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Old 3rd March 2012, 08:14 PM   #1
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Default There are ghosts in the Ground! More grounding advice...

Hey all,

This is my first post, so I hope I'm in the right forum here! I've looked at the thread they suggested, but they don't give me a ton of help!

I'm pretty new to building, but took on a project building a Mid/Side encoder/decoder. It's based on the Wayne Kirkwood circuit, that I've heard about quite a bit over at gearslutz, using the Five Fish Audio power supply. I've put it all into a plastic chassis.

I'm finally at the stage where I can test things out, and I've run into a little issue.

As soon as I attach the ground on the main power input, I'm unable to pass any signal through the processor. So, when I solder to a ground pad, all sound is lost, yet there's still a 60hz ground loop.

When not grounded, there's a loop, and the signal is hugely degraded, and very quiet. Any idea how I could solve my problem? I'm currently at work on my break, but when I get home can link to schematics/drawings and pictures of my project!

Any help would be hugely appreciated!

Thanks!

Dylan
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Old 3rd March 2012, 11:45 PM   #2
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That forum tends to attract lots of musicians and others with little understanding of electronic engineering so the threads have lots of errors.

I never heard of the Wayne Kirkwood circuit or the Five Fish Audio power supply.

You can't safety ground a plastic chassis.
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Old 4th March 2012, 03:09 AM   #3
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OK, I looked them up:
The M/S Matrix Encoder is in the Wayne Kirkwood hosted forum "Pro Audio Design Forum". The members of that forum are extremely knowledgeable. I found one thread on construction of this matrix with 73 posts. Along with other threads and links. This is a neat circuit with THAT brand chips. An M/S Encoder/Decoder is a fun circuit, maybe I should build one.

The FiveFish Studios power supply is a very well done conventional regulated (LM317/LM337) adjustable dual power supply with a phantom mic supply. They also have a transformer primary circuit kit.

The phantom voltage supply along with the phantom voltage blocking rectifier bridges adds complications to the supply wiring and possible errors.

Do you have any drawings on how these different kits are interconnected?

Are you using XLR or TRS connectors?

Is the supply in the same chassis as the matrix? and why a plastic case?
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Old 6th March 2012, 08:30 PM   #4
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Hey Kevin,

The mid/side comes highly recommended, by heavy hitters like Bob Katz!

I'll get a drawing going tonight, or early morning tomorrow latest, but basically it's laid out like this:

Toroidal transformer, hooked up to the mains, the on/off switch, and the safety fuse, into the PCB of the power supply kit. Then, out through the first supply rail (DC1), into the mid/side board.

Clearly, I'm unsure of what to connect the safety ground to on the 110v in, since I'm using a plastic chassis.

The plastic case just was something I happened to have lying about when I came across the kit. This is more of a fun project than anything else.

I'm using XLR connectors, 8 of them (L/r in, L/R out, M-send/return, s-send/retun).

I actually decided to opt out of the phantom power in the M/S circuit, and didn't bother to stuff them, as I had no real use for it for my applications.

In reality, would it be better for me to simply pick up a 1u chassis?

Thanks so much for your time,

dylan
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Old 6th March 2012, 09:14 PM   #5
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I wondered where you were, dylan.

I went back to the "Pro Audio Design Forum" and found several other threads about this circuit board with some of them re- purpose the board for other uses.

I can't see any reason for phantom power either.

The board has so many options that it's easy to mis-connect something.
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Old 6th March 2012, 09:20 PM   #6
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Yeah, it truly is. I've basically simplified it as much as I could, and hooked up from the left input to the left output - my signal is much stronger when neither of the XLR connectors are grounded. There's still a bit of hum, however.

I'm thinking I'm just wasting my time with this plastic chassis, I'm looking for a 1u chassis within Canada (and having a surprisingly hard time), for a reasonable price.

The PSU seems to be working very well, with the rails pushing a very steady 18v (the setting Kirkwood recommended).
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Old 6th March 2012, 09:46 PM   #7
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For now, let's connect all the XLR pins #1 together but not to anything else.
Latter on we will deal with that safety ground.
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Old 6th March 2012, 09:52 PM   #8
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Hey Kevin,

Pins #1 being the usual grounding pin? I'll do whatever you suggest tomorrow (finally have an day/evening off.

If you don't mind me asking - what's your logic behind doing that? Just to help my own learning!
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Old 6th March 2012, 10:10 PM   #9
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That's a common misunderstanding. The pins #1 are only a shield, they connect only to metal chassis's near the connector. They are not part of the audio ground circuit. Although at some point the audio ground will connect to the chassis.
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Old 6th March 2012, 10:18 PM   #10
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Interesting - So when they're connected, I lose most of my signal. I'm testing the inputs and outputs right now, no inserts hooked up at the moment.
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