Can a Cab Break a Head?

[Jimboradley]

So, I just got a new cab, an Ashdown ABM-115H-EVO IV-PRO NEO 1x15". 300 W, 8 ohms. I plugged it into my GK Backline 600 (300 W at 4 ohms) that I've had for years with a 1/4" cable into the speakon dual jack. As far as everything I've read this should have been fine. I played it for a while. It sounded great. I pushed it a little bit, to try to simulate stage levels, but nothing super crazy.

I was excited because it had arrived just in time for my gig that night. When I got to the venue and plugged everything in, no sound out of cab, even though it had worked perfectly hours before. I ended up just going to FOH from the direct out of the head and using stage monitors to hear myself. I figured the cab was somehow defective.

I finally get a chance today to mess around with it. Plug my head into my old cab, a combo I've been running for years, and no sound. So the problem is actually not the cab, but the head. Effects loop send from the cab sends a signal that my tuner can pick up no problem. So it's most likely the power amp. Opened it up, checked the only obvious fuse and it had continuity. Afterward I realized there may be fuses on the underside of the PCB I hadn't checked, so I'll do that later.

My question: can a cab blow a head it's connected to like that? Or is this just weird coincidence? If I replace or repair the head, could this happen again?

 

[agedhorse]

If the cabinet’s defective (shorted input, crossover or driver), then yes it could damage the amp.

 

[mikeswals]

Or-
the effects loop jacks are crusty, not letting signal pass.
Stick a cable in the in & out effects jacks. Does it come back to life?

 

[Pulverizor]

It's not clear in your post but did you try a different speaker cable?

 

[eniac]

I plugged it into my GK Backline 600 (300 W at 4 ohms) that I've had for years with a 1/4" cable into the speakon dual jack.

You're using a speaker cable, not an instrument cable, yes? And if so, I hope it isn't one of those cheapo zip-cord types. I've seen those built with the (very sharp edged) cable clamp pressed hard enough into the insulation to cut right through it.

Plug my head into my old cab, a combo I've been running for years, and no sound.

I assume you mean plugging the amp's output into the combo's speaker. You're not back-feeding the amp section of the combo when you do this, correct?

 

[SteveCS]

If the cabinet’s defective (shorted input, crossover or driver), then yes it could damage the amp.

in the context of this ...

...
with a 1/4" cable into the speakon dual jack.
...

... is it possible that connecting or disconnecting with the amp powered on could lead to (potentially terminal) damage through momentary short-circuit?

 

[-Stingray]

You're using a speaker cable, not an instrument cable, yes?

This was my first thought too. An instrument cable does not have large enough core and will blow an amp head if you push it.

 

[eniac]

Its capacitive load would also worry me.

 

[Jimboradley]

You're using a speaker cable, not an instrument cable, yes? And if so, I hope it isn't one of those cheapo zip-cord types. I've seen those built with the (very sharp edged) cable clamp pressed hard enough into the insulation to cut right through it.

Yes speaker cable (though I haven't tried a different speaker cable yet, don't have a spare lying around

I assume you mean plugging the amp's output into the combo's speaker. You're not back-feeding the amp section of the combo when you do this, correct?

I phrased that badly. The old cab is just a cab, not a combo. I meant the combination of head and cab that have been tried and true for years.

 

[Jimboradley]

... is it possible that connecting or disconnecting with the amp powered on could lead to (potentially terminal) damage through momentary short-circuit?

I'm 95% sure I didn't do this. I generally try to be very careful with new stuff

 

[Tim Skaggs]

You do have a little mystery going on. If the amp sounded good into the new speaker up until the time you turned it off, it’s not too likely the speaker shorted & killed the amp, but also not impossible. I’d try exercising the effects loop jacks on the amp as already recommended. Could be the amp simply failed and would have if you had played it into any healthy speaker.

 

[HolmeBass]

It may just have been that amp’s time?

In my personal experience/opinion, that GK Backline gear is not ready for prime time.

 

[agedhorse]

in the context of this ...



... is it possible that connecting or disconnecting with the amp powered on could lead to (potentially terminal) damage through momentary short-circuit?

Possibly, if there is signal present.

This was my first thought too. An instrument cable does not have large enough core and will blow an amp head if you push it.

That’s not the reason instrument cables damage amps, at least not initially. A small conductor increases resistance which doesn’t bother a solid state amp. If the cable has high enough capacitance it might cause instability and cause the amp to fail.

Its capacitive load would also worry me.

IF it’s high enough,

 

[newfuture]

Another vote here for checking the effects loop with a patch cable. At least as a troubleshooting step.

I replaced all of the jacks on a friend's backline 600 last year due to corrosion. Interior of the amp was very clean except for the jacks themselves. Every one looked like this:

 

[darwin-bass]

If the cabinet’s defective (shorted input, crossover or driver), then yes it could damage the amp.

One morning at church I noticed our subwoofer was not working. Somehow the speaker was dead (shorted). And the amp was also dead. I'm not sure if the amp failed and killed the speaker or the other way around. Yes, it can happen.

 

[darwin-bass]

Check DC resistance of the speaker? Should be about 6 ohms. If that looks good, try plugging it into your phone or some other audio player. It won't be loud, but you can hear it and gain confirmation the speaker is OK.

 

[agedhorse]

Another vote here for checking the effects loop with a patch cable. At least as a troubleshooting step.

I replaced all of the jacks on a friend's backline 600 last year due to corrosion. Interior of the amp was very clean except for the jacks themselves. Every one looked like this:

View attachment 5470070

Somebody sprayed something into those jacks ruining them. No way is that from just environmental corrosion.

 

[Engle]

Yes speaker cable (though I haven't tried a different speaker cable yet, don't have a spare lying around


I phrased that badly. The old cab is just a cab, not a combo. I meant the combination of head and cab that have been tried and true for years.

Before opening up your amp and checking fuses:
Did you check continuity of a speaker cable with a meter?
You could check the DC resistance of the speaker through the cabinet input jack (and the speaker cable if that tested good)

 

[Jimboradley]

The PCB for the jacks looks really clean, but I'll spray it with some air and put some contact cleaner on it when I get a chance. Plenty of dust on the main PCB so that may be a contributing issue.

Resistance on the new cab is just under 8 ohms, which is what I would have expected if you hadn't said it should be 6. I'm curious why an 8 ohm cab should measure about 6.

Thank you all for chiming in. I'm thinking if I can fix this myself, great, but probably not worth sending in for professional repair. Might be a good opportunity to "have to" upgrade my head, too. My main concern though, is if the cab is the cause of this that I'll ruin a brand new head

 

[agedhorse]

Don't spray anything on the jacks. FIRST figure out what's the cause of the symptoms, THEN you will know what needs to be fixed. If you don't have the knowledge or experience to do this, find a QUALIFIED service tech to repair it properly.

It shouldn't be a difficult or expensive repair for a QUALIFIED service tech. Don't make things worse (and more time consuming) for them by spraying "miracle cure-all juice" in there.