DCX2496 Mods

mgalusha · « **on:** 24 Nov 2007, 02:44 am »

I had a chance yesterday to finish building and installing the Jan Didden active output kit for the DCX2496. For those not familiar with this kit, it replaces the entire input and output board in the DCX and provides an analog level control which allows the DCX to function as a preamp in addition to a crossover. More information can be found on Jan's site - www.linearaudio.nl

In addition to the board I put in some RG-179 coax and a BNC jack in place of the ribbon cable and XLR jack. I also changed the termination resistor from 110 ohm to 75 ohm.

As for the sound, I have a stock DCX here as well and the difference is not subtle. Much more transparency and information coming through. The overall impression is one of accuracy. Of course I have no way to verify this other than it seems to lay the recording bare. If the recording is warm, the sound is warm. If the recording is bright, the sound is bright. The modified unit doesn't seem to editorialize the sound much if any. When comparing the stock to the modified unit I used the same settings and of course all cables were the same. Switching back to the stock unit, pianos lost their body, voices were recessed and it the overall sound was a large step back, very much like listening through a blanket.

When I first got it up and running I wasn't happy with the top end, it was fuzzy and smeared, not as clean as I was hoping for. That was when I decided to update the digital input and change it from 110 ohm to 75 ohm. The changes removed the issues I had with the treble. It became clear and delicate with cymbals and triangles very clear and just floating.

Anyway, here are a few pictures.

The original card slot is now home to the IR receiver and display

Input C has been replaced with the BNC jack and you can see the ribbon cable assemblies

The RJ-11 jacks for the serial ports are gone and you can see where the BNC lives. Otherwise it looks stock

cryotweaks · « **Reply #1 on:** 24 Nov 2007, 03:04 am »

Nice work Mike. I would love to hear this with the Emerald Physics loudspeakers.

zybar · « **Reply #2 on:** 24 Nov 2007, 03:10 am »

Looks super Mike.

George

JohnR · « **Reply #3 on:** 24 Nov 2007, 03:26 am »

Do you buy the kit from Pilgham audio? Seems like a great deal!

mgalusha · « **Reply #4 on:** 24 Nov 2007, 02:04 pm »

Quote from: JohnR on 24 Nov 2007, 03:26 am

Do you buy the kit from Pilgham audio? Seems like a great deal!

John,

I did buy this from Pilgham Audio. It took some time to arrange payment but once shipped it arrived quickly. The kit is not cheap but very complete.

mgalusha · « **Reply #5 on:** 24 Nov 2007, 02:06 pm »

Quote from: cryotweaks on 24 Nov 2007, 03:04 am

Nice work Mike. I would love to hear this with the Emerald Physics loudspeakers.

Maybe I could bring it by. We'd have to load the Emerald Physics settings but that is easy if we use a PC to back up yours and reload it to mine.

Perhaps tomorrow? Give me a call if you like.

Mike

richidoo · « **Reply #6 on:** 24 Nov 2007, 02:13 pm »

Nice job Mike. I want one too.

Thanks for the pics.
Rich

TomS · « **Reply #7 on:** 24 Nov 2007, 02:25 pm »

Mike,

I noticed in Jan's original document he used some RCA's at the outputs temporarily and mentioned that later he installed the XLR's. Since very few of us will actually use the balanced XLR outputs, do you think it's a simple matter to just substitute RCA's (electrically and mechanically in terms of fit) on the pcb and rear panel? That way we can just avoid the XLR-RCA adapters altogether.

BTW - it looks great. Very nice to have someone who knows what they're doing blaze the trail

Tom

mgalusha · « **Reply #8 on:** 24 Nov 2007, 07:51 pm »

Tom,

I believe Jan redesigned the board to accept XLR jacks so it would be a drop in replacement. It would be no trouble to wire standard RCA jacks to the pcb, you would of course need to cut a mounting plate but that will be the easy part. Just mount the jacks to a plate and run short wires from the PCB to the jacks.

The majority of the kit runs single ended anyhow, so by going to an SE out you only lose the ability to run balanced cables.

scorpion · « **Reply #9 on:** 27 Nov 2007, 07:04 pm »

Mike,

This is a kit that I also am very interested in, having an unmodded DCX. I can see that you are an experienced builder, how difficult is this kit to build ?
What is your opinion of the preamp- and especially the volume-control functions ?

/Erling

mgalusha · « **Reply #10 on:** 27 Nov 2007, 09:39 pm »

Erling,

The volume control works very well, 1dB steps and silent when changing volume thanks to the zero crossing detector in the CS3318 chip. It's not terribly difficult to build but heed Jan's advice, take your time, work slowly. There are a lot of parts, something like 74 resistors and about 30 caps and of course they all look very much alike, so if in doubt, measure. The cables are not difficult to build but you definitely need to pay attention. If they are wrong, particularly the power and display/logic cables, magic smoke is a distinct possibility.

Mounting the display/logic PCB in the front panel is an exercise in patience, small area, not a lot of room. Same story, take your time and don't rush it and easy on the glue.

The Hi and Lo output adjustments work great allowing amps with different gain factors to be used with no problem.

This might not be the best kit if you have no experience but it can be done with some care. There are two op amps that are surface mount, so care must be taken when mounting those. All other components are through hole except for the CS3318 chip, which, thankfully, comes pre-mounted.

Mike

janneman · « **Reply #11 on:** 28 Nov 2007, 08:48 am »

Hi,

As Mike noted, I had initially done this with RCA's but after a lot of comments decided to go for the XLRs. There is also the issue of mechanical mounting: with the XLRs, the whole PCB becomes a drop-in replacement with mounting using the original screws.
To use RCAs you would need to make a small aluminum strip for the jacks. Not difficult, all holes are 1 inch apart; I did it by holding the alu strip against the back panel, marking the position of the holes and then marking the main holes as exactly between two mounting holes. But it is not easy to mount the PCB to the RCAs mechanically (wiring is simple of course). There are no separate mounting holes on the PCB, so you're on your own there.
If you don't want to use XLR>RCA adapters, you can also fabricate your own XLR>RCA cables as shown on my web site.

Note: I wanted to insert a pic with some of those details, but being new on this forum I don't know how to. Clicking 'insert image' only inserted the tags. If someone tells me how to do it I'll do that.

Jan Didden

Gordy · « **Reply #12 on:** 28 Nov 2007, 10:49 am »

Jan,

If your image is already on the web, click right and from the menu click on "Copy Image Location". Now, in your post, paste the image location between the image tabs. If that doesn't work for you try this thread , especially Papajin's post!

janneman · « **Reply #13 on:** 28 Nov 2007, 11:05 am »

See if this works....

Edit: yes, looks like it.

Jan

TomS · « **Reply #14 on:** 28 Nov 2007, 12:49 pm »

Jan,

By the way, just wanted to say WELCOME to AudioCircle! I will probably order the DCX output board soon and hope you'll provide more insight here as members move forward with their various DCX mods. Don't be shy.

Tom

janneman · « **Reply #15 on:** 28 Nov 2007, 12:57 pm »

Thanks Tom!

I'll try to contribute as best I can. Audio has been my hobby for as long as I can remember (and let me tell you, that's LONG!). Too many audio hobbyist are closet hobbyists, and thanks to forums like this, we can interact and be part of a worldwide family. I always get a lot of stimulation and ideas from other people, even from seemingly unrelated comments. That's very valuable!

Jan Didden

TomS · « **Reply #16 on:** 28 Nov 2007, 01:03 pm »

Jan,

I've been around awhile the DIY hobby myself, back to the original Audio Amateur days. I worked on several of Walt Jung's regulator board layouts for him long ago and remember working through the painstaking parts selection he did for those old Dyna PAT5 based preamps

That was at a time when all parts sounded the same

You had some great collaboration there as I recall, having re-used those regulators a few times myself.

Tom

janneman · « **Reply #17 on:** 28 Nov 2007, 01:13 pm »

Ahh! You're THAT Tom, yes I remember Walt mentioning you a few times when we worked on those regs. Small world.
That reg project was indeed quite fun to do, and generated a lot of interest. I never got around to update those pcb's, but nowadays people use those regs preceding them with a prereg (often based on LM317-type regs). I think you get into diminishing returns then, although to be fair I never measured those combined regs.

Jan

TomS · « **Reply #18 on:** 28 Nov 2007, 01:20 pm »

Yep, that's me. Haven't spent much time with circuits the past few years, as I moved into IT long ago. I am starting to DIY a few things though, having recently built up a DDDAC. Not quite there, but it's close. The DCX is next

This is a great community here and I hope you'll find it has a lot to offer.

Tom

mgalusha · « **Reply #19 on:** 9 Dec 2007, 12:19 am »

Just an update, my DCX has a couple of weeks of playing time on it now and even though I despise the thought it seems to have improved as time has passed. I was missing a sense of harmonic richness at first even though there was tons of information coming through but I seem to have plenty of that now. I suppose I could be breaking it but I've had the rest of my components long enough to know what they sound like and I'm fairly sure the DCX has changed some over the past few weeks.

I'll be comparing it to a stock unit tomorrow driving the Emerald Physics CS2's, should be very interesting.