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Again, grounding
MUFF WIGGLER Forum Index -> Modular Synth General Discussion  
Author Again, grounding
jamos
I apologize for bringing up this much-beaten topic, again. However, the vast amount of information out there is no help, it is literally self-contradictory in many cases.

The question I have, and would LOVE to get a yes/no answer to, is:

Should signal ground be tied to earth ground?

The maddening part of the information available is illustrated at the following link: https://www.analogictips.com/faq-ground-rules-earth-chassis-signal-gro und-faq/ Note the two contradictory statements:

A chassis ground may be used for shielding and grounding to prevent electrical shock. Mains’ earth ground and the (theoretically) 0V power rails are all tied together and connected to the chassis at that one point.

vs

Common sense says that signal ground is isolated from the chassis or power ground.

Since the 0V power rail IS signal ground... the author contradicts himself here. I'm an electrical engineer (though non-practicing, much of my training is past the expiration date), and I can't even make heads or tails of the recommendations here... no wonder Euro-newbies are lost!
hw408
Maybe related not sure but I wondered about this in regard to my DC power supply having a - as well as a ground (i assume that is "earth ground").

After finding information overload online I ended up tying those two together, and when I look at schematics I guess the ground symbol is equivalent to -. Sparkfun had some examples of the same circuit diagrammed different ways and they seemed equivalent.

I had circuits that did nothing routed to "(earth?) ground" as seen in schematic, but worked when routed to negative, so i figured they were the same. If i ever find a need for additional "0 v reference" i will again have to be confused. whether they are the same or not.

***I dont really know what Im talking about as lost noob playing with 555s, but interested in the subject.
Pelsea
Quote:
Should signal ground be tied to earth ground?


YES!

But only at one point. The only current flowing in the circuit ground (which is usually a convoluted web of wires and circuit board traces) should be that flowing back to the power supply from the modules and their constituent parts. Any additional current will be added to the output and be heard as hum and noise.

Your source wrote:

Quote:
Common sense says that signal ground is isolated from the chassis or power ground.


But earlier he said:
Quote:
A chassis ground is typically only made at one point. This prevents a return current path through an available but undesirable means and prevents current circulating through the chassis. Current circulating through the chassis can induce a “ground loop.” But if the chassis is only grounded at one point, current cannot flow through the chassis,


The same applies to the signal ground. If there is only one connection between signal ground and chassis and earth, current will not flow in either of them. I can point to examples of both connected and not connected designs. Some designers (Yamaha comes to mind) make a connection with a capacitor. So common sense is wrong.

There is no harm in an isolated circuit ground unless we need to bring the signal to another system. Then we must convert the signal to an isolated (balanced) form or provide common 0v reference. That's where things get dicey, especially for modular synthesizers.
Pelsea
hw408 wrote:
Maybe related not sure but I wondered about this in regard to my DC power supply having a - as well as a ground (i assume that is "earth ground").

After finding information overload online I ended up tying those two together, and when I look at schematics I guess the ground symbol is equivalent to -. Sparkfun had some examples of the same circuit diagrammed different ways and they seemed equivalent.

I had circuits that did nothing routed to "(earth?) ground" as seen in schematic, but worked when routed to negative, so i figured they were the same. If i ever find a need for additional "0 v reference" i will again have to be confused. whether they are the same or not.


Power supplies do nothing but maintain a constant voltage between two terminals. One of those will be positive relative to the other, and thus marked with +. But voltage is just a measurement like "feet". Feet has no meaning unless we connect one end of our ruler to something like sea level. Likewise voltage is meaningless until one terminal of the power supply is connected to the circuit ground. It's pretty common for the circuit ground to connect to the negative power supply terminal, but you see plenty of circuits with a positive ground and negative on the other side of the components. Our synthesizers usually have two power supplies, one with the negative terminal connected to signal ground and the other with positive connected to ground. (Hence bipolar.)

Yes, the G on that type of power supply is the earth ground, and the best place to make the connection is right there-- it comes out of the box unconnected so you can use the supply with either a positive powered or negative powered circuit.
neil.johnson
jamos wrote:
I'm an electrical engineer (though non-practicing, much of my training is past the expiration date), and I can't even make heads or tails of the recommendations here... no wonder Euro-newbies are lost!

As you have a background in electrical engineering I can highly recommend Henry Ott's "Noise Reduction Techniques in Electronic Systems". The 1st Edition covers sufficient material for this situation and is very readable and informative (the 2nd edition adds chapters on digital noise, EMC and ESD, while the latest 3rd edition is a major rewrite and expands existing chapters and adds several more). While there is some maths most of it is very straightforward. Check out abebooks for a used copy wink

Neil
Rex Coil 7
There's quite a bit of information on this issue within the forum here, admittedly a lot of it is buried within discussions about other topics. However some diligent searching is bound to make useful infos surface.

That is of little help, I know.

seriously, i just don't get it
Rex Coil 7
Is this any help?

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