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.
 
no one's replying...

maybe some pics would help? :D

in the test rig
[IMGDEAD]http://img258.echo.cx/img258/5695/tnpict01554mf.jpg[/IMGDEAD]

closer shot of the chips
[IMGDEAD]http://img248.echo.cx/img248/5508/tnpict01547qn.jpg[/IMGDEAD]

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.
 
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
 
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