sound'. Although the system corrects most of the errors, in doing so it has to work harder and presumably there is some delay while the error correction takes place. There are still arguments about transports, whether they do affect the sound and, if so, why? From my own experience I have concluded that if the sound can be affected by the surface that the CD player is standing on, then the transport has to be a factor in that change.
Assuming that the transport is crucial to sound quality, what can be done to improve it? There are two types of improvement to consider, mechanical and electrical. Mechanical solutions can include:
  • Changing how the CD player is situated, ie, what it sits on.
  • Changing the internal arrangement by which the transport is mounted inside the casing.
I hope that I've covered the first improvement in the section on Equipment supports. The second solution involves something a lot more radical and should be thought about very carefully before you go dismantling your CD player. An article in 'Common Ground' magazine (Issue 3) discussed a method of removing the sled which carries the disc and laser from the plastic tray which slides in and out of the player. The sled was then suspended by strings on each corner which were fastened to 'anchors' on the sides of the casing. I am planning to test this for myself and have purchased a cheapish CD player for the experiment. I will be including details of the work involved here in the not-too-distant future.
I believe that the sliding tray mechanism, although it makes operating a CD player very convenient, compromises the stability of the reading mechanism. After all, we wouldn't expect our turntables to work very well if they were perched on a flimsy piece of plastic which had to be loose enough to slide about. I know that the two are not the same but I believe the principle applies to both.
As regards the electrical side of the transport, I do not have the skills at present to suggest any modifications although I do know of work being done of that nature. At present, I have been asked not to reveal the details of that work.


When it was realized that CD players could be improved, a new piece of hi-fi equipment, the stand-alone DAC appeared on the market. These items were simply plugged into the digital (or optical) output of a CD player with (hopefully) an improvement in sound quality. Since then, external DACs have got better and many designs have emerged for DIY DACs which can be installed in a CD player replacing the standard DAC circuitry. DAC - stands for Digital to Analogue Converter and,as the name suggests, it converts the digital information retrieved from the CD by the laser pick-up mechanism, into an analogue signal which is sent to the pre-amp via the analogue output stage of the CD player.
If you opt to go with an external DAC, you may be able to audition one or two before you make a purchase. The problem with a kit DAC is that you will probably not be able to hear it before you part with your money. The best option in this case is to try and find other people who have built and heard the DAC kit you are interested in and get their honest opinion about its performance. It is possible to build your own DAC and several designs are freely available if you think that you have the skill to build one. Worm

The analogue output stage

The analogue output stage is comparatively simple to understand (compared to the digital circuits) and is often the first part of a CD player to be modified. On budget models which use transistors to mute unwanted noises caused by switching, a popular tweak is to remove the transistors. (Click HERE for details). Other possibilities include replacing the op-amps, capacitors and resistors with better quality items. You could replace the whole circuit with one using different output devices. Options include, op-amps, transistors and valves.

The system clock

To avoid a long and technical discussion on digital electronics which would only confuse those of us who are not expert in the subject, let's just accept that accurate timing in CD players is of great importance. Just as a school has a timetable so that the kids are in the right place, at the right time, with the right teacher to teach them, the clock in a CD player co-ordinates all the operations in various sections of a CD player so that it works properly. The more accurate the clock, the better the CD performs.
When Phillips and Sony set out the standards for the CD format, they specified that the accuracy of the clock could be as low as +/-1000 ppm (parts per million). At the time it wasn't realized how crucial clock accuracy was to good performance. Not surprisingly, to keep costs low, manufacturers produced players with clocks that satisfied the minimum requirement. Later, when the performance of CD players came in for closer scrutiny, it was felt by some that this level of accuracy (or lack of it) was one of the causes of the harsh sound often associated with CD players.
Since then, a number of improved clocks have become available and there is at least one DIY design. It is more or less accepted that fitting one of these 'super-clocks' to a CD (or DVD) player will improve the performance although the amount of improvement is dependant on the individual player.
The only experience that I have of re-clocking a CD player is when I fitted one to a Cambridge Audio CD4SE. Unfortunately, the CD4SE already has a modified clock circuit and the replacement clock only made things worse. Fortunately, I had the clock concerned on a trial basis (most of the suppliers will let you try one to see if it works in your player) so it wasn't a financial disaster. As regards fitting a new clock to a CD player, you can either have this done by the clock supplier or do it yourself. If you can supply a circuit diagram for your player, the supplier will usually be able to provide you with exact instructions for installing their clock. How difficult the installation will be will depend on the CD player concerned but you don't want to make this one of the first jobs you attempt if you have little experience of modifying electronic equipment!
Currently, replacement clocks are available from:
Trichord Research.
LC Electronics.


Don't forget, as with all hi-fi equipment, pay attention to the case work. Strengthen it if necessary and damp it. Then experiment with how you mount it on a platform.
Here are some interesting links for further information on modifying CD players:
Andrea Cuiffoli's very informative site about building and modifying CD players.
Details of some CD player modifications.
Details of some CD player modifications.
Some articles and essays on digital audio.
A DIY DAC project.
Another DIY DAC project with a discussion about jitter.
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Upgrading Tuners and Cassette Decks

You can upgrade just about any item of hi-fi equipment using the suggestions made on this web site. A tuner will respond to modifications but the improvement will probably be less noticeable than with say an amplifier. I have damped the casework and fitted a different power lead to my tuner, a NAD 412 but will probably not do any more as I am quite satisfied with the performance.
Remember, the biggest improvement that you can make to a tuner is to use the best possible arial. This is an often overlooked component but is probably the most important part of the tuner source. If you are in the UK, then check out Ron Smith's Arial Shop for more information on this subject.
I have not yet done any modifications to either of my two cassette decks as I don't really use them much, preferring my Nicam VCR for recording off the tuner. If you do use cassette tapes a lot and your player has seen a lot of use, consider replacing the tape heads and the drive belts although this can be very difficult on some models as most of the tape transport needs to be dismantled to get at the belts. I've no idea which components I would replace but I would guess the power supply would be a good place to start. If anybody has experience of making improvements to cassette decks and would like to pass on their information, I would be pleased to display it here under their name. The same goes for any other hi-fi modifications which I haven't covered, eg Minidisc.
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