So I done the schematic...

[Maples]

Hey everyone,

I am attempting to follow this project: http://sound.westhost.com/project3a.htm

Now I want to make my own PCB because its better that point-to-point and I like the professional look of it. So I copied the schematic into Eagle by re-drawing it myself, when it came to the resistors I just kept copied the resistor symbol from the first one I pulled out the library and changing the value appropriately, then I'd do the same for like components such as caps, pol caps, etc.

The transistors I tried my best to find in the library, if I didn't find them I found the next best thing and just changed its name and as long as the final symbol matched the one of the original schematic I kept going. All in all the schematics match 100% after checking them side by side (printed them out and done the checking by hand).

So I move on to the board, place the components, run the auto router set to only do bottom traces, it only makes it to 70-something % , I set it to do both top and bottom traces it finishes it but I know that the result is not acceptable for various reasons such as the components not being optimally placed close together, high power traces not being wide and such. So I was not about to try to make a board out of what I had.

As a beginner I am asking for some help here, word is the auto router is evil and I should do this by hand, among other things. So as vague as this may seem, what do you guys think I should do now? I also notice that the footprints most of the transistors are not congruent with the ones I got from OnSemi, only one of them look like they should which tells me I picked the transistor types for the others when doing the schematic.

Schematic I made: http://home.neo.rr.com/deviance/p3a.jpg
Resulting board: http://home.neo.rr.com/deviance/p3a-board.jpg

[jaycee]

Yes, the autorouter is evil. It's only really of use for things like low speed digital circuits where things like crosstalk don't really matter.

Also, you've made your first faux-pas by assuming all component packagings are equal. They aren't. For example, the MJL4281/4302 are in a package format known as TO3P, and your layout there shows you've copied the BC546B which is just a TO92 package. Also the size of the capacitors, there is no way 100uF 63V capacitors are that small.

There are other issues to consider. The MJL4281/4302 devices are power transistors, they will need to be near the edge of the board so that they can be bolted to a heatsink. The small signal devices, the BC546B's however should be nowhere near them. The exception to this rule however, is T4 which should be close to the heatsink in order to get what is known as "thermal tracking". There's a whole slew of rules that go with laying out a PCB for a power amplifier. Many books and articles have been written on the subject.

If this is your first time working with actual components, the best advice is to look each and every single part up online - use http://www.onsemi.com for the transistors, and your favorite part supplier for things like capacitors. Look at the shape and sizes of the components, the pinouts of the transistors etc. Then use this information to describe your schematic in Eagle.

I recommend using the "rcl" library for resistors and capacitors - it allows you to change package fairly easily to suit whatever you happen to get hold of. For transistors, use the "transistor" library and the devices under "NPN" and "PNP" there. The MJL4281/4302 are of the "TOP3" pinout there, you may wish to use the "TOP3V" component for those. The MJE15034/15035 are "TO220", again use "TO220V".

PCB layout takes a lot of time and experience. Unless you have the patience and ability (and cash!) to etch more than one board, it's going to get expensive. If what you want is a working amplifier, I'd suggest simply buying a pre-made PCB from Rod Elliot, they are easy to put together and from seeing the way that it is laid out, it will teach you how to lay out your own PCB's in future.

I myself am also constructing a P3A amplifier (with some modification!) and I've already been through 3 layouts (by hand) in Eagle for this amplifier, am in the middle of routing my 4th one, hopefully this is the one I'll be happy with

Rod has his own forum, where a lot of people hang out who have a lot of experience with his projects, this is a great place to go for advice. However he gets very upset by people asking how to make their own PCB's etc, which is understandable since as he makes a living from selling them.

We all have to start from the beginning and make mistakes, so Good luck!

[ChocoHolic]

simple schematic, straight forward instead of fancy games,
for my personal feeling probably better than most of the
material-war-designs!

good luck
markus