Behringer Ultradrive PRO DCX2496

[janneman]

I know that several of you have bought this equipment, so have I. I am running my CD digital output directly into the Behringer, then do equalisation and xover on the Behringer, using its DACs and then to the power amp. No preamp, that means I have to set both the input gain and the output gain on the Behringer to -15dB for normal listening levels. I have the distinct impression that this (digital) attenuation makes the sound less transparent and decreases the resolving power of the set. Anybody has similar or other experiences with this?

Jan Didden

[pinkmouse]

Hi Jan

Pro kit is designed to be used according to a concept known as Gain Structure. Basically, this means that any signal gain is done in only two places; at the input to the desk, and at the power amps. Everything else is designed to have, in theory, unity gain.

By turning down the input and output gains in the Xover, you have drastically increased the noise floor.

I would suggest bridging a couple of fixed, good quality resistors on the output so you can set the level to an appropriate one for your amps/ears.

[haldor]

Hi Jan,

I second pinkmouses suggestion. Leave the Behringers gain settings at unity. What Pinkmouse describes is called an "inline audio pad" and is very easy to make.

Here is a link to explain how to make your own. http://www.epanorama.net/circuits/line_to_mic.html

[ThorstenL]

Konnichiwa,

Originally posted by janneman
No preamp, that means I have to set both the input gain and the output gain on the Behringer to -15dB for normal listening levels.

Which means that with a DAC section having 113db dynamic range you have thrown away 30db, making the dynamic range 83db, which is below 14 Bit performance.

Originally posted by janneman
I have the distinct impression that this (digital) attenuation makes the sound less transparent and decreases the resolving power of the set. Anybody has similar or other experiences with this?
[/B]

Well, if you downgrade a system with around 19 Bit analogue resolution to 14 Bit resolution, what did you expect?

The suggestion to use an L-Pad is okay, even better would be to add a set of 10:1+1 stepdown output transformers, giving 14db and 20db attenuation, lowered output impedances and a true balanced floating output. But no matter what you do, you MUST make sure that DAC's operate near full scale for the loudest portions of the music.

Sayonara

[janneman]

KYW & Pinkmouse, Greetings,

You are right. I got a quartet of 30dB XLR inline balanced attenuators from Farnell, allowing me to run the DCX2496 at almost 0dB gain. Sound is much better now. Noise wasn't such a problem, but I lost resolution, it sounded "dull"?

In passing, I noted a problem in the Behringer: one channel had much lower output than the others with the attenuator. Since the attenuators are 600Ohm, looks like one channel has a much too high output impedance.
Need to talk to Behringer support for that.

Other than that, this is one helluve piece of equipment for 450 euro! You can set xover parameters on frequency and filter type, filter slope, gain etc. Then you have additional filters or parametric equaliser sections that you can insert, all with programmable parameters. The user interface is very intuitive and comfortable. I opened mine, not much to tweak, I'm afraid. In fact, there's not much, period. Still, excellent performance. Gold solid engineering from Behringer!

Jan Didden

[ThorstenL]

Konnichiwa,

Originally posted by janneman

In passing, I noted a problem in the Behringer: one channel had much lower output than the others with the attenuator. Since the attenuators are 600Ohm, looks like one channel has a much too high output impedance.

I take it you checked that the Attenuators don't cause it, I mean that one Att is dodgy?

That said, given you have 600R Att's, may i suggest moving to 10k ones. Any Op-Amp short of my favourite CFB designs will start huffing, puffing and distorting when faced with 600R load. It's worse as in fact the output stage is a bridge, so each Op-Amp of the output delivers up to +16dbu (5V) into 300 Ohm, not comfortable for most Op-Amp's, honestly.

So try making your own att's with 10K input Impedance. Best place them directly on the Amp-Input, maybe INSIDE the Amp with a second XLR input made to work with Pro Levels (+20dbu = Full Scale/Power +/-6db trim usually)?

That should improve the sound further.

Originally posted by janneman

Other than that, this is one helluve piece of equipment for 450 euro! You can set xover parameters on frequency and filter type, filter slope, gain etc. Then you have additional filters or parametric equaliser sections that you can insert, all with programmable parameters. The user interface is very intuitive and comfortable.

Agreed.

Originally posted by janneman

I opened mine, not much to tweak, I'm afraid. In fact, there's not much, period.

Actually, the output stage Op-Amp's are SMD below the Board carrying all the Jacks. As the Op-Amp's are NJM 4580 (I'd even take an NE5532 over these!!) it's worth subbing something better. The AD8620 in SMD looks EXACTLY like what the Doctor ordered.

Also, there are quite a few signalpath coupling Cap's ('lytics) that would benefit from being made something better (Elna Silmic, Sanyo Os-Con SG/SH or if you must Black Gate. No-body disputes that some elcaps distort less than others....

I'd also put Os-Con's or BG around the ADC & DAC Chip and on the digital supply likes. It's worth it.

As a last tweak, the SMPS they use still has a good deal noise left. You have three voltages and some ground leads. I think putting a decent CLC Filtering system in there (does not have to be physically large) will clean up the sound as well.

The above (Op-Amp's, Cap's and Filter) would be my considered minimum to move the box from decent Mid-Fi perfermance to "High End".

Originally posted by janneman

Still, excellent performance. Gold solid engineering from Behringer!

Certainly in view of the price - outstanding. I have the digital EQ here for review (also the Shanling SACD Player and Shanling CDP again, plus some other tasty stuff) and it is not bad at all.

Sayonara

[janneman]

KYW,

Did you figure out the schematic of that output stage? I only had a quick glance, and I assumed that the two ' lytics per channel were supply decoupling. If they really are coupling caps - arrrghh!

Jan Didden

[ThorstenL]

Konnichiwa,

Originally posted by janneman

Did you figure out the schematic of that output stage?

Ages ago. Classic 2 Op-Amp, Balanced in "pseudo transformer" output. You see them in Pro Audio gear every day (arguably I have more experience on the Pro side than HiFi).

It looks like the latter part of the SSM Driver IC AD discontinued recently....

As for the 'lytics, I need to a full trace, but in pro Audio it is common to put caps on the output "just in case". Previous Behringer gear I encountered used PSU Busses for +/-15V or +/-12V with only two caps covering ALL Op-Amp's.

Given that DAC outputs sits at +2.5V DC (which is passed on by the output as common mode) using a simple Cap (not a dual b2b pair) works fine and dandy, if you use decent quality Cap's.

Now what are the bets on that happening in $ 450 Retail, $ 300 to dealer and $ 150 when leaving the chinese factory piece of gear?

Sayonara

[janneman]

KYW,

Thanks for the info, hadn't realised you answered my post for several days.

As for the power supply, maybe I should move to an outboard linear one.
I need to get the data sheets for those DACs, maybe I should redesign it from there on, from i/v to level control to output butter. Kind of 6 ch outboard DAC-cum-preamp.
After I finisched those other projects I'm working on...

Have a nice weekend.

Jan Didden

[janneman]

Just checked, the DACs are AK5493, voltage output. No i/v required. Looks like the PGA4311 would be a perfect fit, under control of a PIC with RC5 remote control....


Jan Didden