Behringer DCX2496 digital X-over - Page 29 - diyAudio
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Old 10th March 2005, 08:05 AM   #281
mige0 is offline mige0  Austria
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hello

indeed this appears to me as a very nice and professional work made by Bill Dipoala.

nevertheless i would like to stick with the original behringer I/O boards.
in chosing a tradeoff between minimizing opamps/ stage count versus the approach of symmetrical signal transfer between boards i prefer the last one.

as the opamps used by behringer seem to be pretty sensitive to power supply imperfections i am heading to further improvements concerning the decoupling of the power supply there.

has anyone yet tried to split PS for the different stages on the I/O board ?

greetings
michael
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Old 15th March 2005, 08:40 AM   #282
mige0 is offline mige0  Austria
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Default out configuration

the PS layout on the I/O board is organised in a way that the opamps for the outputs 1,2 and 3,4 and 5,6 share the same bypassing condensators.

it really is worth to try different "out configuratios".
for 2 way speakers the "LH LH LH" configuration worked best for me. it excels over the "LL MM HH" in detail and over the "LMH LMT" in soudstage

all in all its one more indicator for the pretty insufficient pcb layout of the PS on the I/O board

greetings
michael
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Old 15th March 2005, 08:45 AM   #283
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Hi,

Very interesting, as usual.
Please keep up informing the board about what you find out
Thanks
Thierry
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Old 20th March 2005, 04:03 PM   #284
mige0 is offline mige0  Austria
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Default I/O PS decoupling

hello

who is willing to invest some hours of patient work on smd soldering, try to 'individualize" the decoupling of all the out-opamps.

i lifted pin 4 and 8 of the opamps's and connected 10uf to each (24 condensators all in all, placed on a speerate cnstruction board). the other side connect to ground via the corresponding pin1 of the xlr out. the positive and negative rail take from the x14 connector.

as result i gained improved localisation in the stereo image, als well as easier tracking of bass lines and vocals becoming more precise and pesent.

greetings
michael
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Old 21st March 2005, 04:00 PM   #285
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Default photo?

Michael, could you supply a photograph of this mod? Looks interesting.

Ric
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Old 22nd March 2005, 08:00 PM   #286
mige0 is offline mige0  Austria
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sorry ric

no photo at the time.
it looks more like some scrapyard (quite contrary to sound) right now as i started with some different values of resistors (though non has proven to be best, which means: lowest limitation in space especially for the low frequency end) to form a true r-c filter from the rails and furthermore this place currently appears to me to be a highly sensitive enviroment, just right to make some tries with differnt types of caps to get even closer to the kind of sound i love.

but even without a picture it is really easy to do.
1. first take a board of about 25 x 160 mm - this will fit nice in between of the I/O and digital behringer boards.
2. keep it in place by soldering some solid 0,8mm wires to one of the xlr pins on the upper side.
3. put your 24 caps of coice onto it and connnect them as i described above.
4. a microminimal improvment can be done by connecting the rails only from one of the pins 5/6, 7/8 of connector x14 (you will have to cut a small trace to the neighbour pin) this will leave two a little bit more "isolated" rail pins for a further mod of the input opamps bypassing

greetings
michael
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Old 30th March 2005, 12:52 PM   #287
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Default output using transformer

to petervv
"Just finished major surgery to my DCX, I removed the I/O pcb and
mounted input and out transformers."

Can you explain more about the output using transformers? Witch impedance ?Is there a lundalhl sample good for coupling? Can you make a schematics please?Many thanks...
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Old 1st April 2005, 05:01 PM   #288
petervv is offline petervv  Netherlands
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Default re: output using transformers

hi balthazard ,

>Can you explain more about the output using transformers? >Witch impedance ?Is there a lundalhl sample good for coupling? >Can you make a schematics please?Many thanks...

I don't think impedance is too important in this application where the transformer is driven from a low impedance opamp output, Thorsten has written several posts on this subject. Check this thread and the DEQ2496 thread in the 'digital' group.

Lundahl has several types of suitable transfomers, look in the DAC/line output section. Transformer ratio depends on how much voltage you need in your chain. I get about 0.5VRMS from my 3:1 transformers and this is enough to drive my poweramps.

regards, Peter
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Old 2nd April 2005, 06:23 PM   #289
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Wink Volume control by voltage control?

What did you think about a volume control for the DCX2496 with only a single one-gang pot for all six channels?

I studied the datasheet of the AK4396 D/A converters. For sure you know a D/A converter is a multiplying device. It multiplies the digital input with the reference voltage. The result of this multiplication is the output signal. This means decreasing the reference voltage also scales down the output signal.
In the data sheet of the AK4396 I found the following text:

Analog output voltage scales with the voltage of (VREFH-VREFL).
AOUT (typ.@0db) = (AOUT+-) - (AOUT-) = +-2,4Vpp*(VREFH-VREFL)/5

At the DCX2496 VREFL is 0V and VREFH 5V. This means the output is +-2.4V. Decreasing VREFH down to 0V also will decrease the output signal swing down to 0V!

So my idea is inserting a pot in the supply for VREFH for all three D/A converters. Thatís all. Itís so simple!

But there is another value in the datasheet. It says that VREFH shold not be lass than 0.5V below AVDD which means minimum 4.5V. The question is what will happen below 4.5V? Will the chip die with a cloud of smoke or will it work despite of the limitation in the datasheet? So maybee increasing of VREFL is the better way. There is no maximum voltage for VREFL in the datasheet so it may be inceased up to 5V which also gives an output signal of 0V!

I have not tested this yet and it is not without risk. So think about it carefully before you try. But if it will work it really would be a very cool patch!
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Old 2nd April 2005, 07:45 PM   #290
Mentero is offline Mentero  Spain
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Hi petervv,

Some time ago I made a simulation using Microcap of the input stage of the DCX, and found that there was a build-in treble preemphasis.

It is true that this was my first Pspice simulation, so I may be wrong.

Have you made a frequency measurement after the mod?.

Regards
Miguel mentero
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