Behringer DCX2496 digital X-over

[sendler]

Volume control

Sendler-correct, that post, and I think it's the only negative one I've seen so doubt the measurements as he has gone on to post a number of other questions on the Minidsp's own forum. My problem however will be the same-ultra efficient 4 way horn system well over 100db efficient. I also am confused about how to control gain using the minidsp board- are you supposed to wire in a physical knob to control it? Is it ok to go from a Rogue tube preamp to the analog in's and still get good s/n when playing low, will that cause issues between low and high volume? I'm not an electronics guy, more of a speaker builder. Their website does not seem to clearly explain as they assume more electronics knowledge than I have.

I haven't really studied the Minidsp products but think that you will find the same volume control concerns as DCX users. Digital in or analog in, either way, the best sonics require matchable controls on each amp channel to set the sensitivity so that your max listening level occurs with -0db digital volume settings and/ or full-ish analog input meters. The cheapest way is to experiment with fixed resistor pads, best placed inside the amps input connectors to minimize the passive's interaction with any following cable which will be none at that location. I use direct stepped attenuators which install on the amps inputs and maintain matching at any volume setting. Jan's active output board is also very handy and gives remote volume control. Doing a simple direct out mod to your DCX will also reduce the hiss as the stock DCX outputs are adding a lot of noise to the output of the dac chip. I use either a simple, one leg cap coupled out with no ultrasonic filter which is a very cheap mod, or transformer coupled output. I have found great sound from Jensen JT-11-EMCF or FMCF. Six of those gets expensive though.
.
If the hiss/ hum from your amps alone is too loud into your high sensitivity horns even with the inputs unplugged/ shorted, you may have to consider adding passive pads at the drivers which will also be beneficial in flattening impedance peaks.

 

[doug20]

Is passive pads on my CDs to control the noise floor issue. I liked the MiniDSP because I had a complete unbalanced setup in my office (Outlaw amp, pre/pro) and there simply was no need for any pro audio components.

 

[Davey]

Signal levels are much more 'consumer' friendly with the MiniDSP. Maximum output limited to 0.9VRMS and with much lower noise than a stock DCX unit. Attenuators between MiniDSP and power amp(s) should not be required in most cases.

Cheers,

Dave.

 

[pumpkin1]

Minidsp

Understood- though implementing some of your suggestions for a non-electronics guy is not possible without step by step instructions. I've found that the folks on this site, like yourself, have fairly advanced knowledge about electronics so there doesn't tend to be a how to faq created as I've enjoyed with Tapped Horns for example. Unless someone takes the time to explicitly show how they added attenuation, how to pick the right resister or parts, etc, it's just not possible for me or others like me to implement.

But what appealed to me is the fact that the Minidsp shows it's own gain/vol control-so if that is physically controlable in real time, it would be a very cheap solution vs. having to build separate vol controls for each channel. I do have gain controls on a couple of amps so I can match them to my main tube amp.

 

[doug20]

Just saw this

Recently I've participated in some listening tests of various active crossovers over two separate days in two systems.

We compared
Behringer Ultradrive DCX
Behringer Ultradrive DCX with the Pilgrim audio mods
MiniDSP
DEQX

We did two tests:
1. digital conversions
2. digital active crossovers

We used an instant switching level match box that switches both inputs and outputs. For the first test, we let the units simply act as digital converters of an analogue input - ADC then DAC. We compared to a loop through wire.

For the second, we set up with the same settings and measured to ensure we were comparing level matched and with the filters doing the same thing. It's quite time consuming to set up an event like this, so it was not the last word on perfect accuracy. We did not match to within 0.1 db but we took a decent stab at matching.

We didn't do the test blind. While this may disappoint some, but I felt that using instant switching would be revealing enough. We did this test for our own curiosity, but no one had a point to prove. In a previous informal comparison, I found that was enough even with levels obviously not matched. No one in that test could hear a difference with the digital conversions vs a loop through wire, not even one person there who was certain a difference would be heard.

Our extended tests did show differences, but I'd call them subtle. At certain times, I noticed a difference in imaging where there was a small shift. The instant switch during a sustained note is quite revealing. MiniDSP appeared to have increased treble detail compared to DCX, despite mreasurements showing that it rolls off more above 20k. The measurements from what I recall didn't seem to reveal why that might be the case.

The full write up is here in my blog:
Red Spade Audio: Active crossover listening tests
and there are more comments in the linked SNA thread.

My findings if I can sum it up in a nutshell?
MiniDSP is the first one you want to try out of these.

DEQX sadly didn't quite get a fair trial, we had time limits and something wasn't quite right.

 

[doug20]

Understood- though implementing some of your suggestions for a non-electronics guy is not possible without step by step instructions. I've found that the folks on this site, like yourself, have fairly advanced knowledge about electronics so there doesn't tend to be a how to faq created as I've enjoyed with Tapped Horns for example. Unless someone takes the time to explicitly show how they added attenuation, how to pick the right resister or parts, etc, it's just not possible for me or others like me to implement.

There is a learning curve or you can buy a product like this

NHT Professional PVC Pro Passive Volume Control

But what appealed to me is the fact that the Minidsp shows it's own gain/vol control-so if that is physically controlable in real time, it would be a very cheap solution vs. having to build separate vol controls for each channel. I do have gain controls on a couple of amps so I can match them to my main tube amp.

Currently the MiniDSP does not have real time volume control or atleast I know mine do not.

 

[Pano]

I thought you just had to connect a linear pot to drive the volume control portion.

EDIT: Quick look at the manual says yes. 10K linear pot connected to pins 6, 12, 22 of the expansion connector. You can drive multiple boards with the same pot.

 

[doug20]

I thought you just had to connect a linear pot to drive the volume control portion.

EDIT: Quick look at the manual says yes. 10K linear pot connected to pins 6, 12, 22 of the expansion connector. You can drive multiple boards with the same pot.

Yes sorry, I wasn't clear. If you are not buying the prebuilt one then you can do some of that electrical stuff.

 

[Pano]

OK, I should have figured that!

Yeah, does not look like you can easily do it on the boxed version.

 

[doug20]

Thanks for the post, I forgot about the expansion connector. Maybe some EOM would like to add a Volume control or maybe MiniDSP will add one in the future.

 

[pumpkin1]

Is there a benefit to using the on board vol w/a pot vs an analog vol control/preamp after the minidsp?

 

[Pano]

1 control vs 4 controls. Pot quality not a big issue.

 

[slacker0001]

Hi guys.

Sorry if i interrupt your conversation in any way, but i need some help.

I am reviving an old dcx project that never got finished.
Never got to use the unit properly until now.

I bypassed the i/o card and installed a Selectronic digital input clockmodule and did a passive out mod.
Got it playing music finally.

But i have a (stupid?)question..
How do you guys route the signal internally for digital input and stereo operation?
I haven´t found any guides yet nor clear info in the manual.
I tried the 2way+sub preset and it seems like i am missing the right channel and
the left channel for both channels.

Hope i just was too tired last night to figure it out...
Maybe my filter settings are wrong and something is out of phase?

The question about the digital input and routing is somethig i need to find out anyway.
It all should work if i use a setting in the preset list that claims it is stereo operation?

my set up will be:

Midbass left
High left
Midbass right
High right
summed mono sub

Any suggestions ?

Please advise!

 

[MurphyUHF10]

Hi Slacker,

When digital is selected, the 'left' channel assumes input A, and 'right' channel assumes input B. From here you can choose appropriate "routing" from setup menu, keeping an eye on which outputs the input A & input B are routed to.. You then rename the output to suit your preference and set the appropriate xover settings for each output channel..

The particular "routing" you select is not that relevant, because ultimately you can select any input for any of the outputs and re-name them to match its application.. This includes your mono sub too,, you can sum any inputs together and direct any output to your "summed input" and set xover to suit..

Hope this helps..

Cheers..

 

[slacker0001]

Thanks for your reply.

The b-input should manually be routed even if it is not connected physically outside the box.

I´ll get on it tonight after i get home from work.

 

[Radugazon]

hello ...if I remember,

On the DCX, the only input for AES/EBU or SPDIF is.............A !!!

If you are sure of only using SPDIF (you can connect the Pc here for measuring, no worries), better to by pass all the relays and various stuff : cut the legs of the female XLR connector, solder a short coax and go straight to the transfo and cut the old traces on the PCB.

look here fore more details (there's english translation too)

 

[MurphyUHF10]

hello ...if I remember, On the DCX, the only input for AES/EBU or SPDIF is.............A !!

Yes, but the "right" channel from the digital source assumes 'input B' for left/right routing purposes in setup menu..

btw, that particular page has no english translation :-(

Cheers..

 

[slacker0001]

The block-diagram in the manual actually describes it well enough.
Aes/ebu input is internally routed to a/b and sum(if desired).
Funny(?) that i first modify the unit, replacing the 8420 chip and whatnot-and later prove myself incabable to read the manual...

But since i did just that i thought maybe the signalpath could be different, or that i could have lost some of the alternatives do direct the signal internally in the process.

I have sweet stereo playback now and everything seems to be ok so far.

Thanks Murphyuhf10 for pushing me in the right direction!

Btw.

How do you guys set the input levels when running fully digital?
It seems easy to get clipping ?

 

[SY]

I used a test signal with a full scale 1kHz sine wave encoded, then brought the input gain up until I hit the yellow lights.

 

[Pano]

Ditto. At 0dB gain and no EQ, I don't see clipping with a fully modulated sinewave coming in the digital input.

I do see clipping sometimes, tho. So that's either the recording or the player.