[Abby356]

I've been wading through previous threads in an attempt to gain the info I need but I'm new to the DIY electronics thing and am still confused. My project is a 24v Aikido and I've got the board built/populated and am now trying to wire it all up. The power supply is a 24v Medical SMPS from Mouser and uses the typical 2.5 mm DC power chassis jack to connect with the pre with just a positive and a neutral leg. My questions revolve around grounding. I know its a sensitive topic (in more ways than one) and am looking for some basic guidance. From previous posts it appears as though i should be isolating the various rca jacks and the DC chassis power jack from the chassis ? and should I leave the board "floating" and not use the ground. ? If so how exactly do i ensure that the various jacks are isolated form the chassis ? It appears to me that the two plastic washers included with the rca's will not suffice to prevent the body of the jack from contacting the chassis. Also the DC jack I have is solid metal and by design will contact the chassis. Thanks for your patience and time folks.



Sincerely, Daniel.

P.s. I've tried to attach a picture but i couldn't figure that out either.

[TomS]

Daniel,

Congrats on putting the Aikido together.  You'll be very happy with the results.  I actually have the high voltage version, but can break down some of your questions buried in that post.  You are right, though, you'll get a lot of opinions on this, so I'll start it off.

Think about at least 3 common situations regarding "grounding":
- Safety or chassis ground.  Absolutely necessary where there are significant internal voltages and a metal chassis or exposed components to which humans could possibly be exposed.
- Signal ground. Basically the ground reference point for your signal inputs and outputs.
- Power supply ground.  The ground reference point of your DC power supplies (possibly +/- voltages with respect to ground).  "Neutral" is usually something different, especially in typical AC house power terms.

- In my Aikido, there is a connection for the safety ground directly from the green incoming AC grounding wire to the metal chassis with a star washer.  If someone drops a screwdriver in it, a part breaks inside, or you otherwise come in contact with voltages this provides a safe direct path to the safety ground back to the the house panel/earth ground.  There is not a connection from my power supply ground directly to that chassis ground, but the answer is it depends.

- I always isolate the signal grounds (RCA's) and incoming power grounds from the chassis.  If you have plastic washers, then it is likely intended to be used that way.  I would suggest using some other connector than the 2.5mm coax or at least isolate it from chassis if possible.

- I am not close to my bench at the moment, but I am fairly certain on my Aikido board the signal ground is connected to the DC/power ground there.  There would be no further need to wire other ground points if that is the case and it may actually cause loops or other problems.  It is easy enough to test with an ohmeter to see if there is continuity from the pads first so you might check that (powered off of course).

- In many cases, where you need to run a lot of individual ground wires and there isn't a convenient single PC board ground junction point, it makes sense to plan a single star ground to prevent loops.  In general, you want to avoid redundent wires, especially of different lengths, as this can create varying DC resistance paths among the ground end points.  Sometimes DC and/or signal ground may also be connected to chassis ground point either directly or through various schemes of thermistors, resistors, and/or capacitors.  This is another case where "it depends" on many factors, so I'll let the experts chime in here.

Hope this helps and best of luck!

Tom

[ebag4]

Daniel,
With regard to the plastic washers for the RCAs, it has been my experience that they have a shallow lip on the inside hole on one side of the washer.  This lip is intended to keep the washer centered in the hole so that the body of the jack does not come in contact with the chassis.

Best,
Ed

[BillB]

Power supply wise the medical supplies do not require a ground.

The Aikido 24v is a great piece, question though, what wattage is your PSU? I tried a 40w and it went into protect mode after about a week. I had to up it to 60w to handle heater current. Just an FYI.

[Abby356]

Tom, thanks for the detailed post. Please walk along with me as i try to wade through this.

1) How do i create the chassis/safety ground with only a hot/neg incoming via the DC power supply.

2) I took a closer look at the rca's and think I can manage to isolate the body from the chassis and i picked up another plastic bodied DC input jack today. So if i understand correctly there would be no need to ground the incoming DC signal ? and the rca's could be tied together to a single ground located nearby on the chassis ?

3) and finally the ground on the board which JB says is optional would ground what exactly ?


BillB,
   thanks for the tip. The Medical SMPS I have currently is a 32W , 1.3a version but i could certainly upgrade it as i havent taken it out of the package. Would you mind sharing the amps of the one you ended up with ? I may be mistaken that the amps is the key. (?)

Thanks all, Daniel.

P.S. i'm still trying to attach a picture.

[TomS]

On #1, as they are in separate chassis (mine are too), you can use another wire (green maybe) to tie the two metal chassis together, assuming the SMPS does not have a connection from DC ground to chassis.  The SMPS likely should have a connection from metal chassis to the AC connector ground wire.

#2 The signal grounds and DC grounds can be connected at a single star point or possibly on the Aikido board.

#3 See #2 or maybe BillB can chime in as I don't know that board specifically.

The easiest way on pictures is to upload it to a gallery, then point the url in your post directly to the gallery. 

[JoshK]

Tom, thanks for the detailed post. Please walk along with me as i try to wade through this.

1) How do i create the chassis/safety ground with only a hot/neg incoming via the DC power supply.

2) I took a closer look at the rca's and think I can manage to isolate the body from the chassis and i picked up another plastic bodied DC input jack today. So if i understand correctly there would be no need to ground the incoming DC signal ? and the rca's could be tied together to a single ground located nearby on the chassis ?

3) and finally the ground on the board which JB says is optional would ground what exactly ?

I'm not Tom/Bill, but for #1 the answer is you don't.  You use double insulation techniques to isolate the circuit from the chassis.  That is in keeping with the safety standards.

#2 I agree with Tom.  I wouldn't tie anything to the chassis.

#3 it would be left floating.

[BillB]

sorry my numbers were wrong, I think the original was a 25w and the new one is a 40w.

Here is the one I ended up with, mainly because it was cheap and I needed to find out if it worked.

http://www.allelectronics.com/make-a-store/item/PS-2417/24VDC-1.7A-POWER-SUPPLY/1.html

As you can see it is 1.7a

I think you will be ok with what you are using....my original was under an amp. Sorry about the worry, hard to remember when you are 200 miles from home.

[Watson]

For what it's worth, Morgan Jones' Building Tube Amplifiers has a really lucid discussion of how to handle grounding and safety earthing in tube amplifiers. Worth getting if you're still not sure.

[Occam]

BillB's medical switching ps (great find!) refers to -
http://www.alliedelec.com/Images/Products/Datasheets/BM/POWER-ONE_INC/218-0077.PDF

It does have a connection for a mains ground. But, if you built the Aikido with sufficient seperation between it and the ps, an umbilical would be ideal, it might well qualify as a SELV unit (separated extra low voltage) -
http://en.wikipedia.org/wiki/Extra_low_voltage

and have the signal level chassis qualified as a Class III component-
http://en.wikipedia.org/wiki/Appliance_classes
one whose operating and potentially exposed voltages are simply not a threat to life, limb, or property, and therefore don't require a conductive chassis to be grounded, or even the mains ground to be present.

FWIW,
Paul

PS - and the thing you need to remember dealing with either a Class II or III audio component, is they are not directly mains grounded. Iff'n you forget, one might be so silly as to tie your interconnects telescoping shield to it. Been there, done that 

[BillB]

Just to be clear the Power One is not medical, I was using a Lambda medical prior to it.

Here is what mine looks like (still after 6mo in its temporary chassis):

[BillB]

Man I just fired mine up for the first time in months, holy crap this is a good pre...totally forgot.

[Abby356]

With the help of the friendly folks that posted on this thread and a couple of very helpful vendors, John with Bent Audio (who promptly built a 50K Alps remote volume module) and Lee with Locus Design Group (who provided the nice RCA's), I was able to get the 24v Aikido up and running a couple of weeks ago.






I am currently using it with a Trends amp, Sony PS1 and Cain and Cain Abbys. It sounds wonderful.
Now I just have to finish my DIY F5 and Earl Geddes Nathan 10's to go along with the Aikido.

Thanks again everyone for your help and suggestions.

Regards, Daniel.

P.S. I'm not sure I will ever get the pictures that I attached to work.