simple question about ground loops

[SuperGeo]

sorry the crappy drawing. The PS is in orange. Will ground loops appear?

[JimRayden]

First, what the heck are those?

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Jimbo

[JimRayden]

But as I currently understand from this drawing, no big loops.

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Jimbo

[Peter Snowberg]

No loops so long as the PS is not grounded.

[SuperGeo]

First, what the heck are those?

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Jimbo

PS in orange, stompboxes in gray, shield and ground wires in black, +9v wire in red

No loops so long as the PS is not grounded.

there's a black wire in the third stompbox, that means that PS is grounded so there will be loops?

[R.G.]

Here is how I interpreted your drawing. The orange box is the power supply as you said. The gray boxes are effects, I guess, the black lines are ground conductors, and the red lines are voltage supply lines. I see no connection for signals.

As drawn, no ground loops exist. However, that does not mean it's the best way to do this.

The rightmost pedal gets both power and ground from the power supply. The second pedal from the right gets power directly from the power supply, but its ground and signal currents flow through the signal grounding to the rightmost box and the power supply ground current for the second box then goes to the power supply through the black power ground wire. The third box from the right is the same, except its power ground current flows through both the middle box and the right most box through the signal grounds.

If I understand it right, then there is no possibility of ground loops. There are no loops.

That doesn't say that it is a good setup. The fact that power ground current flows through the signal ground is a good precursor to getting clicks, pops, and feedback oscillation because the leftmost pedal "sees" its ground voltage move around depending on how much current is pulled in the middle and rightmost pedals. That ground voltage movement can easily get amplified up into audio nasties.

[Transmogrifox]

I have not experienced much for problems by tying my pedals together, forming ground loops with the same PS.  This is to say that ground loops can sometimes be a better alternative to signal ground current. 

Ideally, your power supply will have a bunch of transformers: one for each power supply output.  None of the internal "grounds" are connected together in the pedal.  Each output is simply an ungrounded DC voltage potential of 9Volts.  The 9V (-) gets referenced to signal ground potential, and 9V (+) is just the positive supply.  Current flows from the power supply positive, through the stompbox, and returns with its powersupply negative (mate).

No ground loops, no ground current.  The downside is that small transformers are expensive.  I guess we need to start winding our own toroidal transformers.

[R.G.]

The downside is that small transformers are expensive.

Xicon 42PG006 - 12Vac/0.06A, US$2.76 in ones, US$2.20 in 10's.

Used wall warts from the surplus/donation places, usually $1 to $3 each.

[JimRayden]

And here's a few according links:

http://www.geofex.com/Article_Folders/Spyder/spyder.htm

http://www.generalguitargadgets.com/index.php?option=content&task=view&id=78&Itemid=107

---------------
Jimbo

[SuperGeo]

thank for the replies


R.G. got it

I read that by disconnecting the shields of the stompboxes would cause some RF noise into the circuit

The only problem I have is not having experience on PS but I'll give it a try. Can't find those eight-secondary transformer in here so I'll make it with separate transformers, witch will become a little expensive (around 4 dollars a transformer where I live)

[Transmogrifox]

Thanks RG.  I think I need to go surplus/ thift store shopping.  The nice thing about the transformers you referenced is that they are small and relatively cheap.  The downside is that they are only 60mA output...which is more than enough for most stompboxes, and even multiple stompboxes.  You could run about 20 Fuzz Faces on one of those.

Come to think of it, this really isn't a problem.  I was trying to think 'flexible' power supply with 1A / output...but I only need one or two of those kind--and I have just the wallwart to do it: 1A at 30V from an old printer.  With one of those, and 10 of the transformers you listed, I should be able to have a killer power supply quite easily.

That spider transformer you made looked like a really neat project.  Thanks for your projects and articles.

[Processaurus]

Have you tried just daisy chaining them regularly?  I lost some enthusiasm for complex power supply projects (as well realized as they are) when I realized I could do this with the pedals I use without any noise problems.   

If you do decide to go with a multi transformer PS, I'm sure you can get away with running several effects off one of the transformers, especially analog pedals that don't have LFOs or logic that puts audible spikes on the ground lines.  Seperate transformers for each effect seems like overkill, is expensive, and takes up space on a pedalboard you could use for other things.

Alternatively Boss pedals use a simple solution to avoid ground loops in daisy chained effects, its very simple and works well if every pedal thats daisy chained has this feature:  There is a forward biased 1n914 diode in between the circuit and chassis ground and the power supply jack's (-) connection.  This also acts as a protection against a reversed power supply (they also put a reversed 1n4001 power diode between the +9v and circuit ground, in case there is a pedal in the chain that connects the PS ground to chassis ground, or the battery is momentarily put on wrong (the battery's ground is connected directly to the circuit/chassis ground, using the stereo input jack trick)) You could simulate this by putting a 1n914 diode in series with each of your three power supply cords, inside the PS box before you connect them all together to the PS ground.

What do you guys think?  close enough for rock & roll?

[grapefruit]

From my own experience, as long as you have a regulated power supply and keep the lead lengths short, there is no problem connecting V+ and GND between the PSU and each unit, and having the ground connected on all the audio leads. I'm sure there are situations where you can get hum doing this, but if you don't change your setup often it's worth a try.

IMHO it's more important to have a regulated supply than have an isolated supply for each device. If you can have both then even better.

Stew.