| impsick |
ok so built the LM3875 with PDaniels pcbs. it s sounds good buy the way.:D 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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| abid_rehan |
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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| BWRX |
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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| impsick |
| 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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| burnedfingers |
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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| impsick |
| wheres that? whats that? i wanna see |
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| BWRX |
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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| impsick |
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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| burnedfingers |
| 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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| Leolabs |
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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| impsick |
| what about the resister on the caps? what is there value? |
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