Behringer DCX2496 digital X-over

[peterhenk]

I have removed the in / output completely and want to restore the mic input.

I have phantom power sorted out using the +15V lines on the flat-cable. Now I need to build a mic preamp or use a transformer to raise gain. It is unclear to me how much gain is needed (I will use a measuring mic similar to the Behringer)

So I would be much helped by answers to a couple of questions:

1. If using a transformer, what step-up range would work?
2. Suppose phantom power can be connected directly after the transformer without any extra components? Since the transformer isolates the DC from the DCX side.
3. If going with a clone of the original mic pre circuit from the DCX schematics, what opamp would you go for?

Thank you Peter

[Pano]

The only thing the mic will do on the DCX is tell you polarity and delay. Handy, but you can do that with free computer programs, too.

I'll have a look at the mic preamp schematic, it should not be hard to imitate.

[jan.didden]

Originally Posted by peterhenk

I have removed the in / output completely and want to restore the mic input.

I have phantom power sorted out using the +15V lines on the flat-cable. Now I need to build a mic preamp or use a transformer to raise gain. It is unclear to me how much gain is needed (I will use a measuring mic similar to the Behringer)

So I would be much helped by answers to a couple of questions:

1. If using a transformer, what step-up range would work?
2. Suppose phantom power can be connected directly after the transformer without any extra components? Since the transformer isolates the DC from the DCX side.
3. If going with a clone of the original mic pre circuit from the DCX schematics, what opamp would you go for?

Thank you Peter

I have with Pilgham Audio developed exactly that. It's a stand-alone mic preamp on a little PCB and a connector that fits in the digital input hole on the back panel. The connector is a combined XLR (for digital in) with a 6.3mm jack for the mic input.
The board is build, I need to final check it.
Will try to do that next week and report here.
If it works as designed Pilgham will probably offer kits.
I developed this by request from people who build my active DCX mod.

Stay tuned!

jan

[peterhenk]

Hi Jan,

Glad to offer myself as Guinea pig ;-)

Peter

[peterhenk]

Just for info.

This is how I made space available to play around in the DCX.

Turned the output XLR connector 180º and soldered a prototyping board directly on to them. This gives space to play around with first order filters, buffers, volume control (ldr type?).

Since the proto-board sits quite high I can still put transformers under them if I like.

[jan.didden]

Originally Posted by peterhenk

Hi Jan,

Glad to offer myself as Guinea pig ;-)

Peter

OK, sounds like a good plan!
I have the unit completed, need to do some basic measurements to make sure that there are no obvious mistake (like swapped supply lines ;-) and then I can send it to you for a user test.
The input is the same as the original DCX complete with 15V phantom power for the Behringer 8000 (?) mic.

jan

[peterhenk]

Hi Jan, Super!!

You have PM

Regards
Peter

[RevF]

Looking forward to the results of this!
I am having issues with my dcx currently - and have given up trying to fix it as the issue illudes me, and have ordered a new one... once I am up and running again and have the active mod installed in the new box, I would be interested in this mod though! )

[MurphyUHF10]

Hello,

i Thought to post my "tweek" of the Didden active i/o..
Installtion of Burson Discrete OPA's!!

Firstly, +/-9v avaliable from the i/o board is too low for these power hungry modules,, the THD+N is too high (thanks to a thread on here).. Much better at +/-18v.

So I built an external power supply to power these modules, and modified the Burson IC socket adapter so not to get power from the existing i/o board.. Of course, the GND of this new power supply would need to be connected to the GND of the DCX power supply.. Which I did with a fly-lead coming from pin 4 of the power supply connector on the DSP board..
(my aplogies for such poor photos)

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However,, I am getting very loud humming!! I measured this hum with TrueRTA and the analyser shows 2 big spikes at 50Hz and 100Hz.. (mains hum??)

When I use a non-modified discrete module and rely on i/o power, no humming..
Obviously to do with using 2 separate power supplies??

Any ideas??

Ta
CM

[jan.didden]

Looks nice!
The hum may have to do with the connection of the external power ground to the internal DCX ground. If it's only 50/100Hz it is probably not rectifier ground loops; in that case you'd have more harmonics.
Did you put in a direct connection between the external supply ground to the DCX?

jan