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#1
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Blown power amp channel?
I was wondering what kind of damage was caused to my amp and if it's
worth trying to fix it. I accidentally used a 1+/1- speakon cable(wrong one) on my Crest CC1800 with the switch in bridged mode. Now the amp will cut off channel A when the input gets too high. By cut off, I mean the ACL(Automatic Clip Limiter) lights up and the sound is completely stopped, then it returns to normal after a few seconds. Channel B works fine for now. Bridged mode acts similar to channel A. Also channel A works normally under a very small load for at least an hour or more, but I need to get more volume or else this is useless to me. Is this amp pretty much toast on channel A? Or is this a simple easy fix at my nearest service center? Other info that may be important.... This is a part of a bass rig. Ampeg tube preamp, maybe the preamp's output is too hot? 4 ohm speaker cabinet. And yes, I learned my lesson on speaker cables. |
#2
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Blown power amp channel?
need4mospd wrote:
I was wondering what kind of damage was caused to my amp and if it's worth trying to fix it. I accidentally used a 1+/1- speakon cable(wrong one) on my Crest CC1800 with the switch in bridged mode. Now the amp will cut off channel A when the input gets too high. By cut off, I mean the ACL(Automatic Clip Limiter) lights up and the sound is completely stopped, then it returns to normal after a few seconds. Channel B works fine for now. Bridged mode acts similar to channel A. Also channel A works normally under a very small load for at least an hour or more, but I need to get more volume or else this is useless to me. Is this amp pretty much toast on channel A? Or is this a simple easy fix at my nearest service center? It's going into protection for some reason. My first guess would be a blown output transistor, but a tech with an ohmmeter will be able to tell for sure. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#3
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Blown power amp channel?
"Scott Dorsey" wrote in message
... need4mospd wrote: I was wondering what kind of damage was caused to my amp and if it's worth trying to fix it. I accidentally used a 1+/1- speakon cable(wrong one) on my Crest CC1800 with the switch in bridged mode. Now the amp will cut off channel A when the input gets too high. By cut off, I mean the ACL(Automatic Clip Limiter) lights up and the sound is completely stopped, then it returns to normal after a few seconds. Channel B works fine for now. Bridged mode acts similar to channel A. Also channel A works normally under a very small load for at least an hour or more, but I need to get more volume or else this is useless to me. Is this amp pretty much toast on channel A? Or is this a simple easy fix at my nearest service center? It's going into protection for some reason. My first guess would be a blown output transistor, but a tech with an ohmmeter will be able to tell for sure. And for future reference, you should look at the specs for that amplifier and see if it's rated into a 2-ohm load, because when you hang a 4-ohm speaker onto a bridged output, each channel sees 2 ohms. If it's not rated into a 2-ohm load, just use one channel. Peace, Paul |
#4
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Blown power amp channel?
On Mar 8, 11:27 pm, "Paul Stamler" wrote:
"Scott Dorsey" wrote in message ... need4mospd wrote: I was wondering what kind of damage was caused to my amp and if it's worth trying to fix it. I accidentally used a 1+/1- speakon cable(wrong one) on my Crest CC1800 with the switch in bridged mode. Now the amp will cut off channel A when the input gets too high. By cut off, I mean the ACL(Automatic Clip Limiter) lights up and the sound is completely stopped, then it returns to normal after a few seconds. Channel B works fine for now. Bridged mode acts similar to channel A. Also channel A works normally under a very small load for at least an hour or more, but I need to get more volume or else this is useless to me. Is this amp pretty much toast on channel A? Or is this a simple easy fix at my nearest service center? It's going into protection for some reason. My first guess would be a blown output transistor, but a tech with an ohmmeter will be able to tell for sure. And for future reference, you should look at the specs for that amplifier and see if it's rated into a 2-ohm load, because when you hang a 4-ohm speaker onto a bridged output, each channel sees 2 ohms. If it's not rated into a 2-ohm load, just use one channel. Peace, Paul It's capable of 4 ohm bridged or 2 ohm per channel according to Crest. One of the reasons I got it. I played on it again tonight and used Channel A with the ACL light coming on after about 5 minutes. After switching the amp off and on again it kept going steady at a decent volume for around 2 hours til I shut it down. So after warming up it works fine in parallel mode. When I bridged it later on it clipped under higher loads. Any more thoughts before I take it in for repair? |
#5
Posted to rec.audio.pro
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Blown power amp channel?
On 8 Mar 2007 21:49:15 -0800, "need4mospd"
wrote: I played on it again tonight and used Channel A with the ACL light coming on after about 5 minutes. After switching the amp off and on again it kept going steady at a decent volume for around 2 hours til I shut it down. So after warming up it works fine in parallel mode. When I bridged it later on it clipped under higher loads. Any more thoughts before I take it in for repair? Does it play alright on channel B only? It's an interesting problem because most modern amplifier failures are catastrophic (brimstone and treacle). Failures that don't cause a China Syndrome Meltdown are rare and interesting. And, "unfortunate as it was" (Taj Mahal), very specific. Our generic advice here will be less useful. Generic advice (from me): if it works at all, it's well worth repairing. My personal experience of bass amps is of tragic underdesign and terminal cheap-assedness. Just a taste of modern life, really. Find somebody who cares enough to fix the one you've got; better may not be easily buyable, is my point. If this is too harsh an advice and a real picker out there knows of something current and solid, speak! I'd love to be wrong, fersure. Much thanks, Chris Hornbeck |
#6
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Blown power amp channel?
Chris Hornbeck wrote:
It's an interesting problem because most modern amplifier failures are catastrophic (brimstone and treacle). Failures that don't cause a China Syndrome Meltdown are rare and interesting. My guess is that this amp has a whole bunch of paralleled output transistors, and that one or more of them have failed on one leg, so it's unbalanced. The feedback is keeping the thing DC stable, sort of. My other guess is that if you keep operating the amp like this for long, it will have a catastrophic failure and take out the rest of the output stage. Since you really need to go in and replace all the output transistors if one is bad anyway, this is not as bad as it might sound. Generic advice (from me): if it works at all, it's well worth repairing. My personal experience of bass amps is of tragic underdesign and terminal cheap-assedness. Just a taste of modern life, really. Find somebody who cares enough to fix the one you've got; better may not be easily buyable, is my point. If this is too harsh an advice and a real picker out there knows of something current and solid, speak! I'd love to be wrong, fersure. A lot of older ones are pretty awful too. I have... I think... a Precision BB-15 here that I can't find docs on... if anyone has a schematic I would love to see it. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#7
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Blown power amp channel?
"Scott Dorsey" wrote in message
... My other guess is that if you keep operating the amp like this for long, it will have a catastrophic failure and take out the rest of the output stage. Since you really need to go in and replace all the output transistors if one is bad anyway, this is not as bad as it might sound. Yeah, but since it might take out other parts as it went, including speakers, it could get pretty expensive. Go get the amp fixed. Peace, Paul |
#8
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Blown power amp channel?
On Mar 9, 10:31 am, "Paul Stamler" wrote:
"Scott Dorsey" wrote in message ... My other guess is that if you keep operating the amp like this for long, it will have a catastrophic failure and take out the rest of the output stage. Since you really need to go in and replace all the output transistors if one is bad anyway, this is not as bad as it might sound. Yeah, but since it might take out other parts as it went, including speakers, it could get pretty expensive. Go get the amp fixed. Peace, Paul Thank you very much guys. Any ideas how much this will cost me to repair? I just don't know how much repairs like this typically cost, so I don't want to get screwed. Clay |
#9
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Blown power amp channel?
"Paul Stamler" wrote in message ... "Scott Dorsey" wrote in message ... My other guess is that if you keep operating the amp like this for long, it will have a catastrophic failure and take out the rest of the output stage. Since you really need to go in and replace all the output transistors if one is bad anyway, this is not as bad as it might sound. Yeah, but since it might take out other parts as it went, including speakers, it could get pretty expensive. Go get the amp fixed. Peace, Paul Fortunately most current designs have some sort of protection circuitry and it's relatively rare that a blown amp takes out a speaker. Unlike the good ol' days ...... Gareth. |
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