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fuses on speakers

Discussion in 'Misc Electronics' started by exxos, Jan 30, 2006.

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  1. exxos

    exxos Guest

    Hi all,

    I ran a amplifier via a fuse on the speaker and while the audio was loud it
    wasn't as loud as it should be, I took the fuse out (soldered over it) and
    the sound was much greater. For testing I also was running the mains input
    via a 2A variac (which I also took out). The speaker fuse was a regular
    1.25" 2A and Variac was a small 2A type. Current was the mains was just over
    1A so I don't think the Variac was causing problems there... Which leaves
    the fuse limiting the power ?! I did manage to blow the fuse so power in
    watts must have been over 200watts....

    Anyway, has anyone heard of strange things as fuses limiting audio power ? I
    seem to recall reading a article a while ago that fuses on speakers was a
    bad idea or something... Also I recall seeing speaker fuses listed *as*
    speaker fuses... I wonder if they actually have to be a special type...
    anyone come across anything like this ?

    Cheers,
    Chris
     
  2. Don Bruder

    Don Bruder Guest

    Some fuses (particularly the "slo-blow" type) have the unintended
    side-effect of being inductors due to the way they're constructed -
    Namely, a bit of fuse-wire coiled on a form of some type.

    I would expect these to be a *POTENTIALLY* bad thing for speaker/audio
    use - Exact measurement of "how bad" would almost certainly depend on
    what frequencies are being sent through them, among other considerations.

    "Speaker" fuses are almost certainly constructed so as to be "zero
    inductance" - A straight chunk of fuse wire, rather than a coil.
     
  3. exxos

    exxos Guest


    hmmm, these ones I am using are a straight wire cap to cap, they are time
    delay types aswell, I guess there must be *something* different with speaker
    fuses over normal fuses as they are silly money at that.

    Chris
     
  4. CWatters

    CWatters Guest

    hmmm, these ones I am using are a straight wire cap to cap, they are time
    Fuses have resistance. Sometimes several Ohms. Compare with an 8 Ohm
    speaker.
     
  5. exxos

    exxos Guest

    the 2amp fuses measure 0.1ohms, the 1amp fuses measure 0.3ohms....

    Chris
     
  6. I don't think that a regular 2A fuse would have much effect on the
    sound volume. Based on the data at
    http://www.cooperet.com/library/products/GMA_Specs.pdf
    it looks like a fast acting 2A fuse has less than 0.1 ohms
    resistance and maximum of 250 mV voltage drop (this is when
    it is heavily loaded). The other fuse types like slow flow etc..
    could have slightly different resistances.

    Those resistances of the fue should not have any great attenuation
    on the sound. I think the small sound attenuation caused by the
    fuse itse sould not be easily heard on the sound volume...
    the difference in sound volue would be a smll fraction of decibel,
    something so low that you could berely hear it, definately not a
    great difference. The fuse may have some other aspects of
    sound of the speaker, that coudl be heard or not.

    If having the fuse at place has very considerable effect on
    the sound volume, I quess that there would be some other reasons
    for that than jut the fuse itself. Maybe the old fuse holder is
    makign bad connection to fuse, and there is considerable resistance
    there... that could have some considerable effect, both on sound
    and heating of the fuse holder...
    Using variac between maisn power and the equipment can have effect
    that can be heard. If you do comparisions of with and wihtout fuse,
    use the same powering setup (both times with or without variac).
    Fuse starts to limit the power considerable when it blows up.
    Before that the fuse power limitation is generally quite small..
    There is some small resistance, that can get few times higher
    bfore the fuse blows.
    I have heard strange things once when there was an old fuse
    holder making bad connection and old almost blown fuse in it.
    Repairing those got things right. Repairing in this case
    included cleaning the fuse holder with help of contact
    spray and some mechanical work. And then putting in brand
    new fuse.
    Having fuses on the speaker line is not the best idea.
    The fuse has some resistance.. and that resistance can change
    somewhat depending how hot the fuise gets during the use.
    I don't rememeber seeing anything that is listed as speaker fuses.
     
  7. CWatters

    CWatters Guest

    Just had another look at your OP. Seems you changed two things at once? So
    you can't be sure which it was (fuse or variac) that caused the prob. Try
    one at a time.
     
  8. exxos

    exxos Guest

    Yeah, my bad for changing 2 things at once, I think I will have to put the
    variac back on and see what happens.... can't see how either could effect
    the thing though.... will try and retest tomorrow...

    chris
     
  9. exxos

    exxos Guest

    Yeah, according to my meter I get 0.3 ohms...



    I doubt the fuse could have any effect even on audio frequencys up to 20khz
    ?


    its a new fuse holder, even made a point of using 1.25" fuses and holders to
    make sure theres a good connection...

    I can't see the variac having any effect, the amplifier only pulls just over
    1amp on the bass notes, a 2amp variac... ive measued the voltages from it
    and everything seems fine there also..


    At my old job we used to repair power supplies, we had a power supply where
    a 28V rail was only 12V, 28V one side 12V the other... turns out the fuse
    had about 7 ohms across it, we never seen anything like that in the 10 years
    we was doing them! the fuse was supplying about 2amps current at that
    aswell... a new fuse and everything was fine.


    The only thing which seems odd as it seems to limit the entire audio volume,
    you would think if it was limiting something that it would limit the bass
    which needs the most power... Even if the variac couldn't supply the current
    you would expect it to be the same volume on none bassy tracks.... really
    strange, fuse or variac it doesn't make much sence.



    they are normally lised in PA audio sections so unless you look for them you
    may not have spotted them ?, I didnt even know until I was looking though a
    PA section and they listed fuses for speakers, like £8 each of something
    stupid like that :-\

    Chris


     
  10. JANA

    JANA Guest

    A slow blow fuse would be expected to introduce some losses. Slow blow fuses
    are generally of a higher resistance than the fast blow ones. A fast blow
    may introduce a very small amount of loss, but it should not normally be
    great enough for you to hear it.

    --

    JANA
    _____


    Hi all,

    I ran a amplifier via a fuse on the speaker and while the audio was loud it
    wasn't as loud as it should be, I took the fuse out (soldered over it) and
    the sound was much greater. For testing I also was running the mains input
    via a 2A variac (which I also took out). The speaker fuse was a regular
    1.25" 2A and Variac was a small 2A type. Current was the mains was just over
    1A so I don't think the Variac was causing problems there... Which leaves
    the fuse limiting the power ?! I did manage to blow the fuse so power in
    watts must have been over 200watts....

    Anyway, has anyone heard of strange things as fuses limiting audio power ? I
    seem to recall reading a article a while ago that fuses on speakers was a
    bad idea or something... Also I recall seeing speaker fuses listed *as*
    speaker fuses... I wonder if they actually have to be a special type...
    anyone come across anything like this ?

    Cheers,
    Chris
     
  11. larya

    larya Guest

    Please put the fuse back in.....
    The fuse protects both the amplifier and speaker from excess power to
    the speaker...
    I used to work, retired, for a tv station.. During my early years, we
    got a call to the audio room of the studio.. One speaker was dead.. It
    turned out that the fuse, in the speaker cabinet had blown.... It
    turned out that the series capacitor, from the amplifier to the speaker
    had shorted out... If it wasn't for the fuse the amplifier would have
    seen the speaker and would probably had become damaged as well...
    If you want more power then get a larger amplifier and speaker system
    but please keep the fuse in the speaker cabinet.. It does service a
    purpose...
    Larry ve3fxq
     
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