A Audio and hi-fi forum. AudioBanter

Go Back   Home » AudioBanter forum » rec.audio » Pro Audio
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

Blown power amp channel?



 
 
Thread Tools Display Modes
  #1  
Old March 8th 07, 05:53 PM posted to rec.audio.pro
need4mospd
external usenet poster
 
Posts: 3
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.

Ads
  #2  
Old March 8th 07, 06:35 PM posted to rec.audio.pro
Scott Dorsey
external usenet poster
 
Posts: 16,620
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."
  #3  
Old March 9th 07, 05:27 AM posted to rec.audio.pro
Paul Stamler
external usenet poster
 
Posts: 1,614
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


  #4  
Old March 9th 07, 05:49 AM posted to rec.audio.pro
need4mospd
external usenet poster
 
Posts: 3
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?

  #5  
Old March 9th 07, 06:33 AM posted to rec.audio.pro
Chris Hornbeck
external usenet poster
 
Posts: 1,744
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
  #6  
Old March 9th 07, 01:56 PM posted to rec.audio.pro
Scott Dorsey
external usenet poster
 
Posts: 16,620
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."
  #7  
Old March 9th 07, 04:31 PM posted to rec.audio.pro
Paul Stamler
external usenet poster
 
Posts: 1,614
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


  #8  
Old March 9th 07, 04:41 PM posted to rec.audio.pro
need4mospd
external usenet poster
 
Posts: 3
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

  #9  
Old March 11th 07, 02:51 PM posted to rec.audio.pro
Gareth Magennis
external usenet poster
 
Posts: 589
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.


 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
FA: 4 channel QSC Power Amp - CHEAP! arohana Pro Audio 0 September 2nd 05 05:32 PM
FA: DBX BX-2 4 channel 3 voltage power amp Steve Pro Audio 0 August 11th 05 01:10 AM
FA: QSC 602V 2 Channel Power Amp arohana Pro Audio 0 April 11th 05 04:54 PM
car stereo wont power. might be blown fuse. HELP!!!! [email protected] Car Audio 1 April 6th 05 03:39 AM
car stereo wont power. might be blown fuse. HELP Mack Car Audio 1 April 3rd 05 07:09 PM


All times are GMT +1. The time now is 01:14 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Copyright 2004-2019 AudioBanter.
The comments are property of their posters.