Power supply grounding

[rankot]

Hi guys, I've a simple power supply for my pedals. The box is made of aluminum and I use 3-prong power cord with the connection to earth. I have a dedicated screw to connect that earth to the enclosure. My question is: shall I connect circuit ground to that earth point, or not?

[antonis]

No..

3-prong earth/ground is for mains shock prevention, only..
(e.g. in case of loose hot wire inside metal enclosure,,)

[GibsonGM]

No..

3-prong earth/ground is for mains shock prevention, only..
(e.g. in case of loose hot wire inside metal enclosure,,)

But - in the end, if you choose to ground to ANOTHER, separate part of the enclosure using a different screw, jack or what have you - this would be ok, no?  As would be done in a tube amp...

[Yazoo]

Yes, this is what is normally done, so in fact there will be a common ground between them via the chassis. Some amps, like the A/DA Ampulator have a small value resistor and possibly a paralleled capacitor as well between the signal ground and main ground to separate them.

[Rob Strand]

What antonis said is mandatory for safety purposes.
It's not just the enclosure but also the transformer chassis.

You probably don't want to ground the 0V of the power supply because that opens up a whole lot of problems with ground loops  via the mains earth between the power supply and things which are naturally earthed like amps.

What you can do is add a 10nF to 100nF cap between the 0V and the mains grounded chassis.   This does a few things:
- Any high frequencies (RF or switch-mode noise) on the mains side that couples through the transformer is shunted to ground.  That prevent noises getting onto the DC lines and eventually to the audio circuits.
- it reduces the amount of mains leakage making its way through the transformer then to the DC jack and user.
  (If you were selling power supply products you would be forced to confirm the leakage meets safety standards.)

Beyond that you might see variations on this theme like a cap from +V to chassis as well as 0V to chassis.  You might also see 1M resistors across the cap from 0V to chassis.     The extra caps were common in power supplies for RF equipment.  You might see them on some lab power supplies and test equipment power supplies.

[rankot]

OK, thanks to everyone! I've thought of putting some kind of hum-loop block network as described in Merlin's preamp book, but I will try with 100n capacitor only, as Rob said.

[antonis]

But - in the end, if you choose to ground to ANOTHER, separate part of the enclosure using a different screw, jack or what have you - this would be ok, no?

In the faaaar end, anypoint on earth is considered grounded..

P.S.
What Rob said about earth isolation..
(proposed by Rod Elliott..)

[rankot]

But - in the end, if you choose to ground to ANOTHER, separate part of the enclosure using a different screw, jack or what have you - this would be ok, no?

In the faaaar end, anypoint on earth is considered grounded..

P.S.
What Rob said about earth isolation..
(proposed by Rod Elliott..)

Right, that's actually the same idea as shown in Merlin's book: http://www.valvewizard.co.uk/Grounding.pdf

[GibsonGM]

^ That's why I asked that question above, Rankot.  IS it the same as Merlin's book?   

If we take the statement from Merlin's book:

"15.7: Bus Grounding
One logical ground scheme is the bus*ground. This is involves routing a
single, heavy-gauge wire –called the bus wire or bus bar– through the chassis. The
path of the bus wire should follow the natural path of the amp circuit from the
reservoir capacitor, to power amp (if present) to preamp, to input stage, and all
ground connections are made progressively along it in the same natural order.
The bus bar should be CONNECTED TO THE CHASSIS at one point only, at the input end of the
amplifier (see section 15.9)..."


Keeping it very simple and on topic for Rankot's question, and having read Merlin's statement above - how does isolating your audio ground with a 100ncap and 10R resistor in || provide a better ground for the audio than simply connecting the 'electronics ground' to the chassis, separate from safety ground?  The statement above discusses a buss right to the chassis, which is what I do with mains equipment like amps.  The pic seems to suggest something else.  Hopefully this isn't unsafe, LOL....I don't get any problems from noise etc.    I'm probably just not seeing it 

[marcelomd]

Keeping it very simple and on topic for Rankot's question, and having read Merlin's statement above - how does isolating your audio ground with a 100ncap and 10R resistor in || provide a better ground for the audio than simply connecting the 'electronics ground' to the chassis, separate from safety ground?  The statement above discusses a buss right to the chassis, which is what I do with mains equipment like amps.  The pic seems to suggest something else.  Hopefully this isn't unsafe, LOL....I don't get any problems from noise etc.    I'm probably just not seeing it 

Check the next chapters about ground-chassis connections. Specially 15.10: Ground Lift.
That diode+resistor+capacitor block is not the signal ground, it's blocking the return current that causes hum and draining RF
So in the end you'll have THREE connections to the chassis:
- Safety earth;
- Hum-loop block;
- At the circuit input;
Figure 15.17 is an example.

Someone correct me if I'm wrong here.

[GibsonGM]

That's kind of what that looks like to me, based on the image (the ground symbol in front of the 4700u's).  Will wait for actual confirmation that's correct 

[rankot]

If I understood Merlin's book well (and Elliot Sound Projects page too), you either connect ground (regardless it's bus or not) to the chassis directly, or through the hum blocker. There's no connection at the circuit input, because this is the pedal power supply. However, one can provide the ground lift switch to bypass hum blocker, for safety, but I think it's safe enough with that always on - whatever you do you will have more than 10 Ohm resistance to conduct with your body.

However, my PS is finally done:

[GibsonGM]

That's very attractive, Ranko!  What voltages does it output?

[Rob Strand]

However, my PS is finally done:

Cool looking indeed!

[rankot]

That's very attractive, Ranko!  What voltages does it output?

It has two double outputs - one is 9.6V, another one 9.9V with gyrator filtering, so that one can drop depending on load. The first one is LM317 regulated only, so it is stable. I wanted to try this filtering, and I will bring it to my friend who is serious guitar player for a blind test, not telling him what is the difference and which one is which. I can't hear the difference, but he claims he can hear the difference on the distortion pedal if it runs on power supply or batteries, so this will be task for him

Here's the complete schematic:

PDF: https://docdro.id/kzFMBC8

[rankot]

Cool looking indeed!

Thanks Rob! I bought this enclosure on the military surplus site for cheap Added door blockers as a feet and cupboard handle. I will post better images in the morning, gotta sleep now!

[Rob Strand]

Thanks Rob! I bought this enclosure on the military surplus site for cheap Added door blockers as a feet and cupboard handle. I will post better images in the morning, gotta sleep now!

Stuff like that is only available from the web here.


I just remembered I've got one of those rounded corner style power supplies,

Mines is a bit better condition and more blue in color,