Behringer DCX2496 digital X-over

[RevF]

Power supply repaired and main board swapped out on my DCX - Now all working again! I did not realise just how lost I would be without Jan's output board! Not just the volume control, but having lived with it for years, having to take the output from the DEQ instead really showed up the shortcomings of the original Behringher units! No clear smooth sweet 3D audio! I just wanted to turn it down all the time, whereas now it is back working I just want to turn it up! - Many thanks for the aid, Jan and co!

[fredsonqc]

whououhhh!
a lot of work and place and expensive for what improovement?
I'm not sure burson are better than LM4562 at this place for the job...

[MurphyUHF10]

Originally Posted by janneman

Did you put in a direct connection between the external supply ground to the DCX?

jan

Hi Jan,

Yes, a direct connection from the center tap (GND) of the external supply, to pin 4 of the seven pin power connector on the DSP board.
(maybe photo dont show too good, but i have terminated a binding post at each end, for easy connecting of the 2 GND's..

@fredsonqc: Yes perhaps, but this is the fun of DIY :-) Anyhow, Burson products are not so expensive here in Aus..

Even with loud hum, (and music turned up loud) I notice improved channel separation which has improved soundstage and 'space'.. So maybe not so bad ;-)

Ta
CM

[jan.didden]

Assuming there's also a ground connection between the two units via de XLRs, there *could* be a ground loop.
Difficult to say what to do, but try to limit ground to a single connection.
What you could try is to tie the two chassis together only through the pin 1 of the XLRs - that's what they are meant for.
But grounding is always a bit messy...

jan

[MurphyUHF10]

Hmm.. Not quite sure what you mean here..


Ground the 2 chasis together thru pin 1?? Which two chassis you mean?? The external supply has plastic case,, only the shield around the transformer is Earthed (you can see in photo).. GND is not Earthed in either device. I may be confused here but,, the (power) GND of both DCX and external supply have been connected together, at pin4 of X3 (DSP power connector)..


How does pin 1 of XLR fit into this?? Perhaps the interconnects to my amps?? I use 2 core shielded (balanced cable at DCX) and connect pin 1 & 3 at the RCA end (amp) keeping the cables "balanced as long as possible"..


Without the external power supply in use, Eg, using power from i/o board for the discrete modules, I get no hum.. Interesting??


Ta
CM

[MurphyUHF10]

Maybe this gives clues to where problem may exist..??

This is directly across speaker terminal with no music playing,
volume at -10dB (on the remote screen)

speaker-output.jpg


Thanks..
CM

[Pano]

50 cycle mains in Australia, eh?

[AndrewT]

Terrible mains hum and even worse mains buzz.

[jan.didden]

Originally Posted by MurphyUHF10

Maybe this gives clues to where problem may exist..??

This is directly across speaker terminal with no music playing,
volume at -10dB (on the remote screen)

Attachment 282060


Thanks..
CM

If you have followed the standard way then the grounds/earth of the two units are connected through pin1 of the XLRs.
Then there's the direct connection from the aux supply to the DCX supply pin 4.
This can form a ground loop which might cause hum.
However, looking at your spectrum I see a lot of higher line harmonics which are typical of not just hum but a 'chainsaw' buzz. This indicates that there's a common ground path of the rectifier/reservoir cap which causes that ground return current to cause a voltage across for instance a small impedance in that ground path.
The voltage resulting is added to the input voltage because the ground ref of that input voltage is elsewhere. It's probably easier to draw then to explain.
Bottom line: look for ground wires or traces that carry return currents from the rectifier/reservoir cap, probably in the aux supply. Try to ground the two grounds of the pos and neg cap close to each other and close to the xformer ground tap. That localises the currents with the buzz. Then from that common point run a wire to the DCX ground, OR connect the common point to the XLRs pin 1. Or both (but sets up another ground loop...).
Difficult to exactly say what to do in detail with out having the unit in front of me.

jan

[MurphyUHF10]

Thanks Jan!

You were correct.. After reading your post, and then studying the article on here about "grounding", it occurred to me that I had incorrectly wired my external PSU's ground connection

Originally Posted by janneman

The voltage resulting is added to the input voltage because the ground ref of that input voltage is elsewhere...

Bottom line: look for ground wires or traces that carry return currents from the rectifier/reservoir cap, probably in the aux supply.

jan

I had taken GND (external psu) directly from Center Tap, and not "further down" the circuit board where the +/-18v output is.. So I re-wired the ground connection to where the actual GND output was, at the other end near the voltage output.. Instantly, the bad hum/buzz went away..

However!! Further reading this great article, I realised that connecting this GND's at X3 'pin 4' was also incorrect, and needed to be at the chasis star GND connection.. Once I did this, hum/buzz vanishes almost completely..

However, when I mute/unmute on the remote, or change volumes etc,, I get loud "pop" with every button press on the remote..??

I think it might be better if I just power these modules with the +/-15v available from the Didden Linear PSU instead of trying to combine 2 power supplies..

Can the Didden Linear PSU handle an extra 300mA..?? Do you see any issues here with taking power from X3 pin 1 & 2.. At least I wouldn't need to worry about grounding :-)

Cheers..
CM