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need4mospd need4mospd is offline
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Default 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.

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Scott Dorsey Scott Dorsey is offline
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Default 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."
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Paul Stamler Paul Stamler is offline
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Default 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


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need4mospd need4mospd is offline
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Default 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?

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Chris Hornbeck Chris Hornbeck is offline
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Default 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


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Scott Dorsey Scott Dorsey is offline
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Default 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."
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Paul Stamler Paul Stamler is offline
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Default 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


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need4mospd need4mospd is offline
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Default 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

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Gareth Magennis Gareth Magennis is offline
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Default 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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