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Old 3rd May 2005, 02:43 AM   #1
garbage is offline garbage  Singapore
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Default battery powered 3875

hi all

i p2p a 3875 gc running on 4 SLA 12v batteries.
the only psu caps i have are 2 47uF silmic ars at each chip itself.

ran them without cap initially, but got some crackles when i turned up the volume.

just wondering if anyone experienced turn on/off thump with a 3875 on batteries? there is no mute pin on 3875, any one has ways to solve this thumping?

would a relay on outputs help with turn off thump as well?

thanks.
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Old 4th May 2005, 01:16 AM   #2
garbage is offline garbage  Singapore
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Lightbulb no one's replying...

maybe some pics would help?

in the test rig
Click the image to open in full size.

closer shot of the chips
Click the image to open in full size.

is it normal for 3875 to have turn on/off thumps?
there is a thread in here that suggested using a switch on speaker outputs to switch in/out the speaker after and before turn on and turn off.
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Old 4th May 2005, 05:41 AM   #3
scottw is offline scottw  United States
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Yes, they can thump with a battery power supply. I can't tell from the pics how you are switching on the power but it helps if both rails(+&-) switch at exactly the same time. If you are already using a double pole switch for power try a different switch. I had a breadboard battery powered GC that had a separate switch for each rail and even trying to switch them at the same time would cause wild cone movements on my cheap test speakers.

Increasing the cap size(~1000uf) may also reduce the thump but may change the voicing of the amp.

good luck,

Scott
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Old 4th May 2005, 05:51 AM   #4
garbage is offline garbage  Singapore
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hi scott

thanks for your reply.

i'm only switching at 0 now. will be getting a 4P2T/3T switch so that i can switch +, 0 and - and also to toggle between batteries and charging.

4P is required as i would be using 2 x L200CV. one L200CV to charge 2 x 12v cells.

the 47uF value was suggested by peter daniels in response to one of my questions on this forum. when i was using w/o psu caps, the turn on/off is not that audible.

cheers
vincent
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Old 4th May 2005, 10:16 AM   #5
DT is offline DT  Lithuania
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try to switch battery PS with relays.
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