My UcD start oscillation

opor · 4th March 2010, 03:08 PM

There is something wrong with my amp.
When I connected power rail to only one channel it seem OK even it has some noisy . But when I connect same power rail to another channel .I turn it on both there is so much noisy and when I volume up by turn R23 it start oscillate and this oscilation is noticeable from another channel too . So how to fix it?

Andrew Eckhardt · 03:17 PM

The problem you are having seems to be something related to carrier tracking between both amps. I'm sorry I didn't look closely at the circuit, but you would probably do best to start looking into how this could be happening. If the two amps share one sink, is the sink grounded. If that isn't it then look around for other ways two high power square waves could couple between two circuits. It could have something to do with your signal routing too.

opor · 4th March 2010, 03:27 PM

Two channel has its own sink. So how to check even if there is couple.

Andrew Eckhardt · 4th March 2010, 03:45 PM

Well I think your symptoms indicate that there is definitely coupling, so there is no need to check that. Keep in mind that under no circumstances will this problem completely go away. It is a serious problem with switching amplifiers and the only thing you can do is try to minimize it through every trick you ever heard of. Make sure that you can't slow down switching time in the interest of reducing noise any further before affecting other performance parameters. It's a balancing act there. Think of the leakage field around the filter inductors. Try to minimize drain capacitance to the heatsinks. Make sure ground, power, and signal routing is absolutely optimized. After all that, try putting each channel in it's own cage. Like I said, the trouble never ends. You can even put shielding between the power and signal sections of each channel.

Andrew Eckhardt · 4th March 2010, 04:06 PM

I forgot to mention. Before you go absolutely insane trying to make a noiseless PWM amp, check to make sure you don't have output stage cross-conduction occurring. That is probably the most common PWM amp gotcha and of course it will generate very high current ringing far above the normal switching frequency. If you have that going on it'd be the place to start fixing.

opor · 7th March 2010, 01:39 AM

Thank you Andrew, I have changed R46 to 390R so everything is OK.

darkfenriz · 7th March 2010, 12:55 PM

What is the circuit based on 555?
Current regulator at overcurrent?

opor · 7th March 2010, 01:46 PM

Yes,it is overcurrent protection.

stewin · 28th July 2010, 07:09 AM

hi opor pls post the pcb of your schem and are your output irfp 250 heating ?

stewin · 3rd August 2010, 11:13 PM

try increasing r54 & r55 or try to use irf540z instead of irfp250

4th March 2010, 03:12 PM	#2
Andrew Eckhardt diyAudio Member Join Date: Nov 2005 Location: PA	The problem you are having seems to be something related to carrier tracking between both amps. I'm sorry I didn't look closely at the circuit, but you would probably do best to start looking into how this could be happening. If the two amps share one sink, is the sink grounded. If that isn't it then look around for other ways two high power square waves could couple between two circuits. It could have something to do with your signal routing too. Last edited by Andrew Eckhardt; 4th March 2010 at 03:17 PM.

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4th March 2010, 03:27 PM	#3
opor diyAudio Member Join Date: Nov 2005	Two channel has its own sink. So how to check even if there is couple.

4th March 2010, 03:45 PM	#4
Andrew Eckhardt diyAudio Member Join Date: Nov 2005 Location: PA	Well I think your symptoms indicate that there is definitely coupling, so there is no need to check that. Keep in mind that under no circumstances will this problem completely go away. It is a serious problem with switching amplifiers and the only thing you can do is try to minimize it through every trick you ever heard of. Make sure that you can't slow down switching time in the interest of reducing noise any further before affecting other performance parameters. It's a balancing act there. Think of the leakage field around the filter inductors. Try to minimize drain capacitance to the heatsinks. Make sure ground, power, and signal routing is absolutely optimized. After all that, try putting each channel in it's own cage. Like I said, the trouble never ends. You can even put shielding between the power and signal sections of each channel.

4th March 2010, 04:06 PM	#5
Andrew Eckhardt diyAudio Member Join Date: Nov 2005 Location: PA	I forgot to mention. Before you go absolutely insane trying to make a noiseless PWM amp, check to make sure you don't have output stage cross-conduction occurring. That is probably the most common PWM amp gotcha and of course it will generate very high current ringing far above the normal switching frequency. If you have that going on it'd be the place to start fixing.

7th March 2010, 01:39 AM	#6
opor diyAudio Member Join Date: Nov 2005	Thank you Andrew, I have changed R46 to 390R so everything is OK.

7th March 2010, 12:55 PM	#7
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	What is the circuit based on 555? Current regulator at overcurrent?

7th March 2010, 01:46 PM	#8
opor diyAudio Member Join Date: Nov 2005	Yes,it is overcurrent protection.

28th July 2010, 07:09 AM	#9
stewin diyAudio Member Join Date: Jul 2007	hi opor pls post the pcb of your schem and are your output irfp 250 heating ?

3rd August 2010, 11:13 PM	#10
stewin diyAudio Member Join Date: Jul 2007	try increasing r54 & r55 or try to use irf540z instead of irfp250

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