My first LM3886 project (please help urgently!!)

Derfla

Member
2008-03-09 10:13 am
Hi, everyone, I'm new here and I have been reading lots about gainclones and decided to build some of these fantastic amps
I have all the parts ready but I just need some clarfication on some things :confused:
my power supply for each channel will be a 100VA square transformer with bridge rectifier and two 4700uf caps across the DC output (voltage is about 28.5v)
all resistors used are 0.5W and the electrolytics are 50VDC, 100nf's are 100V
the heatsink for the LM3886TF chips was taken from an old amp
now here's my circuit (dogbreath.de has been of much help thank you!)
[IMGDEAD]http://img80.imageshack.us/img80/2913/3886chipampschematicej4.jpg[/IMGDEAD]
I am confused about where all the grounds go, do they all get connected together and to the mains earth? and also where in the circuit does the input signal's 'negative' go? what about the speaker output negative? it would of much help if it was indicated on my schematic (modified from dogbreath.de)
the schematic is correct isn't it? and am I missing anything?

Thanks! =]
Derfla
 

Derfla

Member
2008-03-09 10:13 am
okay! I shall use those two then :D
the snubbers are the 0.1R resistors and the 3.3nF caps right?
i'm having trouble finding those small value caps:
C1 2.2uF, Cs 300pF, C6 3.6uF, and C7,8 3.3nF
are they cube polyester ones, little round orange ones or electrolytics :confused:
[IMGDEAD]http://img218.imageshack.us/img218/8950/lm3886ampgx6.gif[/IMGDEAD]
 
You can use the polyester 'box' (or any shape) caps for any of them for which the values are available in polyester, which would probably be all except the 300 pF. Polypropylene would be better, but would be larger in size. Wima makes some nice polypropylene box caps. For the smaller values (e.g. 300 pF), if you use ceramic caps, try to use C0G or NPO dielectric type. Or you could use polystyrene (best, probably) or silver mica caps.