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Old 10th August 2005, 10:07 AM   #1
trex is offline trex  Sweden
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Default UCD: connecting case or not?

My setup is as follows:

Going dualmono with 2 amps per side.

4x UCD400AD

2x Hypex highgrade PS

2x500VA 2x42V transformers, Softstart and DC mains filter all from LC Audio

Going to use XLR

Both transformers will be connected to the mains ground.

Here comes the question: Shall I connect anything to the chassi?

(like signal ground and/or mains ground)
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Old 10th August 2005, 11:55 AM   #2
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I would keep the signal ground seperate from the main ground.

Don't know about the PS ground though - should this be connected to the chassis?

The IEC ground should be connected to the chassis I believe...

PS. In the EC (european community), when assembling electronics for resale, should tests be conducted on the product, or is it allright if all parts are CE approved?
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Old 10th August 2005, 03:49 PM   #3
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Look at hypex' manual. I think it's clear there.

You must connect the ON pin to ground to get the module functioning. I use a toggle switch to make a delayed power-on, after soft-start action, to get a stable PS. In fact a let my PS ON all the time.

I connected ON pin, PS ground and TX ground together and IEC ground far appart, without any hum.

Good luck.
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Old 10th August 2005, 03:57 PM   #4
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Jan-Peter did tell me not to connect the speaker "-" terminal to the ground, or to other modules "-" terminals, as it would have bad effect on the sound (influencing the feedback)

The reason I asked was because I was looking at passive DC protection that used common ground for all speakers.

I connect the ON line to the power-in ground, and it works perfectly.

I'm also thinking to keep the IEC ground seperate. No need to introduce all the noise on that line to the amplifier.
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Old 10th August 2005, 08:50 PM   #5
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Hi,

All grounds eventually go to earth right? So why not connect them together (supply and mains ground) at a HQG point? Yeah the speakers ground has to go to the module though.

The way to avoid ground loop induced hum is to ensure all grounds reach a common point through a single path.

If you look at the hypex data sheet, you'll notice the output ground and supply ground tying together and going to the cap common point, which is then tied to earth ground (chassis). You'll also see another line from the chassis earth ground which goes to the bridge rectifier /"center tap". You definitly want these chassis connections at the same "star" point.

As per the mains earth ground, you have to ground the case somehow, better it be earth than through the source no? Well maybe not, suppose it depends on a few other things. I still think all the grounds should go to one common point though. Even on systems with one digital and one analog ground, they connect at a common point.

Thanks,
Chris
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Old 10th August 2005, 09:53 PM   #6
trex is offline trex  Sweden
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Yeah the ON pin and PS ground are connected.

maxlorenz: Whats TX ground=? Did you connect the IEC ground to case?

I also believe its a good idea to separate signal ground and IEC ground.

Anyway I'll try without any case connection tomorow, hopefully no hum for me
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Old 11th August 2005, 04:27 PM   #7
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Trex:
Sorry, I meant transformer's "center tap" (I think that's the name of it): I use the simple PS suggested at Hypex' with one rectifier.

Yes, IEC ground connected with brass bolt. Somewhere I read a good reason to separate IEC ground from the "star ground" but I forgot the exact explanation. I think it has to be for security reasons. Maybe to allow an hazardous current to flow far from the circuits and near the mains entrance?
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Old 11th August 2005, 05:13 PM   #8
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Hello,

Just to correct myself, I was reviewing a layout recommendation for amps in general ..... the IEC ground is shown seperate from the star ground.... I think it's a matter of safety or something though. You want to ground the case right where it comes into it, that way the odds of it being cut or damaged are remote. However all ground currents are still forced through a single path, and the case certainly is earthed.

Regards,
Chris
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Old 12th August 2005, 01:42 PM   #9
trex is offline trex  Sweden
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The UCDamp got finished today and it plays

I've not connected neither IEC ground or PS ground to the case. However I've got absolutely no (zero ) hum and extremely low noise floor in the speakers.

Im running an active system so this is really good.

Now to the bad news, Im getting a pretty loud and anoying tranformer humming noise. The expected noise without a DC mains filter.

When I had power on the Power Supply only (both transformers powered) I had absolutely zero humming, that time it looks like the DC mains filter did it job.

But when all UCDs are conntected and tranformers fully loaded no....

The transformers "SCN" cable is connected to IEC ground, no difference not to connect it that way.

Driving only one transformer on the DC mains filter resulted in the same amount of noise.

At the start I seem to get an "on and off" behavior of tranformer poise for about 5 seconds and then a constant noise... Maybe the DC mains filter is broken?

What else can I do to eliminate the noise?
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Old 12th August 2005, 03:37 PM   #10
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Schematics, please...not for me but for the guys that know

Also, I don't know LC Audio's DC filter schematic. Maybe there's the problem...

>>I've not connected neither IEC ground or PS ground to the case.<<
Why not connecting the grounds?
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