Tuesday, November 27, 2007

Chu Moy Headphone amp PCB design

I've built a number of Chu Moy design headphone amplifiers over recent months and recommend them so highly to friends I end up giving them away. Previously written up here.

Ugly construction is fine for one or two off, but it was time to try manufacturing a printed circuit board.

When I last made a printed circuit board, it was done photographically, by exposing a chemical resist to ultra violet light. Having just dismantled my dark room, it was time to try a different technique.

I used some blue "press-n-peel" transfer film. The design was done manually in OmniGraffle, printed on the film with a little HP laser printer, ironed on to the board on a wool setting, etched and drilled all in a couple of hours.

This technique works pretty well, I've had a little trouble with the ironing phase, the transfer moves a bit when I iron it on. On one occasion I had to rub off the bad transfer and iron on again. The instructions say to set the iron to polyester, but our iron doesn't have it so I set it to wool.

The actual circuit for this board uses two OPA134 amp chips (rather than the dual chip) and a TLE2426 rail splitter. I don't include any volume control as the device driving it, generally a computer or digital player has one.

I present here revision 2 of a PCB design. It works but could be more compact and has two links. PDF here, OmniGraffle source here. Note that the writing will be mirrored on the copper side when you make it. (I haven't figured out how to mirror text in OmniGraffle..) 

You are free to use these for any purpose. (Let me know if you improve it).

Be careful that your printer is close enough to 100%, I suggest test printing and lining up the 8 pin IC which is the only critical spacing.


Ken Case said...

There is a trick you can use to flip text in OmniGraffle:

1. Select the text shape.
2. Choose "Copy as PDF" from the Edit menu.
3. Paste the PDF onto your canvas.
4. Using the Geometry Inspector, flip your pasted PDF shape.

Thanks to LinkBack, the text in the pasted PDF shape can still be edited: if you double-click on the PDF shape, it will open a LinkBack window where you can edit the original shape. When you save changes in the LinkBack window, it will update the flipped PDF shape back in your main document.

Hope this helps!

marxy said...

Wow, fantastic customer support - thanks very much!