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Doepfer A100 DIY PSU grounding
MUFF WIGGLER Forum Index -> Music Tech DIY Goto page 1, 2  Next [all]
Author Doepfer A100 DIY PSU grounding
Nisse_D
Hi, a probably not so tricky question that confuses the hell out of me:
I just got a Deeper A-100 DIY PSU that i intend to power my R*S 4U models with. I'm just about to install the PSU in a separate case but i realized that the actual PSU doesn't match the manual; there's chassis ground connection in the manual but there ain't none on the actual PSU. Should i just connect the chassis to one of the 0v connectors? Also, the Serge 4 pin connector uses one conductor for chassis ground, that should preferably be connected to the same point as the PSU ground, right? Many thanks in advance!
Mungo
Nisse_D wrote:
Hi, a probably not so tricky question that confuses the hell out of me:
I just got a Deeper A-100 DIY PSU that i intend to power my R*S 4U models with. I'm just about to install the PSU in a separate case but i realized that the actual PSU doesn't match the manual; there's chassis ground connection in the manual but there ain't none on the actual PSU. Should i just connect the chassis to one of the 0v connectors? Also, the Serge 4 pin connector uses one conductor for chassis ground, that should preferably be connected to the same point as the PSU ground, right? Many thanks in advance!
If the PSU is different from the one that is pictured in the manual (and online) then the wiring/advice might need to be different too. Previously the best way was to ignore the grounding lug on that supply and use only the 0V connection, that is because the external transformers used for those power supplies are isolated and do not pass the mains earth through.

The connection to the chassis depends on how the inputs and outputs of the modules require it. If they are wired for a separate chassis ground you still want everything coming back to a single common point, including the 0V connection. The important point is making sure that there is no single cable that carries both the shield (chassis) currents and 0V connection, they should be run as separate wires back to a single bolt or distribution block.
Graham Hinton
Nisse_D wrote:
Hi, a probably not so tricky question that confuses the hell out of me:


You are only confused because all the manufacturers involved are confused and presenting confusing, conflicting and incorrect information.

Quote:

I just got a Deeper A-100 DIY PSU that i intend to power my R*S 4U models with. I'm just about to install the PSU in a separate case but i realized that the actual PSU doesn't match the manual; there's chassis ground connection in the manual but there ain't none on the actual PSU.


That PSU is floating, there is no mains Earth available to ground anything.
The clue is that the mains connector only has two pins. If there is an Earth tab on the regulator pcb it is connected to the "GND" outputs and that is the wrong place to connect to mains Earth or Chassis. Connecting it to any metal chassis, as the manual states, does nothing.

Quote:

Also, the Serge 4 pin connector uses one conductor for chassis ground, that should preferably be connected to the same point as the PSU ground, right?


No. The Serge connector has two 0V returns which are connected together in the boat. There is no concept of a chassis ground, just a 0V.
Rex Coil 7
Graham Hinton wrote:
...That PSU is floating, there is no mains Earth available to ground anything.
The clue is that the mains connector only has two pins. If there is an Earth tab on the regulator pcb it is connected to the "GND" outputs and that is the wrong place to connect to mains Earth or Chassis. Connecting it to any metal chassis, as the manual states, does nothing.
So that having been said, if a "3 prong" mains input power cable were retrofitted, and connecting the "ground pin" of that cable to an optimal position within the power system/distribution system, would that suffice as a safety ground (aka Tech Earth)? Of course some other work would be required to see that modification through to it's best functional setup, like any other power system that was designed with the 3rd prong mains cable in use.
Graham Hinton
Rex Coil 7 wrote:
So that having been said, if a "3 prong" mains input power cable were retrofitted, and connecting the "ground pin" of that cable to an optimal position within the power system/distribution system, would that suffice as a safety ground (aka Tech Earth)?


You can't make a silk purse from a sow's ear.

Assuming that it is not illegal to do that in your country, and I believe that it is in Germany, if you knew enough to do it properly you wouldn't buy a PSU like that in the first place.
Also assuming that you are in a country that is not still using original 1920s unshuttered mains outlets with no Earths and reversible plugs.
Nisse_D
Thank you so much for your input guys, really appreciate it! Regarding the 4 pin connections, i was a little bit confused by this quote on the 4 pin connector that i found in this thread :

So the modern STS wiring scheme is:

Red = +12vdc
White = - 12vdc
Black = common (analog module ground)
Green = common (chassis ground / digital & LED driver ground

http://analogue-heaven.1065350.n5.nabble.com/re-Serge-Power-Supply-td4 9756.html

But when reading up on R*S build instructions for their power distribution PCB's, it clearly states that both should be 0v, so thanks for clearing that out smile
Nisse_D
Okay so i soldered everything up and it works (checked all voltages etc), but there is a massive ground hum even when the PSU is not on whenever i have my Serge 73-75 at the same time. Connecting them via the ground jacks exaggerates the hum significantly. I noticed tough that if the banana going out from the 73-75's ground jack touched the synths chassis, it all went away. In this case (since the 73-75 obviously don't have another connection between the 0v and the chassis) it should be safe to connect the 0v to the chassis, right?
Rex Coil 7
Graham Hinton wrote:
Rex Coil 7 wrote:
So that having been said, if a "3 prong" mains input power cable were retrofitted, and connecting the "ground pin" of that cable to an optimal position within the power system/distribution system, would that suffice as a safety ground (aka Tech Earth)?


You can't make a silk purse from a sow's ear.
.... just as I thought. Thanks for eloquently confirming the point.
Mungo
Nisse_D wrote:
Okay so i soldered everything up and it works (checked all voltages etc), but there is a massive ground hum even when the PSU is not on whenever i have my Serge 73-75 at the same time. Connecting them via the ground jacks exaggerates the hum significantly. I noticed tough that if the banana going out from the 73-75's ground jack touched the synths chassis, it all went away. In this case (since the 73-75 obviously don't have another connection between the 0v and the chassis) it should be safe to connect the 0v to the chassis, right?
It would help to draw a diagram of the system, describing all the connections with words quickly gets confusing.
Nisse_D
Defiently, should have done that in the first place smile Ok so here's a pic with comments that explains the issue. DUSG = Dual Universal Slope Generator, in this case patched as an audio oscillator. The pins in the R*S boat is just the pins of the XLR connector.
[img]
[/img]
Nisse_D
OK update: As soon as there is a connection between the metal chassis holding the Deeper PSU and the 73-75 the hum is all gone. I guess all it takes then is to set up a copper wire connecting the two and problem solved? Just want to make sure i don't just cure the symptoms of a more severe issue smile
Graham Hinton
Nisse_D wrote:
I noticed tough that if the banana going out from the 73-75's ground jack touched the synths chassis, it all went away. In this case (since the 73-75 obviously don't have another connection between the 0v and the chassis) it should be safe to connect the 0v to the chassis, right?


If you connect between any two or more separately powered unbalanced systems there has to be a 0V common between them. This includes external equipment like mixers and FX. If the equipment is all grounded there will be a default path via the mains cables, but that is not a good audio common and a separate one of lower resistance should still be provided as well. Don't cry "but that's a ground loop!" it is two >0.1 ohm resistances in series, in parallel with a <0.01 ohm resistance.

Your diagram helps, but it has mistakes and is still not clear. It would also help if you said what country you are in.

The Doepfer PSU is not powered by an AC/DC adapter, it is an AC/AC adapter, i.e. a transformer in a box.

You have not explained how the mixer is powered or connected. That is part of the equation too. If it is via an unbalanced mono jack lead there may be a common and/or grounding connection between the mixer and the 73-75. It would depend on whether the mixer is earthed and whether the jacks have metal or plastic bushings.

All in all this is the typical mess that results when you combine various amateur designed equipment with non-amateur designed audio equipment. I count Serge and Doepfer as amateur designed and hesitate to use the word professional without knowing the make of your mixer.

The thing you have to do to sort this out is to take a clear overview of the complete system and implement the common and earthing without randomly mixing up the two. i.e. don't just connect 0V to chassis in different places which may make the chassis part of the signal path. The two should be separate all the way back to the mains Earth--if you actually have one.

Serge boats may be an STS one or a Hammond or another chassis. I usually bolt a 1/4" Faston tab to the back and provide separate wiring back to a known Earth.
Nisse_D
Many thanks Graham, i really appreciate that you take the time looking at this. A pretty big insight for me is how much I'm lacking in basic electronics knowledge, reading up as we speak...
So i updated the pic in the former post. Worth noting is the chassi to chassi connector (orange) that stops all hums. It is not connected to 0v at any point but is kept separate. Also added more details on the mixer, but when looking at the power plug, i realized that it's not even earthed, shamed to notice as i was 100% certain it was! So i guess the first move should be to get an electrician over to get that fixed. Otherwise, I'm in sweden where we have the 230v / 50 Hz system
Graham Hinton
Nisse_D wrote:

Worth noting is the chassi to chassi connector (orange) that stops all hums. It is not connected to 0v at any point but is kept separate.

Also added more details on the mixer, but when looking at the power plug, i realized that it's not even earthed, shamed to notice as i was 100% certain it was! So i guess the first move should be to get an electrician over to get that fixed. Otherwise, I'm in sweden where we have the 230v / 50 Hz system


If you look under the IEC inlet on the mixer you will see printed in two languages "WARNING: THIS APPARATUS MUST BE EARTHED". You should also note that there is a single mains fuse, yet you are in a country that uses Schuko mains connectors which are so bad that they make the old British round pin ones (that were withdrawn in the 1950s on safety concerns) look like advanced technology. This means that the safety measures that should be in place to use that mixer are non-existant. Equipment using Schuko plugs should be double fused because you never know which pin is Live and which is Neutral.

The latter is a common problem with all IEC inlet equipment sold on the world market manufactured in countries that are unfamiliar with the dreaded Type F Schuko. Not that the CEE 7/7 "Euro"plug is any better. The way to cope with this problem is to use an IEC distribution block that is double fused or has an RCD and IEC male-female cables to the equipment.

Also beware that 4mm banana leads fit perfectly into Schuko outlets. Don't leave small children unattended around your gear. "Hey, daddy, guess which boat will electrocute you..."

This illustrates perfectly how it is possible to buy equipment that meets safety requirements as it is sold individually, but when put together by a consumer with no electrical training can make an unsafe system.

There may be a connection between the 3.5mm jack and the chassis, but it won't be a good one for audio or safety purposes.
Nisse_D
Will be ordering such a distribution block tonight, and all equipment is moved to an earthed outlet! For the sake of safety, would the aforementioned trick och solder a IEC connector with only the earth lead and connect that to the boats / PSU's chassis and the distribution block solve the safety problem?
Graham Hinton
Nisse_D wrote:
Will be ordering such a distribution block tonight


Did you find one? They are surprisingly rare. I thought that Bulgin or Schurter made one, but can't find one in their catalogues.

Quote:

and all equipment is moved to an earthed outlet!


Did you have an unearthed outlet because that is legal in Sweden? What are the regulations there? They are different in every European country despite having the EU who only fudge everything on paper divorced from reality.

Quote:

For the sake of safety, would the aforementioned trick och solder a IEC connector with only the earth lead and connect that to the boats / PSU's chassis and the distribution block solve the safety problem?


Only if you use a wireable plug and are sure of what you are doing, but if you go that far a better solution would be to get an IEC inlet with double (sometimes called twin) fuses in a drawer. The fuses will be perpendicular to the panel, rather than parallel like the single fuse + spare variety. Wire the earth pin to the chassis and the 0V and the Live and Neutral to the ac adapter. Better still replace it with a 15V toroidal transformer. I don't know if it's legal for you to do that in Sweden? If it isn't pay somebody qualified to do it.
Mungo
Nisse_D wrote:
OK update: As soon as there is a connection between the metal chassis holding the Deeper PSU and the 73-75 the hum is all gone. I guess all it takes then is to set up a copper wire connecting the two and problem solved? Just want to make sure i don't just cure the symptoms of a more severe issue smile
The diagram is a big help. You started asking about how and where to connect the chassis and 0V but its not shown anywhere on the picture.

Nisse_D wrote:
Okay so i soldered everything up and it works (checked all voltages etc), but there is a massive ground hum even when the PSU is not on whenever i have my Serge 73-75 at the same time. Connecting them via the ground jacks exaggerates the hum significantly. I noticed tough that if the banana going out from the 73-75's ground jack touched the synths chassis, it all went away. In this case (since the 73-75 obviously don't have another connection between the 0v and the chassis) it should be safe to connect the 0v to the chassis, right?
"when the PSU is not on" is confusing. Do you mean unplugged from the power point, or are their some power switches that aren't shown?

Start with no cables patched between the two (none of the 0V either) or to the mixer, just the 73-75 and the Boat with your DIY supply each sitting their alone. Do they each have a low resistance between their chassis and 0V? If they don't you will need to provide that either with a connection inside like this thread started, or with an external cabling as you are doing. The 3.5mm output of the 73-75 is probably connecting the two at that end.

But that wouldn't explain hum being introduced by the Boat connecting its 0V to the 73-75, even when its not plugged into the power point.
smiler
Graham Hinton wrote:
Did you have an unearthed outlet because that is legal in Sweden? What are the regulations there? They are different in every European country despite having the EU who only fudge everything on paper divorced from reality.

In Sweden all new installations (since 1994 if I recall correctly) must be earthed. But of course there are plenty of old installations around.
Shledge
I think having diagrams which show the most optimal or "best" way to wire popular PSUs like the PSU3 would help, especially on larger setups eg. star grounding.
Rex Coil 7
Shledge wrote:
I think having diagrams which show the most optimal or "best" way to wire popular PSUs like the PSU3 would help, especially on larger setups eg. star grounding.
You just talked yourself into a job! You're hired!! So when can we expect to see the drawings you'll be doing?



hihi Haha!

thumbs up
Shledge
I'm not an engineer lol
Rex Coil 7
Shledge wrote:
I'm not an engineer lol
Excuses excuses .... GET TO BUSY!!! DRAW I SAY!!! hihi

Shledge wrote:
I think having diagrams which show the most optimal or "best" way to wire popular PSUs like the PSU3 would help, especially on larger setups eg. star grounding.
Here's one of Graham's diagrams .... beats nothin!

Graham Hinton
smiler wrote:

In Sweden all new installations (since 1994 if I recall correctly) must be earthed. But of course there are plenty of old installations around.


Thanks for that info. With the same wall sockets? So you can have both old Schuko and new 7/7 plugged in to either earthed or unearthed outlets? Like Germany then--a terrible mess.

This is the bane of bands touring Europe.

Anybody else have reliable information on their country? I would like to gather this together. I know about France, Germany, the Netherlands and Switzerland thanks to customers there and would like to fill in the gaps.


Shledge wrote:
I think having diagrams which show the most optimal or "best" way to wire popular PSUs like the PSU3 would help, especially on larger setups eg. star grounding.


There were one or two threads specifically about the PSU3 with diagrams on this sub-forum because both Doepfer's diagram and pcb layout are incorrect. Sorry, the search engine isn't working, try searching for PSU3 and my name when it's back.

Star grounding is a misnomer and people think that any physical star is OK when it is really about resistance. A busbar is the centre of a star when considering the resistances.

Rex Coil 7 wrote:
Here's one of Graham's diagrams .... beats nothin!


Except a more up to date one:



This shows the grounding network of a multiple PSU system. It is assumed that each PSU has its own IEC inlet so the 0V Common is wired to the Earth of each one because they may not all be plugged in. The wire resistances shown are typical of a good system and have to be considered relative to each other, a bad system would have higher values and different paths.
Rex Coil 7
Graham Hinton wrote:
...This shows the grounding network of a multiple PSU system. It is assumed that each PSU has its own IEC inlet so the 0V Common is wired to the Earth of each one because they may not all be plugged in. The wire resistances shown are typical of a good system and have to be considered relative to each other, a bad system would have higher values and different paths.
So in this updated diagram, the assumption of each PSU having it's own IEC "so the 0V Common is wired to the Earth of each one because they may not all be plugged in" takes the place of the zero volt to Earth connection depicted in the older diagram?

Rather than actually depicting it, it's assumed as being tied to Earth?

Not that it's a ~bad thing~ ... I'm only pointing that out to make sure I understand.

cool
Graham Hinton
Rex Coil 7 wrote:
So in this updated diagram, the assumption of each PSU having it's own IEC "so the 0V Common is wired to the Earth of each one because they may not all be plugged in" takes the place of the zero volt to Earth connection depicted in the older diagram?

Rather than actually depicting it, it's assumed as being tied to Earth?


No. It is depicting it.

The Rwire connections are where the distribution 0V is tied to Earth (at the TE point). This wire would typically be <50milliohms.
There was only one Rwire in the diagram you dug up. If that IEC lead were pulled and another one still in the system would lose its Earth reference.

The thick blue lines are busbars or large (16mm2 or 25mm2) cables so the resistance of those paths would be <1 milliohm. Not much compared to the module power cables so any two modules 0Vs are separated by the resistance of two power cables while the safety network is still in place with a higher resistance.
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