Hi Bass Players,
I have a Behringer BLX3000A Bass Amp that I have been using with headphones while doing the beginners course. Tonight I switched on the amp pulled on the headphones and nothing! I took our the headphone jack and sound is coming out of the speakers no probs, then I plugged the headphones into my PC and they worked fine, but when plugged into the bass amp nothing! I get the impression that the headphone jack in the amp may be screwed. Any ideas? thanks in advance.
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Your troubleshooting approach is good, @Browndog! 
Perhaps there is a bit of lint or something in the amp jack? You might try loosening the jack and blowing some air through. Maybe one of those compressed air cans for cleaning computer keyboards, e.g.
Cheers, Joe
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Another possibility is an electronic tuner cleaner such as:
HTH and wish you good luck, Joe 
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You want to be really careful spraying flammable contact cleaners into amps. As in, don’t do it.
Many of these are alcohol-based or have some other extremely flammable carrier. So what happens is you spray them into a power amp and now it’s full of flammable fumes (plus some undried carrier fluid). Then you turn the amp on, and when it heats up, it burns.
This has never happened to me but I have heard horror stories.
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Well, this is a bit embarrassing, turns out it was the battery for my active pick ups. I’ve never owned a guitar with active pick ups before. There was just enough juice to get a bit of a signal to the speaker, but not work with the head phones.
Thanks for all the advice any way guys.
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Hm, I get a pretty annoying “howling” tone when the battery in my active bass is about to give out… it’s not at all like a signal slowing growing weaker… must be different types of circuits!?
Anyway, good you got this sorted out! Always have a spare battery in your gigbag!! 
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Do you think it’s a separate circuit that kicks in when current is low? It’s basically saying “don’t ignore me or adjust your settings to cover for my dying power!” Clever little trickery.
We live & learn. The trick is to only learn once. 
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I honestly don’t know. I was just wondering why the behavior would be so different.
My understanding of electronics is limited (and that’s a friendly way of saying it), but the howling sounds a bit like a circuit that is no longer able to control/contain a developing negative feedback loop. In any case, it is so annoying, you can’t do anything but change the battery 
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In case you hadn’t noticed, on the back of your 504 is a little LED that comes on when the battery is low 
Yay passive mode.
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Yeah, the one thing missing that would have made the TRB5Pii truly outstanding 
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It’s still truly outstanding
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Good point!! 
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Seriously though, this is why I have such a serious bass crush on the SR2400. It’s a lot like your bass, but also with passive mode, Aguilar electronics, and a three-frequency midrange parametric EQ switch. And it’s one of my favorite colors. It’s like my current bass taken to 11.
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Yes, this looks like a really great bass, looks and all. (And about my bass: it is fantastic, I just wished they would have added that little switch to allow for passive mode - should be standard for active basses, really!)
The GAS is strong in you again, young padawan! 
It’s hard not to dream about a new bass… at some point, I will probably go for an Ibanez fretless
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