Some time ago I built a 24dB per octave crossover (you can see it in one of the first of my blog posts). I originally had my two way speakers hooked up via a cheap 4 x 100W switchmode amplifier from Sure electronics. It was good I thought I could do better.
I set up a four channel amp based on the excellent but modestly powered TDA7294 with a UPC1237 plus relay speaker protection circuit.
It did not do quite what I thought it would. I expected better treble but was disappointed. Then the left tweeter became intermittent and then the right too (though not as bad). What to do?
First I suspected a blown tweeter from a few nasty crossover turn on transients (I am still working on that problem and think an easy answer lies in an arduino relay board rather than try and isolate the relays and their flyback voltages using custom boards or point to point wiring). However a second tweeter, wired in parallel with the intermittent one, failed at the same time (and a short circuit was unlikely.)
After months of fiddling on and off (sometimes the fault would go away for a week) I pulled the amp out from under a bunch of stuff, including a laser disc player for example, and found that bumping an amp board sharply would fix the problem and bring back extra detail if the tweeter was already working. The speaker protection relays were surely the culprit. As of right now it seems confirmed.
I think the problem is that the power levels sent to a tweeter (crossed over at 2khz) were so low that they could not break down an insulating layer of oxide/crud on the relay contacts. Embolded by information I found on the web I connected the woofers up to the tweeter amps and cycled power to the amp while playing a loud 100hz tone. Rough measurements (current clamp meter) suggested I was switching about 2A at about 20V at the speaker protection relay, I did this about a dozen times. Looks like the arc burned off the crud. The amps sound fantastic too. WIN!
Benjamin's Bench 