Proudly making Quest AV equipment in Australia since 1988
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abn 99 064 323 255  also t/a Quest Electronics ®  and Quest AV ®
Phone and SMS ... 0431 920 667 Mail ... POB 348  Woy Woy  NSW   2256
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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