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Old 6th October 2011, 12:24 PM   #1
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Default Project CPeDD Preamp and I2S external DAC for Behringer DEQ/DCX2496

Hello,

I m willing to do a all digital preamp & dac box for the DEQ/DCX2496 but feel alone on solving some design aspects and I m sure this thread can be of interrest for all the guys already playing with DEQ or DCX for EQ or Bi/Tri-amping...

Context:
Weakness of Behringer products is their power supply , analog board, lack of spdif switching. But they bring powerful treatment for EQ or cross over.

Idea is basically to use only their DSP board and to export in a separate box:
- the digital input switching
- SRC and master clock (need assessment feasibility)
- DAC by sending I2S over some balanced HDMI connection
- power supply can be limited to providing only 5V and 3V which can be done with separate wall wart and 2 LDO regs...
-RSR232 connection for controlling parameters

Now come User interface.
Lots of work being done for hifiduino or lcduino (respect and credits! ), I have in mind to power all of this with Atmega328p driving LCD 4x40 and conected to encoder, Infra red receiver and then providing I2C and SPI for controling various DACs and IOs.

Ok, you see it ?

In term of feasibility or directions:
- The IR, encoder and LCD 4x40 control and application can be leveraged almost as-is from hifiduino (fonts, menu, pin out, Apple remote control...)
- the DCX/DEQ addon would be nothing different from the famous F.oettle SRC/clock (see on pilgham website) with some hdmi additional connectors and LVDS line drivers on the PCB
- I2S over hdmi can be leveraged from the proposal in the post of PSAudio.
- volume control with LDR and Atmega328 would be optional (as the DACs usually contains digital volume) but this board is already on my bench and should be finished next month or before end of 2011. see other post here.
-I2S dac module : 2 possible direction : leveraging Twisted Pears modules (opus, buffalo...) or building a new clean board (prefered) with the top famous AK4395 or AK4396, including HDMI and I2S line receiver on the module, and header for spi control from Atmega.
-USB input could be just using some sort of miniStream from MiniDSP and injecting SPDIF or I2S in slave mode to the DCX/DEQ (need feasability assessment). looks quite good up to 96k, but other alternative from Twisted pear or so could be ok.

here are couple of pictures/slide I made in order to prepare schematic and ellaborate this with the community.


Big picture
Click the image to open in full size.
Preamp/switching section
Click the image to open in full size.
DCX/DEQ addon
Click the image to open in full size.
I2S DAC module
Click the image to open in full size.
Volume control LDR (optional)
Click the image to open in full size.

for the interface with DEQ/DCX, I forsee 2 scenarios.
- RS232 on DB9 + SPDIF on XLR + 3 mini HDMI from each stereo channel
- one single HDMI connector, handling all signals above ! (preferred) but in single line driver mode, not LVDS balanced then due to limitation for 8 shielded signals.
The preamp might be compatible with the 2 scenarios by offering a specific single HDMI connector for the DEQ/DCX, and separate HDMI inputs on each DAC

Ok this is it so far! appreciate your feedback and contribution
(goal is to get all of this done, with nice PCBs and pre soldered SMD in a 3/4 months time frame, as a DIY kit)

Last edited by Pano; 6th October 2011 at 12:59 PM. Reason: email removed
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Old 6th October 2011, 01:02 PM   #2
Pano is offline Pano  United States
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This looks like a nice project. If it is a kit that you intend to sell, then it should go in the Vendor's Bazaar and those who contribute will know that it is a commercial venture.

If this is a group project, then it can remain here. Perhaps a Group Buy can be done when the project is ready.
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Old 6th October 2011, 01:22 PM   #3
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in fact I dont want to make benefit out of it. So more a group project with probably group buy orders if realistic at this time
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Old 6th October 2011, 03:54 PM   #4
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I feel that 5 optical inputs is too many. I suggest that at least two of those TOSLINK inputs be replaced with one AES/EBU over XLR balanced, and one S/PDIF over BNC coax.
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Old 6th October 2011, 04:25 PM   #5
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make sense, will put in change log
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Old 20th November 2011, 04:05 PM   #6
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slightly related: I found this on ebay and ordered one to play with:

Multi-input/converter for DAC(USB+optic+SPDIF+XLR) | eBay

Click the image to open in full size.

and this may be a good idea (the wm8805) for spdif input selection. you get selection AND de-jittering (reclocking) at the same time.

I'll let you know if this module works; will probably be here in 2-3 weeks.
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Old 22nd November 2011, 07:22 AM   #7
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yep this looks cool you get the 8805 and a couple of digital inputs . But USB is cheap, seem they use CM102 with SPDIF (48kz) output routed to WM, quite basic. You could probably control the WM just with 2 wires , it is probably configured in HW paralell mode. Another #IFDEF statement in your VolumeMaster code
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Old 22nd November 2011, 02:38 PM   #8
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the cm102 is a fine chip! I have zero problems with it. I love cmedia! every time I use their chips, they Just Plain Work(tm). no drivers, no o/s nonsense, and decent enough sound for what they are. various cmedia chips can be modified so that you dump their analog out and use spdif or even i2s (if you can solder to the chip, itself, you can get the i2s signals).

Click the image to open in full size.

ignore the larger board (that's a 'seagate dockstar' unassembled and hacked as a silent linux server). the 2 small boards are both cmedia chips; one is the simpler one and the larger one (on clear acrylic stand-off board) also supports i2s as well as spdif. I tried to solder to the chip and break-out the i2s but my soldering was not up to the task ;(

the other small board, though, I did tap into its spdif and made my own toslink-out. works great.

the cmedia chips stop at 48k but they very much do support 44.1 and that's 99% of my listening. and the dongles are small enough to be embedded in your own DIY. create a rear usb port, insert the adapter card on the port and wire it to spdif. there: you have a switch port with 'usb' on it. easy

going 24/96 on usb is much much harder and also still not standard for o/s level drivers. I don't have any 2496 files so it won't bother me being 'stuck' at 44.1
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