BillFitzmaurice.info

I'm finding that the outputs on the DCX2496 are a little too hot for my amps, and I can't set the limiter low enough (-24db maximum available).

(This didn't show when bench testing with no load connected, which seemed to indicate that -17db limiter would not allow over voltage even under max input)


I seem to remember an earlier post detailing how to install resistors to attenuate the outputs ofthe DCX.


After a couple of hours of looking I can't seem to locate the relevant post. I would greatly appreciate if someone could redirect me to to the post in question.

Thanks

These will do the trick and are cheap enough.

http://www.parts-express.com/pe/showdet ... er=240-412

Thanks Brent, thats an option for sure, although I'd still prefer to mod the DCX as it seems like this will be an ongoing issue with all channels, I try to avoid adapters, I don't mind soldering, and resistors are even cheaper, especially when factoring in freight to NZ.

So if anyone knows the whereabouts of this post I'm all ears...

Boyd wrote: I'd still prefer to mod the DCX

This seems like using a cannon to kill a fly....

Have you really exhausted all avenues to lower the gain in the software? I don't use that unit, but driveracks have an internal gain adjustment for tops and subs - I would have to believe that unit does too.

What amps are you using?

Bruce Weldy wrote:

Boyd wrote: I'd still prefer to mod the DCX

This seems like using a cannon to kill a fly....

Have you really exhausted all avenues to lower the gain in the software? I don't use that unit, but driveracks have an internal gain adjustment for tops and subs - I would have to believe that unit does too.

What amps are you using?

+1. I'm certain there is a gain adjustment.

Boyd wrote:Thanks Brent, thats an option for sure, although I'd still prefer to mod the DCX as it seems like this will be an ongoing issue with all channels, I try to avoid adapters, I don't mind soldering, and resistors are even cheaper, especially when factoring in freight to NZ.

So if anyone knows the whereabouts of this post I'm all ears...

I don't think its as simple as you think it is. To lower voltage by a set account, you have to know and calculate the impedance if the load. Pre-made pads do this for you with transformers. you could build the same thing, but it would probably end up costing just as much if not more.

 

As I see it, gain structure is not the issue. As the limiter is the last process in the signal chain, reducing gain would only change the input level required to engage the limiter, not reduce the limited output level.

Input levels are very low when limiting engages, so I'm not getting the most out of the A/D converters either (bit resolution is better when closer max input). I don't have any gain structure issues with these amps and other processing equipment, and 50V is right on the max the amp will output before clipping, so such low limiter settings shouldn't be required.

Reducing the output voltage will allow more practical limiter settings and better gain structure that utilises the A/D converters while levels on the mixer are where they should be.

The OP of the post I'm looking for realised this also, and posted the mod for a good reason.

I see it more like using a few resistors to fix a behringer design flaw...

BrentEvans wrote:I don't think its as simple as you think it is. To lower voltage by a set account, you have to know and calculate the impedance if the load. Pre-made pads do this for you with transformers. you could build the same thing, but it would probably end up costing just as much if not more.

I find it hard to imagine a transformer fitting in that adapter? And AIUI XLR connections should conform to a standard impeadance?

If someone can find the original post (please), it might help to clear things up....

Doing this mobile, forgive the lack of quotes.

Boyd,

They're really small transformers. I've taken one apart before.

The problem is one of gain structure, namely that that your amp is way too big. Have you considered down sizing to a more appropriate amp? if you're having to limit down that much, its not the dsps fault. the dcx runs to either +22db or +24db, which is fairly standard. There is no design flaw to correct.

Another way to fix this is to just torn the amps down. as long as you secure the app gain controls mechanically, like with a piece v of gaff tape or a tamper panel, the effect will be the same.

Boyd wrote:As I see it, gain structure is not the issue.

Maybe I'm not getting this, but if the internal gains are jacked up before the limiter that would cause what your seeing - wouldn't it?

Have you looked at the internal gains to make sure they aren't pegged?

Bruce Weldy wrote:

Boyd wrote:As I see it, gain structure is not the issue.

Maybe I'm not getting this, but if the internal gains are jacked up before the limiter that would cause what your seeing - wouldn't it?

Have you looked at the internal gains to make sure they aren't pegged?

i think his problem is that even with the limiter at max attenuation, his amps still have too much output. since the limiter is the last thing in line before the amps, that's a problem.

BrentEvans wrote:

Bruce Weldy wrote:

Boyd wrote:As I see it, gain structure is not the issue.

Maybe I'm not getting this, but if the internal gains are jacked up before the limiter that would cause what your seeing - wouldn't it?

Have you looked at the internal gains to make sure they aren't pegged?

i think his problem is that even with the limiter at max attenuation, his amps still have too much output. since the limiter is the last thing in line before the amps, that's a problem.

hmmmmm......something just doesn't sound right. Maybe something ain't kosher with the amp.

It takes a transformer with a pretty healthy sized core to handle line levels >+20db, especially low frequencies. You won't fit a core like that into an XLR shell. Bear in mind you will pay a considerable amount of money for a transformer of any quality, like a Jensen or Lundahl.

If you're talking small core transformers, these are made for mic level applications.

BrentEvans wrote:I think his problem is that even with the limiter at max attenuation, his amps still have too much output. since the limiter is the last thing in line before the amps, that's a problem.

Thats exactly my situation (although I would say the amps have too much input). I'm reluctant to blame the amp as I've used it plenty before with other equipment, and both my top and sub amps are getting an equally hot signal. There is no gain added that I'm aware of, the summing mixer stage has -3db on both A & B inputs, which I figure should give an equal level sum in much the same way as a L.R. crossover (and a couple of db less again on the sum output to bring the higher sensitivity subs in to line with the tops). Eq is mostly subtractive, any boost is less than +3db.

The amp is only just enough, so it's not a case of too big of an amp.

It simply seems like the signals coming out of the DCX are hotter than the input, or what is shown on the DCX output meters.



EDIT: should read -6db on summing mixer A & B inputs for equal level sum - typo.

what amp are we talking about?