C-Audio Pulse Series Amplifier Problem

oliverwestby · 29th December 2008, 07:25 AM

I decided to set myself a challenge to fix a c-audio pulse 4x300 amplifier that was constantly in protect mode. Having replaced a control transistor and the soft start resistors in the power supply, and all 4 output transistors and the previous gain section on channel 4, I finally had a working amplifier, albeit still with some problems.
Firstly, channel 4 has a small amount of distortion added to any signal it amplfies. I took it apart again to troubleshoot this, and in the process decided to compare it to channel 4 that was previously working. Ch 3 now had no output, although the signal light was illuminated.
I turned it up, and once it got to 1/4 gain, the clip light came on, yet still no sound.
after much playing around, I have the following symptoms and hope someone here could point me in the right direction.

Channels 1,2 and 4 amplify the signal, and do not clip with a standard signal, channel 3's clip light illuminates at very low volume, and makes no sound.

When increasing signal ampilutude, both the channel with the signal and channel 3 clip, and noise is heard from channel 3

If the wire that takes the output sections signal to the board where the speakon connectors are, is removed, clipping a channel does not casue anything to happen to channel 3's clip light (it stays off)

with this wire removed, channel 3 still show clipping at low gain with signal on input to ch3

No dc present on output.

Any suggestions will be greatly appreciated

Ollie

audiomachines · 30th December 2008, 05:07 AM

Happy New Year! Hope this helps.http://www.crownaudio.com/pdf/legacy...rvice-info.pdf

Best regards,
audiomachines

ceharden · 1st January 2009, 07:31 PM

I have reasonable experience with the Pulse amps but not the 4ch version.

The service manual is quite useful and describes the circuitry in detail. I do remember reading a bit that said that the amp should never be run with the outputs disconnected from the back panel board so be careful.

The clip light on the amps is actually controlled by effectively a distortion measuring circuit so it indicates that there is something happening that the feedback loop is unable to correct for.

The interaction between channels is very odd, I'm puzzled!

audiomachines · 1st January 2009, 10:38 PM

could it be a fault on the protection scheme?, all the protection of all the channels is controlled by a single chip (PIC Stamp)

HAPPY NEW YEAR!

Best regards,
audiomachines

ceharden · 1st January 2009, 10:55 PM

I've never seen any problems with the microprocessor and associated circuitry on those amps. There is a lot of limiting and protection which doesn't involve the PIC. The PIC mainly controls whether the amp is allowed to run or not and doesn't have any control over the audio path.

audiomachines · 1st January 2009, 11:07 PM

how about the muting, that shuts down the LTP?

alvinj · 7th February 2013, 12:55 AM

i am working on caudio pulse 650. it not starting up the 24v supply for the switching ic sg3525a is pulsating from 5v to 23v. even if the switching ic is disconnected from the the startup supply, checked tr50 all the zeners in the start up supply no joy

29th December 2008, 07:25 AM	#1
oliverwestby diyAudio Member Join Date: Apr 2006 Location: Oxfordshire	C-Audio Pulse Series Amplifier Problem I decided to set myself a challenge to fix a c-audio pulse 4x300 amplifier that was constantly in protect mode. Having replaced a control transistor and the soft start resistors in the power supply, and all 4 output transistors and the previous gain section on channel 4, I finally had a working amplifier, albeit still with some problems. Firstly, channel 4 has a small amount of distortion added to any signal it amplfies. I took it apart again to troubleshoot this, and in the process decided to compare it to channel 4 that was previously working. Ch 3 now had no output, although the signal light was illuminated. I turned it up, and once it got to 1/4 gain, the clip light came on, yet still no sound. after much playing around, I have the following symptoms and hope someone here could point me in the right direction. Channels 1,2 and 4 amplify the signal, and do not clip with a standard signal, channel 3's clip light illuminates at very low volume, and makes no sound. When increasing signal ampilutude, both the channel with the signal and channel 3 clip, and noise is heard from channel 3 If the wire that takes the output sections signal to the board where the speakon connectors are, is removed, clipping a channel does not casue anything to happen to channel 3's clip light (it stays off) with this wire removed, channel 3 still show clipping at low gain with signal on input to ch3 No dc present on output. Any suggestions will be greatly appreciated Ollie

1st January 2009, 10:38 PM	#4
audiomachines diyAudio Member Join Date: Dec 2005 Location: silang, cavite	c-pulse 4x300 could it be a fault on the protection scheme?, all the protection of all the channels is controlled by a single chip (PIC Stamp) HAPPY NEW YEAR! Best regards, audiomachines

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30th December 2008, 05:07 AM	#2
audiomachines diyAudio Member Join Date: Dec 2005 Location: silang, cavite	Happy New Year! Hope this helps.http://www.crownaudio.com/pdf/legacy...rvice-info.pdf Best regards, audiomachines

1st January 2009, 07:31 PM	#3
ceharden diyAudio Member Join Date: Nov 2005 Location: Southampton	I have reasonable experience with the Pulse amps but not the 4ch version. The service manual is quite useful and describes the circuitry in detail. I do remember reading a bit that said that the amp should never be run with the outputs disconnected from the back panel board so be careful. The clip light on the amps is actually controlled by effectively a distortion measuring circuit so it indicates that there is something happening that the feedback loop is unable to correct for. The interaction between channels is very odd, I'm puzzled!

1st January 2009, 10:55 PM	#5
ceharden diyAudio Member Join Date: Nov 2005 Location: Southampton	I've never seen any problems with the microprocessor and associated circuitry on those amps. There is a lot of limiting and protection which doesn't involve the PIC. The PIC mainly controls whether the amp is allowed to run or not and doesn't have any control over the audio path.

1st January 2009, 11:07 PM	#6
audiomachines diyAudio Member Join Date: Dec 2005 Location: silang, cavite	how about the muting, that shuts down the LTP?

7th February 2013, 12:55 AM	#7
alvinj diyAudio Member Join Date: Nov 2010 Location: london uk	i am working on caudio pulse 650. it not starting up the 24v supply for the switching ic sg3525a is pulsating from 5v to 23v. even if the switching ic is disconnected from the the startup supply, checked tr50 all the zeners in the start up supply no joy