PCB Design Questions

[Sherman]

I have wanted to design a PCB for a small single-ended tube amp but really have no experience. So... I decided to start with a GC PCB using Brian's board as a starting point and changing a couple of things just for practice. (I don't actually plan to make the board, it is just that the circuit is simple enough for me to comprehend. )

I was able to draw the basic circuit easily. I even added a Zobel network on the PCB (my big change!). But one question immediatlely came up and that is trace size. On Brian's boards the power and ground traces are very large, occupying basically the entire top of the board. Is this done to provide a sort of groundplane with only a 2 layer board or is it related to power handling? In my research it appears a trace of .120" would be more than enough for the power and ground.

A related question- can anyone recommend a book or website covering PCB design basics?

[peranders]

I can say that 150 mil /1 oz, 35 um copper can take 25-30 A without burning off, meaning 100 mil is OK (if we only talk burning traces off) for LM3875 but always strive to have a wide as possible. It's also important to minimized resistances where you can expect high current, mostly for stability and distortion reasons. I think you should take a close look at Brian's boards and the ground area especially.

[Sherman]

I'll look at the boards very closely but keep in mind I'm only using them as a starting point to learn to design a PCB, not create another GC PCB. (I don't think I could beat the quality and price of Brian's boards by rolling my own.)

Eventually I hope to transfer the knowledge I gain to designing a board for a tube amp. (I know, tubes only sound good wired ptp. ) Basically I am curious about the process and especially curious about why Brian made the power and ground traces into large plates.

[sam9]

go to: http://www.vutrax.co.uk/vbook.htm

click on "tracks and widths"

[joensd]

A related question- can anyone recommend a book or website covering PCB design basics?

IMO you can get quite far with knowing about basic electronics.
The most important will be how you will lead signals and especially grounding techniques are of the essence.
The rest is more or less about aesthetics and keeping it compact.

Texas Instruments has got a nice paper about PCB-techniques and grounding with examples.
Literature number is SLOA089 and it is an excerpt from "opamps for everyone".(SLOD006A or B)

You´ll find many, many more articles about PCB-techniques from other semiconductor manufacturers and websites in general.

If you can´t find them I can post them to you.

Regards
Jens

[Sherman]

Originally posted by sam9
go to: http://www.vutrax.co.uk/vbook.htm

click on "tracks and widths"

Thanks, this is the type of info I was searching for. It gives different values than the calculator I found but since it also provides more general info I think it will be more valuable.

Originally posted by joensd


IMO you can get quite far with knowing about basic electronics.
The most important will be how you will lead signals and especially grounding techniques are of the essence.
The rest is more or less about aesthetics and keeping it compact.

Texas Instruments has got a nice paper about PCB-techniques and grounding with examples.
Literature number is SLOA089 and it is an excerpt from "opamps for everyone".(SLOD006A or B)

You´ll find many, many more articles about PCB-techniques from other semiconductor manufacturers and websites in general.

If you can´t find them I can post them to you.

Regards
Jens

Jens,
Having built a couple tube amps, a discreet solid state amp and several GCs now I have discovered how important grounding is! But up till the gainclones everything was from a kit or very well prepared instructions.

Thanks for the leads on the TI papers. I'll try and dig them up before asking you to find them and post them.

My knowledge of electronics is probably beyond "Rank Beginner" and less than "Advanced Amateur". In other words I know enough to be dangerous. This forum has been one of the best sources of information within (and sometimes outside of) its topic I have ever found.

[peranders]

Walt Jung brick book about opamps

This book is one of the best! A real gem.

And it's for free, for professionals at least.