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Preparing to start my system (and a grounding question)
MUFF WIGGLER Forum Index -> Oakley Sound Systems  
Author Preparing to start my system (and a grounding question)
ProducerMatt
I've recently been learning soldering and DIY, and I'd like to start an Oakley Modular system. If I had my way I'd be doing a few more projects before starting this one, but I don't think i can afford all the kits I'd need to make myself comfortable with a modular sized project.

I was a little too nervous to build the power supply myself, so I'm using a 1.5A Condor power supply which I'll connect to the Dizzy board, after changing the values of the diodes so the higher amps don't blow them up.

I made a Mouser project for the Dizzy, cables, and all connectors/clips for the actual module connections. I assumed that the modules have male connectors as the distro board does, meaning that the cables need female connectors at both ends. I also chose 22AWG solid insulated wire.

So that's the parts list I assembled. As I am a beginner, PLEASE let me know if I'm doing something wrong or missed anything.

My other question was about the ground in the Oakley Buss, as ground issues have always interested me. In the builders guide, Tony says that pin 2 (middle) is floating normally, and grounded with R3. He later says, in bold scary letters:

Quote:
On no account should an interconnect with three wires fitted be used to connect the Oakley Buss to any module. The middle location, pin 2, is ground on the module and this should not be connected to the Dizzy or midiDAC modules. Connecting the two grounds in this way could induce earth loops and introduce hum or crosstalk in your system.

It seems like he's saying, only wire pin 1 and pin 3 and never wire pin 2. What's the problem with connecting the module pin 2 to the distro pin 2, as long as R3 is bridged? If it's not supposed to be used, why have R3 or any traces running from pin 2?

Thanks everyone. smile
Synthbuilder
ProducerMatt wrote:
It seems like he's saying, only wire pin 1 and pin 3 and never wire pin 2.


That's correct. Do not connect pin 2 if all you are doing is using CV or gate.

Quote:
What's the problem with connecting the module pin 2 to the distro pin 2, as long as R3 is bridged?


A module should really only have one strong connection to 0V. By using the pin 2 connection on the bus then you have added another 0V connection that takes a different route back to the power supply. This could cause a current to flow in the pin 2 connection which has the potential to disturb other modules. It's almost certainly nothing to worry about though - nothing will blow up if that connection is made.

Quote:
If it's not supposed to be used, why have R3 or any traces running from pin 2?


The standard Oakley Bus uses just CV and gate. The middle copper 0V track connected to pin 2 prevents the gate signal - a fast moving +5V signal - from capacitively coupling onto the sensitive CV line. The original Dizzy was much longer - something like 15" long - so there was a potential for crosstalk to become noticeable. However, since any crosstalk would be relatively small I thought about allowing this pin 2 track to be used for another CV, eg. aftertouch or mod wheel, if the user desired. Not fitting R3 would allow the middle copper track to float so it could be connected to another CV signal of the builders choice.

Tony
Blake Smith
I'm not much of an expert on power, but as a rule I've used 22 gauge wire for point to point connections in modules only, and thicker 18 gauge wire for power connections. If only because that seemed to be the way other builder did it.
Leverkusen
Okay, while we're at it, something that is occupying my mind for some time now starts to get important since I am building a new case atm...

I found this in the builders guide for the Oakley PSU:

Quote:
All modular panels should be earthed directly, either with their own direct connection to the earth tag on the power inlet, or via the modular's earthed metal mounting rails and suitable toothed washer and screw. If you have a wooden case with wooden mounting rails and you are toying with the idea of using a mains transformer for your DIY power supply project then you may want to rethink your plans.


Is this meant for when you try to build a linear PSU out of the Oakley board with a toroidal transformer and the split 0V / panel earth, or generally?

I just ordered a big Bell linear PSU for my wooden case and was under the impression that this is very common to have. Shouldn't all panels be grounded via the mounted jacks for safeties sake?

What I am planning is to connect multiple connector boards for MOTM and CotK modules to the PSU with a common ground/0V connecting all boards with a thick wire, then to the chassis of the PSU, which again is connected to mains earth.

This should be okay, shoudln't it?
Synthbuilder
Just saw this...

ProducerMatt wrote:
I also chose 22AWG solid insulated wire.


Not too sure about AWG since we don't use that over here but solid core is not normally used in anything that is likely to move or flex. Use multistrand for ordinary hook up wire and power supply connections.

Tony
Synthbuilder
Leverkusen wrote:
Is this meant for when you try to build a linear PSU out of the Oakley board with a toroidal transformer and the split 0V / panel earth, or generally?


Generally.

I'll not say much more but take care to insulate all live and neutral lines and earth all exposed metal.

Personally, if I were to fit an open frame PSU in a wooden case I'd house the PSU (or the just the transformer) in its own solidly earthed metal case or framework.

Quote:
Shouldn't all panels be grounded via the mounted jacks for safeties sake?


They are but this is not sufficient for a safety ground as the resistance is likely to be too high and is not made via a permanent connection like a weld or bolted.

Tony
Paradigm X
So im high jacking others posts, only as they ask similar queries just before me.

if one were to blasphemously use other peoples modules with an oakley psu does it matter which ground to use? i appreciate youl l lose the benefits of the dual grounds.

cheers
ben.
Blake Smith
Synthbuilder wrote:

I'll not say much more but take care to insulate all live and neutral lines and earth all exposed metal.

Personally, if I were to fit an open frame PSU in a wooden case I'd house the PSU (or the just the transformer) in its own solidly earthed metal case or framework.


Are there drawbacks to not enclosing the PSU in a metal case? I'm assuming this is primarily to make sure nothing is exposed?
Synthbuilder
Paradigm X wrote:
if one were to blasphemously use other peoples modules with an oakley psu does it matter which ground to use?


Ideally any new DIY module could be built with the same two separate 0V connections as the Oakley ones. However, nothing is going to break if you connect a standard MOTM format module into a Dizzy. This shorts the two 0V connections at the Dizzy which shouldn't cause a problem in practice.

One has to a little careful when using the word 'ground' as it should mean something different. I sometimes talk about module ground, GND or 0V as being the same thing. This is technically incorrect but it is used a lot. I worked at Marconi in the 80s and Soundcraft in the early 90s, and ground, GND and 0V were used interchangeably even by seasoned engineers. We'd talk about chassis ground, dirty ground, signal ground and clean ground. They'd all be connected to 0V somewhere but the term ground was in common usage.

Module or signal ground when used in this way is a local common reference connection tied to the 0V of the power supply. Used in this way it is not the same as mains earth. Indeed it may or not be tied to mains earth in the unit in question - although somewhere along the signal path it probably will end up being connected to mains earth.

Strictly speaking, ground is mains earth and historically it once was, but usage, incorrect or not, has meant a shift in the meaning. Ideally, we should call our common reference connection within our modular as 0V and not use the term ground.

Tony
Synthbuilder
Blake Smith wrote:
Are there drawbacks to not enclosing the PSU in a metal case? I'm assuming this is primarily to make sure nothing is exposed?


A steel case may reduce transformer radiated hum fields but other than that, it's a safety issue. Safety should be paramount when putting mains voltages into any project. Which is why I recommend that, unless you really know what you're doing and are fully conversant in the appropriate local regulations, you don't do it.

Tony
ProducerMatt
Thanks for explaining the grounds Tony. smile Maybe I'll use that 2nd pin for duophony eventually.

Blake Smith wrote:
I'm not much of an expert on power, but as a rule I've used 22 gauge wire for point to point connections in modules only, and thicker 18 gauge wire for power connections. If only because that seemed to be the way other builder did it.


Looks like you're correct! He says in the builders guide to use .75 mm^2 wire for the power, which it turns out is 18 AWG. I had mistook another one of his statements as referring to wire gauge. Thanks for mentioning it. hihi

The 1N4004 wasn't rated high enough for the power supply I picked, so I chose the EGP20A instead. Is that alright? It's probably fine, but I like to double check since I'm a beginner.

Regarding shielding the power supply -- I believe that this Condor supply I'm buying is open. How do I enclose it? Do I buy a blank steel case, put it inside, and ground the case?

I assumed this would be documented already but I can't find any info about it online, partially because the Google results are all about getting *into* the power supply instead.
Synthbuilder
ProducerMatt wrote:
The 1N4004 wasn't rated high enough for the power supply I picked, so I chose the EGP20A instead. Is that alright?


The diodes on the Dizzy pass no current in normal operation. They are there only to stop odd things happening when you switch on and switch off the power supply. In this case the 1N4004 diodes suggested will be fine.

However, the diodes could also protect modules from a power supply being connected in reverse and I guess it may be useful then to have much more powerful diodes like the ones you have found.

Quote:
How do I enclose it? Do I buy a blank steel case, put it inside, and ground the case?


OK, these are the sorts of questions I don't like to answer since there are legal implications to any suggestions I might make. So I would always encourage any beginner starts not with an open frame power supply but to go the route I offer by using smaller power supplies powered from enclosed external line lump transformers. The dangerous voltages are kept out of your modular and its safer and easier to get things right.

However, I will say just a few things about enclosing an open frame power supply. Any surrounding metalwork must be earthed in accordance with local regulations. Any surrounding metalwork must prevent stray fingers access to any high voltage points. The metal work should not impede air flow so the power supply gets too hot when under load - high temperatures can reduce the life of the power supply and extreme temperatures can cause fire. There must be no chance of cables going in and out of the case to directly rub against the metal work. All high voltage parts which includes the mains connector, fuse and any power switch must also be similarly protected. None of this is a trivial exercise and using an open frame power supply should be avoided if all you want to do is make some modules and play music.

Tony
ProducerMatt
Synthbuilder wrote:

OK, these are the sorts of questions I don't like to answer since there are legal implications to any suggestions I might make. ... None of this is a trivial exercise and using an open frame power supply should be avoided if all you want to do is make some modules and play music.


If you wanted to convince me not to use an open power supply, congratulations! You are winner!

The whole reason I didn't go with the Oakley PSU is so I didn't have a hand in it at all for safety reasons (and to future-proof with a little more amps then needed). But if the open supply is that complex and risky to shield then it's also defeating that purpose as well. The only reason I went with an open supply is so because linear supplies are a little hard to find above 12 volts. So I'll go with a enclosed switching supply instead; hopefully that isn't as noisy as people make it out to be. seriously, i just don't get it

Thanks for your help, Tony and everyone.
Synthbuilder
ProducerMatt wrote:
So I'll go with a enclosed switching supply instead; hopefully that isn't as noisy as people make it out to be.


No don't do that. Switchers do have noisier outputs than linear and they dump all sorts of noise into your mains supply too. A switcher is a good supply but only when used in the correct location. A sensitive analogue system can use a switcher but it will usually need additional filtering on the power supply outlets. The larger ones will often have a minimum load so when run with only a few modules may not produce the desired output voltage.

Tony
Synthbuilder
One other thing to think about is putting the mains power supply in its own metal case separate from the modular. Ventilated cases can be bought and all the mains stuff can be put into the case. Mains goes in via IEC socket and +/-15V can come out on one or two a four way speakon connectors. The Dizzy boards would still be in the modular with one Dizzy board per speakon connector.

Again, proper earthing, insulation, fusing and good lead dress should be used inside the metal case. Any connecting leads from the box to the modular must be made with the shortest and thickest leads you can use.

Even if you use a switcher (which I don't recommend) you'll have to deal with the mains wiring, fusing and switching. Putting it all in one box does make it somewhat easier.

Tony
Paradigm X
thanks for your replies on both threads tony.
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