Mystery problem

[cafe latte]

Hi,
have a couple of high powered Yamaha power amps, come with very detailed hand book/manual, covers lots of topics! In the notes on speaker protection, don't advocate fuses for this purpose as ones with a low enough rating to protect the tweeter will blow on musical peaks and higher ones will offer no protection.
True this is in regard to a PA / Studio situation, but pretty much the same at home.

Regarding the above, a friend and I both have Gale 401 speakers, these come with fuses for mid and treble, (general opinion is to remove them at once!). He used his as monitors in his home studio, treble fuse kept blowing, removed and hard wired the connection, speakers used for many more years (and still going) no problems.
Maybe, My tweeters are 90 watts RMS which is very high for a tweeter. I doubt they well ever see anything like that even in peaks in normal music. I have read that slow blow fuses are the way to go as they handle any peaks better. I was looking for a fuse value high enough not to blow during listening, but that will offer some protection in the event of a wire coming out again.
Regards
CL
Paul

[paul401]

Maybe, My tweeters are 90 watts RMS which is very high for a tweeter. I doubt they well ever see anything like that even in peaks in normal music. I have read that slow blow fuses are the way to go as they handle any peaks better. I was looking for a fuse value high enough not to blow during listening, but that will offer some protection in the event of a wire coming out again.
Regards
CL

Hi,
I understand what your after, but as I say, I don't think it can really be done in an effective way, balancing the continuous blowing against protection is a difficult circle to square. I personally wouldn't trust a fuse to save a tweeter.
The problem is compounded because the nasty sound of a bad connection, like you heard, is at a high level, if this causes the amp to produce a clipped signal then the tweeters cone/dome hits it's travel limit, all the excess energy turns to heat --- result vaporised voice coils!

Paul

[Whitneyville]

As a budding DIY speaker designer/builder, normally a tweeter sees no more than 10-15% of the total input power (watts). Fuses, or even the solid-state Poly-Fuses don't "act right" at high frequencies. They tend to blow too quickly or suddenly, too late, because of the "skin effect" (Google it). Current limiters (fuses, breakers, solid-state fuses) work MUCH better below 1KHz. From my US Air Farce(sic) RADAR training, at high frequencies to microwaves, usually you shut down the driving amp thermally in the case of an overload, and it's easy to shut the amp down REALLY fast, with-in a "few" sensed clipped waveforms. PA amps sense feedback and "back-off" on their own today to prevent meltdowns.
Locking RCA's are a minimum answer. Speakon plugs are PA's solution to cable disconnections. Pull on the wires in screw-type binding posts hard enough, and the wires can slip or break. Speakons lock in and you have to break both wires and the insulation, probably knocking over the speaker(s), so at least you know about it. Five-way binding posts on amps and speakers took decades to become standard. I'd love to see Speakons become standard quickly. And let's dump ANY non-positive interconnect like the "RCA" SOON!

[kelvinMunson]

Skin effect is really only of interest at RF, since the skin depth in copper at 20 KHz, the upper end of the audio band, is 0.471 millimeter.

This means that for wire fuses rated below about 40 amps (listed the data below) there is no increase in resistance due to skin effect.


Fuse wire rating (A) Cu Wire diameter (mm)
3 0.15
5 0.20
10 0.35
15 0.50
20 0.60
25 0.75
30 0.85
45 1.25
60 1.53
80 1.8
100 2.0

[Whitneyville]

Kelvin, most fuses are made of babbit, a lead-tin-antimony-bismuth alloy.Bussman (the largest fuse company in the world) explains in painful detail in their engineering manual on their fuses and circuit breakers how they are not recommended for use above 120 Hz. They have a separate line (and physical sizes) of 400Hz aircraft fuses. There is also a difference in low voltage (32 WVDC) and high voltage (250 WVAC) fuses. Interchanging the types can be deadly.

[kelvinMunson]

Hi Whitney,

Thanks for the aircraft related info, I've just retired after 40 years in the aerospace industry designing avionics equipment so I already had a bit of background. Always willing to learn though

But we are not talking aircraft systems here and most fuses used in hifi equipment are actually not made of babbit, they are enclosed wire type.

For info, the fuse voltage rating relates to the ability of the fuse to withstand the specified voltage after blowing, you wouldn't normally use high voltage fuse in your home hi-fi speaker line, though of course YMMV

[josephazannieri]

Yo cafe latte:

Do you know what caused the high pitched squealing? Have you been able to cure that problem? An amp that's oscillating like that may have some serious problems that need to be looked at.

You might also also want to look at your crossover capacitors and be sure you don't have one that has shorted. That would pass a lot of low frequency energy to your tweeter, maybe more that it was designed for, and allow it to overheat and get killed off. Just whip a DVM or an LCR meter on cap, and see if capacitor charges up and has right capacitance. If it charges up, then it will probably block the lows out of tweeter.

Also, can you replace the fried tweeter? I certainly hope so! You hate to lose a speaker you like, or have to cobble a tweeter in if you can't get the right one.

And those pieces of advice, combined with $1.00, will get you a cup of senior coffee at McDonalds, for what that's worth.

And good luck from that burnt- out old coffee drinker,

Joe Z.

[cafe latte]

Yo cafe latte:

Do you know what caused the high pitched squealing? Have you been able to cure that problem? An amp that's oscillating like that may have some serious problems that need to be looked at.

You might also also want to look at your crossover capacitors and be sure you don't have one that has shorted. That would pass a lot of low frequency energy to your tweeter, maybe more that it was designed for, and allow it to overheat and get killed off. Just whip a DVM or an LCR meter on cap, and see if capacitor charges up and has right capacitance. If it charges up, then it will probably block the lows out of tweeter.

Also, can you replace the fried tweeter? I certainly hope so! You hate to lose a speaker you like, or have to cobble a tweeter in if you can't get the right one.

And those pieces of advice, combined with $1.00, will get you a cup of senior coffee at McDonalds, for what that's worth.

And good luck from that burnt- out old coffee drinker,

Joe Z.

The first time it was a loose power amp rca lead that caused a massive feedback the second time I think it was the missus hoovering that pulled one channel three pin psu lead partly out so it was making partial connection. When I looked round the back of the amp it was all that i could see wrong. I pushed it back in and all was again well. I managed to order replacement coils for my tweeter I bought two just in case and have since replaced the blowen coil and have had no issues since saying this I check all connections after the missus has done her cleaning
Regards
CL

[Blue Angel]

Sorry to hear about the misfortune C/L

Perhaps it will be an idea to post that boxing cow to guard over the wires?

ba

PS I also suffered some tweeter fizzle a while ago. The missus decided to make a phone call and she turned the pre's volume up instead of down

[cafe latte]

Sorry to hear about the misfortune C/L

Perhaps it will be an idea to post that boxing cow to guard over the wires?

ba

PS I also suffered some tweeter fizzle a while ago. The missus decided to make a phone call and she turned the pre's volume up instead of down

Dont you just love em
My fave animal pic was the one of your dog in the pillow case seriously funny

[Blue Angel]

Thanks, C/L

I think it has since discovered it has a reverse gear

Now I'm waiting for another cow story - something along that it has discovered your stash of cold beer...

ba

PS I read your adventures with the ESL's - very interesting. I've been offered a pair which is in superb cosmetic condition but this will have to wait until a do something about a pair of 12" Goodmans Triaxioms sitting in my workshop.

[cafe latte]

Thanks, C/L

I think it has since discovered it has a reverse gear

Now I'm waiting for another cow story - something along that it has discovered your stash of cold beer...

ba

PS I read your adventures with the ESL's - very interesting. I've been offered a pair which is in superb cosmetic condition but this will have to wait until a do something about a pair of 12" Goodmans Triaxioms sitting in my workshop.

Bad dog leave my beer alone!
No new pics I am afraid, but the boxing bull is still in training it has become a bit of a habit.
Re the Esls I have quite a few pics to post but I have held back as I want to post more a tutorial than a saga. I have recieved the new treble unit and the psu, but it has been a very busy few days so I have not had time to connect them yet, I hope this sorts the issues. If you ever do strip any down please pm me as i may be able to save a few headaches, I hope this psu solves mine .
Regards
CL

[Blue Angel]

Thanks Caffe Will do.

Regds

ba

[magnaflux]

I have heard of people using a neon bulb in parallel across the speaker leads. I do not know if this would work. Anybody have an idea if this would prevent the voice coil from getting to much power? Just a thought...