EXPERIENCED LAYOUT PEOPLE

[brian wenz]

Hello Hello--
How do you go about planning a layout for a fuzz pedal??   Is there some kind of  "given" arrangement of parts that assures low noise??  [In other words, if I lay out a Fuzz Face circuit in some manner everytime , am I  going to get  great results EVERYTIME?]
What would be the best layout for two-tranny or three-tranny fuzz circuits?
I know that by looking at a schematic [and maybe laying out the circuit as it is in the schematic] and then looking at a different layout, I see that the positioning of parts [caps, res., trannys, etc.]  is different.  Why choose one over the other??   What is the "science" of positioning parts?
I know that each circuit can be different, but I'm just trying to understand the logic behind it all.
Thanks--
Brian.

[BillyJ]

Ahh...What you need if RG's book "PCB Layout For Musical Effects."
Now to get a copy all you need to do is bug RG into whipping up a new batch.
He binds them himself so they come in batches. Definetly get yourself in line for it.

I know it doesn't help right now but it is a great book and it cover exactly what you ask about and much more.
Hopefully some other forum member can make some suggestions to help you out in the near future.

[Joep]

I think you can say for simple guitar effect circuit, the way you put the components on the board doesn't really matter.

A simple and effective way is to just follow the schematic. Check for example RunOffGroove's Odie and Cabsim.

These layout's are generally not really economic (less components per sq inch). Check Tonepad's layouts for some highschool PCB economy.    :shock:

Bye,

Joep

[Paul Perry (Frostwave)]

Keeping the output away from the input will help.
So will shielded wire in the input.
And yes, RG's book is full of good advice.
To get a feel for layout, you could get a jumbo pad & some pens & just GO FOR IT!!

If you are a beginner though, I'd check out some other people's solutions as well.

[Boofhead]

Conceptually the logic very simple, minimize the effect the PCB has on the operation of the circuit.

You have a circuit on a bit of paper and you want it to perform as close to ideal as expected.   A knowledgable designer will actually add parts to the schematic  to make is less sensitive to layout issues.  When you put real parts on a board the board introduces parasitic effects: the tracks have resistance and inductance, and each track has a capacitance between other tracks.   How important these parasitics are depends on the circuit, in fact, some parts of a given circuit are more susceptable than others.  The "best" layout is one which minimizes the *impact* of the parastitics for that circuit ,as opposed to minimizing the parasitics themselves - ie. reduce the impact to problem areas.  For example try to keep input and outputs of non-inverting high-gain feedback amplifiers away from each other since the capacitive coupling can cause unwanted oscillations.  Another example if capacitive coupling  is to keep fast switching digital signals away from sensitive analogue circuits.

It possible for a layout to make the circuit interact with itself in undesirable ways.  For example, if you are have a guitar amplifier, it amplifies small signals form the guitar and turns this into large currents through the speakers.  The PCB tracks carrying the high currents will have small voltage drops across them, due the resistance and inductance of the tracks.  If low level input signals share these tracks then the voltage drops from the high current signal can get into the input signal - an unwanted situation.  For a completely analogue effect  this is unlikely to be a problem.  If you have mixed analogue and digital circuits the digital circuits produce current pulses when they switch and shared tracks can lead to the digital pulses getting into the analogue circuits.

Yet another source of problems is the effect of external noise sources.  The layout can effect how sensitive a circuit is to external noise sources.  External noise couple capacitively to each track, or couples inductively like a transformer to through "loops" created between the wires/tracks in a circuit (the loops act as a turn of an unwanted transformer).  This is why a breadboard layout with long wire will buzz and humm more than a compact PCB layout.  To reduce these effects you keep tracks short and (usually) run sensitive tracks close to a ground wire to reduce the area of the loop.

All this boils down to:  
- keep tracks for sensitive parts of the away from noisy parts of the circuit, or parts of the circuit involving high voltages and currents.
- don't let low level and high level signal share tracks.
- keep tracks short
- run sensitive track close to (quiet) ground tracks
- add large areas of ground track (ground planes) to help act as a shield and reduce voltage drops in the ground tracks.

By the way, this is by no means a complete list.

Obviously it's impossible to do this for a complete cirucit, the art of layout is to find a balance between all these factor for the specific circuit at hand.
If you keep things compact, avoid long tracks, and spot problem areas you are on you way.

[R.G.]

The answer to your question is long - I did over a hundred pages of text and illustrations to answer just a portion of it.

There is no "given" arrangement, only principles, like separating input from output, simple and logical signal flow on the board, conceptualizing where ground current flows, etc.

Layout is a combination of science and art. I get a discinct impression at a glance at an effect layout whether the person who did it has studied my layouts before or not, just from the "style". I can also usually tell reasonably well how much experience the person has in doing the limited style of layout in effects. It's like the large variation and recognizable styles in a music form as utterly simplistic and thoroughly worked as blues. There is a limited format, but there are large variations and styles within it.

No two layouts of the same circuit by two different people will ever be accidentally identical, even in part.

[Dan N]

One thing I have not seen being taken advantage of is that as DIYers we may have a pretty good idea of the enclosure we will use and the placement of pots, jacks, and switches.

For me, input and output are usually on one end of the board down by the bypass switch. Pots and jacks at the opposite end of the board. I often have the ac jack in the side.

It may be sacrilegious to make a pcb without all the leads politely lined up on one edge. Oh well, I'm don't figure to get into heaven anyway...

[Fp-www.Tonepad.com]

I have done a couple of the more complex layouts available online and have a little to say about it:

When the circuit is very large try to separate the building blocks that the circuit is made of. A little of 'divide and conquer' goes a long way on simplifying things.

Start by redrawing the schematic. That should give you a feel of what you're getting into.

Give yourself realistic limits. Board size, for example, is a very 'real' limit.

Make it look good, if you line up parts nicely, and route tracks in an orderly fashion, the layout will be easier to populate and troubleshoot, and the probability of it working will be greater.

And my last tip is to look at all the different layouts available, study them, try to think what the person who made them was thinking, and what logic they followed.

Fp

[brian wenz]

Hello Hello To All-
 Thanks to everybody who replied so far!
So far my build experience  is confined only to fuzz pedals [and the NOISE produced by same!] .  I'm always looking for the "ideal" layout for a Fuzz Face / Tonebender / 2-tranny / 3-tranny  style circuit.   In the past I've laid out a particular circuit just like the schematic and it worked great [no noise, etc.] and then laid it out according to a "good" layout design and there would be more noise!  Oh well.........
I always keep the input and output  well away from each other and also shield the input and output wires.   Even after doing all the usual layout rituals involving grounding and such,  I still wonder why the placement of something like a feedback resistor in a Fuzz Face circuit would change the amount of noise in the finished product.  The  physical placement oof parts does make a difference.
Anyway, I hope to here more...
Brian.

[javacody]

Not sure about what I am about to type, but lots of knowledgable people to correct me here, so here goes nothin.

I used all metal film resistors in a Fuzz Face clone (the Sili Face from RunoffGroove) and I have zero noise.  I didn't do anything special except try to keep the positive battery lead away from the input. I didn't even use shielded wire for the input (yet).  Anyway, some of you guys who know way more than me can hopefully enlighten me on how much noise metal films produce vs. carbon films?

[brian wenz]

Hello Hello--
    Yeah, I try to use metal film res. too, although I know people who say that if it's a small circuit [Fuzz Face, etc.] it makes no difference between metal film or carbon film.
Thanks for mentioning the batt. lead 'cuz I tend to forget about that in some of my builds!
Brian.

[brian wenz]

Hello Hello--
    Yeah, I try to use metal film res. too, although I know people who say that if it's a small circuit [Fuzz Face, etc.] it makes no difference between metal film or carbon film.
Thanks for mentioning the batt. lead 'cuz I tend to forget about that in some of my builds!
Brian.