The Behringer DCX2496 is a great unit, and I have my prototype speakers up and running using it. Now I need to take the next step.
I looked in the manual before I bought the DCX, and saw it had mike facilities on input C. Based on that, I bought the measurement microphone.
After trying to use it with Speaker Workshop, it appears that the microphone preamp is only active in the Time testing.
While buying a microphone preamp is not the end of the world, I was wondering if someone else could confirm that I need to buy a microphone preamp.
Doug
I looked in the manual before I bought the DCX, and saw it had mike facilities on input C. Based on that, I bought the measurement microphone.
After trying to use it with Speaker Workshop, it appears that the microphone preamp is only active in the Time testing.
While buying a microphone preamp is not the end of the world, I was wondering if someone else could confirm that I need to buy a microphone preamp.
Doug
If you supply a couple of mA's via a resistor to pin 4 of the large flatcable going to the analog output board (X14), relays 2B and 2C energise. That activates the mic preamp at the C input.
The amplified signal can be picked off from pins 9 & 10 of the smaller flatcable on the input area. (X13).
Jan Didden
The amplified signal can be picked off from pins 9 & 10 of the smaller flatcable on the input area. (X13).
Jan Didden
Since we are on topic - another question. I am having problems with the xlr outlets of my dcx - they start a nasty noise in the lower band. Wiggling the outlets helps to solve it for a while. I have tried resoldering, which works for a month or so, then problem reoccurs.
Suspect bad soldering points.
Is ist advisable to remove the pc board mounted xlr connectors and replace them with panel mounted ones, and wire those to the board?
Suspect bad soldering points.
Is ist advisable to remove the pc board mounted xlr connectors and replace them with panel mounted ones, and wire those to the board?
I dunno, hard wiring doubles your chances for bad solder joints.
Is the PCB under some mechanical stress? That is known to loosen solder joint, or at least make them unriliable, after some time.
Jan Didden
Edit: I have located and used an exact replacement for the Behringer back panel XLRs from Farrnell. If anyone is interested I can look up the order number.
Is the PCB under some mechanical stress? That is known to loosen solder joint, or at least make them unriliable, after some time.
Jan Didden
Edit: I have located and used an exact replacement for the Behringer back panel XLRs from Farrnell. If anyone is interested I can look up the order number.
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Thanks for the terminology - describes the problem very well. Yes, I sure would like to find a permanent solution too. Will try again. Maybe cleaning the contacts and then somehow fasten the ribbon band connector - haywire and silicon?
At least - I know theres others out there, maybe we should develop a ten step program for the dcx
At least - I know theres others out there, maybe we should develop a ten step program for the dcx
I think I found the problem for the frying egg syndrom.
Just happened to reoccur, so took unit out and inspected it - no problems with ribbon connectors, solder joints - all nice and tight. Then I noticed: The little metal tabs that on the outlets hold the xlr plug in position were flat against the xlr housing - no spring action to seat the xlr connector properly.
Bent the tabs down 1/8" and reinserted unit into chain - and all noise gone.
Just happened to reoccur, so took unit out and inspected it - no problems with ribbon connectors, solder joints - all nice and tight. Then I noticed: The little metal tabs that on the outlets hold the xlr plug in position were flat against the xlr housing - no spring action to seat the xlr connector properly.
Bent the tabs down 1/8" and reinserted unit into chain - and all noise gone.
DCX2496 output filters
For those who are interested in those things, I ran a sim on the DCX2496 output filter (the 2nd order anlti-aliasing filters implemeted in opamps on the output boards). The attached graph shows the freq/phase curve (labeled "stock") and the passive filters I am going to put in (labeled 'mine' - how original!).
The stock has about -.2db at 20kHz but some 30degr phase shift. The passive has about -.5dB @ 20kHz but less phase shift.
Jan Didden
For those who are interested in those things, I ran a sim on the DCX2496 output filter (the 2nd order anlti-aliasing filters implemeted in opamps on the output boards). The attached graph shows the freq/phase curve (labeled "stock") and the passive filters I am going to put in (labeled 'mine' - how original!).
The stock has about -.2db at 20kHz but some 30degr phase shift. The passive has about -.5dB @ 20kHz but less phase shift.
Jan Didden
The schematics:
The middle one is the passive filter, with the balanced resistor values lumped to one side to avoid differential probing.
The lower one is the input circuitry of the DCX; this is interesting, since it has a kind of pre-emphasis; it has a high pass characteristic. Curves to follow.
Jan Didden
The middle one is the passive filter, with the balanced resistor values lumped to one side to avoid differential probing.
The lower one is the input circuitry of the DCX; this is interesting, since it has a kind of pre-emphasis; it has a high pass characteristic. Curves to follow.
Jan Didden
Jan, If I understand you correctly, you are saying that the DCX has a sort of preemphasis filter for analog inputs. So how does it deal with the digital input? Do you suppose that there is a similar preemphasis in the digital domain? And what would be the point of this preemphasis? It would be interesting to actually probe the unit and measure it's input circuitry prior to the A/D converter.
Regards,
Ron
Regards,
Ron
Ron,
My simulation doesn't show nearly as much "pre-emphasis" as Jan's, but maybe I've got something setup wrong. I'm seeing an approximate 0.9 db shelving action created by the filter. I think the difference is explained by what the load is seen by the circuit. Jan assumed zero ohms because of the two capacitors shunting the voltage divider on the + side of the inverting amplifier.
Anyway, I've looked at the outputs with both digital and analog inputs and they look flat to me. Any frequency contouring that's going on in the analog sections must compensated for in the digital domain somewhere.
Cheers,
Davey.
My simulation doesn't show nearly as much "pre-emphasis" as Jan's, but maybe I've got something setup wrong. I'm seeing an approximate 0.9 db shelving action created by the filter. I think the difference is explained by what the load is seen by the circuit. Jan assumed zero ohms because of the two capacitors shunting the voltage divider on the + side of the inverting amplifier.
Anyway, I've looked at the outputs with both digital and analog inputs and they look flat to me. Any frequency contouring that's going on in the analog sections must compensated for in the digital domain somewhere.
Cheers,
Davey.
If I will activate the mic preamp with this method -- will I be able to get the signal from the mic to the output (output #6, for example)? Or I have to take it just from these 9 & 10 pins only?
Thank you.
OK, it works fine.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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