Why is my fuse glowing?

psykod

Ok, while trying to figure out a strange popping sound/distortion coming from my Polk SR6500's, I noticed that the fuse on the crossover starts glowing in rythm with the music when the volume is turned up. It's not playing all that loudly.

I'm running an Alpine 9855 Head Unit with an Alpine PDX4.150 amplifier. The crossover is set to 80hz with an 18db slope.

The popping sound was occurring even at low volume on some musical content so I grabbed an old 6ohm speaker from a ghetto blaster and connected it to amp in place of the right side Polk SR's. Low and behold, the popping was still occurring so it wasn't the Polk speakers causing the problem.

I then disconnected my Alpine head unit and ran an old home cd player that had built in volume control directly into the input of the Alpine Amp. The popping went away. (This completely removed the crossover so I was sending a full range signal into the speakers).

So I hooked the Polk SR's back up to the Alpine amplifier while still using the home cd player and could not detect any popping. I then hooked my Alpine head unit back up and could not hear any popping any more. I could, however, hear some scratchiness in the speaker even at low volume if I listened very carefully.

I suppose the RCA's could have been making a bad connection but I don't know for sure. I'm pretty sure this problem will return but I'm hoping for the best.

At any rate, it was when I was troubleshooting all of this that I noticed that the fuse in the crossover that protects the tweeter was glowing when I turned the volume up. Is this a normal occurrence?

I checked the DC resistance at the crossover input and it was approximately 4 ohms. The same for the input resistance to the SR's woofer.

I checked the DC voltage at the crossover input from the amplifier and it was about 2.9 millivolts.

psykod

Well it looks like the "fuse" is more of a tweeter protection bulb which glows causing an increase in resistance which reduces power going to the tweeter. It appears to be designed this way.

exalted512

psykod wrote:

Well it looks like the "fuse" is more of a tweeter protection bulb which glows causing an increase in resistance which reduces power going to the tweeter. It appears to be designed this way.

100% correct:cool:

Greg Peters

It is a light bulb/tweeter protection circuit. I've read on the forum here that if it stays illuminated much, you should lower your amp's gains.

An occasional flicker from the bulb during big transients shouldn't cause a problem, but if it's lighting up pretty regular in normal listening you should seriously consider dialling those gains back some.

While I'd trust the tweeter protection circuit to do exactly that, your speakers are rated for 125 watts continuous and it seems you are giving them 150 watts. Are you wiring them with a single amplifier channel powering each crossover or biamped? Single amp channel @ 150 rms shouldn't be a big deal, but 150 rms to each mid and each tweeter biamped is probably too much for long-term reliability purposes. If you have to have it this way, make sure you run minimal gains on the tweeter channels.

audiobliss

Greg Peters wrote:

It is a light bulb/tweeter protection circuit. I've read on the forum here that if it stays illuminated much, you should lower your amp's gains.

An occasional flicker from the bulb during big transients shouldn't cause a problem, but if it's lighting up pretty regular in normal listening you should seriously consider dialling those gains back some.

Personally, I'm thinking that unless the bulb gets really really bright and then goes *pop*, then you're not running enough power! :D


Ok, so obviously I'm either crazy or joking...and I can't believe I'm leaving it up to y'all to decide.

killerb

i had the same problem with that bulb. it would glow and cause a popping sound in the tweeters with very little power. i got sick of it and went active crossover. now can run with plenty of power with no problems.