Behringer DCX2496 digital X-over - Page 50

Padel · 26th December 2005, 01:51 AM

Quote:

Originally posted by Davey

I'm sorry I haven't been following this thread for the past few months, but I've been reviewing it a little bit today. Unfortunately there is quite a bit of mis-information in many of the posts.

I hope not from me

Regards
Padel

Padel · 26th December 2005, 02:05 AM

Quote:

Originally posted by Thmartin

Did I say each on his own ? Yes I did

Thierry

Yes you did!!!

Regards
Padel

AndrewT · 26th December 2005, 07:56 AM

Hi,
now that we are getting closer to the real output impedance of the modified DCX output stage.

Can we estimate the true Zout?
If 10R +33R then 0.1uF is a bit large. 68nF or 56nF might be an option to try.

Thmartin and anyone else,
did you try a range of caps on the output?
How did it sound?
Would moving the RC time constant around help?
What roll off characteristic is ideal following a DAC?

Arcam have used a 3pole Bessel (active) in the past. Also set to the high 40kHz.

Thmartin · 26th December 2005, 08:06 AM

Hi AndrewT

I am VERY happy with what gets out from the DCX now.

However, just to try a more "universal" solution I'm planning to remove completely the DC blocking caps by using the DACs in balanced mode.

That'll include a 1KR resistor on each leg AOUT+ and AOUT- and a 3,3nF polyester capacitor between them.

This will avoid having to block DC (DC shall be cancelled in balanced mode) and 1KR probably provides a better protection for the DACs.

This solution will be tested in the next weeks, I'll let you know what comes out.

But I insist on the fact that the DCX modified as it is is a pure wonder.

Thierry

AndrewT · 26th December 2005, 08:51 AM

Thanks Th,

maybe I will go back to mine and experiment some more.

slowmotion · 26th December 2005, 12:18 PM

Thanks, Thierry.

Simple solution, I am going to try it myself.

I will try it into a valve output buffer,
so I'll be able to run longish cables,
we'll see how that turns out.

Plenty of other stuff to do first, tho,
so probably won't get it done until late spring ,
by that time others may have tried that allready?

cheers

Davey · 26th December 2005, 02:14 PM

Quote:

Originally posted by Thmartin
Hi AndrewT

That'll include a 1KR resistor on each leg AOUT+ and AOUT- and a 3,3nF polyester capacitor between them.

This will avoid having to block DC (DC shall be cancelled in balanced mode)

Thierry

Are you sure about that?

Davey.

Thmartin · 26th December 2005, 04:11 PM

Yup, pretty sure. Let's say 99%.
Anyway I'll measure it before I turn the amps on.

mbroyles · 26th December 2005, 04:19 PM

As best as I can tell, the opamp circuitry is providing:

- current buffering for the DAC
- a high frequency (above audio range), low pass filtering
(both I presume help stabilize the DAC's audio output)

- a shunt circuit for muting signal
- a differential drive circuit for balanced output

Not knowing what the DAC's current drive capability is, how stable and high freq trash free it is, I would be reluctant to chop the first 2 opamps out of the circuit. If you're always going to run an unbalanced output, the last 2 can more easily be chopped without worries.

If the DAC output checks out clean, the mods as shown will work just fine. The downsides are losing the output mute and balanced drive permanently.

MEB

Thmartin · 26th December 2005, 04:51 PM

Hi !

You know what, this is funny but the "Mute outs" is still bloody working even if T1 to T6 trannies are out of business !

Still can't figure out what Behringer has done there

26th December 2005, 12:18 PM	#496
slowmotion diyAudio Member Join Date: Nov 2002 Location: Norge	Thanks, Thierry. Simple solution, I am going to try it myself. I will try it into a valve output buffer, so I'll be able to run longish cables, we'll see how that turns out. Plenty of other stuff to do first, tho, so probably won't get it done until late spring , by that time others may have tried that allready? cheers __________________ - Jan -

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26th December 2005, 07:56 AM	#493
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, now that we are getting closer to the real output impedance of the modified DCX output stage. Can we estimate the true Zout? If 10R +33R then 0.1uF is a bit large. 68nF or 56nF might be an option to try. Thmartin and anyone else, did you try a range of caps on the output? How did it sound? Would moving the RC time constant around help? What roll off characteristic is ideal following a DAC? Arcam have used a 3pole Bessel (active) in the past. Also set to the high 40kHz.

26th December 2005, 08:06 AM	#494
Thmartin diyAudio Member Join Date: Aug 2004 Location: Paris	Hi AndrewT I am VERY happy with what gets out from the DCX now. However, just to try a more "universal" solution I'm planning to remove completely the DC blocking caps by using the DACs in balanced mode. That'll include a 1KR resistor on each leg AOUT+ and AOUT- and a 3,3nF polyester capacitor between them. This will avoid having to block DC (DC shall be cancelled in balanced mode) and 1KR probably provides a better protection for the DACs. This solution will be tested in the next weeks, I'll let you know what comes out. But I insist on the fact that the DCX modified as it is is a pure wonder. Thierry

26th December 2005, 08:51 AM	#495
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Thanks Th, maybe I will go back to mine and experiment some more.

26th December 2005, 04:11 PM	#498
Thmartin diyAudio Member Join Date: Aug 2004 Location: Paris	Yup, pretty sure. Let's say 99%. Anyway I'll measure it before I turn the amps on.

26th December 2005, 04:19 PM	#499
mbroyles diyAudio Member Join Date: Dec 2005 Location: SC, USA	As best as I can tell, the opamp circuitry is providing: - current buffering for the DAC - a high frequency (above audio range), low pass filtering (both I presume help stabilize the DAC's audio output) - a shunt circuit for muting signal - a differential drive circuit for balanced output Not knowing what the DAC's current drive capability is, how stable and high freq trash free it is, I would be reluctant to chop the first 2 opamps out of the circuit. If you're always going to run an unbalanced output, the last 2 can more easily be chopped without worries. If the DAC output checks out clean, the mods as shown will work just fine. The downsides are losing the output mute and balanced drive permanently. MEB

26th December 2005, 04:51 PM	#500
Thmartin diyAudio Member Join Date: Aug 2004 Location: Paris	Hi ! You know what, this is funny but the "Mute outs" is still bloody working even if T1 to T6 trannies are out of business ! Still can't figure out what Behringer has done there