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Old 26th April 2011, 05:55 PM   #1
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Default DCX2496 & MiniDSP for Active Crossovers

In a thread on Class D amps I mentioned that I was planning to use two MiniDSPs 2x8 to allow active crossovers. This will be for our Klipschorns Left and Right and LaScala clone Center that I am converting to 2 way. Also for EQ and HPF for our Danley DTS-10 sub The MiniDSP 2 x 8s will be very expensive and since I already have a DCX2496 Jack suggested I use it with some mods.

I thought this discussion would be more on topic in this forum section, thus this new topic( hope you don't mind Jack). Here was his last post to me:

Quote:
Originally Posted by Jack Caldwell View Post
I presume you are doing this to limit subsonic excursions on the sub?

It might be worth mentioning that if you do the direct out mod on the DCX 2496, you can use smaller coupling caps on each leg of the DAC output, thereby creating a 1st order rolloff at 11Hz if you choose.

OR... use an even smaller value to create HP at 25Hz, then add in a little boost on the PEq section to bring it back up near flat at 20Hz, and voila, you have a pretty good HP filter...

No need to spend big$$ on those mini-dsp units when you've already got a diamond in the rough in the form of the DCX... just mod it, it's easy. Look up the pinouts for AKM4393, trace the DAC pinouts to where the connectors for the ribbon cables protrude from the bottom of the board, connect flying leads to the signal (+) line and signal (-) line, cut those lines on the ribbon to bypass the gazillion op-amps in the output circuitry....

Then connect coupling caps to each (both signal lines from the DAC have +2.5VDC offset) and now you have direct out lines that feed into the amps.... No prying up the smd legs on the DACs or cut traces on the board, just connect to protruding pins... see? It's easy ! no need to ship it or pay me to do it!

BTW the quality of the bass on the modded DCX is stunning.
So Jack thank you again for all your good suggestions. The output mod sounds simple enough. I have long heard that the DCX is excellent for sub duties, but not very good for full range use. What I'm getting from you is that by eliminating the output op amps the worst of the SQ problems with the DCX are eliminated. Sounds great!

Some time back I bought some boards from William DiPoala to do mods on the DCX but haven't used them. I believe they would make some excellent improvements but after getting them realized I would be soldering SMDs. Thirty years ago I would not have hesitated, but now that I'm 2 months from being 70 my thumbs seem to have gotten huge and my eyesight is a long way from being what it used to. So these boards have just sat and when the MiniDSPs became available I thought they might be a good way to go.

Since I already have a DCX2496 here's what I'm now thinking.

1. Do the output mods to my DCX as Jack suggested which will eliminate the Behringer op amps.

2. Use the DCX 3 inputs for L,C & R. This will use all 6 outputs for our two ways.

3. Buy a MiniDSP 2 x 4 in a box for our sub EQ and HPF.

If this works it will save a lot of money over two MiniDSP 2 x 8s, as well as the work of putting them in cases.

Any other thoughts on this approach will be greatly appreciated.

Thanks,
Rod
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Old 26th April 2011, 06:01 PM   #2
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Having modded DCX's both passive and active, I can tell you that you don't have to trace and fly wires etc. All connections are brought out directly to the connector for the cable that goes from the DSP board to the analog out board. Unplug that cable, put in your own cable and presto! Pin numbers on plugs and schematics can be found on the Yahoo DCX forum.

Anyway, I don't understand why you want to use miniDSP WITH the DCX? The DCX already has a capable DSP and the user interface is really neat.

jan didden
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Old 26th April 2011, 06:19 PM   #3
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Wow what a fast response! Thanks very much jan.

With all three inputs, and six outputs being used for my L, C & R, the DCX can't handle the sub. Thus the MiniDSP. And in a case the 2x4 is only $150.

My source all comes from a HTPC with a Asus Essence ST & H6 daughter board sound card. I'm using it in a 5.1 system. The plan is that the the L, C & R outputs will go to the DCX. The LFE (sub) output will go to the MiniDSP. The outputs from the DCX will go to individual Class D amps (probably HiFiMeDIY T1s or T2s) and the Mini DSP sub output will go to my existing Behringer EP4000 amp.

So jan your way of bypassing the output op amps sounds easy. I will look things up on the Yahoo DCX Forum.

Re the DCX user interface, I find the computer software easy to use, but the DCX front panel feels very unintuitive to me. Guess I have some kind of block there.

Thanks again for your help.

Cheers,
Rod
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Old 26th April 2011, 06:46 PM   #4
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Default Yahoo DCX forum

Quote:
Originally Posted by janneman View Post
Having modded DCX's both passive and active, I can tell you that you don't have to trace and fly wires etc. All connections are brought out directly to the connector for the cable that goes from the DSP board to the analog out board. Unplug that cable, put in your own cable and presto! Pin numbers on plugs and schematics can be found on the Yahoo DCX forum.

jan didden
Hi Jan, thanks for the heads up. In the case of the DEQ2496 I've wanted to keep the functionality the same as the stock unit, except for the analog outputs.... so, for the simplest mods I've preferred to run the flying leads rather than disconnecting the ribbon.

I'm taking the same approach on the DCX as in the case of the simplest mods I would not want to lose the digital input and other connectivity and pulling the ribbon connectors would have that effect, wouldn't it?
For a more ambitious mod then yes, replace the connectors board and upgrade the PS and the clock and so on, but that's a lot more involved and costly.

BTW, I'd really like to look at the YahooDCX forum you referred to, but for some reason am having trouble finding it!... would you post a link to it?

Thanks for your great contributions to these forums!
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Old 26th April 2011, 07:08 PM   #5
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Quote:
Originally Posted by nwboater View Post
[snip]With all three inputs, and six outputs being used for my L, C & R, the DCX can't handle the sub. [snip]Rod
I'm probably missing something, but to me L, R & C are three output channels....?

Edit: got it, you're going 2-way active.

jan
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Old 26th April 2011, 10:55 PM   #6
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Quote:
Originally Posted by Jack Caldwell View Post
BTW, I'd really like to look at the YahooDCX forum you referred to, but for some reason am having trouble finding it!... would you post a link to it?
Here's the link to the Yahoo Group. Haven't looked through it yet, but wanted to get this link here first.

Cheers,
Rod
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Old 27th April 2011, 02:21 AM   #7
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Default Link didn't show on post

Can U retry?
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Old 27th April 2011, 02:39 AM   #8
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Quote:
Originally Posted by Jack Caldwell View Post
Can U retry?
Sorry about that! Let's try again.

DCX2496 : DCX2496


Cheers,
Rod
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Old 27th April 2011, 08:40 PM   #9
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I spent some time on the Yahoo board looking at DCX2496 mods. Jan Didden has done a lot there including extensive articles.

At this point I'm into keeping it as simple as possible. I would like to try just bypassing all the output junk and just go straight from the DAC to RCA single ended.

Jans approach apparently does some high freq (20k and above?) filtering while others don't seem to think this is necessary.

So it looks like the very simplest is to somehow disconnect the output from the DAC to the rest of the stuff and connect it to a coupling cap. Use the sig gnd on the XLR output connectors as the new RCA sig gnd.

This all brings up a few questions:

1. What's the best way to get to the DAC output?
A. Cut the ribbon cable and tack onto the ends that go to the DAC?
B. Make and install a new ribbon cable?
1) Does this eliminate some functions of the DCX that are needed?
C. Cut the output leads on the DAC chip and fold them up. Then solder the new output wires to them?

2. Do we need any kind of output filtering?

3. What values for the output caps? In my case I will probably be feeding amps with 50k input impedance.

4. What type of caps.

I'm sure there will be more questions but hopefully this will get some discussion going.

Thanks,
Rod
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Old 27th April 2011, 09:26 PM   #10
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There is a 2.5Vdc bias on the DAC o/p pins so you'll need to decouple that at the very minimum.

Why you are going 2 way on the Klipsch baffles me (I've owned both). Just buy another DCX, use one for L/R 3 way and one for C 3 way and you'll still have the capability of 3 discrete subs.
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