Newsgroups: sci.electronics
Subject: Re: Speakers loose tweeters and filter elements
From: MATGBB@LURE.LATROBE.EDU.AU (BYRNES,Graham)
Date: Tue, 29 Dec 1992 03:31:20 GMT
Organization: La Trobe University
X-News-Reader: VMS NEWS 1.24


In <1517@chorus.chorus.fr> ngk@opera.chorus.fr writes:

..> 
> 
> 	Hi netters,
> 
> 	I have a pair of JAMO-300 speakers. Their specification is:
> 
> 	- 8 Ohm impedance.
> 	- 300 W / each.
> 	- 4 ways SP system with passive filters.
> 
> 	I use them with a Samick SM-6000 Stereo Power Amplifier (250W/channel)
> for dancing parties.
> The problem is that I often have the tweeters and/or some capacitors of the
> filters broken, but never the other elements. I think that the filters for
> the broken tweeters are not well designed or it misses some sort of protection.
> So I'm wondering if any one can tell me how to avoid such a situation for the
> next time I use them (i.e. an active/passive protection circuit or a
> modification in the filters).
> 
> 	I give you here the diagram of one speaker system :
> 
> 
>         +-------+------------+----------------+------------------------+
> 	|       |            |                |                        |
>         |       |        C1 -+-           C2 -+-                   +---+---+
>         |       |           -+-              -+-                   |       |
>         |      |-|           |                |                  + |       | +
>         |      | |          |-|               +----+             |\+-+   +-+/|
>         |   L1 | |       L2 | |               |    |          T1 | | | T2| | |
>   +     |      | |          | |          C3  -+-  |-|            |/+-+   +-+\|
>   o-----+      |-|          | |              -+-  | |            + |       | +
>                 |           |-|               | L3| |              +---+---+
> To PA           |            |              + |   | |                  |
>   o--+          |            |              |\+-+ |-|                 |-|
>   -  |     +----+       +----+----+      T3 | | |  |               R1 | |
>      |     |    |       |    |    |         |/+-+  |                  |-|
>      |     |    |       |   |-|   |         + |    |                   |
>      |   + |    |     + | L4| |   |           +----+                   |
>      |   |\+-+ -+-C4  |\+-+ | |  -+-C5        |    |                   |
>      | B1| | | -+-    | | | | |  -+-         |-|  |-|              C6 -+-
>      |   |/+-+  |   M1|/+-+ |-|   |        R2| |  | |R3               -+-
>      |   + |    |     + |    |    |          |-|  |-|                  |
>      |     |    |       |    |    |           |    |                   |
>      |     |    |       |    |    |           |    |                   |
>      +-----+----+-------+----+----+-----------+----+-------------------+
> 
> 
> 	all capacitors are bipolar chemical capacitors
> 	C1 = 10uF, C2 = 3.3uF, C3 = 4.7uF, C4 = 22uF, C5 = 10uF, C6 = 1uF
> 
> 	Li are air/iron core selves (inductance) values are unknown.
> 
> 	all resistors are winding/carbon 10W resistors.
> 
> 	R1 = 12 Ohms, R2 = 10 Ohms, R3 = kind of varistor (ceramic disk form)
> 
> 	B1 = bommer, M1 = medium speaker, T3 = medium-tweeter, T1=T2 = tweeters
> 
> 
> 	What happened:
> 
> 	T3/C3 are broken very often.
>         T1 and T2 eventually.
>         M1/C5 sometimes.
> 	B1 never broken.
> 
> 
> 	Thank you very much for any advice.
> 
> 
> 				Gia-Khanh Nguyen (ngk@chorus.fr)
> 
Well, my first advice would be to turn down the volume a wee bit. However
there os one other possibility. It could be that the caps are dying first,
which would guarantee the demise of the tweeter(s). Bi-polar electros
have a relatively high dissipation factor, so at the levels you are running
them, it is concievable they are running too hot. Why not replace the smaller
ones with polyester film types? Even 10uF greencaps are cheap compared
to replacing tweeters every week 8-).

Next, it could be worth the following: borrow a cro, hook it across your amp
output, and see at what level it really starts to clip. If you are running
from a cd player, you should be able to find out its max output, and determine
at what volume knob position that will cause clipping. Then put a mark saying
"Il est defendu sur peine d'assasination de faire tourner l'attenuateur au-dela
de ce point".

By the way, do you have any hearing left? any neighbours?
Bon chance,
Graham
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