What is causing me to blow speakers?

[2after909]

I recently blew a couple speakers in two combos and a couple in two different cabs. Pretty pricey problem. A green beret, an et 65, an eminence 15, and an EV all bit the dust. It’s not like I’m a newbie either. I’m 49 and I’ve never blown speakers in my life, and suddenly I’ve blown 4. Could it be the power in my house? I do not have a brown box. My studio power conditioner shows I’m fluctuating between 116 & 117. The only thing that’s different is I recently had my main three amps serviced, and at the time I had speaker line outs that defeat the signal to the internal speaker installed in two of the combos. Is there something to test for or check for?

 

[printer2]

Missing something? Like what amps blew what speakers?

 

[Peegoo]

Possibly DC current going to the speakers. But on two different amps? The chances of that would be pretty slim.

Yorkville, Crate, Peavey (and other makers) have installed current limiters in their PA cabinets in the past. These current limiters consisted of a bayonet socket placed in series of the speaker line, with a 12v automotive bulb, part number 1156. The 1156 was ubiquitous as a single-filament tail light and marker light bulb. It was used in just about every car made up through the early 1990s.

It might be worth a try.

 

[slider313]

The only thing that’s different is I recently had my main three amps serviced, and at the time I had speaker line outs that defeat the signal to the internal speaker installed in two of the combos.

This is the first thing I would be looking at.

 

[2after909]

This is the first thing I would be looking at.

Yeah, I had this done to two combo amps. Their internal speakers blew, and so did the speakers that i sent signal to from the “heads” in those two combos. I guess it’s possible that in doing this mod the guy did something where current is accidentally being sent to the speakers.

 

[Peegoo]

The only thing that’s different is I recently had my main three amps serviced, and at the time I had speaker line outs that defeat the signal to the internal speaker installed in two of the combos.
Is there something to test for or check for?

I MISSED THIS!

YES. Look at the jack your tech installed for the external speaker. Chances are good the tech miswired it. The way to do it is to use a switching jack that disconnects the internal speaker when a plug is inserted in the jack. It should look like this:

NOTE: Not all amps use chassis ground as speaker ground. If your tech installed a Switchcraft style (uninsulated ground) switching jack, that may be what's killing the speaker because there's DC current in the speaker line due to the differing ground potentials.

Pop open the amp and have a squiz at the extension speaker jack.

DO NOT put your fingies in there because you can receive a bad shock.

 

[2after909]

I MISSED THIS!

YES. Look at the jack your tech installed for the external speaker. Chances are good the tech miswired it. The way to do it is to use a switching jack that disconnects the internal speaker when a plug is inserted in the jack. It should look like this:

NOTE: Not all amps use chassis ground as speaker ground. If your tech installed a Switchcraft style (uninsulated ground) switching jack, that may be what's killing the speaker because there's DC current in the speaker line due to the differing ground potentials.

Pop open the amp and have a squiz at the extension speaker jack.

DO NOT put your fingies in there because you can receive a bad shock.

Thank you. Maybe I’ll just have the tech take a look and check his work.

But I’m wondering - would this potential amp tech mistake cause the speakers in the combo amps to blow as well, even when the switching Jack isn’t being used?

 

[Peegoo]

Thank you. Maybe I’ll just have the tech take a look and check his work.

But I’m wondering - would this potential amp tech mistake cause the speakers in the combo amps to blow as well, even when the switching Jack isn’t being used?

Yes, it is possible.

Also: If your tech did screw it up, he owes you two new speakers.

 

[Burning Fingers]

Curious as to exactly what the amps are... like make and model

 

[Apache49]

This is the first thing I would be looking at.

Me too

 

[chas.wahl]

Also: If your tech did screw it up, he owes you two new speakers.

If tech's goof is the cause, then it's 4 speakers, though his defense will be "having blown 1, or 2, why did you keep going?" Still, if the original circuit was isolated from chassis (ground) and the line out (and internal speaker circuit) grounded by the mod, it's the tech's fault -- should know better.

 

[printer2]

WTF? Nobody knows what amps they are, tube or SS? If they are tube amps how does dc get through the output transformer? Diagnose a problem without knowing what is hooked up, and I thought I was good...

 

[Peegoo]

@printer2

We're not diagnosing anything. We're offering suggestions as to the possible cause of the blown speakers.

@2after909 asked for some help.

 

[2after909]

The amps are a 1960 gibson ga-6 lancer and and 1961 Ampro combo that almost nobody has ever seen before, including the TAVA podcast crew. I had the amps modded so that I could keep the heads in the control room and run the signal to the cabs in the isolation booth.

For the record i didn’t think anybody was diagnosing anything. I appreciate the help. I’m gonna ask the tech what he thinks. The help is much appreciated.

 

[Snfoilhat]

If the Lancer is wired like this example, this whole thing is starting to make more sense to me. I can't help but have been trying to follow along

 

[2after909]

I asked the tech and he responded promptly and said:

“All the speaker output jacks do is divert the existing speaker wiring to a tap point where you can take them out to other cabinets. There's no other circuit interaction involved and no other circuit modifications made or required to do that. The theory of the mod is that when you plug into the speaker out, the internal speaker is disconnected by a switching lug and the tip and sleeve contacts of the jack becomes your speaker lead to whatever cabinet you choose..”

He seems to be dismissing outright the possibility that there could be current going to the speaker due to the speaker out mods. Instead, he thinks cranking 15 watt amps into 65 (et65) & 75 watt (eminence 15) speakers could be my problem. The green beret is a 25 watt speaker though. Why’d it blow? He also asked if I was using fuzzes and distortions, as if that was maybe the problem. But I’ve used boosts, overdrives, distortions, and fuzz pedals with these amp for years without problems.

 

[King Fan]

Curiouser and curiouser. Are you sure he said your 15W amps could blow 65 and 75W speakers?

 

[Killing Floor]

Curiouser and curiouser. Are you sure he said your 15W amps could blow 65 and 75W speakers?

Any amp can blow almost any speaker under the wrong circumstance.

 

[MuddyWolf]

I read on a jbl page that if you use a speaker in an open back cab you can cut the rating in half, that may be one factor. Also speaker hate square waves. Fuzzes are square waves. Yes people have been using fuzzes since the dawn of rock music. Just saying that could be another factor.

 

[Peegoo]

he thinks cranking 15 watt amps into 65 (et65) & 75 watt (eminence 15) speakers could be my problem.

Any amp can blow almost any speaker under the wrong circumstance.

@Killing Floor That is true.

But @2after909 driving a speaker below its rated wattage limit is not a threat to any speaker. Pretty much every speaker made today is extremely conservatively rated; most speakers can safely handle transient spikes up to three times their rated wattage.