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What are phono plugs and what is the problem with them? Phono plugs are probably one of the most common types of connectors in use today for connecting audio and video signals. They have been around for many, many years... since the earliest record player pickups needed to be connected to their amplifiers. In fact that's how they got their name, it's an abbreviation of "Phonogram". I don't know the exact history of this next name "RCA plug", but it is likely that they were named after the Radio Corporation of America (or RCA) who, no doubt, used them in phonograms that they used to make in those days long ago. Other names you may see are “Cinch plug” and “Pin Jack”. Phono plugs were designed to interconnect a single, shielded, unbalanced audio signal. You need two of them for stereo and you need to get them the right way ‘round (for left and right channels), so they are usually marked white or black for left and red for right. These connectors have also found their way to being used for connecting composite video signals too, and yellow is usually the colour for that purpose. Their use for video is restricted to domestic and some semi - pro video gear. They are not suitable for critical video or RF applications because they do not have a characteristic impedance of 75 ohms as required for video cabling, and most of them have no locking mechanism, so it is too easy to pull them out. One of the main problems with these connectors (and the reason for this article) is that the outer connection which is used for the screen or earth side makes a pretty poor connection in many instances. With an audio signal you may get some hum and/or some RF pickup, but with video the signal can look really terrible because a good screen connection is essential for the 75 ohm impedance to be maintained. The visible effects of a bad screen connection
include multiple images (ghosting), smearing of fine details, incorrect colours, unstable synchronisation, video signal present in audio (buzzy sound), etc., etc. Why does this happen? Well, the outer shell of a phono socket (the part on the equipment) is mainly manufactured these days with parallel sides. They look nice and straight, but they make no better or firmer connection as the plug is pushed in. Phono plugs are affected too. The nice looking ones with a machined / turned appearance have parallel sides inside and also make no better contact as they are pushed in. Because these plugs are so rigid, it is very hard to squeeze the sides in a bit without cracking the metal they are made from and if you squeeze them too much they just won’t go in. I have measured many problematic phono plug and socket combinations with an ohmmeter and found that the shield connection is not touching at all! Changing to a different cable, but instead with the pressed metal type of shield contact (which is really easy to squeeze without damage to the plug or the fingers doing the squeezing), has cured many audio and video problems over the years. It is also possible to buy many types of very high - quality phono plugs and cables using spring - loaded or other clever internal mechanisms which also make very positive contact. If you are having audio and video problems which are intermittent and disappear as soon as you move the equipment to have a look, it might just be due to the type of phono plugs you have. If your connectors are dull looking or lightly corroded a very little spray of a quality electrical lubricant such as CRC 2 - 26 will help. Wipe off excess with a lint free cloth to prevent marks on furniture. Hint: Spray some onto a cotton bud and use it to apply a thin film. (c) 2000 Quest Electronics abn 99 064 323 255
The Problem with "Phono" plugs