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-   -   RD30 Quad multibit d/a converter (http://www.diyaudio.com/forums/musicaltech/219782-rd30-quad-multibit-d-converter.html)

Lupulroz 15th September 2012 06:12 PM

RD30 Quad multibit d/a converter
 
2 Attachment(s)
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.

Lupulroz 16th September 2012 07:15 PM

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)

Lupulroz 17th September 2012 10:23 AM

2 Attachment(s)
Typical setup with I/V conversion stage RD30IV & simplified diagram

Lupulroz 17th September 2012 10:35 AM

2 Attachment(s)
RD30 Detailed connection diagram and board dimensions ; note that all four I2S outputs are available , for a possible external D/A stage.

Lupulroz 17th September 2012 10:44 AM

4 Attachment(s)
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.

Lupulroz 19th September 2012 10:27 AM

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.

bear 20th September 2012 09:33 PM

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

Lupulroz 21st September 2012 12:55 AM

Quote:

Originally Posted by bear (Post 3172553)
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.

bear 21st September 2012 08:07 PM

Looking forward to seeing that...

eplpwr 23rd September 2012 04:22 PM

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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