Silicon Chip DAC kit

[kimbo]

The lastest SC mag has the first part of an article describing construction of a DAC....... "High-Quality Stereo Digital-To-Analog Converter, Pt.1".

I've been waiting for the last few days to see if anyone would be posting their comments, but as there have been none I thought I'd start the ball rolling.
Of course the circuit is not available from their website (Understandable, they have to sell their mags), but here is the teaser......
http://www.siliconchip.com.au/cms/A_111597/article.html

I had a very quick look at the newstand and see that it uses a PCM1796 (I think).

And here is a thread in the overclockers forum where the author of the article makes some comments. (note that it is not the author who calls it 'ultra high quality'....he was just trying to design something affordable, straightforward to build and best performance within those boundaries)
http://forums.overclockers.com.au/sh...d.php?t=810680

I have no experience with DACs or anything digital having mostly built amps, but occasionally I've thought about dipping my toes into building one, and this may perhaps be a good introduction.

Anyway I'm very interested to hear any comments from members who have actually read the article.

[ttan98]

I am currently conducting a survey of the chipset used in DAC and what to look for and what to avoid. Without going into details which will cover a few pages I like to summarise my take/opinion of the chipset to look for. The analog, power supply and receiver chipset is another story.

Oversampling

AD1955
PCM1794

also a lesser know chipset is AD1852 (*) and also wolfson 8740 and AKM 4394

Non-oversampling
TD1541
AD1865(*)

* If you at looking into getting high quality DAC, Dacs based on these 2 chipsets will give you high end quality sound reproduction without the high price tag.

Go to this site for details:
http://www.audiodesignguide.com/DAC_final/DacFinal.html

[kimbo]

Thanks TTAN, but I don't think that is particularly helpful.
I am curious to hear from others who may have read this particular article in Silicon Chip. It may be a few days before other Austrailan members get their hands on the issue. Perhaps there will be a rush at the local library this weekend.....its always good to give support to these fine institutions!

[ttan98]

There are a LOT of off the shelf DACs from Ebay that are of good value and you can purchased them/it already assembled and plug and play. These boards are based on the chipsets that I mentioned above. I suggest you look into this before building the one from SC.

Log on to US Ebay, ie ebay.com and search for DAC under electronics category. All these boards are of excellent value and sound good too, I purchased a few boards to play with myself. There MANY varieties to pick from. The decision is yours, believe me made in China do not mean inferior quality. Believe me the chipsets you pick determines the type of sound reproduction you want.

Cheers.

[kimbo]

thanks for the prompt response TTan.

I supose my problem is that I just like taking over the kitchen table and putting stuff together......I always learn more and I just love that smell of hot resin, but yes, if the SC one gets the thumbs down I'll probably buy something off the shelf.

I'll see if I can sneak a look at the library and post some more details about the chipset used.

Cheers,

[col]

I recently built a couple of SC projects, The Multi-Function Active Filter KC4580 and the Bridge Adapter for Stereo Amps KC4569. They were very easy to build and have good documentation. The PCBs are good quality but very large. The kits performed very well. I'm not sure how good quality the design is though, they use a lot of NP caps.

http://minirig.org.au/2009/08/14/min...pter-for-subs/

I wouldn't mind having a go at the DAC kit but have no need for it.

col.

[ianrt]

I've read the article in SC

The DAC project is a good one, but not a very good one.

It uses a DIR9001 re-clocker and a DSD1796 DAC providing up to 24/96k decoding.
It has separate power supplies for analog and digital sections (although these use the one transformer and diode bridge)
Output stage is per 1796 datasheet but the project allows for the use of OPA134 instead of NE5534, and is single-ended only (without the pcb layout it is difficult to know how easy one could mod it for balanced output but it should be do-able)

Output frequency response starts falling above 24kHz (but if modded for balanced output you might be able to shift this up to 70kHz)

There is some strange problem (perhaps from using the one analog ps for both channels) that reduces crosstalk performance by 20dB at 10kHz and 30dB at 20kHz. Again without seeing the pcb layout I don't know whether separate supplies are easily adopted for each channel to try to fix this.

This project would be OK for anyone who doesn't have an outboard DAC to improve sound from mid-level CD players or PC-based material but if you're looking for top performance, try elsewhere.

I hope this helps.

Ian

[nvinen]

Originally Posted by ianrt

Output stage is per 1796 datasheet but the project allows for the use of OPA134 instead of NE5534, and is single-ended only (without the pcb layout it is difficult to know how easy one could mod it for balanced output but it should be do-able)

It isn't too hard, this information will be published in a future edition.

Originally Posted by ianrt

Output frequency response starts falling above 24kHz (but if modded for balanced output you might be able to shift this up to 70kHz)

I'm fairly sure there are no (or at least very few) humans who can hear above 24kHz, is there a reason why you care about the frequency response above that?

My own hearing limit is about 18kHz. I don't have particularly bad hearing loss.

Originally Posted by ianrt

There is some strange problem (perhaps from using the one analog ps for both channels) that reduces crosstalk performance by 20dB at 10kHz and 30dB at 20kHz. Again without seeing the pcb layout I d.on't know whether separate supplies are easily adopted for each channel to try to fix this.

It is due to the limited CMRR of the differential amplifier stages and coupling through the power supply. The balanced modification does greatly increase channel separation. However, channel separation performance of the unbalanced outputs is more than adequate. The difference between 70dB and 120dB channel separation will not be audible except under special circumstances - certainly not during regular listening.

Originally Posted by ianrt

This project would be OK for anyone who doesn't have an outboard DAC to improve sound from mid-level CD players or PC-based material but if you're looking for top performance, try elsewhere.

I think you'll find it will be hard to beat the performance in the sense that the output is very clean and low distortion, even compared with a high end CD player. As will be revealed later, typical distortion is actually somewhat lower than originally quoted. If you are looking for something other than low distortion and low noise then all bets are off.

[kimbo]

Hi nvinen,

thanks for the post. I see you have dropped a few hints of more to come both here re 'balanced output', and on another forum with "Keep an eye out over the next few months, there will likely be a USB add-on."

I may be wrong but I'd think that any improvement to the crosstalk can only be a good thing as far as imaging goes.....that soundstage illusion is fragile and every bit counts.

For me, I not concerned about USB. I'm just curious to see what improvement I get if I use an outboard DAC on my yamaha DVD/SACD player. To be honest I'd rather splash a whack of cash on a dedicated quality CD player but being a family man, I can only weedle a little spare cash for my hobby. A DAC would be cool as the trouble & strife wouldn't know what it is, but a CD player, it would be ....'what do you need that for?'

As I said, I'm new to DACs and digital in general so I'm pretty keen to get soldering, however cost will probably be the key factor in me following through with a build, so I'm waiting for the usual vendors to come out with a kit before I jump in. If it is too high for my budget I'll probably think about other options....perhaps something from the states when the missus visits her mom in NJ at Xmas.

[kimbo]

Originally Posted by kimbo

however cost will probably be the key factor in me following through with a build, so I'm waiting for the usual vendors to come out with a kit before I jump in. If it is too high for my budget I'll probably think about other options....perhaps something from the states when the missus visits her mom in NJ at Xmas.

Dropped into Jaycar on the way home for something else and picked up the latest flyer. The kit is advertised as a shortform for AU$139. This is sort of OK....but by the time I cased it and provided a transformer......hmmm is the power supply on board? .....can't remember....anyway final cost will be closer to $200 so I may think twice about it.

I'll wait a few weeks for other members to get around to checking it out and perhaps comment on the bangs for bucks.