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Behringer DCX2496 digital X-over
Behringer DCX2496 digital X-over
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Old 14th January 2010, 03:51 AM   #2321
Pano is offline Pano  United States
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Behringer DCX2496 digital X-over
Quote:
Originally Posted by Gary P View Post
It would not be hard to remove a bunch of circuitry from the Behringer output stage and configure it like Echo does. With this output stage configuration the output can drive either balanced equipment or single ended equipment without the complexity of the Behringer output stage.
Yep, I was thinking the same thing. Just take the signal after the 1st opamp. Maybe even change the gain of that stage. It's all we really need for consumer gear.

I have one of those remote multi-gang pots, too. Never used it because it's 100K. They don't seem to come in other values.
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Old 14th January 2010, 04:45 AM   #2322
AR2 is offline AR2  United States
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Gary, thank you for the detailed description. Quite possibly that I did exactly as you explained - too fast and furious. I will try with my next project this method. I was really disappointed, after I finished soldering with hot air gun, that something was wrong. So I went back to unsolder and start from scratch and to find out balls all over under the DACs belly. So I gave up, which pushed me to become very precise and effective with soldering and it worked very well. Working just with hot air gun will be much easier, cannot wait to try!

Thank you
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Old 14th January 2010, 05:05 AM   #2323
AR2 is offline AR2  United States
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Quote:
Originally Posted by Gary P View Post
I was thinking and comparing notes between the Behringer2496 and the Echo Layla 96/24 that I'm currently using as a DAC. Both circuits start off with the standard cookbook output stage as listed in the AKM data sheets. Echo uses just the balanced to single ended converter and configures the output as a single ended drive balanced output (is there a name for this configuration?). Very simple and sounds good. Behringer adds 2 more stages to create the virtual transformer output.

It would not be hard to remove a bunch of circuitry from the Behringer output stage and configure it like Echo does. With this output stage configuration the output can drive either balanced equipment or single ended equipment without the complexity of the Behringer output stage.

Here is what the output stage of the layla looks like including the stock version and the mods I've incorporated so far
An externally hosted image should be here but it no longer works. Please upload images instead of linking to them to prevent this.


I'm going to try this out on my brothers Behringer with a twist. We are going to add a 6 channel motorized alps 100K pot purchased from a vendor in Hong Kong. The pot includes a driver board and an infrared remote for ~$50.00. The 100K value is too high to be of use directly but we are going to use the second half of the output chip as a buffer to drive the newly created single ended driven balanced output.

Gary

You know, I never understood why Behringer has such a complicated circuit, where they go from balanced to unbalanced and back to balanced output circuit. Add on the top of that electrolytic cap?
I am sure that this mod would crete big improvement over the existing circuit. Now I am not fond of opamps, but the fact is replacing opamp and simplifying the whole thing on the existing board is relatively easy and rewarding task. Any other way requires separate boards, tiny wires, maybe another case...
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Old 14th January 2010, 05:19 AM   #2324
AR2 is offline AR2  United States
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Originally Posted by Legis View Post
I decided to get Elna silmic IIs for capping. I will change the whole capasitor reserve on both I/O card and digital board with them.

For PSU I got some pretty basic Nichicon caps (NICHICON | UPJ1C122MHD | PJ Series 1200 uF 16 V 20 % Through Hole Radial Aluminum Electrolytic Capacitor - Future Electronics to replace the 1000f caps in PSU and NICHICON | UPJ1E471MPD | PJ Series 470 uF 25 V 20 % Through Hole Radial Aluminum Electrolytic Capacitor - Future Electronics to replace the 470f caps) that are optimized to use with switching power supplies.

As said, I decided to get also Ak4396 DACs to replace the stock DACs and LM4562s to replace the stock op-amps.

I will do the modding in phases and take measurements and listening impressions after every mod. The order in which the mods will be done has not yet clarified to me.

What other (and easy) mod besides ferrites and capping could one make to original PSU, suggestions?

You know I would be interested in learning what do you find after these improvements. My experience is that any work on this PS doesn't make a big difference. I tried very good analog PS instead of switcher and I didn't find any improvements worth mentioning. What I believe will make impact is working on regulators and caps after the switcher, the ones that are on the DSP board. Replacing basic 7805 regulator with something more sophisticated would be good. Next I replaced all bypass caps, 10uF 25V for equal value OSCONS. OSCON doesn't recommend adding any additional lower value baypass cap next to the main 10uF and that would be hard to do anyways on that crowded board. So that should be good improvement to try. I cannot say that I could hear improvement since I didn't do A/B listening tests, but while I was working it was easy to do that as well. I also did that with all other improvements, so I didn't have isolated step by step progress in order to pinpoint and value single change.

I mentioned before, there are two mods that are very audible and that are making a big difference. The output circuitry mod and new digital input circuit with SRC and new clock with dedicated low noise regulator which changes your DAC into asynchronous DAC. That is hard mod but worth every bit of effort.
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Old 14th January 2010, 09:58 AM   #2325
Legis is offline Legis  Finland
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Quote:
Originally Posted by AR2 View Post
You know I would be interested in learning what do you find after these improvements. My experience is that any work on this PS doesn't make a big difference. I tried very good analog PS instead of switcher and I didn't find any improvements worth mentioning. What I believe will make impact is working on regulators and caps after the switcher, the ones that are on the DSP board. Replacing basic 7805 regulator with something more sophisticated would be good. Next I replaced all bypass caps, 10uF 25V for equal value OSCONS. OSCON doesn't recommend adding any additional lower value baypass cap next to the main 10uF and that would be hard to do anyways on that crowded board. So that should be good improvement to try. I cannot say that I could hear improvement since I didn't do A/B listening tests, but while I was working it was easy to do that as well. I also did that with all other improvements, so I didn't have isolated step by step progress in order to pinpoint and value single change.

I mentioned before, there are two mods that are very audible and that are making a big difference. The output circuitry mod and new digital input circuit with SRC and new clock with dedicated low noise regulator which changes your DAC into asynchronous DAC. That is hard mod but worth every bit of effort.

Thanks for the info. I will contribute my findings once I can get to work.

Any good drop ins for 7805 regulator that one could sample or buy? Dexa uwb would be great but IMO they are too expensive for regulators.

Are the two in the PSU (agains the aluminum socket with thermal paste) also voltage regulators? Any good drop ins for those?
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Old 14th January 2010, 10:31 AM   #2326
mige0 is offline mige0  Austria
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Quote:
Originally Posted by AR2 View Post
You know, I never understood why Behringer has such a complicated circuit, where they go from balanced to unbalanced and back to balanced output circuit.
...

There is a lot to consider about interfacing two circuits that do not share (exactly) same mass potential.

Best is to work through those "easy to read" papers:

http://www.analog.com/static/importe...ts/ssm2142.pdf
http://www.analog.com/static/importe...ts/ssm2141.pdf
http://www.audiodesignline.com/howto...sing/196604119


Bottom line :

In the context of the DCX analog board, the topology chosen by Behringer is pretty much "state of the art" – meaning :_

– they first reference the DAC output to the supposedly less noisy mass potential of the analogue board in order to not transmit any unnecessary common mode HF noise form digital board mass over the cables to the amps (this is done by going asymmetric first)
– then they implemented a floating differential out which has some benefits about non floating topology.

Very clever and unbeatable in its performance if implemented well.
There's some irony that the beauty of that approach is widely misunderstood in this thread.

Sadly, Behringer missed to do adequate analogue filtering at first, use closely matched resistors and to work out adequate trace layout in the analogue section.
This done (plus solving the 'lytics and IC's PSRR issue) I'm sure – no one ever would have felt a need to mod the analog section.


Michael

Last edited by mige0; 14th January 2010 at 10:36 AM.
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Old 14th January 2010, 11:18 AM   #2327
pidigi is offline pidigi  Italy
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Quote:
Originally Posted by Gary P View Post
....
I'm going to try this out on my brothers Behringer with a twist. We are going to add a 6 channel motorized alps 100K pot purchased from a vendor in Hong Kong. The pot includes a driver board and an infrared remote for ~$50.00. The 100K value is too high to be of use directly but we are going to use the second half of the output chip as a buffer to drive the newly created single ended driven balanced output.

Gary
Quote:
Originally Posted by panomaniac View Post
Yep, I was thinking the same thing. Just take the signal after the 1st opamp. Maybe even change the gain of that stage. It's all we really need for consumer gear.

I have one of those remote multi-gang pots, too. Never used it because it's 100K. They don't seem to come in other values.


Hi Gary and Michael,

100k is quite common in this applications, why do you consider it too high in this case?

Ciao!

Paolo
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Old 14th January 2010, 02:18 PM   #2328
Pano is offline Pano  United States
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Behringer DCX2496 digital X-over
100K works fine inside a tube amp. But in this case (and I think Gary's), we are driving medium impedance solid state amps thru a bit of cable. My amps have an input impedance of 20K and 10K. The output impedance of that 100K volume control does not allow much current to drive what is after it.

It will work, but I've found that lower impedances work much better for me. I'd be happy with 5K, but 10K seems to work OK.
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Old 14th January 2010, 02:27 PM   #2329
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Quote:
Originally Posted by panomaniac View Post
100K works fine inside a tube amp. But in this case (and I think Gary's), we are driving medium impedance solid state amps thru a bit of cable. My amps have an input impedance of 20K and 10K. The output impedance of that 100K volume control does not allow much current to drive what is after it.

It will work, but I've found that lower impedances work much better for me. I'd be happy with 5K, but 10K seems to work OK.
If you did a cap-coupled direct out mod from the DAC, you could then run it into this volume control, which would allow pretty small and comfortable film caps to be used, and follow it up with three LME49720's as buffers (unbalanced). Could be a nice end result.
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Old 14th January 2010, 02:29 PM   #2330
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Behringer DCX2496 digital X-over
Yes, a buffer after the pot would be the ticket.
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