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Behringer DCX2496 digital X-over
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Old 23rd March 2010, 05:13 PM   #2661
Beelde is offline Beelde
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Check there: Tweaking the Behringer DCX2496, audiophile digital active crossover

Everything's explained and illustrated.
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Old 23rd March 2010, 05:18 PM   #2662
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by Beelde View Post
Check there: Tweaking the Behringer DCX2496, audiophile digital active crossover

Everything's explained and illustrated.
Everything's explained and illustrated

http://www.linearaudio.nl/6chan-1.htm

jd
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Old 26th March 2010, 07:54 PM   #2663
Beelde is offline Beelde
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I know your awesome work on the dcx, no offense meant ;-).
Thierry Martin's solution seemed to correspond to kalmi79's approach (quick and cheap parts swap)
I consider adapting the relay/mute circuit of your passive solution to his tweak. The on/off thump being THE drawback of his approach, even though I can easily live with it.
As you're around, would you be so kind as to "decode" Oetlle's earlier remarks? I'm missing something I guess (if this has already been addressed, a link to the answer would be nice.I've read most of this huge thread but have skipped pages...I shouldn't have I guess)

I just received two freerider PCBs and two SRC AD1896 which you can get for free on Analog Device website (they sent me two samples totally free of charge). I also wonder on the TCXO clock. Wouldn't a 33.8688 clock allow true 192 compatibility?
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Old 26th March 2010, 10:30 PM   #2664
Beelde is offline Beelde
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I found the answer on pages 124 and 142 (I wish I could edit my previous post):

"I myself use an ultra low jitter 24.576 MHz oscillator, which supports digital inputs up to 96 kHz. The advantage is that PLL; SRC, DSP and DACs run absolutely synchronous for best sonical quality. You can also assemble a 28 or 30 MHz oscillator to support 192 kHz but then you have to stay with the existing high jitter 24.576 clock on the DSP board or you have to add an additional low jitter clock. Regarding sound quality it doesn’t make sense for me to down sample a 192 kHz input to the 96 kHz internal frequency of the DCX."

The selectronic solution does indeed do both, providing a replacement 24.576 clock replacing the original dsp one and adding a 28000 TCXO to support 192Khz. The debate around the audible degradation OR enhancement of the signal through upsampling is still open (last time I tried, I didn't hear a difference)

Wouldn't the use of a 24.576 clock on the freerider board (plus removing R34 + C77 +strapping c77) work as a general clock replacement?
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Old 27th March 2010, 08:48 AM   #2665
oettle is offline oettle  Germany
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Originally Posted by Beelde View Post
Sorry if those are complete noob questions but I'm also about to receive two freerider pcbs and I'm not sure I understand either what brgds tries to do and Oetlle's reply.

When Oettle says "half of the story": what does the freerider board lack? If it's reclocking, I get it yet, the selectronic kit includes that option (that's why I'm confused)

Aren't the freerider board and Pilgham audio's essentially the same design?

Are there any more "surgical" connections needed than those on the pins of the previous src chip? (apart from derived 5v and the replacement of TR1 with a 75Ohm transformer to match spdif specs...this last point being taken care of by the selectronic kit)
The Freerider solution solves the 'dull sound' problem but there is no sonical improvement (jitter). Also the Oettle design has an improved SRC/PLL design (supply, layout and cabling) for more accurate PLL operation.

The Selectronic solution (152 Euro) is similar to the Freerider one but it has an optional additional 'non low jitter' temperature controlled oscillator (TCXO). The TCXO doesn't make sense at all because your ear isn't a frequency counter. That means we can't here absolute frequencies but we can hear relative frequencies very well.

So important is the phase jitter RMS of the oscillator. The Oettle design (80/140 Euro) uses a 1 ps ultra low jitter oscillator. But the best oscillator wonít help if it doesnít has a high PSRR (ripple rejection) and low noise power supply. This page (Tent) might help you understanding: Low jitter clocks
Also cabling is very important for low jitter because 1 ps is an equivalent frequency of 1000 GHz! So we are talking about every single millimetre but not centimetres.

You can measure the improved jitter. Ergo did it (link: The improvement Ö) SRC/Clock
I and also others could hear this difference.

You can also replace the existing S/PDIF transformer with a Scientific Conversion one (independently of SRC/PLL mod). My experience is that there is NO sonical difference at all because the digital input is reclocked anyway by the SRC to the internal 96 kHz sample rate of the DCX.

So the different designs seem to be more or less the same but they arenít! The Oettle design is an improved Freerider solution plus a low jitter Tent clock.
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Old 27th March 2010, 09:37 AM   #2666
boconnor is offline boconnor  Australia
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Originally Posted by oettle View Post
You can measure the improved jitter. Ergo did it (link: The improvement Ö) SRC/Clock
I and also others could hear this difference.
My understanding is that unless the implementation is pathological (and the DCX doesn't seem to fit that category), jitter is not a problem and is inaudible.

Was your listening test(s) done double blind?
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Old 27th March 2010, 11:14 AM   #2667
oettle is offline oettle  Germany
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Originally Posted by boconnor View Post
My understanding is that unless the implementation is pathological (and the DCX doesn't seem to fit that category), jitter is not a problem and is inaudible.

Was your listening test(s) done double blind?
Yes, and the earth is not a globe because all Australians otherwise would fell into space. Nevertheless I was sure this is true I travelled to Sydney and lived there for about a year. So meanwhile I have the experience Australians won't fell into space. And this is for sure because my wife and my two children were part of this double blind test.

So, why donít you buy a mod kit and share the experience of this sonical improvement with meanwhile a lot of other DCX users. I promise you there is absolutely no risk to make your own experience.

Btw: Sydney was a great experience for me and if it wouldnít be so far away I would like to be there more often. So enjoy living there and perhaps you will also enjoy listening to my mod soon.
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Old 27th March 2010, 12:09 PM   #2668
boconnor is offline boconnor  Australia
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Originally Posted by oettle View Post
So, why donít you buy a mod kit and share the experience of this sonical improvement with meanwhile a lot of other DCX users.
Hmm, thanks for the suggestion but I don't see a lot of audio engineering research support for jitter mods so I might just pass on that.

BTW, I really enjoyed Germany when I visited there in my younger days - but that was before the fall of the wall!
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Old 27th March 2010, 12:18 PM   #2669
oettle is offline oettle  Germany
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Originally Posted by boconnor View Post
Hmm, thanks for the suggestion but I don't see a lot of audio engineering research support for jitter mods so I might just pass on that.
I thought the same way before I made different experience.
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Old 27th March 2010, 01:25 PM   #2670
Beelde is offline Beelde
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Thanks for the answer! As for Jan, I don't want my remarks to be taken as "attacks", I'm just a DIYer with a couple of Dcxs trying to sort it out (one for my active three way front speakers and the other for the remaining channels of my HT...a third one is coming for a further bass expansion). I will certainly end up with your SRC/clock in one and selectronic's in the other (I will measure and report here for everybody's sake of course). I don't mean to rain on anybody's parade and I know that differences are audible when the less-than-optimal power supply and clock circuits are replaced.

I disagree on the "non low jitter"...the selectronic clock is <10ps and yours is <2ps
and there is a sonic improvement with their design*. (no reason not to trust Thierry Martin and other French diyers who, like you, have no commercial interest in saying so) Their clock is an improvement on Tent labs X02 on the same lines as you describe and is meant to be connected to their low noise/high PSSR power supply. Your power supply is integrated (hence a cheaper solution) yet their power supply also provides the Dacs with cleaner current)
I can understand the point you make about cable length: your solution does indeed provide the shortest path.

To summarize:

Freerider : removes original SRC bug. Improves jitter rejection (claimed <5ps could be optimized by reduced cabling ? and power drawn from selectronic low noise linear module instead of IC1 pads?) 192Khz compatibility
no reclocking (which could be DIYed IMHO since it's done from the same pins on the other two solutions but at the expense of 192Khz).

Oetlle: best jitter improvement <2ps. Full sync reclocking 96Khz. Integrated optimized power supply. (Already improved Freerider solution)

Selectronic: jitter improvement <10ps. 192Khz compatibility and Reclocking (optimized from Tent Labs x02) Draws power from external low noise power supply (which also regulates DACs supply). Most expensive solution but includes scientific conversion transformer for true spdif & AES impedance matching (this can be important depending on the source/connection).



It comes down to a matter of price/ease of installation and a somewhat audiophile audibility frontier (Is a less than 10ps jitter difference audible...I doubt it). I do believe that the price of each solution does correspond to what they offer.

Thanks everybody for the fascinating work!

*The fact is that Thierry's site is much more complete in French (and justifies the power supply changes and other design choices) and that some other personal sites (also in French) do tell of comparative listening.
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