UCD: connecting case or not?


2005-02-17 4:24 pm
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)
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?
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.
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.


Disabled Account
2004-02-13 3:35 pm

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.

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?


Disabled Account
2004-02-13 3:35 pm

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.



2005-02-17 4:24 pm
The UCDamp got finished today and it plays :cool:

I've not connected neither IEC ground or PS ground to the case. However I've got absolutely no (zero:angel: ) 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?


2005-02-17 4:24 pm
Now I have the IEC ground connected to case and still no humming in the speakers :) so I'll keep it this way, a little safer I guess.

The Transformer centertap and Supply ground from the Hypex HG Supply unit is hard to get without soldering cause there are no space around the fastons, see my attached picture. So I'll leave as it is now.

The DC mains filter still do no good for the transofmer humming.

Here's the schematic: http://www.lcaudio.com/dcfilterdias.gif

I guess it'll be a support issue for Lc Audio.


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2005-02-17 4:24 pm
I've measured red-red and yellow-yellow, both give 44,4V AC (My mains show up a rather high 231V)

The marks on transformer are red 0V red 42V yellow 0V yellow 42V


I've conntected red 0V together with red 0V on the "0" on the PS board. This does indeed not look like your picture with center tap :eek:

Shall I instead connect red 42V and yellow 0V (the red and yellow wire that are next to eachother) togheter on the "0" on the PS board?

On the other hand I still meassure +-61,3V DC right before the 400 modules and they play beautifully.

No more power on for me untill this is cleared up :D
Your transformer gives;
0VAC -- 42VAC / 0VAC -- 42VAC
Red ---- red / yellow -- yellow

You MUST connect the middle red AND yellow together to the center tap of the power supply. Please check the following to see if you have connected in the right way; measure on both AC fastons (marked ~ / ~) of the HG power supply a voltage of 88VAC. When you measure 0V you have to change one AC wire with the other from the same colour.

A proper DC voltage doesn't tell you that you have connected everything in the right way! Only measuring the AC voltage tells you if you have connected it in the right way.

Congratulations Trex :D

It was all due to the "center tap" issue after all!
My Plitron Tx has different colors for center tap wires and this makes everything easier.

Some comments/doubts:
1) It seems from the pic that two pairs of speaker BP are connected to the box. Aren't they? If yes, what for?

2) I would recommend placing the UCDs with the T attached vertically to the lateral side of the box (two external UCDs) and the remaining also with vertical T attached to a new vertical metal plate/heatsink. In this maner you could get better heat dissipation and convective cooling plus isolation from the new plate.

Best regards.


2005-02-17 4:24 pm
maxlorenz your right, ive got 2 different pairs of speaker BP's, I run out of WBT's, so I had to use the Supras for the second pair of amps :D

The left/right sides of the case actually is big heatsinks.
Maybe I Should mount the 2 ucd's vertically on those instead, obvisosly better, Ill see if I'll do that... It plays pretty damn good :D

I have a rather high voltage of 61,4 VDC after PS, however its not running scaringly hot either....
Hi trex:

I'm glad you're glad :D
They are good, aren't they :cool:

I was reffering that BP's seem to be "connected" with the box paint removed...:eek: Or maybe the pic is not detailed enough.

however its not running scaringly hot either....

What is not hot? The heatsink? If it's not hot it may be good or bad: good if they manage to get rid of heat (as they seem) or bad if the heat never reached them in the first place.
I believe T plate is good for the transistors attached to them but the other sensitive items (output coil, etc...) must use convective air cooling, IMHO :angel:
I want mine to last decades...

Best wishes