possible earthing issues with Doepfer DIY kit in wooden case

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possible earthing issues with Doepfer DIY kit in wooden case

Post by matttech »

Hi all

I posted a similar thread in the eurorack forum, but haven't had many replies ....and some seem to contradict other opinions i've had.


I purchased a Doepfer DIY Kit number 1 from EMIS this year, and have mounted it in an empty LC9 wooden case that somebody had lying around. All connections have been made exactly as detailed in the instructions.

I have not used the earth spade terminal on the PSU board of the DIY kit, as it said to only use it if the case was metal.

However, I have just noticed that it doesn't seem to be earthed to ground, unlike the Doepfer Monster Base Case that I also own.

The issue is this: If I have an unbalanced cable going into my audio interface (MOTU828 mk1) and I touch the tip of the cable on any of the following I get an earthing hum, much like the one I would get if I held the tip of the cable between my fingers):

1 - any of the screws mounting the modules to the rails
2 - the screws mounting the rails to the sides of the wooden case
3 - any metal sockets (not the cliff ones, but the type typically used by MFB, Malekko and others)

This means that, as I am plugging in the final cable that goes to my audio interface I get a short hum as it touches the input sockets on the way in.

This is NOT the case when i do the same thing between my Monster Base and the audio interface....and there is NO hum produced by touching the tip of the cable against any of the modules sockets/ screws mounted in the Monster Base.

The problem disappears once a patch cable is connected between the Monster Base and the LC9, but means that, if I was to use the LC9 out on its own (at, say, a gig) this problem would still be there.

I am no expert on earthing, but, after speaking to Andy at EMIS a solution was suggested: make a connection from the spade terminal on the PSU board of the DIY kit/ LC9 to the earth pin of a mains plug (leaving the live connections completely unconnected - maybe even removing the pins completely). However, when i discussed this with one of the electricians at the college I work at, he said that - as the transformer is an "isolation transformer" - this could be in some way making a dangerous connection that is usually isolated by the transformer.

He said to check with the manufacturer...and I have emailed Dieter.

Any help gratefully received (ideally in layman's terms!)

So - is my case correctly earthed?

And, if not, how do I safely achieve this?

I am in the UK, and the external transformer has a three pin plug coming from it.
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Post by EATyourGUITAR »

I have no idea what a spade is but I'm also not adept at speaking the british electrician street slang. the MFOS power supply has one of the high voltage mains wires connected to modular ground. some electricians would never do it and some say its not to worry about. I think this stems from electricians having different requirements in their respective fields. whats good for a computer might not be good for a power plant or space program, or a toy factory. having something completely isolated is the most safe but not required in every case. all that said, I'm still an amateur with no real schooling so my opinion is the most anecdotal.
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Post by fonik »

if i get it correct the DIY Kit has no connection to the safety conductor (earth) of the mains, but the monster case has. and as soon as you connect the DIY kit with the monstercase the hum is gone?
so you actually want to connect the GND/COM of your DIY rig to the safety conductor (earth) of the mains.
i see no problem with this. why not just remove the cheap twp pin plug and replace it by a correct three pin plug, in order to add a thrd wire that goes straight from the mains earth to your DIY rigs GND?

did you try adding ferrites?

again, the third plug of the mains is nothing special, actually. it has no connection/reference to the actual mains. it is there for safety reasons. using the DIY kit your rig has no direct connection to the mains, and the transformer of the kit is obviously built in a safety class that does not ask for the earth (double secured and/or all plastic housing). your monster has direct connection to the mains and therefore needs the earth connection: in case something goes wrong inside your monster the current shall be conducted awa from you to the earth...
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Post by qu.one »

i didnt realize until now that you have a DIY kit inside an LC9 house. why not just run the ground as shown in that image of the LC9 you posted? (mains center pin to a metal mounting screw/nut on a busboard and to a GROUND spade connector)

can you also confirm that the PSU/transformer is not the culprit?

images of an LC6 below:

Image

Image
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Post by EATyourGUITAR »

I would put a ground lift switch like on studio equipment. sometimes when you have two pieces of gear that are both connected to the mains earth AND have grounds connected through signal ground on the cables it will produce a ground loop. in a well designed studio everything is star grounded. two identical cases with ground lift switches are compatible if you lift the ground on the switch on one of them. star grounding...wham!
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Post by matttech »

right - thanks for all the replies.

the wires that come out of the DIY kit's PSU board are simply two AC cables that go down via a moulded cable into the external transformer (different from the LC9 shown above). there is no connection made from the earth lug right next to the two AC connections on the PSU board into the transformer itself.

see below: (this is actually an older version of my DIY kit, but is similar enough. mine has a three pin plug coming from the transformer)

Image

in the manual for the DIY kit, it says to only use the earth connection on the PSU board if you are putting it in a metal case, so i left it alone.

wiring diagram below:

Image


however, what i have done now (and this seems to have solved my hum issues) is to run an earth cable directly from this lug into a mains plug (with only the earth pin connected - the other pins removed completely!). this goes into the mains, and simply carries an earth directly from the case's PSU board to the mains earth. all hums gone!

why on earth this isn't implemented some way on the original kit, i've no idea. it's not a pretty fix, but at least it means i don't have to start messing around inside the transformer etc..

this was a solution i got from Dieter himself. thanks to everyone who helped me get this sorted - andy from EMIS, Dieter, and Tony from Oakley

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Post by EATyourGUITAR »

there is also this for when you need a ground but the ground in the mains is noisy.

http://www.ebtechaudio.com/humxdes.html
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Post by Graham Hinton »

You eventually got the right answer, the PSU 0V must be grounded, but there has been some incorrect and misguided advice given on this thread.

Without picking on anybody, nobody here understands the problem and no advice given, both contributed and reported, should be acted upon. Some of it is irresponsible.

ALL synthesizer and audio equipment needs the 0V of the PSU grounded to the mains earth or an external earth if there isn't one. There are two reasons for this:
1) to provide a common reference and 2) safety.
There are no exceptions.

There are two classes of electrical equipment and the concept of "double insulation" only applies to consumer items that are self contained. Any other equipment that has exposed metal parts and/or is connected to other equipment MUST be properly grounded at one place and one place only.

In a synthesizer or any other audio devices nearly every cable has an exposed 0V that may be touched and therefore must be grounded. Lifting grounds on equipment does not really solve any hums problems, instead it shifts the problem elsewhere, and it compromises safety. If you hold a metal jack lead from one equipment that is not grounded in one hand and from something else that is in the other you may get a shock. Equipment must not derive it's ground via patch cables that may be removed.

Anybody who says they removed a ground and the hum went away has a problem with the monitor amplifier they were listening to.

Using external ac adapters with no grounds is a ploy by cheap manufacturers to evade paying for safety testing and is a measure of their general standard of engineering.
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Post by Matos »

Graham Hinton
Thanks for dropping science on us. I have no idea if my systems grounded, but until now never gave it a second thought. I was hoping for it all to be as simple as -12v to -12v.
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Post by EATyourGUITAR »

I agree with on everything but I just wanted to point out that a 12DC adapter like the one supplied with a $99 plastic Yamaha IS intended to make the product cheap and simple but I do not think it is as deadly as say an early fender princeton reverb guitar amp with a 2 prong plug. obviously it is illegal for fender to make such an unsafe product like that now. but the yamaha only has 12VDC inside the case so no big deal they say. we don't want to scare people off modern keyboards for safety reasons eh?
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Post by fonik »

Graham Hinton wrote:There are two classes of electrical equipment and the concept of "double insulation" only applies to consumer items that are self contained. Any other equipment that has exposed metal parts and/or is connected to other equipment MUST be properly grounded at one place and one place only.
by saying MUST you don't mean official safety rules, right? as far as i know the material of the cabinet and the controls (i.e. knobs) does not matter at all, as long as the PSU inside the cabinet is double insulated. maybe i am wrong? BTW wallwarts have exposed DC connectors and don't have necessarily an earth connector (see the transformer doepfer uses in his DIY kit).
i agree that you need a common reference, thus i recommended earthing of the DIY cabinet to the mains ground. anything wrong with this?
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Post by EATyourGUITAR »

doepfer is allowed to sell it as a kit but not a finished product if the mains is in the case. read the metasonix article that goes into great detail. I'm looking for it but I can't find it. maybe Eric @ Metasonix can post the link again. it is a great research paper on international power regulations on musical instrument manufacturers.
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Post by fonik »

EATyourGUITAR wrote:doepfer is allowed to sell it as a kit but not a finished product if the mains is in the case.
this is is slightly different issue, i think. in germany you have to certify gear with mains connection, and this can get expensive. therefore doepfer decided to use this certified external double insulated transformer from another manufactuer.

or am i completely wrong? (just pick on me, i have no problem with that as long as we all learn something)
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Post by Graham Hinton »

Matos wrote: I have no idea if my systems grounded, but until now never gave it a second thought.
If you measure the resistance between a jack plug screen and the earth pin on the mains plug you will soon find out. It will be <1 ohm if grounded. There are more specific tests to measure how well it is grounded using a PAT tester, but a multimeter will suffice for a yes/no answer.
I was hoping for it all to be as simple as -12v to -12v.
It is. All power regulators should be connected together at one point and that is grounded to mains earth. Usually there is a green or green/yellow wire going back to the main inlet and maybe a chassis connector.
EATyour GUITAR wrote: I just wanted to point out that a 12DC adapter like the one supplied with a $99 plastic Yamaha IS intended to make the product cheap and simple
The irony is that it doesn't. The manufacturer can buy a really decent transformer for the price of a wall wart, they choose not to for their convenience not yours.
there is also this for when you need a ground but the ground in the mains is noisy.
If it's noisy it is not a proper ground and cannot be fixed apart from replacing the wiring with heavier gauge. Ground is a low impedance connection to a rod in the ground outside the building, it is the reference for 0V so by definition cannot be noisy, other voltages may be noisy with respect to it. The "Neutral" of the mains voltage pair is nominally the same. Older distribution practise (which may be still current in some countries) used to derive Neutral as a balance point in a three phase system. That is the three phases are shared over an area like a street and if each one has a similar load the common point is about 0V, but as the loads vary it will shift around. It could be as much as 70Vac, but nowadays (in the UK at least) it is bonded to ground and they try to keep it to within a few volts. This may lead to misunderstanding where noise is coming from, any interference that is not common between Live and Neutral will come through a mains transformer as a component of the mains waveform.

fonik wrote:by saying MUST you don't mean official safety rules, right?
If there is possibility of a loose live wire causing exposed metal parts to become live then it must be grounded. All synthesizers have exposed metal parts: the patch leads. Even if all exposed metal is covered and the mains is external it still needs to be grounded for reference, so between the two reasons it is not optional.

When a linear PSU is ungrounded it tends to float at around half the raw rectified voltage. The first time it is connected to something grounded it will discharge and become refered to ground and if it has large capacitors that may be a large charge transfer. As jacks make contact tip first this may stress circuitry, eg output stages. It may not be lethal, but it is still undesirable.
fonik wrote:in germany you have to certify gear with mains connection, and this can get expensive. therefore doepfer decided to use this certified external double insulated transformer from another manufactuer.
In Europe anything with more than 50V in it has to meet the CE Low Voltage directive. (Low in this case means compared to the thousands of volts on the grid.) Buying in CE certified parts does not convey the certification to associated products.

Certification is only expensive if you use a rip-off test house to do it. Any competent engineering company can self certify if they do the paperwork, it is just that most small firms are scared of that. I can forgive them not knowing what to do after wading through the EU documentation which goes out of its way to obscure and confuse with legalese, but it is not really as complicated as most people think. Most of underlying principles in the LV directive are common sense and well established good engineering practise, the same cannot be said of the EMC or WEEE directives though.
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Post by fonik »

thanks for your explanations, and for taking the time, Graham. I am still not sure if i got it right.
Graham Hinton wrote:
fonik wrote:by saying MUST you don't mean official safety rules, right?
If there is possibility of a loose live wire causing exposed metal parts to become live then it must be grounded. All synthesizers have exposed metal parts: the patch leads. Even if all exposed metal is covered and the mains is external it still needs to be grounded for reference, so between the two reasons it is not optional.
that's exactly what i meant, actually. and you are talking about Protection Class I, true?
however, if the item is built according Protection Class II (and even III?) with Double Insulation, the material exposed to the cistomer does not matter at all - i.e. my table lamp has no earth connector to the mains, built with double insulation according Protection Class II.
the reference is another thing, and this was the reason i recommended earthing the DIY cabinet to the mains earth.
When a linear PSU is ungrounded it tends to float at around half the raw rectified voltage. The first time it is connected to something grounded it will discharge and become refered to ground and if it has large capacitors that may be a large charge transfer. As jacks make contact tip first this may stress circuitry, eg output stages. It may not be lethal, but it is still undesirable.
the doepfer complete systems are using linear PSUs, and are built according Protecion Class I, i believe.

the doepfer DIY Kit we are talking about uses an external 3rd party transformer that is built according Protection Class II (see picture in 1st post), therefore it has no earth connector.

however, the actual PSU (without the transformer) is open frame, and therefore the DIY system should be built according Protection Class I - is that what you mean? i did not consider that!
I know there has been an international agreement in addition to SELV that defines voltages that don't have to be protected by the manufacturer, cannot find it know...
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Post by EATyourGUITAR »

@ Graham I respect and admire you for your expertise. you are way more knowledgeable and experienced than me. with respect to yamaha, they can take products to market faster and have a smaller more predictable liability as a result of NOT doing product testing. the money they save is most definitely not in the cost of the parts. a CEO of a company has a responsibility to the shareholders to minimize and define the companies liability whenever possible. companies that make products for babies have huge markups to cover the cost of infant death. its a business. faster time to market means they can respond any changes in market demand and current product trends. this could translate to huge profits for a global company like yamaha. I also don't think anyone will die from a yamaha keyboard.
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Post by daverj »

It sounds like right now you have solved the hum problem by adding a second mains plug which only carries the earth connection.That means you are using two plugs. One on the transformer with the line and neutral connection and one on a second plug with the earth.

Why not rewire it with a single 3-prong earthed connector? Cut off the 2 prong mains connector on the transformer and connect those wires to the line and neutral of a 3 prong mains connector. Then connect the earth pin of that connector with a wire going to the PSU earth connection. You could just twist that wire around the wire to the transformer to keep them together. Maybe even use some heat shrink every few inches to hold them together.

Then you would have a single 3 prong earthed connection to mains, with the transformer getting it's signals and the PSu correctly connected to earth. Plus you end up with only one mains plug to have to plug in.
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Post by Graham Hinton »

fonik wrote: that's exactly what i meant, actually. and you are talking about Protection Class I, true?
however, if the item is built according Protection Class II (and even III?) with Double Insulation, the material exposed to the cistomer does not matter at all - i.e. my table lamp has no earth connector to the mains, built with double insulation according Protection Class II.
These classifications are really describing single standalone consumer objects. When you are building a studio there are dozens of such objects and you are the systems integrator. Yes, you can have exposed metal on a double insulated device, but when that gets connected to another device that does have mains in it the situation is different. A patchable audio system is very complex and it is too complex to analyse every path for safety considerations, it is easier and better to ground everything and then sort out any audio problems (but NOT by removing grounds).

the reference is another thing, and this was the reason i recommended earthing the DIY cabinet to the mains earth.
This is the overriding consideration.
It gets tricky discussing grounding because it is used for safety, for reference and for RF screening and there is often confusion and conflicts between the uses, especially in an unbalanced audio system that may contain digital circuitry.
There is no good argument for not having mains earth present on everything. Just because there are lower standards does not mean that products have to be built down to them.
the doepfer DIY Kit we are talking about uses an external 3rd party transformer that is built according Protection Class II (see picture in 1st post), therefore it has no earth connector.
Yes, it's just a tacky cop out.
however, the actual PSU (without the transformer) is open frame, and therefore the DIY system should be built according Protection Class I - is that what you mean?
No, there is no mains voltage requiring double insulation to be present, but the 0V still needs to be grounded for reference.

[quote=""EATyourGUITAR"]I also don't think anyone will die from a yamaha keyboard.[/quote]

Well I have seen a few Yamaha products that were incorrectly earthed, TX816 (UK version) at £5k+ being one of them. Like I said, they are not doing it for the customers' convenience, the real reason that international products have external PSUs is that it enables the company to mass produce one product and then regionalise it.
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Post by fonik »

daverj wrote:Why not rewire it with a single 3-prong earthed connector? Cut off the 2 prong mains connector on the transformer and connect those wires to the line and neutral of a 3 prong mains connector. Then connect the earth pin of that connector with a wire going to the PSU earth connection.
that's what i am saying, dave. thank's for emphazising 8_)
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Post by fonik »

and thank you, graham, for verification/explanation. really appreciated. :party:
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Post by EATyourGUITAR »

Another interesting thing is that yamaha sells third party power supplies as another way to side step liability if the wall wart starts a fire or kills someone. You are exactly right that they want to make one product for the global market. That relates closely to bringing products to market faster, reducing costs etc.. Its a win win.
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Post by matttech »

fonik wrote:
daverj wrote:Why not rewire it with a single 3-prong earthed connector? Cut off the 2 prong mains connector on the transformer and connect those wires to the line and neutral of a 3 prong mains connector. Then connect the earth pin of that connector with a wire going to the PSU earth connection.
that's what i am saying, dave. thank's for emphazising 8_)
it actually HAS a three prong mains plug on the "mains side" of the transformer....but on the "case side" there is only a 2 cable connection to the AC connections on the case's PSU board (and no earth)

i'm a little bit wary of breaking open the transformer and messing with the standard, supplied Doepfer DIY kit, just in case I ever have to sell it on

I can live with an extra plug for grounding purposes - no big deal for me. the MAIN thing is that it's SAFE, and that the hum is gone - it's perfect now, with NO difference between my DIY case and the Monster, sound-wise.

it's definitely an interesting area, and one I wish I understood more about (although i'm learning more as the days progress!)

I am starting to wonder whether my audio interface (MOTU 828 mk1) is actually grounded....as, if it was, wouldn't the simple fact of connecting the output cable from my DIY case have grounded it? (much like it did when i connected a cable from the Monster Base to the DIY one)
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Post by fonik »

so it does not have a two pin mains connector (euro) like in the picture you posted, but a three pin?

anyways, i think we all agree that it would be good to connect the GND of the PSU to the mains earth - don't we?
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Post by matttech »

fonik wrote:so it does not have a two pin mains connector (euro) like in the picture you posted, but a three pin?

anyways, i think we all agree that it would be good to connect the GND of the PSU to the mains earth - don't we?
no - mine has a three pin (pretty sure i mentioned that in the relevant post, but maybe not....) - i think the pictured one is the european (not UK) version....and an older one

connecting the PSU earth to mains ground definitely solves the problem

thanks for all your input!! makes me feel a bit more confident in my fix
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Post by Graham Hinton »

matttech wrote: i'm a little bit wary of breaking open the transformer and messing with the standard, supplied Doepfer DIY kit, just in case I ever have to sell it on
That is not what is being suggested. Just share the mains plug and run a heavy stranded cable outside the transformer to the case. Keep them together to prevent them ever becoming separated. What Doepfer should have done in the first place.
I am starting to wonder whether my audio interface (MOTU 828 mk1) is actually grounded....as, if it was, wouldn't the simple fact of connecting the output cable from my DIY case have grounded it? (much like it did when i connected a cable from the Monster Base to the DIY one)
Yes, but that is not the way to do it. Do not use signal cable screens to provide safety grounds. An audio interface is a digital device full of high frequencies and although it may have CE and FCC certification that does not stop cables acting as aerials when used incorrectly.

Here's some simple rules for a complex system:
1) All safety grounds should go back to the mains Earth in heavy gauge wire capable of conducting at least 6A (eg an IEC mains lead), but 16A or more is better, or the chassis should be bonded together with a similar rated wire.
2) All power 0Vs should referenced to the mains Earth.
3) Think of cable screens as a 0V tube covering the signals and linking two outer boxes at the same 0V. These should not be carrying current. When people talk of disconnecting one end or "telescoping" it means they are carrying current and that is what should be fixed and not by cutting wires.

For 1) and 2) don't build to a minimum, beef it up as much as possible. Safety testing is often done by injecting 25A between the mains plug Earth and bare metal, although this is relaxed for more delicate equipment. Every wire has a small resistance which means that a voltage drop occurs if current is flowing. This is how 0Vs get "noisy" or "dirty" (not terms I like using) so the resistances should be minimised in all safety paths and power distribution.

If you look underneath a large SSL analogue console (a place I have spent too much time on my back) you will find two massive copper busbars running across the full width to which all channel strips are bolted with heavy gauge cable. You won't find that in a cheap 16 channel mixer. Synthesizers are subject to the same laws of physics so you have to decide if you want a Mackie or an SSL. A small system can get away with it, but a large system cannot and you cannot expand a small one indefinitely without hitting these problems.

There is a conflict between 2) and 3) in unbalanced audio problems, but 1) and 2) override. You do not automatically get a "ground loop" by grounding two points, there has to be a source of power with gain to drive it and this is often the audio amplifier which is fixed by isolating its inputs from its outputs, eg with an audio transformer. Don't use hi-fi amplifiers for monitoring.
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