Layout/Circuit board design

[qtcustom]

Hello venerable gentlemen (and ladies?) of the electron,

Disclaimer:

Though I probably have enough experience with a soldering iron to be considered just barely out of the "noob" phase, I have no formal electronics training and therefore everything I've learned has been a result of hundreds of hours of research and reading. My conceptual understanding is decent, but obviously nowhere near the standard of even the moderately experience here on this wonderful board. My question is, how do you design a circuitboard layout? I understand this question is probably much larger in scope than can be answered in one thread, so if there are any particular relevant articles reading material or other threads the deal with this topic please point me in that direction and I will be happy to take it from there. I'm not afraid of homework. After a few weeks of studying and reading I've got a pretty good handle on reading the schematics on the site, but I know many of you guys can look at a schematic and derive a layout down to the fine details, something which I have no idea how to do, or even where to begin or what rules to pay attention to when doing so. Any information you can point me to regarding this discipline would be much appreciated. thanks very much.

[xtian]

Are you asking about the design of tube amps for guitar? My approach was to start with the simple builds, like Fender Champ, where the schematics and layouts are available for you to see. There are several systems that need to be integrated, but kept separate to avoid noise: signal, grounds, power, heaters. After working with more and more complex layouts, and suffering a lot of trial and error, now I can (at least try) to improve the layouts of those old amps.

So I'm suggesting you "apprentice" yourself to the proven, documented designs, and that will be your education.

[qtcustom]

Xtian, thank you. I guess what I'm asking is what are the design principles used to lay out the original circuitboard for a Fender champ, for example. I should have perhaps omitted the word "layout" from my original post as that's not specifically what I'm asking about at this point- i'm more interested in the circuit board itself. I can look at the schematic for the amplifier and look at the populated board and see what goes where, comparatively, but I'm wondering if there's a systematic approach to designing a circuitboard rather than just building everything as if it were a champ with more features. Does that make sense? For example, (and this may be a stupid question, but how else do you learn anything?) why does the ODS have separate boards for power supply and signal? Why not just combine it all into one big board? I'll freely admit that I don't know enough about electronic theory to be able to reason the stuff out myself, though I'm sure there's probably a good and simple explanation for all of it. I'm just curious mostly because I have enough knowledge to be dangerous but not enough to have a thorough understanding of anything, yet. I suppose this is like how I was when I was learning music theory- I wanted to know WHY stuff works the way it does, not just HOW it works. Still working on it!

[xtian]

Naw, we're talking about the same stuff. I mentioned some of the principles, above--integrating several systems but keeping your design noise free. We're talking about lead dress here. The shortest path from component to component is usually best to keep noise low. Except when placing elements too close together (e.g., high current AC heaters near sensitive grid inputs). Also important is to keep ground wires short (grounding is an art in itself), and I prefer to stage power filters near their triodes, instead of off on a separate board. But we also balance these design imperatives with other goals, namely organization, ease of maintenance/modification, and beauty.

Again, how do you learn this stuff? There is no one reference. Merlin, Aiken, Keen and others have published great material on all of these topics and more. Again, you have to study the existing designs, because in most cases, these designs are evolved, advanced, bug-free, etc. And we get to stand on the shoulders of giants!

[Phil_S]

You are right when you say it won't be covered in a single thread. I think layout is absolutely the right word to use. You cite an amp with a separate power supply board. Sure you can integrate that into the layout. It requires some knowledge of the "rules" some of which can be broken by those who really know how and others may be sacrosanct.

In general, as already noted, the object is to avoid introducing noise and to get some amount of efficiency into it. You want to avoid long wire runs, keep a/c heaters and B+ power supply away from the signal path. Construct the ground scheme without ground loops. Sometimes you need a wide berth, other times 1/8" might be enough clearance. It depends on lots of things.

One way to get into this is to build something more complex than a Champ and less challenging than a high gain multi-channel affair. (The latter will be very noise sensitive.) A new builder is likely to do enough wrong to get some noise. The troubleshooting that ensues will teach you a great deal. It might also have a high frustration factor.

[John_P_WI]

It is good to ask questions. Historically amps - right or wrong - generally have had separate power supplies and signal sections.

If you truly want to learn, I would suggest that you learn how each section of an amp works and what is the power, load, and ground. Soon you will be able to identify how the current flows in loops "around" each circuit allowing the proper decoupling and grounding techniques to be used in each section, preventing hum and other problems, understanding why the speaker jacks should not be grounded to the chassis etc. Remember, the power supply is the important "other half".

Regarding the capacitor placement, distributed decoupling or distributed capacitance works. Check out the attached diagram from the master, VacuumVoodoo here:

https://tubeamparchive.com/viewtopic.ph ... ght=ground

Also check out "Larry Grounding".

Understanding these points will unravel much of the amp mystery.

[schaublin65]

Hi

I found Mr.Hoffman's approach really helpful when I first encountered them.

His layouts are so elegant and easy to understand.

Take care...

John

[matt h]

(deleted)

[xtian]

Dude, I'm being helpful!

[matt h]

Dude, I'm being helpful!

I'm not suggesting otherwise... (which was my point)

[RWood]

Sounds odd but doing my first point to point really helped me understand board layouts much better. It also blew my mind even with long wire runs it did not introduce noise. The quietest amp I've built was a 5D6 PTP with every socket, cap, and jack grounded right next to it except the mains, PT, and first node grounds being a single ground. It also had miles of wire and should have been a noise generator, but quite the opposite.

My point being...after that build I could see the relationships of components on a board much more clearly, which helps tremendously with designing one.

Also the venerable sages on this forum are more than willing to help with the exception of a few trolls and a couple of nameless know-it-alls who think that all their knowledge is proprietary!

[qtcustom]

Actually this thread is a tremendous help already. I'm certainly not looking for a checklist kind of answer, just more of a general idea of what to leave look at and read, and the references in this thread or helping already, thank you. As to the external combustion engine with troll...that's hilarious. I understand that this is an entire field of study, and I'm not looking for shortcuts, but there is simply a lot of terminology thrown around on the site and in these threads that is taking is common knowledge, understandably so. For someone with no engineering background, it's valuable to have the more experienced point you in the direction of the right articles and information, as of course I'm trying to understand basic electronics theory viewed through the lens of tube amplification. Thanks again guys, and if you have any more suggestions or insight please keep them coming.

John

[xtian]

Don't miss our sticky thread: Reading Material on Steroids.