Power Supply Project questions.

[niftydog]

1. Look on google for "earthing", "grounding" and "bonding" and the important (and sometimes dangerous) differences between them.
2. Don't ever refuel aircraft

I don't appreciate your tone, Torchy. You must have read between the lines of my post, because we were just having a discussion about this.

I understand the topic perfectly well; I have built a custom isolated power supply, wound several of my own transformers and work full time as a qualified electronics engineer. I beleive our problem stems from misunderstanding, so I have drawn a diagram in the hope that it will clarify what I'm trying to express.

IF THE FX UNITS SHARE DC GROUND WITH SIGNAL GROUND YOUR PS OUTPUTS CANNOT BE ISOLATED FROM EACH OTHER.

I refer you to my previous post;

all the taps are completely floating until you plug one of the taps into an effect. Even then, the effects only ground path is via the amplifier that it's plugged into.

Put simply, to form a ground loop you require TWO paths to ground from one device. Usually, an effects pedal has one ground via the signal cable. If you introduce a second ground path (via a non-isolated power supply) then there's the potential for a loop.

If on the other hand, the power supply is isolated from ground internally, then there can be no second path to ground!

the blue line is the effective ground return path through the signal grounds that link the pedals together. I drew the blue line to show HOW the grounds are linked ...

Yes, the grounds are linked, but that in itself does not constitute a ground loop. (NB: amp ground and PSU ground are connected via the mains power earth/neutral connections - or even simply via your multiple outlet power board!) check it out!

[crawler486]

I wonder if u guys would ever draw those things when not in debate with someone...

nevertheless, your drawings were all very helpful !!
Thanks !!

[Torchy]

crp

[Kleber AG]

So, I have a normal (non-isolated) power supply, would it be a good idea to have "only" one effect grounded by the power_supply_ground or not?

Or...
Still with my "non-isolated" power-supply would be an alternative to have the audio linkable pach cords without the ground shield at one of the ends?? :?:

I'm having some noise on my pedal board and I don't why, it's the kind of noise that changes with the positions you turn the guitar, facing the amp, or oposite, or turn guitar right or left, keeps changing "how" the noise is perceived but it's almost "there" all the time  :?
I have more than 10 effects at the pedal board... and a 1A power-supply.

Thanks for your help.
Kleber AG

[niftydog]

I wonder if u guys would ever draw those things when not in debate with someone...

well, you know what they say, a picture speaks a thousand words!

Tell you what I'll just stfu and keep my opinions and advice to myself then. I'll stick to what I'm good at (once I find out what it is).

Hey, dude, chill. Sharing opinions is what this place is all about. Just sometimes it's all too easy to misunderstand what someone is trying to say, that's all.

I have a normal (non-isolated) power supply, would it be a good idea to have "only" one effect grounded by the power_supply_ground or not?

Well, it reduces the number of loops, but loops are definately still a possibility.

Still with my "non-isolated" power-supply would be an alternative to have the audio linkable pach cords without the ground shield at one of the ends?

Yes, that would break the loops, but it may lead to other noise problems. This is often an option on DI boxes and many Mic cables are wired like that.

it's the kind of noise that changes with the positions you turn the guitar, facing the amp, or oposite, or turn guitar right or left,

Yup, I live with that too. Basically that is environmental. You'll find that flourescent lights are a big contributor to that sort of noise, but often the noise source in unfortuately your amplifier! It can also be practically impossible to determine the source of noise, it may even be a mains power cable running through the wall near to where you're standing.

Best thing to do is do a killer job on re-shielding your guitar. Make sure the shield connections in your guitar are well connected, get good quality cables with proper shielding (foil is best). Have someone experienced check over your amp for proper grounding and power supply filtering.

but it wouldn't hurt to be able to eliminate ground loops as a contibuting factor.

[David]

Torchy and Niftydog:

I've been trying to follow your exchange, and I think I got left behind a few convolutions back.  I'm using a power supply I recently built which, according to your exchange, should be noisy as hell.  But it's not.  Perhaps diagnosing this would help figure out this debate.  You guys obviously both know what you're talking about.

OK, here's what I've got.  I made a power supply from a 12VAC 1A center-tapped transformer.  I rectified the AC with a diode bridge (DIY, of course).  Next in the chain is NTE's equivalent of a 7809, with filter capacitors before and after it.  Basically, I took Scott Swartz's four-output supply and changed it into a one-output supply.  Worse yet, I've got it in a plastic case.  Now it does have a metal cover, which the regulator is connected to for heat sink purposes.  For the final insult, my pedals are connected in parallel -- and I've connected the grounds.

This thing is feeding a DOD graphic EQ, a DOD compressor and my DIY Bobtavia and distortion.  I've had no noise or hum problems at all.  If there was hum, I should be getting it when I kick the distortion in because it doesn't have any filtering on it.

Any ideas why my power supply is quiet?

[Kleber AG]

Thanks Niftydog!

Yeah, I guess I have to live with that

As I thought it's not "the" power supply generating the noise... even that it's a non-isolated and may have many GND loops there, wich leads me to a question:
Can these GND loops "inside" a pedal board be heard? :?: (high gain pedals)

How does it would sound and how to test if it's really a GND loop sound? I mean turning the guitar vol all the way down (or any way to easy test it)would stop that if it's a GND loop?

What I'm trying to figure out is how is suposed to sound or behave a GND loop noise?

BTW: Has anyone seen or tried that "HUM KILLER" circuit from a "russian?" website?
It places a 100ohm resistor in line with the GND pach and then filters the V+ to GND with a cap from V+ to the point "after" the 100ohm R...
Would it improve something?

Thanks
Kleber AG

[niftydog]

Any ideas why my power supply is quiet?

you're lucky.

Ground loops don't necessarily automatically create hum, but they often have the potential to be a problem. Generally, larger ground loops are more suceptible. (like the one from pedals to amp to mains neutral to power supply to pedals)

Small loops inside pedals are less likely to hum, but not immune.

Again, it's also environmental, walk into your local Safeway with all the fluros turned on and they might start acting up!

How does it would sound and how to test if it's really a GND loop sound? I mean turning the guitar vol all the way down (or any way to easy test it)would stop that if it's a GND loop?

For the US folks, it's what is called 60 cycle hum, it's a low frequency (60Hz) buzzing sound. For many other people it would be 50 cycle hum due to the different mains power spec.

To test it you need to determine the potential loops and break them. One easy way is to have a handy patch cable that doesn't have the shield connected at one end.

If we're talking the power supply scenario we've been discussing, try disconnecting it and runing everything off batterys.

If you turn your guitar volume down and the hum goes away, it's your guitar, not a ground loop.

a series resistor can sometimes help, but only put it in signal paths, never in the mains power path!!!

http://www.epanorama.net/documents/groundloop/index.html

[David]

Any ideas why my power supply is quiet?

you're lucky.

That's what I was afraid of.  OK, guess I need to start hunting up those little transformers R.G. cited in the Spyder build article.  I'm not ready to roll my own transformer yet.

[Hal]

AC should be like 20 hz - something out of the hearing range :-D

just for us guitarists.

[bigjonny]

With a non-isolated supply, there is a chance that a ground loop from one effect to another, via the power supply ground will cause a hum.

Assuming all your pedals share a PS ground with signal ground, couldn't you just put a "situational" ground lift for each jack on your PSU, then?  For each jack, you could run a connection from PCB to jack in series with a SPST switch.  If a ceratin effect causes a ground loop, lift the ground for that jack.

I just thought off this based on info previously stated in this thread &mdash I'm no whiz.  Am I way off base, here?  It seems to me this solves the loop problem on a per-case basis (but not the "pedal interaction" problem as noted in another thread).  It's obviously not as "safe" as doing something w/ multiple transformers, but seems like it would work for most, 90% of the time for less effort/expense/space?

AC should be like 20 hz - something out of the hearing range

Nice idea, and cute joke, Hal, but we also hear harmonics of 60Hz when we hear hum (e.g. 120Hz, 240Hz, etc, etc → 20.5kHz), so 20Hz would give the same problem.

[niftydog]

couldn't you just put a "situational" ground lift for each jack on your PSU, then? For each jack, you could run a connection from PCB to jack in series with a SPST switch. If a ceratin effect causes a ground loop, lift the ground for that jack.

in theory yes, in practice, possibly not a good idea.

For one, you're relying on the power circuit being completed by all of the (possibly dodgy) ground connections in your effects chain. It's going from circuit board to jack, to cable to jack to circuit board to jack to cable... it could all fall over in a screaming heap with one faulty connection.

Also, the ground connections in the signal path are not designed to carry much current at all, and any hum in the form of power supply ripple may leak into your signal path.

On my pedal board, this setup could require the last pedal in the chain to be passing current for all 12 of my pedals, which could be in the order of half an amp or more. This is likely to create DC offsets due to the resistance of the ground path.

I would think that it'd be better to lift the grounds on the signal cables. Just make up some leads with the shield only connected at one end, and use them as firefighting tools when you get a hum.