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Behringer DCX2496 digital X-over
Behringer DCX2496 digital X-over
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Old 8th January 2010, 10:15 PM   #2231
SY is offline SY  United States
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Behringer DCX2496 digital X-over
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Hi Sy
still don't think its correct to refer to jitter as kinda harmonics
It isn't and I didn't. The effect of jitter in the D/A and A/D process causes harmonics in the analog output- i.e., harmonic distortion.

"Clock Jitter, D/A Converters and Sample Rate Conversions", Adams, Robert W., 95th AES Convention, Preprint #3712. Available from AES.

"Theoretical and Audible Effects of Jitter on Digital Audio Quality", Benjamin, Eric and Gannon, Benjamin, 105th AES Convention, 1998, Preprint 4826. Ditto.
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Old 8th January 2010, 10:51 PM   #2232
Xoc1 is offline Xoc1  United Kingdom
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Default DCX Output stage schematic

Unsure about the Audiosmile mods but their website does contain a handy link to the output stage schematic.
http://www.audiosmile.co.uk/images/a...deq-output.jpg
My initial thought was that replacing R11 (2K32) with a 1K would reduce the gain by about 6dB. I am unsure about all the resistor network associated with the output op amps. I would like to think that with a few resistor pulls on the resistors that change the gain when pin 3 is shorted, and maybe a few resistor subtitutions to adjust the output gain structure, this could be simplified to a simple balanced output that would not require pin 3 to be shorted for unbalanced outputs.
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Old 9th January 2010, 01:05 AM   #2233
Gary P is offline Gary P
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Quote:
Originally Posted by Xoc1
Yes, reducing R11 will reduce the gain of the output stage. Changing R11 to 1K will reduce the gain of IC1B from 2.32 (7.33dB) to 1.002 (.017dB) reducing the gain by 7.31dB.

Another place to reduce the gain is by by lowering the value of R13 and R153 on IC1A. If R36=R37 and R13=R153 the gain of the balanced to single ended conversion stage is defined by R153/R37=4.99k/2K=2.495 or 7.94dB.

My head is too rummy now to try and decode the virtual transformer output stage (IC12A/B)...

Getting the output voltage of the DAC stage to meet your needs is an important detail of setting up a system. Too much system gain that results in high attenuation else ware in the system is not a good setup. With the Behringer being setup to deliver pro sound output levels we end up with more gain than necessary.
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Old 9th January 2010, 01:35 AM   #2234
Gary P is offline Gary P
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Originally Posted by mige0 View Post
On the other hand - I entered the discussion here at the point where analog versus digital volume adjustment was the topic seems there is no long lasting interest in this?
Michael
Hi Michael,

I for one am interested in digital volume control. Not sure if it belongs in this thread as the Behringer does not have remote capabilities or in the "A how to for a PC XO" That ShinOBIWAN started a long time ago. There is a lot more traffic in this thread.

I've been following in ShinOBIWAN and your steps setting up a computer based music server and digital crossover package. I'm quite happy so far but am still getting the system dialed in and details worked using a simple free crossover VST from www.rs-met.com out before graduating to the better FIR crossovers or going all the way to using "Acourate".

At this time the system is using the gain control VST from BlueCat audio controlled via MIDI to control the system volume. Seems to work well but I'll setup the system using Nyquist EQ as the gain control and see if I can hear any difference. I spend a lot of time listening to music at low levels so good performance at higher attenuation levels is plus.

Gary
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Old 9th January 2010, 01:42 AM   #2235
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Originally Posted by Legis View Post
audiosmile
Replacing the switcher with an analog supply is a pretty standard mod. For those in North America, Michael Mardis does that using special made (& very special) O'Netics transformers.

dave
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Old 9th January 2010, 10:47 AM   #2236
mige0 is offline mige0  Austria
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Quote:
Originally Posted by SY View Post
If it affects the A/D or D/A, the result is easily measurable- plain ol' harmonic distortion.
Quote:
Originally Posted by SY View Post
If you distort a signal, you get harmonics- it is exactly analogous to a linearity error. See Bob Adams's JAES paper on the effects of jitter.
....
Quote:
Originally Posted by SY View Post
It isn't and I didn't. The effect of jitter in the D/A and A/D process causes harmonics in the analog output- i.e., harmonic distortion.

"Clock Jitter, D/A Converters and Sample Rate Conversions", Adams, Robert W., 95th AES Convention, Preprint #3712. Available from AES.

"Theoretical and Audible Effects of Jitter on Digital Audio Quality", Benjamin, Eric and Gannon, Benjamin, 105th AES Convention, 1998, Preprint 4826. Ditto.



Don't buy in that AES stuff
- sure, if you force opamps beyond their limits, you always can squeeze out a lot of fancy distortion, including harmonics – but this isn't our usual "any day" case with digital equipment like the DCX.

Jitter is a mere intermodulation (FM) – meaning it produces side bands, not harmonics at first hand.

Depending on the underlying source of intermodulation you get either rather descrete side bands like here :

Behringer DCX2496 digital X-over




or a "smear hill" both sides of your frequency like here

Behringer DCX2496 digital X-over



These outcomes are rock solid backuped by simulations and theory – and in case you don't trust my work I'll recommend to go through the reference links provided in my papers...


Michael

Last edited by mige0; 9th January 2010 at 10:51 AM.
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Old 9th January 2010, 11:00 AM   #2237
mige0 is offline mige0  Austria
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Hi Michael,

I for one am interested in digital volume control.
Gary
Yes - not sure if that isn't too much off topic either.

But to me its interesting to see that no one has made an attempt towards using the digital attenuation capability of DAC's.

IIRC there is a plug in replacement to the DCX DAC that could do comfortable.

Might be, I have missed that part, as was not following throughout the thread.

Michael
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Old 9th January 2010, 11:13 AM   #2238
mige0 is offline mige0  Austria
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Quote:
Originally Posted by planet10 View Post
Replacing the switcher with an analog supply is a pretty standard mod. For those in North America, Michael Mardis does that using special made (& very special) O'Netics transformers.

dave
There is pro and con to switched versus analog PS you know.

From mere measurement a switcher is plain heaven – depending on further treatment I guess there is no real need to step back to analog.

Here are measurements from the already linked thread about crossover distortion of amps – where as a by-product of that discussion measurements reveal, that analog PS have pretty ill effects to be addressed:

Geddes on distortion measurements


Behringer DCX2496 digital X-over


Behringer DCX2496 digital X-over



What we see at the left of the plots is that analog power supply introduces a lot of 50/60Hz harmonics whereas the swiched PS is pretty clean here.

This are measurements at the *speaker terminals* of poweramps – mind you !


Michael

Last edited by mige0; 9th January 2010 at 11:19 AM.
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Old 9th January 2010, 11:23 AM   #2239
SY is offline SY  United States
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These outcomes are rock solid backuped by simulations and theory and in case you don't trust my work I'll recommend to go through the reference links provided in my papers...
I looked at your site and it was very unclear what these were plots of, how they were taken, whether there were bin and apodization effects, reference levels, and how the plots were confirmed to be related to jitter.
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Old 9th January 2010, 11:27 AM   #2240
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Quote:
Originally Posted by planet10 View Post
Replacing the switcher with an analog supply is a pretty standard mod. For those in North America, Michael Mardis does that using special made (& very special) O'Netics transformers.

dave
I think audiosmile is not going to replace the supply but will add LC filter(or i got you wrong): DCX2496

Quote:
The Power Supply is the next weakest link in the DCX2496. Switch-mode power supplies, as found in the DCX, emit high frequency switching noise which can contaminate the purity of the power and leak in to the audio signal. Making matters worse, in stock form the Input Receiver chip (affects jitter) is run from a completely unregulated line shared with the electrically noisy DSP chips.
To remedy this, AudioSmile add LC filtering to the output of the critical supply lines, greatly reducing transient high frequency switching noise and giving the DAC and ADC a cleaner supply. The Input Receiver chip is then isolated and fitted with an independently regulated power line.
What about those input and output mods, is the analog transformer going to actually increase THD% from the original design?

Does anybody sell plug and play LC-filters for original PS of DCX, or is there some schematics how to make one?

Last edited by Legis; 9th January 2010 at 11:39 AM.
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