# DCX2496 modifications



## kflory

I am wondering if anyone here has modified their DCX2496 and has any stories or feedback they can share.

There are lots of mods floating around the internet, and some that will do the mods for you (at quite a price).

I use my DCX2496 as an active crossover for my system, but it is audibly noisy (granted need to put my ear to my mid range to hear it, but the fact I hear any hiss at all is bothersome).

Things I am considering:

- Replacing/redesigning the I/O board. The stock I/O board is intended for PA equipment and the line levels are not matched well for consumer equipment and could be a much simpler design (and use better op amps). There are a few on the market, but they do not quite fit my need (as I want to keep the analog in and PC interface), but would love to just buy a board and drop it in. 

- Update/replace the clock

- Update/replace the power supply (there are a few on the market).

- Update the DACS/ADCs to the later AKM devices (AKM5393 to AKM5394A, and AKM4393 to AKM4396)

Thanks in advance for your thoughts and comments.


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## bambino

I have not heard of any mods for the unit, i would be interested hearing and knowing about them as i own one but have not used it yet. I'll have to Google it and see what comes up.:T


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## kflory

Here are a few of the ones I am referring to:

http://www.dcx2496.fr/en/index_en.php
http://www.linearaudio.nl/Documents/dcx passive article.pdf
http://www.pilghamaudio.com/index.php?page=dcx-passive-upg
http://www.tweakaudio.com/EVS-2/Behringer_DCX2496_mods.html
http://www.referenceaudiomods.com/M...nger_2496&Category_Code=MODS&Product_Count=28

Added the following after original post:
http://www.asi-tek.com/behringer2.html


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## bambino

All good reads, thank you.:T


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## Wayne A. Pflughaupt

There are a couple of guys at the AVS Forum who have butted heads on the DCX2496 noise issue; one is adamant that it is dead silent, the other had the noise issue you’ve noted. I suspect that perhaps it is a gain structure issue (i.e. levels not properly set on the various pieces of gear downstream from the AVR), or that there may be some variance between DCX units – like maybe it was better in some years than in others. This certainly seems possible, since Behringer has noted that they often had QC problems with their Chinese vendors before they opened their own factory in China.

Pro audio or not, the DCX should at least be able to pass a signal straight through without adding any noise. There’s a crude but easy-to-accomplish test in Part 8 of my gain structure article to determine if a piece of gear adds noise. Basically, with all gain controls set for flat, no properly designed piece of equipment should add noise, or at least not enough to matter.

The extensive work you’re considering, what is it going to cost? Seems like a lot of trouble and expense when you could simply get a different processor, especially if you consider the used market. Perhaps from a different manufacturer - the DCX is a fairly mature product; there is no shortage of legacy processors from other companies that can be had for a faction of their original prices.

Regards,
Wayne


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## kflory

Thanks for the comments Wayne!



Wayne A. Pflughaupt said:


> There are a couple of guys at the AVS Forum who have butted heads on the DCX2496 noise issue; one is adamant that it is dead silent, the other had the noise issue you’ve noted. I suspect that perhaps it is a gain structure issue (i.e. levels not properly set on the various pieces of gear downstream from the AVR), or that there may be some variance between DCX units – like maybe it was better in some years than in others. This certainly seems possible, since Behringer has noted that they often had QC problems with their Chinese vendors before they opened their own factory in China.


Certainly possible. My unit has boards that are rev H, and the schematics I have are for rev E. Not that I have found the differences yet, but does support the fact that not all units are the same.



Wayne A. Pflughaupt said:


> Pro audio or not, the DCX should at least be able to pass a signal straight through without adding any noise. There’s a crude but easy-to-accomplish test in Part 8 of my gain structure article to determine if a piece of gear adds noise. Basically, with all gain controls set for flat, no properly designed piece of equipment should add noise, or at least not enough to matter.


Good suggestion . It has been a while since I read it, so was definitely worth re-reading. 

I did re-do my experiments and bypassed the DCX2496 on one channel. When I did this the first time, I just disconnected the input to the amp to compare (and the amp alone was dead quiet). When I did it this time, I found that the noise from the DCX is comparable to the preamp.



Wayne A. Pflughaupt said:


> The extensive work you’re considering, what is it going to cost? Seems like a lot of trouble and expense when you could simply get a different processor, especially if you consider the used market. Perhaps from a different manufacturer - the DCX is a fairly mature product; there is no shortage of legacy processors from other companies that can be had for a faction of their original prices.


Some of these guys will charge as much ~$2500, more that I am willing to pay (also seems like over kill to me). 

Assuming I did it all and I did it myself:
- Replacing/redesigning the I/O board (assuming I fab my own):
~$350 ($220 to fab PCB, + parts)​
- Update/replace the clock
~$150​
- Update/replace the power supply (there are a few on the market).
~$200​
- Update the DACS/ADCs to the later AKM devices (AKM5393 to AKM5394A, and AKM4393 to AKM4396)
~$40​
So I could see it costing on the order of $750-$1000. With that said, I am not sold on the mods and why I was pinging folks here to get their take. 

The I/O change due the the signal level difference is the most interesting to me, but re-reading your article on gain structure along with the experiment above has convinced me the even that is mute at least from the signal level point of view.

Also certainly open to recommendations of other devices to consider, but also not so bad that I feel it have to make a change. More so curious what other have done.


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## jtalden

Kevin,
You seemed originally to be looking for reinforcement to justify some expensive DCX mods. There are lots of rave reports out there of improved sonic performance for these. I’m just a hobbyist and I have no experience with any of these, but am very skeptical that most of these really provide significant benefits. I must also say that I don’t think that most of the mods you listed will have any significant impact on your noise issue in particular. Personal opinions aside, I mostly just wanted to jump in to reinforce the suggestion that you first exhaust your options with the stock unit. 

I have 2 stock DCX units in my setup and do not have a noise issue. I did notice some elevated noise initially, but that is not surprising as I have unbalanced P-amps so the DCX was running a very low signal level relative to its design level. I adjusted the gain structure by reducing the input sensitivity of the P-amps by 12 dB. This increased the signal through the DCX by 12 dB and has the effect of reducing the DCX effective noise floor by 12 dB. The DCX now adds about the same additional noise as any other piece of unbalanced AV gear. [The higher the efficiency of the speakers and the larger the P-Amp the higher the noise issue will be however. I am not surprised when those with 112 dB sensitivity pro horns and 500 W amps have trouble in small rooms at close distances. That would be tough to throttle back. Your situation would seem to be closer to mine and should be manageable.]

I see your pre/pro and P-amp have balanced I/O's. Are your using XLR interconnects and still having this issue? That approach should provide a consistent signal level for the 3 units and I would think it should be pretty quiet. If you are using unbalanced interconnects for the P-amp as I am then the problem should be more like mine. In my current setup (with the adjustments) I have occasional peaks that light the 3rd level I/O indicators (-10 dB). Even if you only get the second level I/O indicators to occasionally light, I would expect the DCX noise floor to be acceptably low assuming typical room size and LP distances.

Of course if it is hum rather than noise floor that you are hearing then that’s a different issue entirely.


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## kflory

Thanks for the reply.

Yes, I am using the balanced inputs/output.

The noise was kind of tangential to the mods. It just got me thinking about them again when I came across it.

I had seen the mods floating and around and have been contemplation them. The noise issue is really more bothersome that I know it is there, and got me re-considering the mods wondering if they may make a differencefor the noise (new i/o board?, power supply?), but as I mentioned, I have to put my ear right up to the speaker to hear it at all. (I mean right up the midrange). 

I initially thought this was exclusively the DCX, but Wayne comments got me to re-do the experiment, but by by-passing the DCX (vs. disconnecting the amp and pre-amp), where I found the noise is on par with the receiver.

I did listed for this when (with the pre-amp/amp) when I first got it a couple of years ago and did not recall hearing any hiss (maybe I just missed it), as my Adcom system was dead quite in this regard and I wanted to compare them, so was surprised when I heard any this time around. 

To give yo guys some more background, the only reason I noticed it at all is I was using new test record my wife got me for Christmas and was listening for noise from the turntable. Had I not been going through that (and putting my ear to the speaker), I would not have noticed it. So it was only bother some that I heard some (any) hiss, not that it is pervasive for normal listening (background noise far outweighs it). 

Thanks for all the comments guys.


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## tnbubba

simple jrc 4850 op amps x 24 plus shitty design = noise.. if yo wan tot know about mods i been working on these thing for 6 yrs and i can tell you all you want to. i posted soem general on another thread here.. somewhere


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