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Kurt

Pre amp clipping blows speakers?

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I've had a poke about in the amps forums here and on TB trying to find an answer to my question but am now more confused than when I started!. Here's the deal. I've got an Aggie GS112 which, for rehearsals I run on its own with an ABM500. The amp's master vol is never turned up much above 10 (o'clock) and there is no extreme eq'ing going on. I did notice the other night that the VU meter was full scale on every note as I had mis-set the input gain (ie the pre was clipping). Now the speaker in the GS112 is distorted at anything approaching a useable volume. I've tried different cables, my bass into another amp etc, all pointing to the cab still. The only thing I can't try in my amp into another cab at the moment, but I guess if I'd fried the amp I'd get nothing out of it.

Thanks in advance for your help, but please keep it simple. I don't know what xmax, excursion and all the other tech terms I've come across are!!!

Peace

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You could try turning the preamp down, (to zero). Turn your master, (power amp) volume up (say to 2 or 3 o'clock). Gradually turn up the preamp volume to a desired level.

Your master, or power amp should be doing all the work, so that's why I suggest turning that up and turning the preamp down.

Hopefully this may help!

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[quote name='Pikefloyd' post='27403' date='Jul 5 2007, 12:58 PM']You could try turning the preamp down, (to zero). Turn your master, (power amp) volume up (say to 2 or 3 o'clock). Gradually turn up the preamp volume to a desired level.

Your master, or power amp should be doing all the work, so that's why I suggest turning that up and turning the preamp down.

Hopefully this may help![/quote]

And i would add turn off the tube in the pre to start with.

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[quote name='Kurt' post='27310' date='Jul 5 2007, 09:10 AM']I've had a poke about in the amps forums here and on TB trying to find an answer to my question but am now more confused than when I started!. Here's the deal. I've got an Aggie GS112 which, for rehearsals I run on its own with an ABM500. The amp's master vol is never turned up much above 10 (o'clock) and there is no extreme eq'ing going on. I did notice the other night that the VU meter was full scale on every note as I had mis-set the input gain (ie the pre was clipping). Now the speaker in the GS112 is distorted at anything approaching a useable volume. I've tried different cables, my bass into another amp etc, all pointing to the cab still. The only thing I can't try in my amp into another cab at the moment, but I guess if I'd fried the amp I'd get nothing out of it.

Thanks in advance for your help, but please keep it simple. I don't know what xmax, excursion and all the other tech terms I've come across are!!!

Peace[/quote]

Well, you've obviously got a knackered speaker on your hands, but one thing's certain: it won't have been caused by clipping of the ABM's pre-amp stage. Despite popular myth, clipped signals cannot in themselves damage LF (low frequency) drivers (although they can damage tweeters on account of the greatly increased HF component in a clipped waveform). There are two forms of damage that can occur to an LF driver: thermal or mechanical, and both are caused by the same thing: having more power put into it than it is able to dissipate, either as sound or heat. The GS112's driver is only rated to handle 300Watts RMS, and you've been driving it with an amp capable of 575 Watts RMS, so it's quite possible that you've accidentally over-taxed the poor thing with clean power (yes, even with the amp's master gain down at 10 o'clock).

Looks like you'll have to replace that speaker, I'm afraid. :) Make sure your next one is capable of handling at least 600 Watts.

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Thinking about this made me remember that my MAG combo went funny just after a year of having it (or maybe it was just under, i cant remember now).
After loads of gigs suddenly i couldn't turn it up to half way on the master without the sound breaking up. It was like a soft distortion.
I tried all sorts of combinations to narrow it down and im convinced its the power section of the amp.
I ran another head (ABM300EVOII) in to the speaker and it was fine. I ran the pre out from the MAG (fx send i think) in to a deck and it was fine. I ran the pre out from the ABM in to the fx return of the MAG and the distortion was back.
I took it to the Bass Centre for them to have a look at and it was there about 3-4 months. They said it was fine and i got it back minus a knob.
Make of that what you will but its certainly not as usable as it was when i got it.

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Kurt, just to clarify: you have tried running the GS112 cab off another amp and found it still to be faulty, haven't you? I was basing my advice on that assumption.

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[quote name='dave_bass5' post='27485' date='Jul 5 2007, 03:21 PM']I took it to the Bass Centre for them to have a look at and it was there about 3-4 months. They said it was fine and i got it back minus a knob.[/quote]

The knobs there seem to congregate around the till. So uncalled for but I couldn't resist.

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[quote name='The Funk' post='27493' date='Jul 5 2007, 03:32 PM']The knobs there seem to congregate around the till.[/quote]

which side?
:)

This is what i miss over on TB. they dont seem to have the same outlook on other peoples problems as we do over here LOL

Edited by dave_bass5

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I'd say that the speaker's been blown by too much signal.

Distortion like that happens in a speaker when the coil melts slightly when being overdriven (thats in a speaker sense, not as in fuzz...) and reforms slightly mis-shapen. Its catching on the side of the driver (magnet) and will slowly wear itself out.

Also, its important that usually the master output control is not really a control of the overall output power, but a control of the gain applied to the signal from the pre-amp. So if the pre was really loud (i.e. clipping) the sound would be a lot louder than normal, and may well have pushed your amp over what the speaker could handle.

Basically, like Oxblood sed.

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Sounds like you need one of these to me:

[url="http://www.aguilaramp.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=AA&Product_Code=JDK12-8"]http://www.aguilaramp.com/Merchant2/mercha...ct_Code=JDK12-8[/url]

Or, even better, get that then another GS112 so it doesn't happen again! I believe there are a pair for sale at the moment on here.

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Kurt, this may be a long shot but have you checked the coil cover (in the center of the speaker)? I once had the glue break up on a coil cover so it was flapping around with every note - farty party! Fixed mine with some rubbery glue stuff. :)

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Guys, we are talking about Ashdown here. why do you all think its the cab?

Kurt, if you are ever passing through Central London you are welcome to try your amp through my UL115 cab.

Edited by dave_bass5

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[quote name='dave_bass5' post='27669' date='Jul 5 2007, 11:10 PM']Guys, we are talking about Ashdown here. why do you all think its the cab?

Kurt, if you are ever passing through Central London you are welcome to try your amp through my UL115 cab.[/quote]

Fair enough I guess it could well be the amp. He did say he hasn't tried another. The sound he describes sounds very similar to that produced by speakers I've blown in the past though. :-)

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you could always cut the centre coil out of the speaker and see if its burnt...... but then the speaker would be useless anyway :)

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[quote name='joegarcia' post='27681' date='Jul 5 2007, 11:24 PM']Fair enough I guess it could well be the amp. He did say he hasn't tried another. The sound he describes sounds very similar to that produced by speakers I've blown in the past though. :-)[/quote]

Im not disagreeing with anyone, its just that it sounds like the problem i have with my MAG.
In fact at the last gig i did with it not only did me and the drummer smell burning coming from my combo but the speaker was very distorted and i thought i had blown it. I dont know what it was but after the gig we realised the radiator was up full and my combo was only inches from it.
Its back to being "just" distorted now. If i turn it up to around 11 o'clock it starts to break up in a soft distorted way and going higher on the master just makes it more compressed and dirty sounding.
If thats not the same type of sound then i guess im wrong.

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[quote name='Oxblood' post='27479' date='Jul 5 2007, 03:13 PM']Well, you've obviously got a knackered speaker on your hands, but one thing's certain: it won't have been caused by clipping of the ABM's pre-amp stage. Despite popular myth, clipped signals cannot in themselves damage LF (low frequency) drivers (although they can damage tweeters on account of the greatly increased HF component in a clipped waveform). There are two forms of damage that can occur to an LF driver: thermal or mechanical, and both are caused by the same thing: having more power put into it than it is able to dissipate, either as sound or heat. The GS112's driver is only rated to handle 300Watts RMS, and you've been driving it with an amp capable of 575 Watts RMS, so it's quite possible that you've accidentally over-taxed the poor thing with clean power (yes, even with the amp's master gain down at 10 o'clock).

Looks like you'll have to replace that speaker, I'm afraid. :) Make sure your next one is capable of handling at least 600 Watts.[/quote]

The ABM puts out 575w into 4 ohms. As the GS112 is 8 ohms it will only recieve a max of 350w (roughly) I only had the master up to about 10 o'clock, so I think this is a non issue. Having checked everything out, it's definately the driver in the GS. I might put one of the new Celestions in it, have to see.

Thanks for the help everyone

Peace

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[quote name='Kurt' post='27724' date='Jul 6 2007, 06:16 AM']I might put one of the new Celestions in it, have to see.[/quote]

The minimal specs I've seen for the new Celestion speakers suggest they're pretty rubbish for bass, the low Xmax in particular. I've heard of people changing the stock GS112 speaker to a DeltaLite II 2512 and being very impressed so that's the route I'd suggest taking.

Alex

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double check (particulary if you are poking around with speakers etc) that there aint any loose solder joints, I had distortion problems with my Peavey BW cab and i thought it was everything from a bust speaker to a bust amp but in the end it was a simple as a rusted joint on the input jack of the cab.

Edited by d-basser

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