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Old 31st January 2007, 12:49 AM   #1
impsick is offline impsick  United States
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Default 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
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Old 31st January 2007, 05:28 AM   #2
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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.
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Old 31st January 2007, 11:01 AM   #3
BWRX is offline BWRX  United States
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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?
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Old 31st January 2007, 11:10 AM   #4
impsick is offline impsick  United States
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no just an alps blue. but i've been turning the volume down and then i would hit the power switch
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Old 31st January 2007, 11:13 AM   #5
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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.
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Old 31st January 2007, 11:14 AM   #6
impsick is offline impsick  United States
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wheres that? whats that? i wanna see
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Old 31st January 2007, 11:26 AM   #7
BWRX is offline BWRX  United States
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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.
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Old 31st January 2007, 11:44 AM   #8
impsick is offline impsick  United States
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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.
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Old 31st January 2007, 11:52 AM   #9
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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.
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Old 1st February 2007, 01:05 AM   #10
Leolabs is offline Leolabs  Malaysia
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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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