Service Bulletins . . . . .

frayed wires touch each other at where they connect to either the amplifier or the speaker

speaker wiring has been joined

thick "monster" cable is connected to amplifier or speaker terminals which cannot readily accept such thick wire

a staple (or other such device) retaining the wire has gone through the plastic insulation of the cable

Most of us never realise that our speakers may be performing well below their ability. This is because many speakers deteriorate very gradually over time, so we do not notice the performance degrade.

The common problem is that the foam rubber that delicately suspends the cone perishes. This causes flabby and reduced bass with little definition.

The coil (attached to the cone) moves inside a very small gap within the magnet. When it is not suspended correctly, it can rub against the magnet causing potentially serious damage to your amplifier and risks permanent damage to the speaker.

Fortunately, at Dr. Hi Fi we can usually do a very thorough job in repairing speakers. Rather than just replace the foam rubber (which some firms do), we first remove the cone and spider entirely to inspect the voice coil. Any damage to the coil is usually repairable with some delicate surgery. The cone is then re-mounted and centred precisely with a new high quality foam rubber surround.

It is a great joy when you get the speakers back home. You will be astounded at how much better they now sound (and realise how sick they were!).

The deterioration is primarily caused by humidity. Foam rubber is generally used on better quality speakers as it provides ideal suspension which is critical to a speaker's performance. The foam rubber can deteriorate significantly in only a few years, so it is a good idea to check speakers regularly. Sometimes only one may clearly show deterioration, but it is always recommended to do both speakers.

Checking most speakers is easy. The front panel is designed to be removed by gently pulling it away. Look for cracks in the foam rubber around the outside of the larger speaker cones. Sometimes the foam rubber will become tacky to the touch. If you detect a fault, have it repaired quickly as this will minimise further damage (that can be permanent).

Speakers themselves rarely develop problems other than those described above. The other main cause of damage is of course playing them too loudly! Speakers that suffer from this "disease" are easily diagnosed when the voice coil is removed and inspected.

It is a misconception that if a 50 watt speaker is driven by a 25 watt amplifier, that the speaker can therefore handle all of the amplifier's power. When the volume is turned up to a level where the amplifier is running out of power, the amplifier distorts the signal. The distortion component of the signal can then damage the speaker, especially tweeters. Of course, an amplifier of 100 watts can damage a 50 watt speaker by overload.

Put simply, any amplifier can damage any speaker, irrespective of power figures. Ideally, an amplifier should be as powerful as possible, and controlled by a sensible user! When the volume is turned up, there will come a point of audible distortion. Whether the distortion is caused by the amplifier or speaker is irrelevant - the maximum safe volume for the hi fi system has been reached, and the volume should be turned down to safeguard against damage.

Amplifiers can develop a fault that can destroy a speaker in a brief instant. This occurs when the amplifier blows up and goes what is known as "D.C." (often a loud hum is heard). Most amplifiers have a protection system designed to shut down the output of the amplifier to the speakers when this problem occurs. Sometimes it doesn't work quickly enough. It is a common misconception that amplifier protection systems are designed to protect the amplifier. They are designed to protect your speakers from the damaged amplifier. If an amplifier has gone "D.C." it must be repaired, often with the speakers.

As with all repairs at Dr. Hi Fi, they are guaranteed. Naturally, that does not include speakers damaged through excessive volume levels or if an amplifier has caused the fault and not been repaired at the same time.

The main advantage of Compact Discs over vinyl records is that a healthy player itself will not wear or damage the compact discs. In most other respects, they are the same.

Compact discs must be handled with much care. They should be kept very clean, free of dust and finger marks. The player itself must not be allowed to collect dust.

Dust is the enemy of compact discs. Being plastic, they attract dust. Care is needed in handling them. They can scratch easily, causing problems that are worse than a scratched vinyl record.

When dust gets into a compact disc player (through its ventilation holes or via the disc), the damage can be permanent. Dust on the laser's lens can be removed; dust that settles in the cavity in which the lens sits can often not be removed. The lens is delicately suspended within this cavity, and moves up and down to focus on the disc, and sideways to track the disc.

With compact disc players, a variety of faults can cause the common symptom of mistracking or inability to correctly read the compact disc. Diagnosis can be an involved procedure as each possible cause must be assessed and repaired.

The problem may be simply dust on the lens. Next time, however, the laser itself may produce the identical fault.

As such, with these symptoms, repairs of compact disc players can be guaranteed only if the laser is replaced.

Unfortunately, all too often pre-recorded cassettes utilise inferior mechanisms. With blank cassettes one should avoid cheap ones; expect to pay at least $7+ for a C90 cassette. Do not expose cassettes to heat or sunlight (common in cars) nor moisture.

As a cassette is being chewed, the sound will usually become garbled and the pitch may seem to alter. Try to detect this and immediately stop the machine and remove the cassette to avoid damage to the machine itself. If the cassette will not come out do not force it as this may compound the damage.

FM radio reception is similar to television reception. A good "clean" signal is needed for quality stereo sound.

FM reception can suffer from the effects of "ghosting" where the same signal is received twice – once directly from the transmitter and the second signal a fraction of a second later after it has bounced off a building for example. This is also called Multi-Path reception. A "clean" signal is where only one signal is received.

If the signal strength is good, yet there is distortion, then the chances are multi-path is to blame. If moving the antenna does not help, then a directional antenna is needed, which is pointed at the transmitter, just like a TV antenna. Quite often using an existing VHF TV antenna will solve the problem. In the worst cases a separate external antenna for FM may be needed.

Many are fortunate in that the supplied internal or indoor FM antenna is sufficient. These come in various forms such as a one metre length of wire, a "T" shaped antenna made of flat ribbon cable or a telescopic metal whip antenna.

Should the internal antenna not be satisfactory, then the next step is to try connecting the receiver to an external VHF TV antenna. This requires normally a connection to a wall socket using coaxial cable (a "splitter" may be needed). Failing that, then an external antenna for FM may be required.

It should be noted that antenna boosters are useless if you are have receiving multi-path signals. Boosters are rarely required in metropolitan areas.

As AM radio reception is directional, the orientation of the receiver’s antenna will significantly affect reception quality.

With most modern tuners or receivers the aerial is an external device, often connected to the receiver with two wires (one goes to the "Ant" terminal and the other to a "Gnd" terminal). The antenna can then be moved for good reception and hopefully placed in a convenient spot. Sometimes the aerial is a rod like device on the back of the receiver. This can usually be rotated for optimum reception. If the antenna is within the receiver then you must position it for good reception (often inconvenient!). An alternative is to run a length of wire (at least five metres; any type of insulated wire is fine) which connects to the AM Antenna terminal on the back of the receiver.

AM radio is more susceptible to interference than FM. This can be generated by large electrical appliances (fridges, lifts in nearby buildings). Changing the direction of the antenna can reduce the level of interference.