RD30 Quad multibit d/a converter - diyAudio
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Musicaltech Musicaltech specialize in top digital audio concepts using powerful programmable logic devices. Original designs include total replacement of off-the-shelf chips - seen by the Musicaltech team as a limitation in performance and flexibility. Information about one of the the most sophisticated dacs avaialable for DIYers, either multibit or delta-sigma, are available in the dedicated forum.

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Old 15th September 2012, 05:12 PM   #1
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Default RD30 Quad multibit d/a converter

We all know how good a PCM1704 can be. Currently priced at 75$ per mono chip, and it seems to be the only 24bit R-2-R “dinosaur” available. I wanted to give to this chip that well-deserved digital front end, with a reclocker that offers superb jitter rejection(asynchronous FIFO style), a powerful digital filter, I2S, S/PDIF, AES and USB inputs (all accepting HD audio), convenient user interface with alphanumeric display and remote. I wanted the digital filter to be switched off when needed – for pure NOS operation. I wanted true balanced operation and this requires four PCM1704 on board. Could not stop it – I wanted the current outputs summed 2 by 2 for single ended output if needed – with the benefits of double current swing and double sample rate through analog linear interpolation.
The current outputs from PCM1704 are directly available, so any compatible I/V stage can be used, tube or solid-state.
The result is the RD30 dac, which took about 2 years of tests and bare r&d in all these critical areas to be completed. It is a very compact design, due to the fact that all the features are built into the powerful Xilinx Spartan6 chip XC6SLX16. Measuring only 124 x 125 mm and including all ultra-low noise power management and all input conenctors on board, only AC power is needed to fire up the RD30.
Attached Images
File Type: jpg RD-30B.jpg (173.6 KB, 1065 views)
File Type: jpg RD-30A.jpg (175.2 KB, 1028 views)
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Last edited by Lupulroz; 15th September 2012 at 05:41 PM.
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Old 16th September 2012, 06:15 PM   #2
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Custom building blocks FPGA :

- custom digital receiver
- asynchronous FIFO with digital PLL / DCXO, loop corner frequency 0.5 Hz
- Bytemorph 2.0 digital filter,60 bit internal, 384/768k , 1500 taps, -145 dB stopband att.*
- audio formatter and volume control , 256 steps
- user interface manager
*can be bypassed for native(NOS) mode

Digital inputs :

- AES/EBU : discrete lvds translator - 192/24
- S/PDIF : discrete lvds translator - 192/24
- USB : asynchronous, FX2LP interface 192/24*
- I2S over HDMI (native LVDS or CMOS) 192/24
*drivers available for Win,Mac, Linux

D/A conversion stage/supply/outputs :

- PCM 1704 x 4 multibit
- true balanced operation or single ended
- direct current output : 1.2mA x 4, 2.4mA x 2 respectively
- linear power supplies only, low noise regulators
- schottky rectifiers

User interface options :

- control buttons + led indicators
- control buttons + alphanumeric display, 4 x 20 characters
- remote control (rc5)
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Old 17th September 2012, 09:23 AM   #3
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Typical setup with I/V conversion stage RD30IV & simplified diagram
Attached Images
File Type: jpg RD30+IV typical setup.JPG (29.2 KB, 980 views)
File Type: jpg RD30 simplified diagram.JPG (40.6 KB, 948 views)
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Old 17th September 2012, 09:35 AM   #4
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RD30 Detailed connection diagram and board dimensions ; note that all four I2S outputs are available , for a possible external D/A stage.
Attached Files
File Type: pdf RD30connect.pdf (55.6 KB, 94 views)
File Type: pdf RD30_revB_assy.pdf (61.3 KB, 82 views)
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Old 17th September 2012, 09:44 AM   #5
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Optional front panel board :
- type A : 4x20 alphanumeric display, IR sensor, control switches
- type B : leds for sample rate signaling, IR sensor, control switches
Remote control also works with T30 transport.
Attached Images
File Type: jpg RD30_char_display.JPG (39.7 KB, 952 views)
File Type: jpg RD30_remote.jpg (48.3 KB, 235 views)
Attached Files
File Type: pdf RD30_char_display.pdf (82.3 KB, 32 views)
File Type: pdf RD30_LED_display.pdf (50.0 KB, 32 views)
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Last edited by Lupulroz; 17th September 2012 at 09:49 AM. Reason: photo
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Old 19th September 2012, 09:27 AM   #6
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There are many product levels :
- digital front end only (no PCM1704 on board)
- digital front end + 4 x PCM1704
Each version can be ordered with or without front panel board, either led or alphanumeric version.
A custom toroidal transformers set is available as well.
Feel free to contact me about pricing & availability.
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Old 20th September 2012, 08:33 PM   #7
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Looks promising.

Folks who are expert at digital stuff have said about the made in China DACs that they are not so good due to layout and bypassing errors... I wonder about such things... have you got published data and graphs, like off an Audio Precision that shows technical performance by any chance?

Regards,

_-_-bear
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Old 20th September 2012, 11:55 PM   #8
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Quote:
Originally Posted by bear View Post
Looks promising.

Folks who are expert at digital stuff have said about the made in China DACs that they are not so good due to layout and bypassing errors... I wonder about such things... have you got published data and graphs, like off an Audio Precision that shows technical performance by any chance?

Regards,

_-_-bear
Hi Bear,
our company is located in Europe - Romania and all products are designed and manufactured locally. There is no relation with China whatsoever.
The pcb is 4-layer with impedance control over certain signal traces. Routing BGA chips is not a trivial task, and we spent a lot of time optimizing the layout. I will post performance graphs soon.
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Old 21st September 2012, 07:07 PM   #9
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Looking forward to seeing that...
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Old 23rd September 2012, 03:22 PM   #10
eplpwr is offline eplpwr  Sweden
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Some technical questions on the RD-30:

- Are you generating the clock in the FPGA (soft PLL), or are you using crystal(s)?
- Is the Bytemorph DF oversampling to 768kHz or 384 kHz?
- Are you doing oversampling in integer multiples, or ASRC? I see only 384/768 kHz mentioned - for n x 44.1 kHz input I'd like to see 352.8 or 705.6 kHz.
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