[MttBsh]

I have encountered a problem this evening that has me scratching my head....maybe someone smarter than I am can offer a suggestion?

I received a new pair of interconnects this evening and plugged them in between my Tortuga preamp and my Job 225 amp (I recently put the same interconnects between my Schiit Yggdrasil DAC and my Tortuga preamp)  I turned on the preamp at very low volume and then turned on the Job. I immediately heard a screeching sound from my left Cain & Cain Abby speaker, so I turned everything off after just about 2 seconds. Next, I made sure everything was plugged in properly and tightly (preamp, amp, speakers) then turned the preamp and amp on again. No screeching sound this time, everything works fine except my left Abby speaker now produces no sound - but what's weird is the Fostex supertweeter wired to the binding posts of that speaker puts out sound just fine.

I have switched the new interconnects to the each other's imputs on the amp, I put the old interconnects back in, I attached the right speaker cable to the left speaker, always the same result. The tweeter works fine, no sound from the speaker itself.

Because the Job amp has the speaker outs directly above (and close to) the interconnect input, it's possible I accidently plugged the interconnect into the speaker out when I reached behind the amp, but I don't think I did.

The fact that the left tweeter is working makes me think the amps are  fine and the speaker is getting a signal, could I have shorted something inside the main speaker?

Any thoughts you have would be greatly appreciated!

Thanks

[Thirsty]

It sounds to me like the speaker voice coil is fried. The best way to check is to remove the speaker from the cabinet, disconnect the wires on the two speaker terminals and check for continuity with a meter. No continuity means the voice coil opened up and the speaker is shot.
Good Luck!

[MttBsh]

Not the answer I had hoped for, but hey - I love the Abby cabinet, replacing the speaker is not that big of a deal, thanks so much for your thoughts Thirsty! I'll check it out 

[timind]

It's always good to have a pair of speakers on hand to test a suspect amp. I keep an old, inexpensive pair of Polk speakers on hand for troubleshooting.

[Davey]

If you swapped amplifier channels and the problem is still there, it's 100% sure you've blown the main driver in that speaker.  The Fostex tweeter is still working since it has a high-pass capacitor (or network) in series that pseudo-protected it, whereas your main driver has no such protection.

I'm puzzled by why a faulty interconnect or connection would cause a large screeching sound, (you would expect a strong 60hz hum or similar) but audio equipment is weird sometimes.

Live and learn.

Dave.

[MttBsh]

It was more of a high pitch squeal, never a good sound when hooking up your sound system. I immediately  suspected a bad interconnect or a loose connection, but when I swapped the positions of the interconnects it worked fine with the other speaker. The only thing I can think of is that I accidentally plugged one of the interconnects into the amp's left speaker out instead of to the amp in, but would that fry a speaker?
The speaker is at least twelve years old, so maybe it was just its time, a death scream? 

[G Georgopoulos]

bad joint on the driver resolder joint...

[Davey]

bad joint on the driver resolder joint...

Highly unlikely.  This is almost assuredly a burnt out voice coil on the driver.

I'm wondering how an interconnect (RCA connector?) could be plugged into a speaker output accidentally.  This would seem a very poor choice of output connectors for a well-designed amplifier.
Line-level signal connectors and high-level speaker output connectors should (obviously) be a different types of connectors. 

Dave.

[srb]

I'm wondering how an interconnect (RCA connector?) could be plugged into a speaker output accidentally.

An RCA center pin will fit inside the banana opening of a 5-way binding post far enough to short the interconnect - but only if the ground shell then makes contact with an all-metal post - but since the pin is smaller than the opening it wouldn't actually "plug in" and at best could only cause a momentary short condition.

It's possible that a component could sustain damage if the interconnect was connected to an output, but it doesn't seem like it could damage a speaker - unless component output current was conducted through the voice coil and back through the speakers common ground?

Steve

[S Clark]

So what happened with a continuity test that Thirsty proposed?  That's the key question before any more speculation can occur.  If you have doubts, remove the leads from one side of the woofer, connect the leads of your volt/ohm meter with the meter measuring resistance.  If the voice coil is burned out, there will be no reading compared to the normal 4ohm-8ohm resistance. 

[*Scotty*]

It sounds like you essentially turned on the amplifier with the input of the left channel of the Job 225 unterminated. This can lead to the amplifier oscillating at a very high frequency at high power levels. This can also kill the outputs of an amplifier if the condition persists for long.
 In as much as the Fostex FE166En is rated at 22W RMS with 65W music power and the Job 225 can output continuously over 200 watts at 1.0% THD at clipping, it is no small wonder that the voice-coil probably fried.
Scotty

[MttBsh]

I want to thank you all for your thoughts and suggestions, I sure appreciate it.

I've got 2 left thumbs when it comes to electronics (taking things apart/testing them) so I'm going to take the speaker in tomorrow to an audio repair shop here in the Seattle area and have them figure out what's going on. I'll report back on their findings.

Over the past dozen years I've owned lots of amps, preamps, DACs, CDPs, etc. but what I've never changed are my beloved Cain & Cain Abbys with Fostex Sigma 168 drivers. I augment them with a pair of Fostex T900A supertweeters and a pair of good subs. The sound I get is so good I can't imagine changing my speakers, just fixing them!

Thanks again
Matt

[Davey]

It sounds like you essentially turned on the amplifier with the input of the left channel of the Job 225 unterminated. This can lead to the amplifier oscillating at a very high frequency at high power levels. This can also kill the outputs of an amplifier if the condition persists for long.

Any amplifier that will oscillate at high power levels with no input connected is either faulty and/or horribly designed.  If that is a possibility with these Job amps, they would never see usage in any system I had. 

Dave.