Idea to avoid ground loops with power supply

[shredgd]

Hi,
First of all, I have never used a power supply with more than one pedal (but I will do it soon), so what I'm going to say is not proved by experience.
   I know about the problem of creating ground loops when using a power supply with many pedals, because of ground passing from a box to another via two wires (the shield wire of the signal cable connecting the pedals and the ground of the DC cable powering the pedals). One effective way to solve this problem is, as I read somewhere (I would like to give credit, but I can't remember), to disconnect the shield wire from one ending in each signal cable, thus breaking the loops. The drawback of this approach is, if you decide to use batteries in your pedals once in a while, you have to use another set of signal cables (which are not that cheap...), or spend time soldering the shield wires back.
To avoid that, the approach I was thinking of today consists in doing a similar thing to the "powering side": if you connect only one pedal to the power supply ground, all the others will be grounded through it through the shield wires of the signal cables connecting them each other.
In other words, you'll be powering all your pedals, except one, only through a single wire cable, connected to the positive side of your power supply.
However, I'm still not sure if the common pathway of all the circuits to the power supply ground can generate other problems/noise, so I'll make an experiment as soon as possible and let you know.

Giulio

[Lobsang]

I recently wrote here because I am doing something similar to your approach, this is, running several pedals with a single power supply. I read somewhere that " the only way to avoid ground loops would be using isolation transformers" Amen! I want a schematic or some explanation here, not such a death sentence. I am already experimenting but I had no problems with this, instead I burned one of my pedals ( voltage was too high...) Ground loops sound to me like you can get shocked, isnt it? I am using a 12v 5A transformer and I wouldnt like to be shocked. What voltage/ amperage are you using, anyway? Your approach on disconnecting the ground sounds cool. I will try it soon. Take care!

[smoguzbenjamin]

Ground loops won't shock you so don't worry. I use a daisy-chain and it works fine for me, unless I turn a high-gain ckt on (MetalZone), it doesn't hum at all. 12V is too high for a pedal that wants 9v. 5 amps is way more than enough, unless you're driving 10 digital delays Normal pedals don't consume more than 10mA.

But anyway, try getting a wallwart that's 9V, and supplies sufficient current for the pedals you're using. Just add up the current consumption of all your pedals. Disconnecting ground from the power can help prevent ground loops, but you have to have 1 pedal that has the power ground connected, otherwise the current can't flow in the first place.

Good luck

[Ge_Whiz]

I can think of some snags. If a pedal uses op-amps, chances are that the negative power lead is not connected to the signal earth, since the 9V supply is split into +/- 4.5 V lines inside the box. You can't assume that the power negative and signal ground are coupled. I even have some commercial pedals which run the power supply straight into a bridge rectifier, which allows for AC or DC supplies to be used, and it doesn't even matter which way round the DC is connected. A cheap and sensible precaution.

Meanwhile, if you keep leads short wherever possible, earth loops are unlikely to pose a problem - high-gain pedals with insufficient screening picking up hum is likely to dominate. Some folks can get a bit anal about ground loops, IMHO - they are more of a problem in badly-designed power amps.

[shredgd]

Lobsang:
you won't get shocked with the low voltages used in the majority of pedals (usually 9v DC).
" the only way to avoid ground loops would be using isolation transformers" probably means the best way to avoid ground loops would be using one transformer (one power supply) for each pedal, which is something excessive in my opinion. This approach (the "Spyder" power supply) is explained by R.G.Keen here http://www.geofex.com/Article_Folders/Spyder/spyder.htm
You can also see what a ground loop is, there. By the way, that's the page where I read about disconnecting the shield wire at one end of the cables (finally I remembered, so I can give R.G.Keen his credit).
Your transformer is ok, it is even overdimensioned as smoguzbenjamin said. However, I hope you know you can't simply connect a pedal to a transformer, don't you? In any case, read here http://www.smallbearelec.com/Projects/SmWart/SmWart.htm to build a very steady 9v DC power supply for your pedals out of your transformer (be careful, this time you'll be working with lethal voltages! Ask for help if you are new to these things).

Ge_Whiz:
actually I don't even know how a ground loop "sounds", I was simply trying to solve the problem before having it!... I entered the "power supply world" only recently, I still have to build/get the cables to power/use the few pedals I have simultaneously, but I always try to think of what problems might arise when I change something...
I didn't know about pedals with uncoupled power negative and signal ground, thanks for the tip. Anyway I don't think they are the majority but yes, one should check that before doing what I said.

To return to my first post, I did a first test with two pedals and there seemed to be no additional noises. However I could only use headphones, so I still have to investigate.

Giulio

[tambek]

I use a daisy-chain and it works fine for me

where could i gte one?

[GFR]

Boss pedals simply have a diode in series with the adapter's (-) input to break ground loops, seems to work well. You'll need a slightly higher voltage to compensate the diode drop.

As for the "sound" of ground loops, it's a very LOUD hum.

[Kleber AG]

Sorry GFR, I could not understand it, how should it be wired?
Just at the 9V/GND output it must have a diode in series with the GND wire, catode facing wich direction?

Thanks
Kleber AG

[smoguzbenjamin]

Tambek, you can get a daisy-chain cable at almost any music store, just tell them you want a daisy-chain to power all your FX, and don't believe any crap they tell you because they'll try to sell you something that doesn't work half as well

Kleber, I think GFR means that you wire a diode with the band facing the - part of your DC jack. It'll stop current flowing "backwards" into the pedal.

[shredgd]

Yes, smoguzbenjamin.
GFR, the diode you see in the power section of a Boss pedal is a protection diode with cathode facing the +9v side and anode facing ground. It serves to shortcircuit most of the current if you accidentally reverse the polarity of the power supply or of the battery, to avoid damage to the components (it is very common to grab a 9v battery and touch the contacts on the battery snap, and then realize you have to turn it 180 degrees...!).
A diode in series with either +9v or ground would work as an even better protection against reverse polarity (because it would really stop the reverse current flow) with the cathode facing ground (with the cathode facing +9v, instead, current would only flow in the wrong direction).

[smoguzbenjamin]

Call me Ben

[zener]

What is that diode in series with the ground? A diode of my name (zener)?

I was thinking of putting a switch that will cut the ground loop whenever I use an adapter. Isn't that god enough?
Thanks.

Zener

[smoguzbenjamin]

Unless you decide you might want to use only that pedal with an adapter, the switch is a gooed idea. Other than that I don't see the point... Just "cut" the wire... :?

I think a regular Si diode should work.

[shredgd]

Call me Ben

Sure, Ben