Bass amp stopped workinh (phantom pwr)

[dudiluty]

Hi there.

I guy i know is bringing his amp to me this week because there is a problem with it. Some idiot has put a cable in the input jack with phantom power on it. The amp stopped working after that. He's said that you can hear the amp is on but there is no signal going to the speaker.

Anyone has any idea where to begin looking before i deassamble the whole amp ? (Input jack it self?)

Thanks.

[SlyFoxx]

Not even sure how somebody managed to plug a bass amp into a haunted microphone input?? I'm no amp tech but the first thing I'd look for is a fried fuse on the amps circuit board. They always say "no user serviceable parts inside" but even my dumb ass knows how to change a fuse.

[Mincer]

I have no idea how this would happen. So, they plugged an XLR cable from a mixer carrying phantom power into a 1/4" mono input jack of the amp? What?

[dudiluty]

I'll check the fuses first.

Yeah it's a mistery.. i know. I'll ask him what exactly happend lol

[Ewizard]

To the best of my knowledge, there is no way to get phantom power into a 1/4" cable UNLESS you go directly from an XLR to a TRS connector. IIf you go through a DI box first, there is no phantom power that will come in on the input side of the DI box. The 1/4" inputs on any mixer do not pass phantom power. So if he went 1/4" from the mixer to the amp, he could not have had phantom power going to the amp. I would also be hard-pressed to believe that even having phantom power on the input of the amp would do any real harm. The voltage from most mixers is not 48 volts as most would believe, it is highly dependent upon the load applied to it and can range between 2.5 volts to as much as 48 volts ( the latter is not typical these days ) and the voltage that does pass is very low current.

I would bet that he just borked the input connector, or some other part of the circuit just happened to let loose at that moment. Tough to say without more storyline. If it worked at all after he plugged it in with phantom power ( if that is even possible ) it can tell us that it is likely something else to look at. if he never got sound at all, it is likely that whatever broke was broken the moment the amp was turned on.

[Mincer]

To the best of my knowledge, there is no way to get phantom power into a 1/4" cable UNLESS you go directly from an XLR to a TRS connector. IIf you go through a DI box first, there is no phantom power that will come in on the input side of the DI box. The 1/4" inputs on any mixer do not pass phantom power. So if he went 1/4" from the mixer to the amp, he could not have had phantom power going to the amp. I would also be hard-pressed to believe that even having phantom power on the input of the amp would do any real harm. The voltage from most mixers is not 48 volts as most would believe, it is highly dependent upon the load applied to it and can range between 2.5 volts to as much as 48 volts ( the latter is not typical these days ) and the voltage that does pass is very low current.

I would bet that he just borked the input connector, or some other part of the circuit just happened to let loose at that moment. Tough to say without more storyline. If it worked at all after he plugged it in with phantom power ( if that is even possible ) it can tell us that it is likely something else to look at. if he never got sound at all, it is likely that whatever broke was broken the moment the amp was turned on.

This was my thought as well.

[alex1fly]

Maybe it was one of those XLR outputs that also has a 1/4" kind of in the middle? I've seen those on a couple of inexpensive mixers. No expertise beyond that, just sharing a thought.

[Mincer]

Maybe it was one of those XLR outputs that also has a 1/4" kind of in the middle? I've seen those on a couple of inexpensive mixers. No expertise beyond that, just sharing a thought.

Maybe, but those aren't common outside of mixers and speakers, not so much on bass amps. I'd still love to know how this could have happened.

[devastone]

Sounds more like it may have been a powered mixer and he plugged one of the speaker outs on the mixer to the input of the bass amp, that would wreak all sorts of havoc on the circuit.

If that is what happened, hopefully it just blew the first cap it came too and didn't take out a lot of the circuit.

[Erlend_G]

I once managed to plug one of the speaker cables (from speaker output) of my peavey head, into the input on the front. ( :/ no, I don't drive a car, or work as an electrician. Or have small kids).

Needless to say, this produced a ear-deafening loud feedback from the speaker that was still connected. I'm happy I didn't fry the amp! :o

[dudiluty]

The amp is delivered this week to me so when i have it i can look into it. I'm still contacting the owner what exactly happend. Weird story

[dudiluty]

Someone had put a phantom powered cable into the balanced line out of the amp he's telling me now. After that there is only some noise and crackle left.

[Ewizard]

Placing phantom power on the D.I. out of the amp shouldn't hurt it. The D.I. out usually is just a feed off of the power amp, but in some instances is pre-power amp. In either case, the voltage from phantom power shouldn't hurt it. I get the feeling his problem is just a coincidence. But stranger things have happened I'm sure. Good luck with the repair.

[Erlend_G]

I thought my Blackstar had blown up yesterday, it suddently started to make a loud crackle/static noise.

Turned it off, and saw that the end of my aux-in cable was rubbing against the plug of a non-used guitar cable laying behind the amp .

...but getting phantom power into places it shouldn't... does sound kinda bad to me.

Is it possible to open the amp, and use a suitable multimeter to check caps, diodes & other parts? And look for any burnt PCB or stuff.

[devastone]

Placing phantom power on the D.I. out of the amp shouldn't hurt it. The D.I. out usually is just a feed off of the power amp, but in some instances is pre-power amp. In either case, the voltage from phantom power shouldn't hurt it. I get the feeling his problem is just a coincidence. But stranger things have happened I'm sure. Good luck with the repair.

Yep, most DI XLR outs are designed knowing this will happen, usually phantom power is in groups on boards so XLR outs need to be able to deal with it even if they don't need it.