fuses and subwoofer overload

[invictius]

The latter, I posted in sound and video, but the guys there may not have the expertise to answer it:

I don't normally use my logitech z-680 speakers, but yesterday, I did, and noticed the bass didn't sound quite "right". Anyway, I started up vmware later, and everytime I'd start it up, even with the systray's volume control muted, I'd get a very low, loud, constant hum. This happened each time I ran a virtual machine (e.g ran the app), 3 times. I thought my sub was finally ruined, but it turns out that the mike being plugged in caused it - vmware was ignoring the fact that I had the mike muted. This huge humming was the loudest and lowest form of bass I've ever heard (and I'm used to VERY heavy bass), looking back, it sounded a lot like inteference - imagine the sound of putting a mike too close to a speaker, but a lot lower. Has this damaged the sub? Wouldn't my fuse have blown before anything could have been damaged?

Also, the sub takes a slow-blow fuse. It seems I only have fast-blow fuses, but they're the same amp rating. Is it safe to use these in a pinch, and do slows generally have a thicker wire inside them/fasts have a thinner one - these are what mine look like?

[GigaForce310]

If your sub takes a slow blow fuse, then a fast acting fuse will probably blow out. While there isn't a danger as it will act faster, you will more than likely blow out your fast acting fuse.

Slow blow fuses are typically used in applications where a surge of current is normal and will not cause damage to your equipment.

For example, a DC motor might use one as they draw a high amount of current the moment you give it power. As the motor speed increases, the current draw decreases. So if you give a 1.25 amp 12 volt DC motor 12 volts, it might draw 10 amps initially. As the speed gets higher, the current will lower untill the motor speed approches the final speed. At that point the motor should draw a fraction of an amp. You could put a 1 amp slow blow fuse on it to keep it from blowing during the surge and protect the motor from being overloaded. Say the motor is locked. It will draw 10 amps continuously which will allow the fuse to heat up and blow out. The other option would be a burnt out motor.

As for the actual cause of the noise, I suspect your getting 60 hz from an AC line. For example, if your signal wire is parrellel to a power cord, it may couple to the 60 hz. Another problem might be a ground loop.

[four4875]

basically, what he said ^

the slow blows usually take a sustained current to blow, and can handle the spikes (when the psu of it is first plugged in, and the caps all charge up)

i dont think the fuse would prevent you from damaging the sub, but i would be confident that logitech designed their system with an amp incapable of blowing that sub, unless you were driving it with a square wave or somethin. but yeah it sounds like something was pickinup some 60 hz or some feedback loop from the mic.

[invictius]

As for the actual cause of the noise, I suspect your getting 60 hz from an AC line. For example, if your signal wire is parrellel to a power cord, it may couple to the 60 hz. Another problem might be a ground loop.

The mike is taped to the speaker (not directly on it, but on the plastic shell) and this has never happened whilst the phone is being used.

[Skeith]

I would think its probably a ground loop. But if your mic has got a poor connection, like if the cable has been snagged or just wore out you may just have an incomplete loop on the mic. When this happens you end up with basically an antenna on the tip of the mic input. It pics up noise and amplifies it. It also creates a capacitance inbalance that can react with the line frequancy or noise on the DC line to create a buzz or hum.

For example if you play guitar or have a stereo with an aux conenction plug in the cable to the amp/stereo but not to the component. You should notice a buzz. This is from an incomplete loop. Now touch the tip (the center pin on the guitar cable or RCA cable) you should notice the hum get louder. This is because you increase the capacitance on the line. It is much easier to hear this with a guitar amp because It has a very high gain. Also since your speakers are self powered pull the plug from your sound card and touch the tip of the plug, you should hear a buz or hum make sure the volume is low so you dont damage it. In all the cases dont touch the shild or outer conductor on the plug or you will partialy complete the loop and the hum will become quieter.

Im thinking your mic has a bad connection and the hum is being pulled into the sound card, being amplified and then sent to the speakers where it is amplified once again.

I highly doubt you killed the woofer. The amp would probably die before the woofer. I have put the woofers on my stereo through alot of torture. Good ol 80's stereo equipment Sound beautiful.