Re: fuses on speakers


"Tomi Holger Engdahl" <then@xxxxxxxxxxxxxxxxxxxx> wrote in message
news:lajr76orccs.fsf@xxxxxxxxxxxxxxxxxxxxxxx
> "exxos" <exxos@xxxxxxxxxx> writes:
>
>> 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.
>
> 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.
>

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



> 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.


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



>
> 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...

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


>
>> Current was the mains was just over
>> 1A so I don't think the Variac was causing problems there...
>
> 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).
>

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..


>> Which leaves
>> the fuse limiting the power ?! I did manage to blow the fuse so power in
>> watts must have been over 200watts....
>
> 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.
>
>> Anyway, has anyone heard of strange things as fuses limiting audio power
>> ?
>
> 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.
>


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.



>> I
>> seem to recall reading a article a while ago that fuses on speakers was a
>> bad idea or something...
>
> 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.
>

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.




>> 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 ?
>
> I don't rememeber seeing anything that is listed as speaker fuses.
>

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



> --
> Tomi Engdahl (http://www.iki.fi/then/)
> Take a look at my electronics web links and documents at
> http://www.epanorama.net/


.

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