What happens when you use the wrong cable?

[Rusty2867]

So what happens when you use an instrument cable between a head and cab? I put an output jack in my Ba115 head so I could use a different cab but I was stupid and plugged in a instrument cable,blew the fuse and now it blows fuses everytime I turn it on,hooked to speaker or not.Is it now trash?

 

[B-string]

Instrument cables can not handle the current of an amps output. The very fine wire overheats, melts insulation and the leads inside short together, with a SS amp that can destroy the SS output devices. You shorted the output of your amp. It could most likely be repaired, but you will have to weigh the cost against an entire new unit.

 

[flameworker]

That sucks man. Yeah, that's not a myth , instrument cables really can't be speakers cables. That's a lesson I had to learn the hard way too. Twice. Maybe 3times. Ok, ok, I have an instrument cable hooked up to my cab right now.

 

[flameworker]

But seriously, what actually gets fried usually when that happens?

 

[tom-g]

It could be the output jack you put on the amo. Take it off and try again.

 

[Rusty2867]

It could be the output jack you put on the amo. Take it off and try again.

Yeah,I tried that,blew fuse right away! It is probably trash.Just wondered what actually gets fried when you do this?

 

[tom-g]

Could be the output transistors and more.

 

[tom-g]

Like B-string already mentioned.

 

[Rick James]

So what happens when you use an instrument cable between a head and cab? I put an output jack in my Ba115 head so I could use a different cab but I was stupid and plugged in a instrument cable,blew the fuse and now it blows fuses everytime I turn it on,hooked to speaker or not.Is it now trash?

An instrument cable can overheat, melt the insulation and short out, but that would take a while to happen. I bet you messed up the jack wiring and that's shorting the output, blowing fuses, and it might have blown output transistors and power supply components too. The first thing you should do is to undo whatever you did in the amp and hope that the amp protection circuits saved it from serious damage.

 

[Arjank]

For convenience it's better to use speakon connectors on the amp and cab(s).
I vote for removing output jacks on amps and cabs

 

[Steve Dallman]

Does your added jack turn off the internal speaker when you plug in an external speaker, or is it just in parallel with the internal speaker.

If you just added the external speaker in parallel with the internal speaker, you lowered the speaker load to below safe levels. Running the amp at lower than designed impedance causes the amp to try to develop more power than the components can safely produce and the amp will fail.

Usually the output transistors will fail, and some related resistors or driver transistors may as well.

You can't just hook up extra speakers to an amp, willy nilly. Likely, the cable used had nothing to do with the failure of your amp.

IF the audio cable was the problem, there are a couple issues. The main one would be the size of the wire and the next the capacitance of the cable. These have been described earlier.

The time to ask about using the wrong cables, or adding external speaker jacks is before you burn up your amp.

 

[ggunn]

It could have been the cable or it could have been that adding the extra speaker dropped the impedance in the speaker output circuit below the minimum the amp could handle. If it was the cable, what you did probably damaged the cable as well as the amp, so checking the cable might tell you something.

But the blowing of fuses every time you try to use the amp is an indication that there is trouble with it irrespective of what caused the problem. It needs to go to the doctor.

But at any rate, using instrument cables in speaker circuits is indeed very risky. I have seen a connector on a molded instrument cable melted into a blob of plastic when it was used to connect a speaker to an amplifier, and the amp had to have its output transistors replaced.

 

[Scottkarch]

Good tips up there... sounds like the first thing to do is undo any changes you made to your amp and see what happens. I added an external jack on my BG250 combo, but since it only supports 4Ohms, and the combo speaker is 4Ohms, I had to put in a heavy duty switch to switch between the combo speaker and the external jack. If it's blowing instantly, I dont think that it's wired correctly and is overloading from the lower than 2 ohm load. If it's blowing instantly, I think it's more likely you've shorted out the output section.

If you have a volt-ohm meter or continuity tester, drop it across the the tip/ring of either of your output jacks and see if it's shorted closed.. 0 Ohms. Also, do the same with your instrument cable and see if you damaged it.. see if it's shorted across the insulation... then also test to make sure the tip to tip connection is fine, and the shield to shield is fine. If it's blowing instantly, your instrument cable may be a red herring.. don't use one any longer, but if it blew instantly, I can't see a cable insulating melting and shorting instantly.. that usually takes a while.

 

[Coolhandjjl]

For convenience it's better to use speakon connectors on the amp and cab(s).
I vote for removing output jacks on amps and cabs

I had some old amps with just 1/4" outs. Since I don't have a metal hole punch, just a drill, I put in binding posts and made a custom speakon cord with banana pins on one end. Anything's better than 1/4" jacks.

 

[Rusty2867]

An instrument cable can overheat, melt the insulation and short out, but that would take a while to happen. I bet you messed up the jack wiring and that's shorting the output, blowing fuses, and it might have blown output transistors and power supply components too. The first thing you should do is to undo whatever you did in the amp and hope that the amp protection circuits saved it from serious damage.

Only 2 wires to the jack wiring,unhooked original speaker and cab I was using is 4ohm.

 

[Rusty2867]

Good tips up there... sounds like the first thing to do is undo any changes you made to your amp and see what happens. I added an external jack on my BG250 combo, but since it only supports 4Ohms, and the combo speaker is 4Ohms, I had to put in a heavy duty switch to switch between the combo speaker and the external jack. If it's blowing instantly, I dont think that it's wired correctly and is overloading from the lower than 2 ohm load. If it's blowing instantly, I think it's more likely you've shorted out the output section.se ins

If you have a volt-ohm meter or continuity tester, drop it across the the tip/ring of either of your output jacks and see if it's shorted closed.. 0 Ohms. Also, do the same with your instrument cable and see if you damaged it.. see if it's shorted across the insulation... then also test to make sure the tip to tip connection is fine, and the shield to shield is fine. If it's blowing instantly, your instrument cable may be a red herring.. don't use one any longer, but if it blew instantly, I can't see a cable insulating melting and shorting instantly.. that usually takes a while.

I totally unhooked original speaker before the jack and after it blew the fuse I undid what I did replaced the fuse,turned it on without a speaker connected and it lit up fuse instantly.

 

[Rusty2867]

Thanks to all of you for your replies.I think I'm in the market for an amp!

 

[B-string]

Actually the grey matter started firing a little better this AM. Many new amps the output jacks are not grounded to any metal, they can not be.
If you used a regular metal jack instead of isolated one, the jack shorted the output before you could even plug in a speaker. They bridge two smaller output devices, this means both wires are "hot" and can not be grounded like the old days.

 

[Scottkarch]

Actually the grey matter started firing a little better this AM. Many new amps the output jacks are not grounded to any metal, they can not be.
If you used a regular metal jack instead of isolated one, the jack shorted the output before you could even plug in a speaker. They bridge two smaller output devices, this means both wires are "hot" and can not be grounded like the old days.

Very interesting... I'll try and run a test later on an old Peavey head with 1/4 speaker outputs to see if they are insulated or not from the chassis. I found a mix of speaker jacks for sale, most seem that they would have their shielding/sleeve connected to ground... there are some specifically insulated models, but most seem not to be. I'll post back.

 

[ggunn]

Actually the grey matter started firing a little better this AM. Many new amps the output jacks are not grounded to any metal, they can not be.
If you used a regular metal jack instead of isolated one, the jack shorted the output before you could even plug in a speaker. They bridge two smaller output devices, this means both wires are "hot" and can not be grounded like the old days.

Ah, yes, good catch. If he grounded one pole of a floating speaker circuit that could be the problem. It actually may not have damaged the amp.

To the OP: try completely severing the speaker outputs from the jack and see if the fuse still blows when you turn it on. If it passes that test, hot wire a speaker to the leads and see if it plays. You may just need to insulate your speaker circuit from the amp chassis.