a pop when i power down

impsick · 31st January 2007, 12:49 AM

ok so built the LM3875 with PDaniels pcbs. it s sounds good buy the way.

but when i flip the power switch to off the speakers do a little pop. how do get rid of that? i dont know where to even start trouble shooting that.
the rectifier board i added the snubber components if that helps. the big caps are 50v 4700uf.
id appreciate any help. thanks

abid_rehan · 31st January 2007, 05:28 AM

Though I have never used the chip but its datasheet does not show that it has a popup noise control circuit while powering on/off.
I hope P.D and other experts here could enlighten more however, as far as I am concerned there is nothing to troubleshoot about as in the abscence a popup noise control its natural for the amp to behave like that.
You could also add bleeder resistor on powersupplies.

BWRX · 31st January 2007, 11:01 AM

On the first page of the datasheet it says: "Supply under-voltage protection, not allowing internal biasing to occur when |V+| + |V-| = 12V, thus eliminating turn-on and turn-off transients"

If you shut down the supply while listening to music you will hear the chip shut down when the supply caps discharge below around 12V. You will hear a little click but it shouldn't be harmful to speakers. Do you have an active preamp that shuts down at the same time?

impsick · 31st January 2007, 11:10 AM

no just an alps blue. but i've been turning the volume down and then i would hit the power switch

Original Burnedfingers · 31st January 2007, 11:13 AM

There is a chip amp mute circuit thread. I have a circuit to eliminate the power on power off noise.

Unfortunately it won't apply to the chip that you are using. It will work with the LM3886 however.

impsick · 31st January 2007, 11:14 AM

wheres that? whats that? i wanna see

BWRX · 31st January 2007, 11:26 AM

It won't help because the LM3875 doesn't have a mute pin like the LM3886.

How loud is the pop you're hearing? When I power down my LM3875 I just hear a click when the rail voltage drops below ~10V. However, I also have opamps in front of the LM3875 that I turn off after the chip's supply discharges.

impsick · 31st January 2007, 11:44 AM

its not really that loud. its kind of a click or pop. but where is some info on your curcuit i got some 3886's im gonna put together here.
would changing the value of resistr between the big 4700uf caps do anything? they are .2ohm right now.

Original Burnedfingers · 31st January 2007, 11:52 AM

Quote:

It won't help because the LM3875 doesn't have a mute pin like the LM3886.

If you read my edited post you will see that I already made a mention to this.

Quote:

Unfortunately it won't apply to the chip that you are using. It will work with the LM3886 however.

Leolabs · 1st February 2007, 01:05 AM

It's kind of strange to me there is a 'pop' when switch off a GC.My DDGC
doesn't exhibit such problem with a pair of 2200uF caps and a LM3875 and a 200VA EI transformer.

31st January 2007, 12:49 AM	#1
impsick diyAudio Member Join Date: Dec 2006	a pop when i power down ok so built the LM3875 with PDaniels pcbs. it s sounds good buy the way. but when i flip the power switch to off the speakers do a little pop. how do get rid of that? i dont know where to even start trouble shooting that. the rectifier board i added the snubber components if that helps. the big caps are 50v 4700uf. id appreciate any help. thanks __________________ "Nothing happens for a reason. There are just reasons why things happen." Quote me on that. http://stores.ebay.com/AudioGrade?_rdc=1

31st January 2007, 11:01 AM	#3
BWRX diyAudio Moderator Emeritus Join Date: Jan 2005 Location: Pennsylvania	On the first page of the datasheet it says: "Supply under-voltage protection, not allowing internal biasing to occur when \|V+\| + \|V-\| = 12V, thus eliminating turn-on and turn-off transients" If you shut down the supply while listening to music you will hear the chip shut down when the supply caps discharge below around 12V. You will hear a little click but it shouldn't be harmful to speakers. Do you have an active preamp that shuts down at the same time? __________________ Brian

31st January 2007, 11:10 AM	#4
impsick diyAudio Member Join Date: Dec 2006	no just an alps blue. but i've been turning the volume down and then i would hit the power switch __________________ "Nothing happens for a reason. There are just reasons why things happen." Quote me on that. http://stores.ebay.com/AudioGrade?_rdc=1

31st January 2007, 11:14 AM	#6
impsick diyAudio Member Join Date: Dec 2006	wheres that? whats that? i wanna see __________________ "Nothing happens for a reason. There are just reasons why things happen." Quote me on that. http://stores.ebay.com/AudioGrade?_rdc=1

31st January 2007, 11:26 AM	#7
BWRX diyAudio Moderator Emeritus Join Date: Jan 2005 Location: Pennsylvania	It won't help because the LM3875 doesn't have a mute pin like the LM3886. How loud is the pop you're hearing? When I power down my LM3875 I just hear a click when the rail voltage drops below ~10V. However, I also have opamps in front of the LM3875 that I turn off after the chip's supply discharges. __________________ Brian


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31st January 2007, 05:28 AM	#2
abid_rehan diyAudio Member Join Date: Mar 2007	Though I have never used the chip but its datasheet does not show that it has a popup noise control circuit while powering on/off. I hope P.D and other experts here could enlighten more however, as far as I am concerned there is nothing to troubleshoot about as in the abscence a popup noise control its natural for the amp to behave like that. You could also add bleeder resistor on powersupplies.

31st January 2007, 11:13 AM	#5
Original Burnedfingers diyAudio Member Join Date: Nov 2002	There is a chip amp mute circuit thread. I have a circuit to eliminate the power on power off noise. Unfortunately it won't apply to the chip that you are using. It will work with the LM3886 however.

31st January 2007, 11:44 AM	#8
impsick diyAudio Member Join Date: Dec 2006	its not really that loud. its kind of a click or pop. but where is some info on your curcuit i got some 3886's im gonna put together here. would changing the value of resistr between the big 4700uf caps do anything? they are .2ohm right now. __________________ "Nothing happens for a reason. There are just reasons why things happen." Quote me on that. http://stores.ebay.com/AudioGrade?_rdc=1

1st February 2007, 01:05 AM	#10
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	It's kind of strange to me there is a 'pop' when switch off a GC.My DDGC doesn't exhibit such problem with a pair of 2200uF caps and a LM3875 and a 200VA EI transformer.

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