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Help! Blown head or cab?

dmccuiston

dmccuiston

mediocre post-rock bass person
Jul 24, 2011
60
27
Richmond, VA
#1
Hello!
I recently bought an Alpha Omega 500 head from darkglass. It was used, but tested. I have been using it with headphones as I was waiting for a cab. Today I received my darkglass 2x12 cab (which is brand new). I plugged my head in, using my speakon cable, and flipped it on. I immediately got a loud low hum that almost blew the speakers, smell and all, and a puff of smoke came out of the fan area on the head. I immediately turned it off and checked. Fortunately, the speakers were not blown. I also tried the head again with headphones and it worked fine. I tried with a different cable and got the same thing.
I don’t know if it is the head or the cab and don’t know how to check. I’m asking around to see if anyone has another head I could test to see if it’s the cab, but no luck yet. Does this sound familiar to anyone? I know it’s hard to diagnose from just a description, but would love any thoughts anyone may have.

Thanks!
 
#2
You could use an ohm meter to test if your speakon cables or new cab might have been wired wrong with the + & - wires making contact & shorting against each other, that could have possibly damaged the amp.

You'll find lots of how-to videos/info by googling: 'testing speakon connectors & speaker cab with an ohm meter'.

Then If they all pass the ohm meter test:
It's possible your used amp had an intermittent problem (resulting in it's first owner to send it back to Darkglass for warranty replacement) that simply wasn't acting up when Darkglass tested & shipped it back off to you; but then the amps intermittent malfunction was simply re-activated by the rough handling of the amp being shipped to you.
 
#4
Seems to me the amp must have generated the loud hum because the speakers can't. It sounds as if something very undesirable has happened to the output stage of the amp. Whether that was triggered by a cabinet or cable fault or was entirely in the amplifier is difficult to tell. In the circumstances I would be very reluctant to plumb the speakers into a known good amp in case the same thing happens to it. Testing the cables and the DC resistance of the cabinet (DC resistance should be less than, but over half of, the rated impedance of the cabinet) are good things to do.
 
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#7
I'd wager that Agedhorse would ask about the speakon cable. Are these Neutrik connectors?
Furthermore, what were the amp settings when you plugged in?
Was something plugged into the amp at that time?

If the master was very high and the gain set about halfway up, and a cable was in the input, but the other end was shorted against carpet, some unpleasant sound with quite a lot of volume might have escaped ...
 
#8
I picked up a new speaker cable today just to test. Same thing. When I originally hooked it up, I had my passive bass connected to the input and the mute engaged on the head. I am talking to Darkglass to see if there is anything that can be done under warranty.
 
#11
I'd wager heavily that agedhorse would strongly recommend this amp be evaluated by a trained technician and if he did that, then I would be in agreement with him. It sounds like that is your agenda anyway.

I sometimes work on amplifiers, but would not be remotely qualified to touch this one.
 
#12
The amp needs to be addressed by a Darkglass approved tech, if ANY hope of a warranty claim is expected. They are not easy to work on unless the service center has the support and documentation from the factory (including parts)
 
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#17
Hello all - for those following along - Darkglass has been amazing. They paid for the head to be shipped back to them in Finland. Keep in mind, this was a secondary buy that I could not register, but they stood behind their product. Their communication has been stellar and after a week, it is repaired and on it's way back to me.
The problem was in the power module. From their last email:
"Regarding the repair, the defective power module was changed to a new power module. The amp was tested thoroughly and has passed all the quality assurance tests. Please note that the minimum load is corrected to 3 ohm"
The load was a minimum of 2ohm prior. Not exactly sure why there was an update, but my 4ohm cab will work just fine with it.
 
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#18
Last update on this one - got the amp back today. Plugged it in and held my breath. It purrs, growls, and makes the noises it is supposed to. The cab is holding strong and the speakers sound clear and loud. Hooking this combo up to my Troy Sanders Fender Jag with the EQD Huzimitas fuzz will likely open some portals of doom, but I’m here for it.
Hats off to Darkglass for the customer service and to the TB commmunity for walking with me in this one!
 
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