trying to post board lm3886t

[psychosteve]

i realy hope this works,

if it does what do you think and what did i get wrong?

if it didnt work how should i be doing it?

see you all soon, steve.. ..

[psychosteve]

any one?

[boholm]

AFAICS:

No feedback resistor between output and -input

No +input resistor connected to ground


Please also post schematics.

[psychosteve]

feed back resistor is on pins under board, i forgot to show it on the schem.

the input to ground is through the pot to the right marked E$1. as per the schem on national data sheet.

apart from that any thing else?? see you soon, steve.. ..

[boholm]

Still, it is IMHO a good thing to add an input resistor, simply because a potentiometer in time wil become affected by wear or may brake the wiperarm (or what's it called?) or maybe even loose contact (dust and/or wear).

Still no diagram? Else we cannot see, what you are missing out.

And I would put some more capacitors (decoupling) on the board.

Otherwise . . . looks neat .

[psychosteve]

yes i was going to put some ceramic caps pin to pin under the board as well, what would you recomend for the input res.?? if im using a 10k pot and i picked say a 5k res. would not a 5k paralleled with the pot affect the rest of the circuit?

[psychosteve]

damn, schem. didnt work. its the circuit on page one of the data sheet. see you soon, steve.. ..

[richie00boy]

Board looks OK. Your resistors look at bit small (maybe it's just the image size). Standard 1/4 watt resistors are 4 tenths of an inch (400 mils?) long.

I'd second the idea of adding an input grounding resistor. You can make it 100k or something. That way it will have negligible effect on the pot law, but still offer a DC path to ground to bias the input in the event of momentary jumps.

I've put a zobel network on my board. It's still not finished though. I'm good at the design thing, but use ancient software. Maybe you can give me some lessons in Eagle?

[psychosteve]

im just learning eagle myself, i usualy do artwork on a drawing board 4x size then scale down on a photo coppier onto transparency for etching with photresist copper clad to make boards. but let me know what problems you have and ill try, or let you know how i got arround it.

they are not standard 1/4 watt resistors, they be metal film 1% 0.6 watt, and are the corect pin out size, the pins come out of the bottom, like the poly caps you can get!!!!! and i know you cant get them any more, ive got a small box left over from when i was at the naval yard in portsmouth.

so a 100k res from input pin to signal grnd, can i put that strait accross the pot???

[boholm]

As Richie00boy said, 100k is an OK value. It is of course possible to mount it on the pot, but then you snap a wire . . . No, put it on the board and save yourself that kind of trouble - and OMHO it is best to put as much as possible on the board, so you don't have problems related to cabling, interference and other things. And there is room on the board for the resistor, so why not put it there?