Buzz after replacing dbx 260 with factory processor

Harley Morgan

Harley Morgan

Member
For the last several years, the theater I work for has been using DBX Driverack 260's to power their EV XLD 281(triamp) line array systems, and subs. The racks were split house left and house right, with a separate processor in each rack. Long story short, a guest engineer came in, said the system didn't sound right, and confirmed that they had the wrong driverack settings. So, 8 months later they decided to order the recommended EV Dx 46 processors to replace the 260's.

In theory, this should be a simple swapout, load new settings, connect outputs from processor to their respective amplifiers. The system has 6 boxes a side, in two zones, top 3, bottom 3. We are also running the subs off this processor, so 4 outputs for sub, low, mid, high. Seems simple enough, and when testing each rack individually, all seems well.

When connecting "Left" to one processor at a time from the soundboard, all is well. When "Right" is connected to the second processor, I get a 60hz buzz out of both Left and Right arrays. My first thought, was that I had a bad xlr cable. Swapped both out, no change. Then I put both racks and the board on the same outlet to eliminate grounding issues between circuits, unchanged. Then I checked that all xlr cables were wired correctly, and they were.

So finally, I decided to throw the driverack back in and see what happened. Everything was fine. I put the EV processor back in, and I decided to throw a pin 1 lift on one of the processors. The buzz goes away in both arrays. My boss is content to leave pin 1 lifted on one processor and call it good. During actual setup for the summer shows, the l+r and sub lines run down 150ft of snake line, plus an additional 50 feet of xlr from snake head to the racks. With all of the sources for RF interference, I would prefer to not leave it like that, but instead find out what the true culprit is. During


Any Thought?
 
Last edited:
Hi Harley,

Off the top of my head; one thought is there is a problem with the unit from the factory. Unlikely, but possible. Have you tried swapping the L+R inputs? That would tell you if the problem is at the DSP or further upstream.

How are you splitting the L+R to each processor? Have you tried using the thru-put connections on the Dx46?
 
L+R is just coming out of their respective output from the console. Those aren't being split in any way. SOP for this system in the past was to use a xlr y-split on the input side for the subs. However, since I'm wiring this rack, I plan on changing that, and using the pass through. I haven't even tried connecting the subs to the processor yet.

Sent from my HTCONE using Tapatalk
 
Swapping inputs made no difference. I even checked all of the ICC cables just in case. No luck.

Sent from my HTCONE using Tapatalk
 
It isn't improper to to lift pin 1 at one end of the cable to solve a ground loop. I doubt that it will affect susceptibility to RF interference. The cable shield only needs a connection at one end to be effective.

One processor hums and the other doesn't simply due to differences in design and construction. This is just a normal issue when interfacing components in spread out systems.
 
Harley Morgan said:
Long story short, a guest engineer came in, said the system didn't sound right, and confirmed that they had the wrong driverack settings. So, 8 months later they decided to order the recommended EV Dx 46 processors to replace the 260's.
Click to expand...
First, what was a guest engineer doing playing in your system processors and second, how were the DriveRack settings "wrong"? No arguing you may get slightly better results with the Dx46, especially if EV provides factory presets for your system, but the DR260 has a 1X4 mode so they are capable of driving a single four way system while if you have aux fed subs it seems that one DR260 unit could be configured as a stereo three way processor with the second unit then used as a dedicated 1x1 or 1x2 subwoofer processor. So unless you were experiencing problems with the DR260 units then while they may have needed to be reconfigured and/or reprogrammed, I'm not clear on why they needed to be replaced.

Harley Morgan said:
In theory, this should be a simple swapout, load new settings, connect outputs from processor to their respective amplifiers. The system has 6 boxes a side, in two zones, top 3, bottom 3. We are also running the subs off this processor, so 4 outputs for sub, low, mid, high. Seems simple enough, and when testing each rack individually, all seems well.

When connecting "Left" to one processor at a time from the soundboard, all is well. When "Right" is connected to the second processor, I get a 60hz buzz out of both Left and Right arrays. My first thought, was that I had a bad xlr cable. Swapped both out, no change. Then I put both racks and the board on the same outlet to eliminate grounding issues between circuits, unchanged. Then I checked that all xlr cables were wired correctly, and they were.

So finally, I decided to throw the driverack back in and see what happened. Everything was fine. I put the EV processor back in, and I decided to throw a pin 1 lift on one of the processors. The buzz goes away in both arrays. My boss is content to leave pin 1 lifted on one processor and call it good. During actual setup for the summer shows, the l+r and sub lines run down 150ft of snake line, plus an additional 50 feet of xlr from snake head to the racks. With all of the sources for RF interference, I would prefer to not leave it like that, but instead find out what the true culprit is. During
Click to expand...
Both the DR 260 and Dx46 have electronically balaced inputs and outputs. And assuming that the DR260 has the factory default input and output gain jumper settings and that the Dx46 does not have the input pads engaged, both units then appear to have similar nominal and maximum input and output levels, thus system gain structure should not be a significant factor. So I see no obvious reason for there to be any difference, but that does not mean there may not be some not so obvious detail involved.

I doubt it's an issue but you might want to verify that the XLR connectors going into the DSP do not have Pin1 tied to the XLR case.

The resistance to EMI noise for the long cable runs is related to the twisted pairs, impedance balancing and differential inputs, thus that noise reduction should remain the same with or without Pin 1 lifted at one end. However, if you are worried about RF getting in at the DSP input then rather than simply lifting the cable shield at the DSP units, instead connect the cable shield to Pin 1 via a 0.01 microFarad capacitor.

Another option to break any ground loops would be to add high quality, such as Jensen or Lundahl, 1:1 isolation transformers at the DSP inputs.
 
Harley Morgan said:
L+R is just coming out of their respective output from the console. Those aren't being split in any way. SOP for this system in the past was to use a xlr y-split on the input side for the subs. However, since I'm wiring this rack, I plan on changing that, and using the pass through. I haven't even tried connecting the subs to the processor yet
Click to expand...

Ok, I am on the same page with you now.

Harley Morgan said:
Swapping inputs made no difference. I even checked all of the ICC cables just in case. No luck.
Click to expand...

Did you swap the L+R on the "Right" DSP, or at the console?

If you swap outputs on the console: Noise follows, problem is at the desk. Noise stays, problem is down stream.
If you swap inputs on the one DSP: Noise follows, problem is upstream (or in the DSP). Noise goes away, problem with the input.
If you swap inputs from one DSP to the other: Noise follows, problem is upstream. Noise stays, problem at the DSP.
 
I swapped inputs on the dsl. From input 1 to 2. And no change.

So while troubleshooting today, I connected the processor to the pc software. It told me there was a firmware update. Updated, and now the problem disappeared. So it's possible there was a firmware update that corrected the issue, but I can't confirm because EV doesn't issue release notes with the firmware.

Sent from my HTCONE using Tapatalk
 
Harley Morgan said:
I swapped inputs on the dsl. From input 1 to 2. And no change.

So while troubleshooting today, I connected the processor to the pc software. It told me there was a firmware update. Updated, and now the problem disappeared. So it's possible there was a firmware update that corrected the issue, but I can't confirm because EV doesn't issue release notes with the firmware.
Click to expand...

Glad to hear you figured it out. Out of curiosity, where both units out of date or just the one?
 
Harley Morgan said:
Museav, the guest engineer just noted it didn't sound good. Our system tech confirmed the driverack was set wrong.
Click to expand...
"Was set wrong" doesn't seem to equate to needed to be replaced. Just curious as to why you chose to replace the dbx units rather than reconfiguring and/or preprogramming them.
 
Harley Morgan said:
*TD. The dbx doesn't support FIR filters, which EV uses in their settings.
Click to expand...
To be clear, I prefer system DSP boxes that support FIR filters and am a fan of using factory presets for the actual speaker processing, however if the dbx units you had would work for the system then it seems a bit extreme to replace them solely on the basis of FIR versus IIR filters. Getting the system configured and processed properly in general will almost certainly make more difference than will the processor having FIR filters. But it's not my money and maybe there were other factors involved.

What might be interesting to know is whether the system was ever right or if somebody installed and accepted it as it was when the problems were noted.

I'll also note that the process of programming the new DSP units should involve more than simply loading the factory presets. The factory presets probably address the processing for the speakers but not the processing for the room and not necessarily for the system as installed (e.g. there may need to be some tweaking to account for the number of boxes in each array and any resulting low frequency summation). You may also have to adjust settings at your amplifiers and/or settings in the DSP to match your amplifiers, particularly if your amps are not models directly supported by the factory DSP presets. You probably know all that but I just wanted to note it as it is not really as simple as simply swapping units and loading the presets, at least not if you want to get the best results possible.
 
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