pedal PSU question

[daz]

I get that, but what i'm saying is that regardless of whether it's in any one of the pedals or in the wall wart or anywhere in between, if i wire up a single supply to several pedals in parallel the cap is connected to ALL of the pedals the same way....across the +/-. 2 thoughts come to mind when considering that...why he said....well, i won't go over that again i wrote it above a number of times. And secondly the PSU i use i'm sure had a cap across it inside the wart so why another? I didn't read anything about using a resistor so how is it decoupled?

[eschertron]

I get that, but what i'm saying is that regardless of whether it's in any one of the pedals or in the wall wart or anywhere in between, if i wire up a single supply to several pedals in parallel the cap is connected to ALL of the pedals the same way....across the +/-. 2 thoughts come to mind when considering that...why he said....well, i won't go over that again i wrote it above a number of times. And secondly the PSU i use i'm sure had a cap across it inside the wart so why another? I didn't read anything about using a resistor so how is it decoupled?

As minimal as the resistance of the wire between PSU and pedal is, it still counts for something. So fixing the noise hash issue as close to the source makes most effective use of the capacitor used. If you need to choose 'somewhere', why not make it an informed, best (or at least better) somewhere?

[rjb]

I get that, but what i'm saying is ...the cap is connected to ALL of the pedals the same way.

As minimal as the resistance of the wire between PSU and pedal is, it still counts for something. So fixing the noise hash issue as close to the source makes most effective use of the capacitor used. If you need to choose 'somehwere', why not make it an informed, best (or at least better) somewhere?

This may not be helpful- but it's like when you install a small decoupling cap across every logic chip in a circuit...
https://en.wikipedia.org/wiki/Decoup...itor#Placement

[Jazz P Bass]

Essentially, an added cap becomes it's own power supply.

[Enzo]

Also, I wouldn't assume all power inputs are strictly speaking in parallel,. Isolation diodes are in some, or protection diodes if you prefer. Currents matter, after all, you can "ground" everything in a system and still have ground loops.

[Mark Hammer]

In some contexts, a choke of some kind is needed to produce a sort of lowpass filtering between the supply and any given pedal. The suggested cap can also provide the sort of lowpass filtering that bleeds off spikes and hash on the power line, but usually there is insufficient resistance provided by the power cord to deliver the sort of filtering needed in the absenceof a fairly large cap value. The situation can be improved by inserting a small-value resistor in series, to form a single-pole RC filter between power source and pedal. So, for instance, a 10ohm resistor and 100uf cap form a lowpass filter with corner frequency of 159hz.

Many pedalboards use daisy-chain cables to provide power to multiple pedals. While these may look like series, in the absenceof any additional components, they work like a parallel distribution of power. Although ideally, power bricks with multiple outputs, each feeding a separate pedal, should provide the sort of isolation neededto keep pedals from interfering with each other via the power lines, many such power bricks are switching supplies, that can sometimes interact poorly with digital pedals. I would imagine that power cables with in-line chokes would make them behave better.

[Mick Bailey]

I referred to lead length as a factor and as you point out the cap forms an RC filter with the lead resistance. Some of the boards I work on have very long leads, cable-tied neatly in little hanks and tucked between pedals by the owner. Some can be quite a few ohms and lower the corner frequency to a useful value.

Some of the linear power supplies have multi-tapped transformers to give isolated outputs. I've had fair success feeding a number of 7809 regulators from a common supply and treating each output as pseudo-isolated.

[daz]

Guys, i don't think lead resistance will create isolation because i would have literally maybe 4" of lead in total between the Y to each pedal. We're talking what..... maybe .1 ohm?

Anyways, thanks for the replies but none of this matters anymore because the chorus arrived and i realized 2 things. One, it's a EH small clone and it sounds fine but it's so noisy i'm selling it asap ! And 2, i thought it would sound better having a analog chorus on the floor in front of the amp than using the digital chorus in my DSP that i use from my amp's DI out to a second small wet amp. I was wrong. I'm sticking with the chorus in my DSP. I just remember years ago it seemed like i preferred chorus before the input but i guess memory fails me, so that plus the noise and i'm done with this idea. But the noise alone was a deal breaker so i'm no longer in need of splitting the PSU to my boost.