Roland KC-350 blown speaker and tweeter

[lowell]

I see these often with the same issues. Blown speakers/tweeters. What gives? Are they underrated? Any suggestions on repairing and making them more reliable?

I've connected the amps to my speaker/tweeter and it sounds fine, so i don't think the amp is causing the issue, which leads me to think they're either underrated or there is a weakness in the PA design.

Here's a PA schematic:

http://music-electronics-forum.com/a...339-195801.jpg

[J M Fahey]

+/-55V rails amount to some 125W@8 ohms, nothing to write home about.

But I bet players drive them to squarewave so that doubles "burning power" for the woofer and multiplied burning power sent to tweeter by, say, 10X , thatīs why they burn first.
And then since sound becomes dull , keyboard player rises volume even more.

I see no protective measures there, neither lamp/fuse/PTC protecting tweeter nor a hard limiter protecting woofer (and listenerīs ears, distorted keyboards are horrible).

[Enzo]

Often? How many have you seen? I have to ask, of the tens of thousands of them, how many did NOT burn up their speakers?

I agree with Juan, too many players think that if there is room on the volume control to turn up, then it must be OK to do so.

I have a number of DJ customers who continually burn out the tweeters on their speakers. Just from turning it up too much.

[lowell]

I've seen 3 in about 4 months. I agree, distorted keyboards are terrible sounding, and I've heard many a player drive these into distortion. I'll look into a bit of protection. By hard limiter do you mean in the power amp, or some "flyback" type diodes to the rails on the output? I'd think those would limit, but still cause hard clipping.

[J M Fahey]

You should fuse the speakers, using internal floating pigtail fuse holders, so he has no access to them.
Use 4A regular (fast blow) for the woofer, it allows endless 120W RMS which is max clean output but will blow in a few minutes if driven to squarewave.
Add a 12V , 15 to 22W car lamp in series with tweeter, it will limit current to somewhere abov 1 or 1.2A and is self resetting.
IF the keyboard player is Terminator he will eventually blow the lamp .... his problem not yours.

A similar Peavey Keyboard (or PA or Bass or Pedal Steel) amplifier again with +/- 55V rails will work flawlessly 24/7/365 no matter what, because it includes excellent DDT compression.