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Tam Lin
01-11-2008, 21:54
This looks like a very friendly forum; I’m glad to have found it.

My current audio passion is DIY DACs. Actually, make that singular DAC; one I’ve been tinkering with for the past five years. It’s been a fun learning experience but every time I think I have made it as good as I can I learn something new and, more often than not, start again from scratch. One of these days I’ll actually finish it. In the meantime, I really enjoy the hardware design and PCB layout process. I like it better than programming, which I did for many years.

Tam Lin

Mike
01-11-2008, 21:56
Hi Tam Lin, and welcome to AoS.

You may may find this thread interesting: http://theartofsound.net/forum/showthread.php?t=315

Cheers...

Marco
01-11-2008, 22:19
Hi Tam Lin,

Welcome to the forum :)

There are plenty of DAC discussions here, D.I.Y and otherwise, so you should enjoy yourself.

May I ask where is Carterhaugh?

Marco.

Mike
01-11-2008, 22:27
http://www.gaddgedlar.com/tlin.htm

Work the rest out for yourself! :ner:

Oh I'll save you the bother....

http://en.wikipedia.org/wiki/Carterhaugh

Marco
01-11-2008, 22:39
LOL, thanks. I could have done that myself! I always love it when people join from obscure places and announce: 'Hi from Upper Smogsborne', or suchlike, automatically presuming that everyone knows where it is! :lol:

No offence, Tam Lin :)

Selkirk's a lovely area - I've been there many times. The Borders are an underrated part of Scotland for scenery, with everyone usually raving about the Highlands and Islands.

Marco.

Filterlab
03-11-2008, 10:12
Hi Tam Lin and welcome, I see the DIY DAC is becoming a very popular subject these days.

Enjoy!


...I always love it when people join from obscure places and announce: 'Hi from Upper Smogsborne', or suchlike,...

I used to live in a quaint village called Upper Drakes Bottom.

:D

Tam Lin
03-11-2008, 19:01
You may may find this thread interesting: http://theartofsound.net/forum/showthread.php?t=315
Thanks for the link. I read the thread but I didn’t see anything about DIY, as I know it. There’s nothing wrong with building kits and modifying inexpensive components to maximize their performance. It is an excellent way to get started on the path to real DIY. That’s how I started but I’ve moved beyond that now. Here’s a brief description of the DIY DAC I’ve been working on:

The objective is to compare different DAC chips and topologies.

A local oscillator and synchronous counter provide all timing and export clocks to slave a CDP or PC sound card. Digital to analog conversion is non-oversampled, 2x or 4x oversampled with null insertion and/or analog interpolation, or 8x oversampled with digital interpolation. There is also a hybrid mode that combines 2x and 8x oversampling. Analog output is via passive I/V, transformer, and deemphasis and reconstruction filters.

Additional features and options include:
· 256Fs or 384Fs system clock.
· Slow or fast digital filter roll-off.
· Input to the clock divider from MCLK instead of the oscillator for occasional use with unsynced digital sources.
· S/PDIF input via transformer-coupled coax or via twisted pair using the same differential transceivers that transmit the CDP clock; i.e., one Cat5 cable between the DAC and CDP.
· The sample position within the sub-frame is optimized for best sound. Right-shifting the sample reduces the maximum and RMS sample value, which reduces the maximum and RMS output current of the DAC. Right shifting also reduces the maximum and RMS step size, which reduces di/dt and DAC settling time.
· With different DAC and fan-out modules almost any kind or number of DAC chips can be evaluated.

I have designed two DAC modules so far: One uses four PCM1704K that can be configured as two parallel or differential pairs and the other uses two PCM1794A that can be configured as two singles or one pair. Each DAC module has a corresponding fan-out module: 1:16 and 1:4. Summing the output of many parallel DACs improves S/N, dynamics, and reveals more low-level detail. The observed effect is greater than the theoretical +3dB S/N per doubling because human hearing and perception are not simple linear processes. BTW, this technique is also used in astrophotography.

The project started with the idea of comparing NOS with 8x digital interpolation using four PCM1704 and a DF1704. Then it grew in successive stages:

· Added shift register to time-align the left and right sub-frames.
· Added shift register to optimize sample position in the sub-frame.
· Added 2x OS with null insertion.
· Added 1:16 fan-out for PCM1704 modules.
· Added 2x OS with analog interpolation.
· Added 4x OS with null insertion or analog interpolation.
· Added PCM1794 module.
· Added 1:4 fan-out for PCM1794 modules.
· Added hybrid 2X & 8X OS.

I think I’ve stretched this idea as far as I can and it’s time to stop designing and start building. The interfaces are robust and will support any other DAC chip I might want to compare in the future. I’ll keep you posted.

Mike
04-11-2008, 13:58
Nice!... Please, DO start a thread about it all in the DIY section! :)

Cheers...

Tam Lin
05-11-2008, 17:50
Nice!... Please, DO start a thread about it all in the DIY section! :)
Done.

Filterlab
06-11-2008, 09:36
Nice one. :)