[Paragon]

You have to insulate the metal case is you are just laying the board in say a tin. You can line the bottom with electrical tape. I would probably do a two layers of electrical tape myself. The bottom of the board can have sharp points if the part leads are not cut down enough and they could make their way though the tape. Some people use a piece of thick plastic as their insulation. You can get some really thick tape similar to electrical tape but a few times as thick if you have nothing else around.

 

[Slaughter]

I use foam sheets from a craft store in the kids section. The kind of foam they use for cutting out flat shapes. Link

 

[Paragon]

Quote:

Originally Posted by Slaughter /img/forum/go_quote.gif I use foam sheets from a craft store in the kids section. The kind of foam they use for cutting out flat shapes. Link

Good idea

 

[arspy87]

AFAIK, if you're using two batteries already, then you don't need those 4.7Kohm resistors to divide the voltage; just use the node between your two batteries as the virtual ground.

Also, I used two index cards as insulation between the board and the casing... works pretty well and more sturdy than electrical tape.

 

[mminutel]

Everything is working great. I ended up using a couple of my Digi-Key labels for insulation. The only problem is that I couldn't get two batteries to fit so I am going to have to use jsut 1.

 

[bellsprout]

Quote:

Originally Posted by arspy87 /img/forum/go_quote.gif AFAIK, if you're using two batteries already, then you don't need those 4.7Kohm resistors to divide the voltage; just use the node between your two batteries as the virtual ground.

but then if one battery drains faster than the other, there will be a dc offset

 

[Paavola]

Quote:

Originally Posted by bellsprout /img/forum/go_quote.gif but then if one battery drains faster than the other, there will be a dc offset

I wonder how this could affect the dc offset... If the other battery drains faster you only get uneven supply voltage, other supply rail is lower voltage than other. With adequate headroom in supply voltages this should not be a problem. If the other battery drains much, there could be some clipping, but in this occasion you would change the battery in every case.

 

[arspy87]

Quote:

Originally Posted by Paavola /img/forum/go_quote.gif I wonder how this could affect the dc offset... If the other battery drains faster you only get uneven supply voltage, other supply rail is lower voltage than other. With adequate headroom in supply voltages this should not be a problem. If the other battery drains much, there could be some clipping, but in this occasion you would change the battery in every case.

Plus the resistor divider isn't perfect either, due to tolerances.

 

[Paavola]

I really don't now how the PSU is hooked up in this situation, but it is possible (of course) to make an PSU with two batteries, without any dividing resistors.

Of course when using one battery as in one sided supply, and you have created an dc offset to the input of amp circuit to create a virtual negative supply voltage, the difference in resistor values gives you offset. Maybe there should be an coupling capacitor in the output to filter DC...

Maybe im getting a bit off from the original topic