'Hot' signal input to DCX2496 problem

[dabbler]

Originally Posted by panomaniac

I'm lucky, so far no frying eggs for me.

Unless you have a faulty DCX, there is no way a consumer CD player will over drive it. As noted above, just look at the VU meters.

So there are a few things to do to troubleshoot this.

• Your mixer does not cause the problem. Why? Are you running it in balanced?
• Set the mixer to unity gain. Check the VU meters on the DCX to see that they are the same as when you connect the CD player directly. Still have the problem?
• What is your connector/cable from the CD player to the DCX?
• Are your power amps wide open, or have you turned down the input volume? For best gain structure they should be at 12 o'clock or lower.
• Try the digital input. You'll have to buy or make an RCA to XLR connector. Beware the level going in digital, it will be max! (turn stuff down, first)

I have tried to set the mixer to the same level as the CD input using the VU meters and yes, same problem! So it seems the attenuation of the signal through the mixer is preventing the noise, not the mixer itself.

When I had the CD player input direct I attenuated using volume pot of my integrated amp. When I plugged in the mixer i turned the amp to 12 oclock and attenuted through the mixer.

Is there a lazy mans digital RCA to XLR cable i can buy? Or maybe I should finally buy myself a soldering iron. I some times forget this is a DIY forum!

[Saurav]

I ran into what I think was digital clipping after I added a 6-channel analog volume control downstream of the DCX. Until then I was using the DCX for volume control, so the inputs would always be at around -10. Once I added the analog VC, I set all inputs and outputs to 0 (so I wouldn't 'lose bits'). The CD player has a digital connection to the DCX, and on 'hot' CD's, it would light up the yellow LEDs on the inputs (I think that's -3 or -5). Then my midrange drivers have about 8dB of EQ to handle the dipole rolloff. That's the channel that would clip the most easily, and it sounded like pops / crackling.

For me, setting the DCX's inputs to about -6dB took care of the problem. I hope I'm not losing too many bits by doing that.

Is there a lazy mans digital RCA to XLR cable i can buy?

I got some advice on this on another forum. I'm using an RCA 75 ohm digital cable from Monoprice, which goes into an RCA-BNC adapter, and then Markertek has AES/EBU - S/PDIF converters, which are BNC-XLR. You just need to pick the right male/female combinations so everything hooks up. This also takes care of the 75/110 ohm impedance issue (not sure exactly what that affects, but I've seen some people mod the DCX to accept S/PDIF).

[Xoc1]

I know you have said that the leads are securely glued down, but in my experience with the DCX 'frying bacon noise' the problem was with the 26 pin IDC header connected to the input PCB
This header is soldered in position and the cable clipped in.
If its new & faulty then try to get it replaced!
You would not be the first person to receive a faulty DCX...

Behringer Ultradrive Problems Poll - Speakerplans.com Forums - Page 1

[ttan98]

Originally Posted by panomaniac

I'm lucky, so far no frying eggs for me.

Unless you have a faulty DCX, there is no way a consumer CD player will over drive it. As noted above, just look at the VU meters.

So there are a few things to do to troubleshoot this.

• Your mixer does not cause the problem. Why? Are you running it in balanced?
• Set the mixer to unity gain. Check the VU meters on the DCX to see that they are the same as when you connect the CD player directly. Still have the problem?
• What is your connector/cable from the CD player to the DCX?
• Are your power amps wide open, or have you turned down the input volume? For best gain structure they should be at 12 o'clock or lower.
• Try the digital input. You'll have to buy or make an RCA to XLR connector. Beware the level going in digital, it will be max! (turn stuff down, first)

panomaniac is right, just use the RCA to XLR converter cable and attach it to the terminal A.

[ttan98]

panomaniac is right use RCA to XLR converter cable and plug it into terminal A on DCX. Then set DCX's terminal A to digital.

[dabbler]

Originally Posted by panomaniac

You can check them with an ohm meter. Most likely you will find that XLR pin 1&3 are tried to ground, XLR pin 2 is connected to the center of the RCA.

You might want to mute all inputs and outputs. Then unmute and check each channel 1 at a time. Use the same output cable! Is there a difference between the noise of each channel with nothing else happening? Is there any difference in noise with the channel you are testing muted or not muted?

That test will tell us a lot. Then we can proceed to others.

I'll try it tonight and report back...

[dabbler]

Originally Posted by Saurav

For me, setting the DCX's inputs to about -6dB took care of the problem. I hope I'm not losing too many bits by doing that.

How many bits does 6db equate to? And how many bits of loss would be noticable?

[dabbler]

Originally Posted by Xoc1

I know you have said that the leads are securely glued down, but in my experience with the DCX 'frying bacon noise' the problem was with the 26 pin IDC header connected to the input PCB
This header is soldered in position and the cable clipped in.
If its new & faulty then try to get it replaced!
You would not be the first person to receive a faulty DCX...

Behringer Ultradrive Problems Poll - Speakerplans.com Forums - Page 1

If it is the ribbon connector, im not sure why the noise stops when the input is attenuated. I'll play with it some more before shipping it back to behringer. I hate having to delay my project!

Originally Posted by ttan98

panomaniac is right use RCA to XLR converter cable and plug it into terminal A on DCX. Then set DCX's terminal A to digital.

Thanks, Ill pick up an RCA digital cable from Jaycar today

[dabbler]

Originally Posted by ttan98

panomaniac is right use RCA to XLR converter cable and plug it into terminal A on DCX. Then set DCX's terminal A to digital.

Actually, im confused, can I just use the RCA cable i have now and plug that into the DVD players digital output and then run the cable to the XLR adaptor in DCX input A? Then set input A to digital on the DCX software?

Does the digital out from the DVD player output video as well as audio and will this be a problem for the DCX?

Thanks for your patience everyone.

[Pano]

Originally Posted by dabbler

can I just use the RCA cable i have now and plug that into the DVD players digital output and then run the cable to the XLR adaptor in DCX input A?

Yes, you can. There "may" be better ways to do it, but this will certainly work.
There is no video on that digital signal, no worries.

When you get the time to systematically test the DCX, you want to know if you have noise when there is no music playing (no signal). Test each of the 6 outputs for noise with no signal. Test for any difference with the channel muted or not. Also with inputs muted or not. That will be 4 tests per channel:

• Input + output muted
• Input unmuted, output muted
• Input muted, output unmuted
• Input + output unmuted

Seems like a lot, but it will go really fast. Keep notes!
What we are looking for is if you have any noise that is just coming from the DCX circuitry. If it is not, then it most be signal related. That's the next step.