Yes, backengineering the schematic for I2S DAC feed signals + DAC supply + DAC clock signals is one of the first on my todo list. I'm also still trying to figure out if there is a point to try to draw out the current analog stages.
I have also contacted Guido Tent to find out if anyone has successfully used his XO-DAC on DCX. I have not yet got a reply.
We should also figure out what format I2S (or something else) the DCX is using and then to see if any candidate DAC IC's can handle it without bigger hassle.
Ergo
Creating a third digital input on the DCX
Wow, after reading this whole thread, you folks are serious about re-engineering this unit. Well I have, what should be a simple question for a group such as this, How can I get 3 channels of digital input to this unit instead of just two? I want to use the unit for my Left Center and Right speakers. And I see no reason to convert the pre-amp signal to analog then back to digital inside the DCX. I want to send all three signals in digital to the DCX.
Any way to make input C digital or any better ideas?
Thanks James
Wow, after reading this whole thread, you folks are serious about re-engineering this unit. Well I have, what should be a simple question for a group such as this, How can I get 3 channels of digital input to this unit instead of just two? I want to use the unit for my Left Center and Right speakers. And I see no reason to convert the pre-amp signal to analog then back to digital inside the DCX. I want to send all three signals in digital to the DCX.
Any way to make input C digital or any better ideas?
Thanks James
Ergo,
Strictly speaking, we do not need the schematics for the analog stages if we are going to bypass them anyway. What is necessary is to determine the convenient point where we can pick up the necessary digital signals. Whether it is I2S format or not is not important, but this choice will be dictated by what the DCX is using. Now, what is it using, I do not know.
However, the reason I still would like to see the stock DCX schematics is to determine if all that ‘taking’ the signals outside is strictly speaking all that necessary. Those AKM DACs are quite good and I am not sure if we can pick up any more resolution by going outside with different DACs. There is no free lunch here, and the outside DAC will need its own power supply with consequent noise to handle, etc. Perhaps, it may be just as good to simply replace and/or modify the existing DCX circuitry, while preserving the AKM DACs. There is ample real estate inside the box and I can see a circuit board with anti-imaging filters and necessary buffers, all fitting inside.
Anyway, if the topology lends itself to such modification I would like to concider it before I do a major ‘surgery’ and take the signals outside.
Vadim
Strictly speaking, we do not need the schematics for the analog stages if we are going to bypass them anyway. What is necessary is to determine the convenient point where we can pick up the necessary digital signals. Whether it is I2S format or not is not important, but this choice will be dictated by what the DCX is using. Now, what is it using, I do not know.
However, the reason I still would like to see the stock DCX schematics is to determine if all that ‘taking’ the signals outside is strictly speaking all that necessary. Those AKM DACs are quite good and I am not sure if we can pick up any more resolution by going outside with different DACs. There is no free lunch here, and the outside DAC will need its own power supply with consequent noise to handle, etc. Perhaps, it may be just as good to simply replace and/or modify the existing DCX circuitry, while preserving the AKM DACs. There is ample real estate inside the box and I can see a circuit board with anti-imaging filters and necessary buffers, all fitting inside.
Anyway, if the topology lends itself to such modification I would like to concider it before I do a major ‘surgery’ and take the signals outside.
Vadim
As for the I2S extraction point, I quess we really have only one place to take it - on each respective DAC IC legs.
Even if we could trace the PCB track back to DSP chip legs I suppose it is much safer to do the soldering in DAC end. The DSP is much more vulnerable and would leave no room for mistake.
Vadim, you are right about the built in DAC's. With a decent analog stage and perhaps a better supply (better decouling or analog supply alltogether) they should have quite a bit of potential. Designing only the analog stages is a magnitude smaller tast than the whole DAC + analog stage.
As the unit is quite ok even off the shelf suggest that with analog stage tweaking there can be a huge merit and the sound should get a whole lot better.
Perhaps I still need to do a "prototype" first with only new analog stages and then make a decision if and how much it improved.
I still want to try the XO-DAC also. So Guido Tent, if you are reading this please let us know if you have any positive info.
Ergo
PS. As for jdreier question - there are two ADC-s inside. One for A and B inputs and one for C. If digital receiver IC is connected to I2S lines of the respective ADC (disconnecting the original) it might work. I suspect though that in digital input mode input C is disabled. So as you can not change the software the only way would be to use two receiver IC's for each SPDIF and to feed them to the pins of original ADC outputs - not an easy task to do.
Where do you get SPDIF for center channel only anyway???
Even if we could trace the PCB track back to DSP chip legs I suppose it is much safer to do the soldering in DAC end. The DSP is much more vulnerable and would leave no room for mistake.
Vadim, you are right about the built in DAC's. With a decent analog stage and perhaps a better supply (better decouling or analog supply alltogether) they should have quite a bit of potential. Designing only the analog stages is a magnitude smaller tast than the whole DAC + analog stage.
As the unit is quite ok even off the shelf suggest that with analog stage tweaking there can be a huge merit and the sound should get a whole lot better.
Perhaps I still need to do a "prototype" first with only new analog stages and then make a decision if and how much it improved.
I still want to try the XO-DAC also. So Guido Tent, if you are reading this please let us know if you have any positive info.
Ergo
PS. As for jdreier question - there are two ADC-s inside. One for A and B inputs and one for C. If digital receiver IC is connected to I2S lines of the respective ADC (disconnecting the original) it might work. I suspect though that in digital input mode input C is disabled. So as you can not change the software the only way would be to use two receiver IC's for each SPDIF and to feed them to the pins of original ADC outputs - not an easy task to do.
Where do you get SPDIF for center channel only anyway???
3 digital inputs
Thank you ergo, for the reply,
I am not as up on DSP surgery as you all, so let me take it slow.
I do not have a block diagram in my mind yet of exactly what the input stage looks like. When AES/EBU is selected does the digital signal pass through the ADC un-modified and get put on the I2S bus? Or does the digital signal from input A get re-routed altogether and get to the I2S bus through some other IC?
If the former is true then I wonder if it would work to lift the pass-through control pin on input C's ADC and tie it to the same pin on input A&B's ADC? If the later is true then I would need a duplicate of input A&B’s digital routing IC and run allot of bus and control wires from input C?
Which way do you think it is?
BTW I am not familiar with I2S protocol can it be feed directly with AES/EBU or does a conversion need to be made?
Also, there is no indication in the DCX2496 literature or software that input C is disabled when input A&B are in AES/EBU source mode, but maybe some one could try it and let us know?
Thanks James
Thank you ergo, for the reply,
I am not as up on DSP surgery as you all, so let me take it slow.
I do not have a block diagram in my mind yet of exactly what the input stage looks like. When AES/EBU is selected does the digital signal pass through the ADC un-modified and get put on the I2S bus? Or does the digital signal from input A get re-routed altogether and get to the I2S bus through some other IC?
If the former is true then I wonder if it would work to lift the pass-through control pin on input C's ADC and tie it to the same pin on input A&B's ADC? If the later is true then I would need a duplicate of input A&B’s digital routing IC and run allot of bus and control wires from input C?
Which way do you think it is?
BTW I am not familiar with I2S protocol can it be feed directly with AES/EBU or does a conversion need to be made?
Also, there is no indication in the DCX2496 literature or software that input C is disabled when input A&B are in AES/EBU source mode, but maybe some one could try it and let us know?
Thanks James
A new analog output circuit would also suit my needs perfectly
i belive that the output of the DAC´s ( voltage output - AKM converteres ! ) can be taken at the connector from the main PCB - we only need to track down the pin assignment.
Furthermore addition of volumen control in the form of TI PGA 2311 or other equivivalent would be most relevante
Morten
i belive that the output of the DAC´s ( voltage output - AKM converteres ! ) can be taken at the connector from the main PCB - we only need to track down the pin assignment.
Furthermore addition of volumen control in the form of TI PGA 2311 or other equivivalent would be most relevante
Morten
Solid state volume control always raises arguments and mostly not to it's favour.
I plan to use an ALPS motorized pot from old Marantz Dolby surround amp. Those are old and no-one wants a unit without DD/DTS anymore so can be had cheaply. This gives a way to get remote controlled volume
Ergo
I plan to use an ALPS motorized pot from old Marantz Dolby surround amp. Those are old and no-one wants a unit without DD/DTS anymore so can be had cheaply. This gives a way to get remote controlled volume
Ergo
Henckel,
Well, it seems that this way we can preserve the functionality and the look of the DCX, but we will have an improved output stage. I got to think about it some more, but it may be a way to go.
Ergo,
I am also using Alps motorized pots, - the 4-gang in my case. It is a good choice, but I am looking at the VCA implementation now. The modern VCA chips are quite good now with less then 0.01% THD across the audible band. There are TI and Analog Devices parts that are worth looking into.
Vadim
Yes, it seems that you are correct. So, here is what can be done. We take the analog signals from the DCP board connector and process them on the DIY board. We then remove some components from the XLR board so that we can have a direct signal path to the output XLR connectors and connect the processed signals from the DIY board to the XLR board.
Well, it seems that this way we can preserve the functionality and the look of the DCX, but we will have an improved output stage. I got to think about it some more, but it may be a way to go.
Ergo,
I am also using Alps motorized pots, - the 4-gang in my case. It is a good choice, but I am looking at the VCA implementation now. The modern VCA chips are quite good now with less then 0.01% THD across the audible band. There are TI and Analog Devices parts that are worth looking into.
Vadim
ergo said:Solid state volume control always raises arguments and mostly not to it's favour.
I plan to use an ALPS motorized pot from old Marantz Dolby surround amp. Those are old and no-one wants a unit without DD/DTS anymore so can be had cheaply. This gives a way to get remote controlled volume
Ergo
I've just been informed that Blue Sky International's Bass Management Controller can be converted to a balanced 6 channel volume control. with individual channel gains at the flick of a switch. This would allow the DCX's output gains to be set for maximum performance, and then the BMC handles the additional gain (+/- 6dB IIRC).
Blue Sky BMC
Here is another product that is not too expensive, just trying to figure out if it will control 4 channels. It states 2x stereo inputs & outputs.
M-Patch
An externally hosted image should be here but it was not working when we last tested it.
M-Patch
On a bit different note.
How complicated crossovers are you guys using with DCX?
I mean here something like 2nd order LP but with additional EQ to for example dampen the cone resonance of the woofer and also compensate baffle step etc.
Have you developed any neat tricks to insert a type of curve needed for any particular occasion.
Ingemar Johansson the author of LspCad (http://www.ijdata.com/) has mentioned that he is working on a way to control the DCX2496 straight from the LspCad software. I do not know the progress he has. I've been asking in lspcad mailig list but unfortunetly no response yet, but anyway this could be a real asset.
Ergo
PS. I will try to work on DCX this weekend and I hope I can figure out the pinout for analog stage connectors and also make some measurements and put the unit to work with some real hard crossover curves.
How complicated crossovers are you guys using with DCX?
I mean here something like 2nd order LP but with additional EQ to for example dampen the cone resonance of the woofer and also compensate baffle step etc.
Have you developed any neat tricks to insert a type of curve needed for any particular occasion.
Ingemar Johansson the author of LspCad (http://www.ijdata.com/) has mentioned that he is working on a way to control the DCX2496 straight from the LspCad software. I do not know the progress he has. I've been asking in lspcad mailig list but unfortunetly no response yet, but anyway this could be a real asset.
Ergo
PS. I will try to work on DCX this weekend and I hope I can figure out the pinout for analog stage connectors and also make some measurements and put the unit to work with some real hard crossover curves.
M Patch
Spearmint--My impression is that you get two sets of stereo outputs from one stereo input using the M Patch, so I believe the answer is no--it won't control four (separate) channels. Thus you would still need two of these inits for biamping or three for triamping (as you would only be using one of the output channels from each M Patch).
Have you tried the passive 6-channel attenuator from Decibel HiFi yet? Let us know how that works out if you do. I'm also going to be on the market for some type of post-DCX volume control as I just ordered a DCX yesterday for tri-amped dipoles I'll be building soon. Maybe I'll look into that Blue Sky unit that Mudge mentions, too.
Cheers,
Jeff
Spearmint--My impression is that you get two sets of stereo outputs from one stereo input using the M Patch, so I believe the answer is no--it won't control four (separate) channels. Thus you would still need two of these inits for biamping or three for triamping (as you would only be using one of the output channels from each M Patch).
Have you tried the passive 6-channel attenuator from Decibel HiFi yet? Let us know how that works out if you do. I'm also going to be on the market for some type of post-DCX volume control as I just ordered a DCX yesterday for tri-amped dipoles I'll be building soon. Maybe I'll look into that Blue Sky unit that Mudge mentions, too.
Cheers,
Jeff
Thanks for the feedback NH7RO
I just received the Decibel HiFi kit last night, probably won’t get a chance to test it until the weekend.
Ergo...
Please keep us informed as to how you go, I think what you are try to achieve is great. For me at this stage anyway, I will only be using the DCX to xover between the mains & sub, and using the parametric eq's on my 4x subs. The important thing for me I guess about what you are doing is input & output levels. Playing with the software the unit has plenty of potential especially the Dynamic Eq's.
I just received the Decibel HiFi kit last night, probably won’t get a chance to test it until the weekend.
Ergo...
Please keep us informed as to how you go, I think what you are try to achieve is great. For me at this stage anyway, I will only be using the DCX to xover between the mains & sub, and using the parametric eq's on my 4x subs. The important thing for me I guess about what you are doing is input & output levels. Playing with the software the unit has plenty of potential especially the Dynamic Eq's.
Re: Bass phase
Hi Coolin...
I have 3x subs at the front and 1x at the rear about 1.5mtrs behind the listening position, I set the phase on the first sub then running an 80 Hz tone I introduced each sub and played with the phase control of the DCX. The thing I love is how you can mute and play from the computer, so as you modify it is basically in real time.
As far as the parametric eq's go I just set them the same as when I was using the BFD. Hopefully this weekend I will have time to play and fine tune the filters with ETF5.
At this stage have not had the mains in circuit, had been waiting for the Decibel HiFi kit, as the output level was too much for the input of my power amp. Again hopefully get to play with this on the weekend.
Coolin said:
Hi Coolin...
I have 3x subs at the front and 1x at the rear about 1.5mtrs behind the listening position, I set the phase on the first sub then running an 80 Hz tone I introduced each sub and played with the phase control of the DCX. The thing I love is how you can mute and play from the computer, so as you modify it is basically in real time.
As far as the parametric eq's go I just set them the same as when I was using the BFD. Hopefully this weekend I will have time to play and fine tune the filters with ETF5.
At this stage have not had the mains in circuit, had been waiting for the Decibel HiFi kit, as the output level was too much for the input of my power amp. Again hopefully get to play with this on the weekend.
I'm sure you chaps have been looking hard at the DCX. Has anyone yet determined the connections on the multiway connectors? It really does look to me as though it's the I/O board that is the problem.
The analogue inputs can accept up to +22dBu, which is another way of saying that if you don't apply peak voltages of 9.76VRMS, then you're throwing away resolution in the ADC.
The digital input of the DSP chip looks for a balanced AES3 signal. AES3 is generally 10x the size of S/PDIF (the unbalanced stuff that dribbles out on RCA sockets). It's far better to attack the source and pick up the CMOS signal going into the S/PDIF driver (or the TOSLINK) and apply it to a proper RS485 driver. Applying a decent signal to the DCX will allow it to recover those digits cleanly.
The outputs are rather large, and it seems daft to use a (fairly reasonable) op-amp to amplify them, only to attenuate them again. Being a digital system, simply turning down output level throws away resolution in the DACs.
My take is that the outputs simply need buffers, not gain, and the input needs a buffer, not gain. I note that the data sheet for the ADC gives an approximate input impedance, which suggests that it may vary with digital code? Traditionally, ADCs were very nasty loads indeed to drive...
Finally, when playing with (someone else's) BSS fed with digits, I found the treble was harsh, but reducing its input gain by 3dB cleared the problem.
The analogue inputs can accept up to +22dBu, which is another way of saying that if you don't apply peak voltages of 9.76VRMS, then you're throwing away resolution in the ADC.
The digital input of the DSP chip looks for a balanced AES3 signal. AES3 is generally 10x the size of S/PDIF (the unbalanced stuff that dribbles out on RCA sockets). It's far better to attack the source and pick up the CMOS signal going into the S/PDIF driver (or the TOSLINK) and apply it to a proper RS485 driver. Applying a decent signal to the DCX will allow it to recover those digits cleanly.
The outputs are rather large, and it seems daft to use a (fairly reasonable) op-amp to amplify them, only to attenuate them again. Being a digital system, simply turning down output level throws away resolution in the DACs.
My take is that the outputs simply need buffers, not gain, and the input needs a buffer, not gain. I note that the data sheet for the ADC gives an approximate input impedance, which suggests that it may vary with digital code? Traditionally, ADCs were very nasty loads indeed to drive...
Finally, when playing with (someone else's) BSS fed with digits, I found the treble was harsh, but reducing its input gain by 3dB cleared the problem.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.