Intripped wrote:can i ask something about ground and power lines routing?
i know that ground routing is not critical for pedal effects, but anyway i'd like to have some guidelines to understand how the perfect routing should be
"less critical", not "not critical".
Imagine a LED that switches on or a LFO circuit that switches state. Imagine that circuit sharing a ground line with an amplifying circuit for few centimeters to the point where the DC power supply enters the stompbox.*
When that LED or LFO switches the change in current draw (and corresponding voltage drop) over that trace, while having only a few 10's of ohms of resistance can be very audible in the amplified signal becasue of the sudden supply voltage change of the amplifier stage.
Yes. Ideally one wants to consider his power supply having such an low output impedance that it will "suck up" all power supply noises. In the non ideal world there's usually a few meters of cable in between the supply's filter caps and DC regulation. There may be some daisy chain in place that feeds other effects and their own noise. One cannot take this into consideration, other than by adding a power supply decoupling cap at the DC input.
star grounding is the optimum, and ground plane are very good too (not sure about power planes...),
Even in the few 100's of kHz's star grounding starts to decrease in performance rapidly already. Star grounding might be considered "good" from an audio frequency perspective but was obsoleted years ago already with digital stuff and incresing clock frequencies. If you introduce a noise, provide a good, low impedance return path close to it. For instance a ground plane.
Ground planes are part of the subcollection of power planes. If you go 4 layer, have a ground plane, VCC plane and 2 signal layers.
but let's say that we only have one-sided PCBs and star ground is too difficult to obtain: where to connect input and output signal grounds? and +9V? chassis ground? supply ground? LED ground?
Indeed. Back to one layer
What are you going to do with your signal? You''ll probably going to amplify/buffer it first? This means you're going to amplify a voltage potential at the input compared to a reference (ground). Now if that "ground" needs to travel say 10cm from a central grounding point upto the reference of that amplifier that's another 10cm of increased impedance and noise pickup. So, preferably keep both input and reference connection as friggin short as possible.
Output, same thing but less inmportant in FX as they usually drive with a low impedance output.
Chassis and LED ground,
At the entry point of your power supply. That's the supply ground.
....there's shitloads of exceptions to be brought up to all above that happen to work, that happen to "sound good" etc.... but suddenly don't happen to work on a Bogner, or are "terrific with Fenders" but "Suck with Marshalls". Very smart engineers tried to make designs pedals in such a way they would respond the same, as much as possible, regardless of the amps used. Unfortunately guitarists are guitarists and the immediate complaint was "toan suck". Immediately after this far less talented "engineers" started to remake these designs with all the "situation vulnerability" again and marketed them as boutique and "full of toan" and "made by real musicians".