Troubleshooting speaker/amp

[PMazz]

I've got a wierd one.....

Background and equipment:
B&K AVR307 reciever 7 channel.
B&K 7250 5 ch amp.
Center channel speaker - DIY Eros MTM using series xover designed by Wayne J. at speakerbuilder.net.

I had built the Eros in a sealed enclosure originally using Wayne's parallel xover. I then changed it to his updated serial xover for a listen and it wound up staying that way. It was powered with the B&K receiver. At some point....don't remember when exactly.....the output resistor blew in the reciever. The symptom was a very noticable hum and the woofers were being pushed out only when the receiver was off. When on it worked fine. I did some research and found out it was likely an output resistor on the CC amp of the reciever. Since then I've been using the 5th channel of the amp to power it. I was watching a movie the other nite and noticed considerable distortion out of the CC. It sounds like clipping. I then switched amp channels and it sounds fine. I then switched it back to the reciever and it sounds fine...as long as it's on. I switched the CC with an old JBL I had and it works fine. Thinking it was something blown in the xover, I took it apart and checked the components. Everything checked out.

One of the caps looked a little burnt, but it checked out . My soldering must've been a little sloppy.....

Is there something else besides capacitance to check for a cap?

Any other ideas?

Pete

[ThomasW]

Just say no to series crossovers :?

If the cap has ANY signs of damage it should be replaced regardless of how it measures. It could measure fine at room temp then do weird things as it heats up.

Do you still have the speaker's original parallel XO? If so put it in and see how the speaker sounds.

Hard to say which caused what, more than likely the speaker (XO) may have harmed the receiver. Sounds like the receiver could benefit from a trip to the hospital.




theAudioWorx
Klone-Audio

[PMazz]

The parallell xover is at the shop. That was my next test.

According to Wayne, the series xover is supposed to be more benign than the parallel.

I've already contacted B&K, some time back. I was going to wait until the upgrade was available, which it is now, since they want me to ship it back to them.

What could have happened to the amp? It seems fine driving the JBL.

Thanks,
Pete

[ThomasW]

A little hard to diagnose without having the device on the bench.

Some designs use resistiors in the circuit as protection. If the load gets too weird they blow to save the amp. It's a cheap form of protection. I have some old Adcom 555/565's. They have resistors that function in this manner.

Having never seen the insides of any B&K gear I don't know if that's what they're doing. Since they're more high-end oriented I'd think that they would use a more refined circuit design.

Don't really know though... If the receiver drives the JBL fine then obviously there's something not right with the Eros




theAudioWorx
Klone-Audio

[PMazz]

I hooked the parallel xover back up. I measured the resistance across the input leads and got 3 ohms. I know it fluctuates with freq but does this sound right? I should have done this with the series xover before I tore it apart....

I have to let the speaker warm up before hooking it back up, as it was out in the garage and it's a might cold right now.

Pete

[PMazz]

Well, the original xover seems to have done the trick. I guess that cap was in fact shot.

Thanks for the help, Tom.

Pete