The Down Side of Buying a Custom Built Cab

[CDweller]

I want to post my experience with a custom built cab, and hopefully get suggestions for gracefully resolving an issue with a custom built cab I purchased.

I purchased one the bleeding edge custom speaker cabs you see discussed here on TalkBass. It worked fine for an hour or so of total playing, and then it produced a loud hiss followed by a loud pop. The pop had a significant hf component to it, in fact hurting my ears to hear. Afterwards, it sounded to me like the tweeter was not functioning. I brought the cab to a local amp repair shop, and the tech there concurred that the tweet was not functioning.

I returned the cab to the builder. The builder's determination was that the tweet was in fact functioning. My opinion of the builder is that he has nothing but integrity, and I can tell you that my gut tells me he's on the level. Yet my experience of this cab was different, and I don't know how to explain that difference. Regardless, the builder replaced the tweet, on the premise that perhaps the output of the original tweet was substandard. He went over the cab with a fine tooth comb, inspecting the circuitry and everything else. He gave it a clean bill of health, and shipped it back to me. Though I paid to ship it back to him, he paid to ship it back to me.

The cab sounded great when I received it again. The tweet worked, and I could here why people wrote positively about the cab. Yet once again, the cab started to hiss. I disconnected the speakon cable, and reattached it to the other input on the cab, thinking that maybe the input being used was malfuntioning. The hiss went away, but returned ten minutes or so later, followed by that same God-awful pop. At this point, it sounds like the tweet has either no output or a significantly degraded output as before; this of course is my opinion as heard through my ears. I've asked the TB braintrust how to check the tweet leads for a signal, as well as how to verify that the tweet itself functions, hoping for an electronic method of testing rather than listening to the tweet playing program music when installed in the cab.

I have tested the amp, a WW Ultra, with other cabs at my disposal, and it appears that it works just fine. No hissing or popping from my 12/6/1, my 1212/6/1, my TC112AF, my GK Neo112 ll, nor my Carvin LSX 15 or whatever that thing is called. I have not been able to use this cab to make money with as its reliability is suspect (at my end), besides being out of my possesion for the 2+months it took for the cab to be evaluated and returned by the builder. Though I was not pleased with the two month turnaround on the cab evaluation/repair, I accepted it as par for the course because the builder is in demand. Any thoughts on this matter would be welcome- I am hoping to determine a course of action that preserves the dignity of both affected parties.

Rich

[Downunderwonder]

Play some sinewaves through it with a PA anp and mixer and record the results.

What is your definition of moral?

[ChuckTrucks]

Get rid of it, and move on. Learn from this.

[Mr. Foxen]

Wonder if a cap in the corssover was put in the wrong way and popped, or just leaked and popped, in amps you can get a hiss from that happening, as the cap heats up then goes. Would mean the tweeter itself is 'working' but the crossover that feeds it isn't.

[Jim C]

Rich,
Nice post; very respectful.
Could it be that you are pushing this cabinet harder than the designer's intent, and/or you are using an unusual EQ?
If not, I would have to agree that the problem is in the crossover based on hiss and the ability for the cab to work correctly for 10 minutes after a change of input jacks.
Might want to forward this chain to the builder for his private opinion.

[jeffmensch]

I think Mr. Foxen nailed it here. Based on the hiss/pop sound you described, it likely a capacitor in the crossover. This would drop the signal level going to the tweeter.

Luckily the fix is straight forward. Open up the cab to get at the crossover and inspect the capacitor for physical damage. Typically one end will have a small hole in it and there is nasty smelling brown soot on the cap and board. Have your tech check that the orientation is correct and replace it with a new one that has a much higher voltage rating. Good luck, and please let us know how it turns out.

[AstroSonic]

Rich,

This sounds suspiciously like a polar cap or a film resistor in the crossover blowing out (the pop), perhaps due to some dc offset in the output of your amp. The result is a substantial loss of capacitance or greatly increased resistance. They sometimes hiss due to current leakage through them. Could be that a bad cap or resistor was installed on the crossover board. The blown cap will usually appear swollen and may show some leakage. The blown resistor will usually be discolored and may be swollen or cracked. Check the crossover board. The bad part should be relatively easy to spot. The tweeter is probably ok.

Good luck.

[Codger]

I wonder what the impedance curve for that amp looks like? I suppose it is possible that a certain load not normally encountered by that amp might cause it to oscillate. That could certainly damage something.

When you get the hiss and pop, then shut down and disconnect everything, does the tweeter work when you try again or is it hosed from that point on? Edit: should have read OP more slowly.

[BassmanPaul]

The first thing I would do is to measure the amps output for a DC component. There should be almost zero volts across the output. I suspect the amp has a problem. Possibly the load presented by your particular cabinet is exacerbating that problem.

Edit: The caps in the crossover work with AC signals and should therefore be non-polar. That being the case it's immaterial which way around they are wired.

[fdeck]

I'm betting on some interaction between the amp and the crossover myself, which could be a wiring error or bad component in the crossover, or something going on with the amp where it's having a hard time dealing with a complex reactive load. Or both.

Not only have these cabs been around for a while, but they are not radically different from mainstream PA cabs that have been around forever.

[B-string]

Have little to add other than a cap does not have to look externally bad to be defective. DC offset check should be done and a new crossover installed.

[::::BASSIST::::]

Worse case scenario... replace entire crossover, replace tweeter. Problem solved.

Instead of shipping the entire cab back the builder can ship you a new crossover and you can install it yourself. Its pretty easy to do.

[carldogs]

Originally Posted by fdeck

I'm betting on some interaction between the amp and the crossover myself, which could be a wiring error or bad component in the crossover, or something going on with the amp where it's having a hard time dealing with a complex reactive load. Or both.

It sounds like this could be the problem, a high frequency oscillation can just be a hiss or above audible range, it can seem like there is almost nothing there and yet there is a huge signal that the crossover will push to the tweeter, basically frying the voice coil.
With some of the older mosfet power amps they could not use the wire wound balancing restors on the outputs of the mosfets like on transistor amps, they are in a sense an inductor and could cause the mosfets to become unstable, those amps would use small restors on the inputs to the mosfets. I think some kind of inductive load in the crossover could be making the amp oscillate.
Does the manufacturer of the cab have any suggestions, or can they send you a different type of crossover to try if you really like the cab?

[CDweller]

Guys, I feel the love, and thank you all for your input. More details when I return home tomorrow, though my with my limited experience I suspect a cap malfunctioning. The cab has been used at conversational levels thus far while practicing in my living room. I turned it up once, but it worked fine for those few moments. I only really turn up on a gig, and the cab's not gig worthy yet.

[Muziekschuur]

Make sure the speakerwire is not damaged. When you have a damaged speakerwire and min and plus are touching eachother at full blast this can damage a cross over...

[fdeck]

One thing to add is that there are certain crossover designs where a detached high frequency driver results in a dead short at certain frequencies as seen by the amplifier.

[CDweller]

Originally Posted by Muziekschuur

Make sure the speakerwire is not damaged. When you have a damaged speakerwire and min and plus are touching eachother at full blast this can damage a cross over...

The cable is fine, and the cab has not been played "at full blast" . I've verified that with multiple cabs subsequent to the cab in question's malfunction.

[CDweller]

Originally Posted by fdeck

One thing to add is that there are certain crossover designs where a detached high frequency driver results in a dead short at certain frequencies as seen by the amplifier.

I'll check the connection to the hf, but I don't get the sense that that's the failure here. Still, it'll be checked!

[pacojas]

swap cross-overs with the builder or just send it to him.