Behringer DCX2496 digital X-over - Page 294 - diyAudio
Go Back   Home > Forums > Source & Line > Digital Line Level

Digital Line Level DACs, Digital Crossovers, Equalizers, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 19th January 2011, 01:47 PM   #2931
diyAudio Member
 
linuxworks's Avatar
 
Join Date: Jul 2008
Location: santa clara, CA
I guess noise is relative, then. I'm using fairly low noise equipment whenever I can and often the preamp and dac stages end up in a headphone amp and if there is noise or flaws in the chain, you'll hear it.

perhaps I was not fair in how I tested the avr; but I set its volume control to 0db hoping it would minimize any preamp stages. it allows you to go in the positive gain direction (up to 20 or 30) and its super noisy then, but even 0 gives hiss in my spkrs when I get right next to them. all my other gear does not (hafler dh200, some diy amps, even the lm3886 chipamp). the 2 yamahas (5.1 systems from about 5-8 yrs ago) are acceptable at -20db or so (on their display) but beyond that, they get very noisy very fast.

and again, its relative. that older yamaha is still quiter than a lot of the music that gets/got released by so-called pros. you can still hear noise levels in material so the equipment is not *that* bad for playback; its just that those all-in-1 boxes don't concentrate on low-noise on their pre sections. my sample size is 2 yamahas that were a few model years apart but I can't believe that this is unique. not to mention that the avr buying audience would not know real hifi, generally (they are buying a convenience box and not a serious audio system).
__________________
My Photostream:http://www.flickr.com/photos/linux-works/
  Reply With Quote
Old 19th January 2011, 01:54 PM   #2932
diyAudio Member
 
linuxworks's Avatar
 
Join Date: Jul 2008
Location: santa clara, CA
Quote:
Originally Posted by janneman View Post
I would agree; while there are always cases like that, it certainly is not common. Maybe the 'noisy' case was with lower-than-usual input signal.

jan didden

nope, not in this case. I could feed things hot or not (lol) and its because I was doing relative comparisons that I concluded the avr chain was too noisy to be useful (again, I wanted it as a simple 2ch amp, feeding in a 2v analog signal from a decent dac).

at the time I was fighting some hum problems on my hafler (physical trafo hum). I loved the hafler sound but the trafo could be heard across the room when it was very quiet (at night, say). I had a couple of yamaha avr's from a few years ago and I toyed with the idea of just using it as a 'headless' 2ch amp, leaving its vol at 0 and treating it as a slaved amp. it solved the trafo hum alright (no phys chassis noise) but the hiss level was now the problem. even in their 'pure direct' mode (bypasses tone and other crud in the path, in theory at least) there was noticeable noise.

I'm now using some diy chip-amps and while they don't have the drive of the hafler, they have none of its trafo hum; and there's nearly no hiss (lower than all my other spkr amps) from the chipamp. this means (getting back to your comment) that its not my source or dac or signal levels. it really was that the yamaha kind of sucked on its pre- stage and its not really defeatable by setting the vol control to 0. you always go thru it.
__________________
My Photostream:http://www.flickr.com/photos/linux-works/
  Reply With Quote
Old 26th January 2011, 05:00 PM   #2933
diyAudio Member
 
MikeHunt79's Avatar
 
Join Date: Aug 2003
Location: Bristol, UK
Default Direct out mod with AK4396

Hi, I'm looking to do replace the AK4393's with AK4396's, then do the direct out mod, using a single cap on each channel to block DC in the signal.

I've got all the parts I need I think, but I've got few questions about the direct out mod before I start soldering... I plan to DAC swap first, then test the unit then go for the direct out mod.

I've only seen a few pictures of completed but I've also seen the schematics so I know that I can use the AOUT signals straight from the ribbon cable from the DSP board.

Now, I've seen a photo a direct out modded DCX on the Yahoo group which has had the direct out mod here:
Click the image to open in full size.
And it appears that the signal is going directly to the legs of the XLR pins on the original IO board. Now if I do the same thing, so I need to cut the legs of the IO board in order to stop the signal going into the IO board? Or would removing some components on the IO board (resistors?) be a better option in order to stop the signal reaching the op-amps on the IO board. Or am I worrying over nothing here?

Finally am I right in assuming the it's best to also get AGND from the ribbon cable also?

Thanks
  Reply With Quote
Old 26th January 2011, 06:41 PM   #2934
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Not sure if this is important but the pic above is not from a DCX.

jan didden
__________________
If you don't change your beliefs, your life will be like this forever. Is that good news? - W. S. Maugham
Check out Linear Audio!
  Reply With Quote
Old 26th January 2011, 06:42 PM   #2935
sendler is offline sendler  United States
diyAudio Member
 
Join Date: Aug 2004
Location: ny
Default Direct out mod

The direct out mod for the DCX2496 eliminates all of the circuitry after the dac chip, taking the analog output straight out of the chip through a stack of foil coupling caps to the xlr pins. I have tried many different active outputs with opamps and none can compare to the transparency of running direct as has also been discussed regarding the CS4398 dac chips here. Jensen JT-11-EMCF transformers also sound excellent but get expensive when six are needed for a DCX.
.
Experience with this DIY DAC ?
.
The ribbon wires between the digital and output boards are cut to get the audio signal before being polluted by any cheap coupling caps,balanced to single ended conversions, active filters and single ended back to balanced conversions with servo shifting output. This eliminates a series of 4 opamps and countless capacitors and resistors which yields unbelievable sonics with a slight loss of gain. If you want to try it yourself, the wires that you need starting from the red are 3-14 for the outputs from 6- to 1+ in that order. Note that counting from the red is the opposite to the way the wires are numbered on the schematic. The Dayton foil caps were chosen in listening tests over several other popular film type caps. In general I can safely say after trying tens of different high end caps that were recommended to me, that a good foil cap will sound much better than any poly film cap in a critical application such as this. The AudioCap Theta or ridiculously over priced boutique types such as the MIT should also give good sonics but the Daytons maintain a price performance advantage of 500% over the next reasonably priced contender, the Thetas. There is limited empty space under the hood of the 2496 Behringers so the maximum amount of capacitance is limited to what will fit which is 4uf, 3uf, 1uf for low, mid, high in the DCX and 4uf in the DEQ. The output pins are cut where they come up from the board in order to accept the signal wires from the caps and remove the connection to the stock output. Only bend the cut pins on the board side to create the open space. If you bend the output pin side it will snap off way up into the plastic of the output connector. I like the paired strands of the 1701a for hook up wire. I run these in a 8 foot length for my interconnects. They sound great and have replaced my Nordost Interconnects so the 1701a should make a nice hook up wire. The 4395 dac chip is my preference along with a dedicated voltage regulator. Or, you can use an AK4396
which will drop right in with no other mods. Beware! The legs of these chips are tiny and difficult to solder without bridges forming. Use plenty of flux to keep the solder flowing where it belongs. Also, the chips are very fragile to heat. Use the minimum amount of time on each leg and count to ten before proceding to the next leg or use a very quick drag soldering technique. Your chances of getting three out of three working when you are done is pretty slim on your first try. It would be worth $100 of frustration to take the board and chips to a tech and let them do the swap. It is also easy to lift a trace from the board and digital boards are not available as a separate part. Don't cut pin 1. Just leave it as it is for the output ground.
.

Quote:
Originally Posted by MikeHunt79 View Post
Hi, I'm looking to do replace the AK4393's with AK4396's, then do the direct out mod, using a single cap on each channel to block DC in the signal.
__________________
Scott
  Reply With Quote
Old 26th January 2011, 08:00 PM   #2936
sek is offline sek  Germany
diyAudio Member
 
sek's Avatar
 
Join Date: May 2003
Location: Berlin
I would advise to do like in the pictured mod and replace the original ribbon cable. It looks harder to begin with, but it will likely turn out to be the most clean and tidy way.

I'd then pick any signals (AOUT+ and AGND) directly from that new and very own ribbon connector, customizing it as needed.

As Jannemann correctly noted, it's a DEQ, but nevertheless.

An alternative way would be to sacrifice the original ribbon and cut the required wires just before the I/O-Board connector in order to pull the strands off the ribbon (pair wise, ideally). You'll then have the selected output channel signals available while maintaining the original input functionality. Don't forget to also cut the (probably unused, but still connected) noninverting signal lines (AOUT-). As a bonus, short the now open inputs to the opamps, too. Takes care of any possible oscillation-induced noise.

Last edited by sek; 26th January 2011 at 08:06 PM.
  Reply With Quote
Old 26th January 2011, 10:29 PM   #2937
AR2 is offline AR2  United States
Master Burner
 
AR2's Avatar
 
Join Date: Dec 2002
Location: San Francisco, California
I will join the chorus - do it at the ribbon cable and ideally use this opportunity to replace this with your own. Be careful in counting pins/wires as it is easy to make a mistake. The other option is taking out first set of resistors where signal comes on I/O board and running thin wires from there but I really would not recommend this as it is very fragile. In any case you do not want to have any signal to go toward original output circuitry - op amps, so ether method will work for that - cutting ribbon cable or lifting resistors.

When you change DACs here is what you will need:

In ideal case - hot air solder gun - just to unsolder chip. It works like a champ, but you have to be careful not to loose any close SMD parts. I never found hot air soldering good, but for unsoldering is the best. VERY IMPORTANT - Do not pull chip until you feel that it is going off on it's own, otherwise you will pull traces EASILY!

After you unsolder 4393s carefully clean up pads with braided wire first, to remove existing solder, and than use alcohol to clean it up. Your goal is to have a very FLAT and clean surface so when you place new chip on those pads, it sits nice and flat without wiggling.

Use smallest gage solder you could fine. I mean the thinnest one. Do not use those very, very thin solder tips for your iron since they do not transfer any heat. More like something in the middle. If you create bridges between the pins, do not panic, just use braided wire to pick it up. Likewise braided wire has to be of really fine mesh in order to work well. As mentioned earlier, use flux in order to aid you in soldering. I use flux that is like gelatin and I put some underneath the chip in order to sort of keep chip in the place, until I solder the first pin. After that it is easy... sort off

The most important - use ether microscope or 10x loupe in order to see what you are doing and how good are connections and if you created any bridges.

I would strongly advise you to unsolder bypass electrolytic caps that are on one side of the chips. They are really on your way when you are soldering. If you do that use that opportunity to replace them with lets say OSCONS - just suggestion.

When I work on this, I pull the whole DSP board out of the case so it is much easier to handle it and to come close to it since you most likely you will be viewing through the loupe and you have to be very close to be able to be in focus.

Good luck!
__________________
www.burningamp.com

Last edited by AR2; 26th January 2011 at 10:31 PM.
  Reply With Quote
Old 26th January 2011, 11:14 PM   #2938
AR2 is offline AR2  United States
Master Burner
 
AR2's Avatar
 
Join Date: Dec 2002
Location: San Francisco, California
While I am at it, here is the pasive output board I am just finishing. Lundahls and ballanced jFet buffers!
Attached Images
File Type: jpg 10277_small.jpg (183.2 KB, 322 views)
File Type: jpg 10286_small.jpg (169.8 KB, 312 views)
__________________
www.burningamp.com
  Reply With Quote
Old 27th January 2011, 01:55 AM   #2939
diyAudio Member
 
Join Date: Nov 2010
NICE, Why are the tranys tyed together? Andy
  Reply With Quote
Old 27th January 2011, 02:03 AM   #2940
AR2 is offline AR2  United States
Master Burner
 
AR2's Avatar
 
Join Date: Dec 2002
Location: San Francisco, California
Quote:
Originally Posted by 4pyros View Post
NICE, Why are the tranys tyed together? Andy
I am not sure that I understand your question. The only point they are tied together are shields that are connected to earth/chasis ground. Could you please be more specific.
__________________
www.burningamp.com
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 09:23 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2