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Can the gain kill the amp?


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sedate 
Silver - Posts: 1,173
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Joined: July 03, 2004
Location: Colorado, United States
Posted: December 02, 2005 at 2:29 PM / IP Logged  
Hi guys:
So I've had my stereo working properly for all of a month now so its about time something expensive broke.
So I was fine tuning the gains on my JL e6450... seen here.. I nudged my gains on channels 3, 4, 5, and 6 up a bit.. maybe a 1/4 turn on the knob and upped the gain on the front channels up another 1/8 turn or so.
Anywho fast forward a good hour or two and my amp cuts out. Shuts straight off into protection... then cuts in and out and in and out... i know its not the voltage not only b/c my voltmeter says so, but I know when JL amps drop off under 8v or so they just shut down the protection light doesn't come on.
The usual suspects are all eliminated: Ground is good, I know my voltage is nailed to like 12.5 even with the woofers going full swing and the speakers have otherwise been playing fine in thier locations... a short would provide ample audible clues.
If I turn the gain wayyy down.. and I mean WAYY below where I've had it with no problems for the last month, it'll play fine again..but certainly not at a satisfactory volume! Arg!
So anywho, is my thinking right on here? I mean I guess if I was running the amp really hard I mighta damaged it somehow.. but even right after it first shut into protection I checked it and the amp really hadn't even gotten real hot yet.. (not to mention my trunk was like 2 degrees last night)...
What can I do to test this amp straight? I mean I kinda want an excuse to buy a Multimeter..
BTW, I took it up the dealer.. and I kid you not, they wouldn't even look at it. The guy made some comment about him not being a tech guy and told me for $50 he'd pull it around the back and have someone check it. But then I'd have to pay more to get it fixed...
"I'm finished!" - Daniel Plainview
arrow12 
Silver - Posts: 527
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Joined: October 06, 2005
Location: United States
Posted: December 02, 2005 at 2:59 PM / IP Logged  

Ok my last post didn't post so I'll try again.  Your amp could have been right on the edge of working hard but not too hard before you turned up the gain.  When you turned the gain up you might have sent the amp over the edge.  This could have fried or damaged some internal mechanisms that would cause the amp to work efficiently and sound good.  Keeping the gain down my mask these problems, but they still might exist just at lower levels.

That's my opinion. Take it, leave it, or correct me.
DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: December 02, 2005 at 3:11 PM / IP Logged  

Why were you messing with the gains in the first place?  Didn't you set them to match the HU output?  Once set, a gain adjustment should never be turned up.  Down, yes, up, no.

But yes, it is possible to fry the input stage of an amplifier by feeding it too hot a signal (gain too high.)  Usually you simply drive the amp into clipping and blow your speakers, but if it went into protection and now it's not functioning, you probably broke it.

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customsuburb 
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Joined: January 17, 2004
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Posted: December 02, 2005 at 3:25 PM / IP Logged  
By turning the gain up you could have caused the amp to over heat and go into protect... you would have to have been really driving it hard though. Set your gains right and leave them alone. Do a search and look at one of the 1000000000 topics on setting the gain if you don't know how.
tcss 
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Joined: June 07, 2004
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Posted: December 02, 2005 at 3:33 PM / IP Logged  

I'm not totally convinced it's an amp problem. Sedate I remember you were going to use this amp in a bi amp system for your highs, try this. With the amp at it's original gain settings, disconnect one channel at a time and turn up the volume. If it doesn't go into protect, you have a coil that's only shorting out at higher volumes ( I have run into this). This voice coil might have failed BECAUSE of your gain increases

God, you have a crappy JL dealer where you live. I would have checked it for free looking for a new amp sale, or repair and gaining a new loyal customer in the process.

There is no such thing as free installation!
JMaxx93 
Copper - Posts: 73
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Joined: December 02, 2003
Location: United States
Posted: December 02, 2005 at 5:24 PM / IP Logged  
tcss wrote:

I'm not totally convinced it's an amp problem. Sedate I remember you were going to use this amp in a bi amp system for your highs, try this. With the amp at it's original gain settings, disconnect one channel at a time and turn up the volume. If it doesn't go into protect, you have a coil that's only shorting out at higher volumes ( I have run into this). This voice coil might have failed BECAUSE of your gain increases

God, you have a crappy JL dealer where you live. I would have checked it for free looking for a new amp sale, or repair and gaining a new loyal customer in the process.

agreed don't count out the amp yet.  try it with different speakers if you don't know how to test the speakers.

tcss 
Silver - Posts: 1,623
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Joined: June 07, 2004
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Posted: December 02, 2005 at 5:35 PM / IP Logged  
Just to clarify my post, disconnect speaker leads not RCAs.
There is no such thing as free installation!
geepherder 
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Posted: December 02, 2005 at 7:20 PM / IP Logged  
Yes, disconnect the speakers and let us know if it's still in protect.
My ex once told me I have a perfect face for radio.
sedate 
Silver - Posts: 1,173
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Joined: July 03, 2004
Location: Colorado, United States
Posted: December 02, 2005 at 9:46 PM / IP Logged  
DYohn wrote:
Why were you messing with the gains in the first place? Didn't you set them to match the HU output? Once set, a gain adjustment should never be turned up. Down, yes, up, no.
Yea I derserve the scolding. I seriously wanted to beat my head against the pavement when that amp first cut out I wish I had someone standing over my shoulder reminding me not to be greedy. Can the gain kill the amp? -- posted image.
Naww I was playin with it cuz I was doing some back to back listening between a stellar pair of monitors I have on an Onkyo reciever and my car... the monitors have this certain mid-bass warmth that I was trying, with little success, to duplicate. DYohn, my front stage is hopelessly complitcated and I have like 1000 ways to play around with the sound so 'once set' never is. Can the gain kill the amp? -- posted image.
DYohn wrote:
Usually you simply drive the amp into clipping and blow your speakers
That's the thing! The rear 4-channels (they are running bridged to a 4-ohm CDT EF series midbass) had the gains up right high, but listening to *only* the midbasses playing to set them (I mean I just listen real careful like for distortion with the tweeters, rear mids, and subs off) I always play somethign with alot of bass-drops and aggressive midbass.. in this case Tupac.. and they didn't seem to have any problem with the gain setting when I was actually playing with it. The HP was set up at like 120hz and the speakers are rated to take like 110watts@100hz HP.... they sounded really, really loud and flawlessly clean..
tcss wrote:
If it doesn't go into protect, you have a coil that's only shorting out at higher volumes ( I have run into this). This voice coil might have failed BECAUSE of your gain increases
BINGO! I was having a really hard time swallowing that I killed that amp over that little gain twist ... especially with no audible distortion AND no real heat buildup! I've done wayy worse things to that amp and had it come out a hummin'. Summer time the thing would get so hot you couldn't even touch it...
Okay so last question though... the one thing the dealer did tell me before he refused to look at the amp was that if its cycling protection like that its either 1)Shorted xover or speakers or 2)bad power supply on the amp... so what started occuring to me was that the amp could take a certain 'limit' of total output before it would protect itself again but I think the VC idea sounds alot more likely..
tcss wrote:
God you have a crappy JL dealer where you live
These clowns. They have these reciepts that say "The Audio One - Service After the Sale!" and I pointed that out to the guy that wanted $50 to have a tech look at it and his reply was "Oh then I'll be taking money out of their pockets" gesturing loosely toward the install bay. "So what if I take the amp out then will you tell me if its broken?" "No the diagnostic fee still applies.."
I really don't get it they do like more volume than every other shop in town put together. Just look at this write up. I dunno I guess success has gone to their heads.
I'm seriously never giving them money again.
"I'm finished!" - Daniel Plainview

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