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Old 1st November 2005, 04:50 PM   #411
diyAudio Member
 
Join Date: Sep 2004
Location: A bloke from Stoke
Default Re: Re: Re: First impressions

Quote:
Originally posted by Kuei Yang Wang
Konnichiwa,


So, if you make sure to correctly match the Sensitivities of the Drivers and Amplifiers driven from the DCX crossover you can attenuate the signal (analog) ahead of the DCX with no real penalty sonically.

Sayonara

In practical terms, to be clear, does this mean setting the max output from the preamp so that the DCX input is just running into the red bars on full volume on music peaks, with the internal digital gains all set on 0dB?

Thanks for putting some numbers to the gains and sound levels, it's beginning to make some sense to me

Kev
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Old 1st November 2005, 04:58 PM   #412
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default Re: Re: Re: Re: First impressions

Konnichiwa,

Quote:
Originally posted by KevinTams
In practical terms, to be clear, does this mean setting the max output from the preamp so that the DCX input is just running into the red bars on full volume on music peaks, with the internal digital gains all set on 0dB?
Yes, pretty much so.

Adjust the coarse differences between amplifier input sensitivity and driver efficiency using attenuation in the analogue domain after the DCX. Use the digital attenuation only for fine tuning the system, leaving around 6db OUTPUT headroom.

I did in another thread some basic calculations illustrating how to do this, based on driver sensitivity and amplifier input sensitivity, cannot quite remember where that one went.

I would still change the DCX from 10V to 2.5V full scale levels all around and do the other mods discussed if it is mainly for domestic use.

Sayonara
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Old 1st November 2005, 06:28 PM   #413
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Join Date: Sep 2004
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Default Re: Re: Re: Re: Re: First impressions

Quote:
Originally posted by Kuei Yang Wang
Konnichiwa,


I did in another thread some basic calculations illustrating how to do this, based on driver sensitivity and amplifier input sensitivity, cannot quite remember where that one went.

I would still change the DCX from 10V to 2.5V full scale levels all around and do the other mods discussed if it is mainly for domestic use.

Sayonara

I saw the thread on sensitivity /gain matching but I couldn't use that with too much confidence as I don't know the sensitivity of my speakers and gain of my amps, so I used the "suck it and see" approach, using the attenuation in the ic cables that you outlined for balanced to SE and then changing the input resistors on the amps to get a better match. This will all be fine tuned as I progress.

I'll open the DCX in a few days and see how confident I am in making the changes you've outlined.

My pre is your DC phono into TX102's. If I rewire the TX102's to the +6dB setting would it drive the DCX at 20K input impedance?

regards
Kevin
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Old 1st November 2005, 06:59 PM   #414
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default Re: Re: Re: Re: Re: Re: First impressions

Konnichiwa,

Quote:
Originally posted by KevinTams
My pre is your DC phono into TX102's. If I rewire the TX102's to the +6dB setting would it drive the DCX at 20K input impedance?
Yes, BUT.... The worst case load on the Phonostage itself would now be 5KOhm.

HOWEVER, good news. The DCX has an input impedance notably higher than 20KOhm, so as long as the cable behind the TX-102 is low enough capacitance (as this also stepped up to be effectively 4 X what it is nomrally with the volume all up), there are no real worries about loading.

I'd say less than or around 100pF cable capacitance will be fine, not the limit is the loading on the Phonostage, not the TX-102 per se.

Sayonara
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Old 2nd November 2005, 05:58 AM   #415
JinMTVT is offline JinMTVT  Canada
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Join Date: Jul 2004
Location: MTL
woa ..that was some fooookin long read ..
now i am seriously exhausted ..

with all that info ( old and new )
i am still a bit mixed up about this unit!!

quick things i need to know :

- If i use digital input , what is the connection type?

- will i be able to adjust the volume from within my computer ?? i never used digital output from my soundcard yet ..


I'd use this unit for :

digital output from computer -- >
setup crossovers and filters
analogue out to amplifier ...

Is this the correct use for this unit ?


Then about the DAC
has anyone found a direct upgrade ?
like a chip that can replace the ones on this unit
and gives better performance ?
( i can only do simple electronic stuff like changning parts, i do not have the knowledge to think about the change and analyse it )

Is there direct stuff to do on the PSU that will help the quality ?
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Old 2nd November 2005, 11:16 AM   #416
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Konnichiwa,

Quote:
Originally posted by JinMTVT
- If i use digital input , what is the connection type?
XLR. Simply attach your coax cable to pin 2 & 3 of the XLR plug and solder a 220R resistor across the pins as well.

Quote:
Originally posted by JinMTVT
will i be able to adjust the volume from within my computer ?? i never used digital output from my soundcard yet ..
Yes, but most likely the volume control in your PC will not be a good idea to use. Much depends on the exact programs, devices and soundcard.

Quote:
Originally posted by JinMTVT
digital output from computer -- >
setup crossovers and filters
analogue out to amplifier ...

Is this the correct use for this unit ?
Yes, except the outputs are at Pro-Level (that is around 10V for digital full scale) meaning you need to apply attenuation (usually a LOT of attenuation) to the outputs prior to applying the signal to your amplifiers. The key to getting the most from Digital Crossovers and Equalisers is to get the level right, which can be trickey.

Quote:
Originally posted by JinMTVT
Then about the DAC
has anyone found a direct upgrade ?
The DAC chip's on this unit are pretty decent and certainly not the limit in terms of performance, the analogue stages and powersupply need upgrading much more desperatly than the DAC (and ADC) chips.

Quote:
Originally posted by JinMTVT
Is there direct stuff to do on the PSU that will help the quality ?
Replace it with a low noise linear one, external to the DEQ (inside there is not enough space).

Sayonara
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Old 2nd November 2005, 02:38 PM   #417
konut is offline konut  United States
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Location: Pacific Northwest
Does anyone know where I can get the schematic for the stock power supply in the DCX? The DCX Yahoo group has schematics for everything but. TIA
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Old 2nd November 2005, 03:37 PM   #418
JinMTVT is offline JinMTVT  Canada
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Join Date: Jul 2004
Location: MTL
thank you Kuie for your informative replies ..again

though some basic question remains in my head ..


With digital output from my sound card i should be able to control the volume then that is all good..
but you mentionned that it might not necessailry be a good idea ? i remember reading here that software volume controls are not always good..could that be what you are pointing?
do you have any reading reference or advice on that matter???

i do not have time to make an external digital volume control or stuff like that...not much time available at all with the buisness

For the digital input, this seems pretty simple ..
should this be supported by almost all sound cards with digital output ? no impedance problems ??
is there necessary shielding for difital connections like that??


For the pro level outputs..
i am only using Bryston amplifiers, does that count as pro ???
my amplifiers ( 4B ST ) don't have volume knob
will i have sound level problem ?
my 2b has the volume control, but i won't be using this
amplifier on my main system ..

and i guess that one adjusted. i don't want to have to fiddle with the volume on the amplifiers individually

all my amps have XLR connectors ...


Did you guys found out a simple replacement for the DACs?? something that could be just resoldered there with minor modif and give good improvement ?
from akm website, the DACs used on the behringer are pretty much top notch ...

And for the power supply, do you have any simple advices on devices that i could use directly. ..




thanks again for your time ...

if this device does what i need
i'll be looking at the newwer creative X-fi cards to send out thedigital signals...
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Old 2nd November 2005, 09:13 PM   #419
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Join Date: Nov 2002
Location: Sweden
Kuei wrote (as regards to RCA digital to AES/EBU digital XLR input to DCX)

Quote: "Simply attach your coax cable to pin 2 & 3 of the XLR plug and solder a 220R resistor across the pins as well"

To Kuei san: Sorry for primitive question, but please confirm that it means that the Pin on RCA (from DVD/CDP in my case) connects to Pin 2 XLR, Sleeve on RCA connects to Pin 1 & 3 together. 220 Ohm resistor across Pin 1 & 2.

Also, some people recomends Neutric adapter http://dv411.com/neutaestran.html - but it should not be necessary - right ?)

I am confused as usual


LageB
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Old 3rd November 2005, 07:56 AM   #420
AndrewT is offline AndrewT  Scotland
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Join Date: Jul 2004
Location: Scottish Borders
Hi Kuei yang wang,
when using a digital input
Quote:
coax cable to pin 2 & 3 of the XLR plug and solder a 220R resistor across the pins
what is the purpose of the 220r?
With analogue input presumably we should omit the 220r.
__________________
regards Andrew T.
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