Think I've just blown at least 1 speaker in my GK neo 212 - Advice Needed

[Jateca]

So in rehearsal this evening I think I blew at least one of my speakers but I'm not sure!

My rig is a Gallien Krueger 700rb - II running via the GK biamp into an old-design GK neo 212 cab (8 ohm).

Whilst playing my volume dipped and I noticed a strong burning smell that came from the speaker cab. Checked the crossover on the back panel and all the components seem fine (except for a little external damage to the full-range 1/4" jack port) and the burning smell seemed to be from inside the cab.

I'm going to inspect them properly tomorrow but I'm not sure what I'm looking for. I'd guess that I've fried the voice-coil somehow, but how do I tell if this is the case?

Also, could the problem be my amp? I got it 2nd hand but all that was wrong with it were dirty pots. Any way it could have a fault that is causing the damage to my speakers?

The cab is rated at 600W rms at 8 ohm and my amp puts out about 380W at 8 ohm (480W at 4 ohm). I got the impression from reading here that underpowering shouldn't be a factor, right?

[MIJ-VI]

[quote name='Jateca' post='728564' date='Jan 29 2010, 07:06 AM']So in rehearsal this evening I think I blew at least one of my speakers but I'm not sure!

My rig is a Gallien Krueger 700rb - II running via the GK biamp into an old-design GK neo 212 cab (8 ohm).

Whilst playing my volume dipped and I noticed a strong burning smell that came from the speaker cab. Checked the crossover on the back panel and all the components seem fine (except for a little external damage to the full-range 1/4" jack port) and the burning smell seemed to be from inside the cab.

I'm going to inspect them properly tomorrow but I'm not sure what I'm looking for. I'd guess that I've fried the voice-coil somehow, but how do I tell if this is the case?

Also, could the problem be my amp? I got it 2nd hand but all that was wrong with it were dirty pots. Any way it could have a fault that is causing the damage to my speakers?

The cab is rated at 600W rms at 8 ohm and my amp puts out about 380W at 8 ohm (480W at 4 ohm). I got the impression from reading here that underpowering shouldn't be a factor, right?[/quote]

Hi Jateca.

First off, the obvious: please don't power up your amp until the issue is identified and has been remedied.

As long as you weren't playing your rig loud enough to clip (distort) its power amp then none of the woofers should be fried.

(Please note: I've never used this make & model of bass amp. Hopefully someone who has will chime in.)

Does this cab have a tweeter? If so, did you have it completely turned off? Doing so can result in the L-pad (which is what I believe the tweeter's attenuation device is called) being overpowered at high volumes. The prevention here is to keep the tweeter turned up a bit to better handle the power being fed to the L-pad and tweet' by the crossover.

Also, you mentioned damage to the cab's 1/4" jack. Is it scorched? What is the condition of the speaker cable you were using.

Do your amp & cab have Speakon connectors as well?

[Jateca]

^

Cheers for the reply

Not to worry, first thing I did when I smelled burning was to disconnect and separate the amp and cab.

The power amp section on the amp never went past 1 o'clock, though I do make a lot of use of overdrive pedals. I wouldn't have thought they would actually damage a speaker though.

The tweeter attenuator is low but never completely off. The damage to the 1/4" jack port is just cosmetic I think, just sheared off the plastic outer part in transit. The rest of the component seems fine. Think it was just coincidence that I noticed that just before the problem happened, but thought I'd mention it anyway.

The input to the cab I was using at the time was GKs own speakon input which has separate signals going to the tweeter and woofers. It uses their 4-core cable but I don't think these have taken any damage.

[MIJ-VI]

[quote name='Jateca' post='728643' date='Jan 29 2010, 08:10 AM']^

Cheers for the reply

Not to worry, first thing I did when I smelled burning was to disconnect and separate the amp and cab.

The power amp section on the amp never went past 1 o'clock, though I do make a lot of use of overdrive pedals. I wouldn't have thought they would actually damage a speaker though.

The tweeter attenuator is low but never completely off. The damage to the 1/4" jack port is just cosmetic I think, just sheared off the plastic outer part in transit. The rest of the component seems fine. Think it was just coincidence that I noticed that just before the problem happened, but thought I'd mention it anyway.

The input to the cab I was using at the time was GKs own speakon input which has separate signals going to the tweeter and woofers. It uses their 4-core cable but I don't think these have taken any damage.[/quote]

Well the good news here is that you're a player who knows how to use their gear (I've seen many 'different' approaches on TalkBass).

An amp's volume knob setting is relative to the strength of the signal being fed to the pre-amp. Do you play an active bass?

Overdrive pedals won't cause speaker damage but they can obscure the sound of a power amp which has been driven into clipping.

A burning odour indicates that something in the cab is fried and possibly partially shorting out the signal to the speakers (which would explain the loss of volume you mentioned in your OP).

A next step would be to confirm that the woofers are OK.

To do so, place your fingertips around the circumference of each woofer's domed dust cap and gently & evenly push the speaker cone into the cab slightly while listening & feeling for any scrapping that would indicate a voice coil which has been deformed due to overheating.

Next, remove one of the woofers, and using a flashlight, peer into the cab to examine the tweeter and wiring for any sign of scorching.

Please note: speaker cabs are usually stuffed with fiberglass insulation (to damper resonant frequencies) so wear old clothes and gloves if you have to reach inside the cab any distance.

[Mr. Foxen]

I reckon it might be the old cooked crossover. I think that is the actual result of clipping a power amp into the dreaded 'square wave' territory. The square wave killing speakers might be a myth, but it is effectively lots of very high harmonics, it can stick much more power into a crossover/tweeter than it anticipates handling.

[stevie]

[quote name='Jateca' post='728564' date='Jan 29 2010, 12:06 PM']I'm going to inspect them properly tomorrow but I'm not sure what I'm looking for. I'd guess that I've fried the voice-coil somehow, but how do I tell if this is the case?[/quote]
Push the cone in using even pressure all round and listen for the coil scraping behind the dustcap. If you smelled burning, it's likely that the driver is damaged.
I've just noticed that MIJ has already suggested this. Still, great minds and all that .....

Edited January 29, 2010 by stevie

[Jateca]

Well, I removed and checked both coils and they both seem ok. Pushed both in evenly at the dustcap as suggested and didn't notice anything obviously out of place.

There was also very little sign of any burning apart from a slight brown mark at the very back of one speaker (which could easily be something else harmless) and some of the fibre glass lining appeared melted near to the point where the cables connect to the other speaker cone.

I'm stumped, think I'm going to get a fella at an electronics shop to look at it. Thanks for the help anyways. Any more suggestions would be welcome!

[MIJ-VI]

[quote name='Jateca' post='729353' date='Jan 29 2010, 07:22 PM']Well, I removed and checked both coils and they both seem ok. Pushed both in evenly at the dustcap as suggested and didn't notice anything obviously out of place.

There was also very little sign of any burning apart from a slight brown mark at the very back of one speaker (which could easily be something else harmless) and some of the fibre glass lining appeared melted near to the point where the cables connect to the other speaker cone.

I'm stumped, think [u]I'm going to get a fella at an electronics shop to look at it.[/u] Thanks for the help anyways. Any more suggestions would be welcome![/quote]

I concur. At this point it's tech time.

Please keep us posted re any further developments.

[Jateca]

Well, the people at PRS electronics in Liverpool were unable to find anything wrong with the cab itself, so I've dropped off the amp for them to check. I got the 700rb II 2nd hand about a year ago and it has been fine so far, so I'll see what they say.

One other thought, could the power source have anything to do with this? The reason I ask is that the electricity in my band's rehearsal room is a bit dodgy (turn a lamp on from one socket and the PA powered from a different socket goes pop, kind of thing) and it's a possibility I haven't considered yet.

[MIJ-VI]

[quote name='Jateca' post='732478' date='Feb 1 2010, 08:52 PM']Well, the people at PRS electronics in Liverpool were unable to find anything wrong with the cab itself, so I've dropped off the amp for them to check. I got the 700rb II 2nd hand about a year ago and it has been fine so far, so I'll see what they say.

One other thought, could the power source have anything to do with this? The reason I ask is that the electricity in my band's rehearsal room is a bit dodgy (turn a lamp on from one socket and the PA powered from a different socket goes pop, kind of thing) and it's a possibility I haven't considered yet.[/quote]

Perhaps [url="http://www.gallien-krueger.com/dealers_world.html#"]G-K's dealer in England[/url] could recommend alternate repair shops?

Have you tested your cab with a different amp?

Do you have something like one of [url="http://www.pat-training.co.uk/socket_testers.htm"]these[/url] in your gig kit as a countermeasure to the inevitability of stage-wiring-by-club-owner's-brother-in-law?



Here in the colonies an equivalent device is considered to be a potential life saver...

[Jateca]

[quote name='MIJ-VI' post='732501' date='Feb 2 2010, 07:10 AM']Perhaps [url="http://www.gallien-krueger.com/dealers_world.html#"]G-K's dealer in England[/url] could recommend alternate repair shops?

Have you tested your cab with a different amp?

Do you have something like one of [url="http://www.pat-training.co.uk/socket_testers.htm"]these[/url] in your gig kit as a countermeasure to the inevitability of stage-wiring-by-club-owner's-brother-in-law?



Here in the colonies an equivalent device is considered to be a potential life saver...[/quote]

Unfortunately Polar-Audio, GK's UK distributors are completely useless. The staff seem to know nothing about the gear from the various companies they handle (GK, Beyerdynamic, etc.), only what the computer screen tells them. Most retailers I've questioned have also had little nice to say about them.

Not had a chance to yet, will try over the weekend when I get my old head back from long term loan.

I actually have a socket tester within arms reach as I type this. I'll re-test the room but I doubt I'll find anything.

No worries, cheers for the advice anyway.

[JTUK]

yep, not sure if you have isolated the problem to one piece of kit or the other...

The cab needs testing with a different amp to rule that out..
The amp needs to go to someone who knows what they are doing..

And just because the the cones travel well on the speakers doesn't mean they are, or one isn't damaged and needs replacing.
Both my speakers looked physically perfect and travelled without any coil scrape but had to be replaced. It wasn't the crossover either, 2 new chassis sorted it.

From what you have said, I'd start with the cabs being a problem and put the amp to a decent tech. From some reason though, I think you'll find a problem with both... as these sort of things shouldn't just happen. The amp has over-cooked the speakers, is my guess..

Hope you get someone decent to check it all out..

[bassbloke]

Does the cab sound any different? I don't know if the Neo cabs have a tweeter protection circuit but the burning sound you describe could be the tweeter diaphram. I owned a peavey 210 cab years ago and used to seriously overdo it on the top end and fried 2 or 3 diaphrams before I learned to rein in the top end.

It's a simple enough fix, provided you can get your hands on the part.

That's a cab with 600watts power handling. Unless there is some inherent fault with your amp or cab that caused the failure, you need to seriously think about turning down!!!

[Jateca]

So I got both the amp and cab back from the electronics shop yesterday, the tech said he could find nothing wrong with either.

I managed to get a spare head to try though and have confirmed that the problem is definitely the head.


Compared the GK 700rb II with an old Ashdown electric blue 180 watt amp. Set them both to approximately the same settings (EQ flat, master at halfway, input gain just below half) and the 180 watt ashdown was pushing out a hell of a lot more volume than the 320w (8 ohm) GK.

Tried the GK in a rehearsal setting again. Where in the past I would turn the master up to about 11 o'clock, I now had to turn up the GK to around 3 o'clock just to be heard over the drums. Would not push it any more for obvious reasons.

Used a different cab with both amps to double check, and different speaker cables. Don't know why there was a burning smell in the cab initially, but the most obvious problem is the head.

Somehow the GK head is not producing the output it should (and has in the past). I've ruled out every other bit of my rig, and I'll be able to test the GK cab for any faults over the weekend when I get my Hartke head back from loan.


Problem is I'm not aware of any amp techs in my area. I could take it back to the electronics shop again, now I now where the problem is, but I may get the same answer. Any ideas what could cause the amp to lower its ouput so much, so I can tell him what to look at?

[MIJ-VI]

Let me pitch this thread to TalkBass' techs....

[MIJ-VI]

It's scarcely dawn over here. It may take a while...

[url="http://www.talkbass.com/forum/showthread.php?p=8645645#post8645645"]http://www.talkbass.com/forum/showthread.p...645#post8645645[/url]

[MIJ-VI]

Mr. Obvious here: You might want to avoid powering up your 700RB-II in the interim.

[Jateca]

[quote name='MIJ-VI' post='734924' date='Feb 4 2010, 12:04 PM']Mr. Obvious here: You might want to avoid powering up your 700RB-II in the interim.[/quote]

No worries, now that I know it's the problem. I only tried my rig again after the tech said he couldn't find anything obviously wrong.

Also, thank you for the effort you're putting in here

[JTUK]

I had the same problem trying to find a decent tech.... I asked at studios and my muso mates... and eventually found a gem.
I go direct to them and not via a shop,

Ask anybody on the biz..like gtr makers or somesuch.
The cream tends to rise to the top..sort of..!!

As regards the amp...I'd only guess, but am glad you got away with apparently no damage to the cab..
I'd be very wary that you don't compound a problem there though..and using effects can mask a noise that turns into a bigger problem..
I'd be listening VERY closely to the cab in use for the next few weeks... only sayin'..

[MIJ-VI]

[quote name='JTUK' post='735220' date='Feb 4 2010, 11:33 AM']I had the same problem trying to find a decent tech.... I asked at studios and my muso mates... and [u]eventually found a gem.[/u]
I go direct to them and not via a shop,

Ask anybody on the biz..like gtr makers or somesuch.
The cream tends to rise to the top..sort of..!!

As regards the amp...I'd only guess, but am glad you got away with apparently no damage to the cab..
I'd be very wary that you don't compound a problem there though..and using effects can mask a noise that turns into a bigger problem..
I'd be listening VERY closely to the cab in use for the next few weeks... only sayin'..[/quote]

Hi JTUK.

Who? Where? When? Link please.

Don't Bogart that tech bro'!

[MIJ-VI]

Hi Jateca.

Please check your TB amp problem thread.

[Phil Starr]

First of all you shouldn't get burning smells from a speaker cab. I think you said their was some discolouration of the fibreglass. If it isn't actually fibreglass but polyester wadding then this will singe even with speakers working normally at high power levels. You will have at least explained the smell. Move it around until it no longer contacts with the speaker. Neo's have smaller magnets so less area to dissipate heat. The easies way to test the speakers is to push some recorded music through them and listen at low volumes with your ears right up to each speaker one at a time and then with the volume up at a high level. If there is no obvious distotrion or funny noises then the speakers are ok. Have the closest look at your tweeter as this takes the bashing if you use overdrive.

I can't think of anything that would cause a loss of gain without causing other problems with a power amp though I suppose a component failure around an op-amp in the preamp stages might change the gain of a stage. Tricky to find without the amp and a circuit diagram in front of you. There are two possibilities if it is the amp, it is actually ok and you just need to turn it up or you need a better tech. Don't worry about the volume settings between the amps though, that's al about gain and sensitivity and a halfway position on one amps gain control need bear no relationship at all with halfway on any other amp. There is an excellent piece on this on this site but you could look at this too [url="http://www.youtube.com/watch?v=EbVKWCpNFhY"]http://www.youtube.com/watch?v=EbVKWCpNFhY[/url].

Again if you play recorded music through the amp you should hear any problems as distortion. If you get the chance to try this then let us know what you find

[JTUK]

[quote name='MIJ-VI' post='735729' date='Feb 5 2010, 01:34 AM']Hi JTUK.

Who? Where? When? Link please.

Don't Bogart that tech bro'! [/quote]


Hi

I am in Kent, England.

This guy designed the original Wem/Watkins Copycat. He knows his onions IMO..

I can do contact details by PM if required

[Jateca]

[quote name='Phil Starr' post='735791' date='Feb 5 2010, 08:19 AM']Don't worry about the volume settings between the amps though, that's al about gain and sensitivity and a halfway position on one amps gain control need bear no relationship at all with halfway on any other amp. There is an excellent piece on this on this site but you could look at this too [url="http://www.youtube.com/watch?v=EbVKWCpNFhY"]http://www.youtube.com/watch?v=EbVKWCpNFhY[/url].

Again if you play recorded music through the amp you should hear any problems as distortion. If you get the chance to try this then let us know what you find[/quote]

Fair enough, but it is definitely pushing out less volume than two weeks ago (through different cabs when tested). Previously my master volume would be a shade under halfway for rehearsal, now it has to be almost fully up just to be heard faintly (not going to turn it up all the way, obviously). Currently the amp would be completely unsuitable for gigging.

A fella on talkbass suggested that it may be something to do with the FX loop, so I'm going to try patching between the send and return to see if it makes a difference.

Thanks for the link, I will try and get some music going through the amp later today.

Edit: I've just watched the link

Edited February 5, 2010 by Jateca

[MIJ-VI]

[quote name='JTUK' post='736068' date='Feb 5 2010, 07:37 AM']Hi

I am in Kent, England.

This guy designed the original Wem/Watkins Copycat. He knows his onions IMO..

I can do contact details by PM if required[/quote]

Hi JTUK.

Thank you for your response.

Jateca may have need of your contact.

Gary