[topher]

aos,
NPO/COG do have good temp coef. but they also have
very low dielectric absorption, and to all
accounts sound much better than other ceramics.
I would guess polypropylene would sound best, but
I don't know whether mica, poly or NPO would sound
best. I would like to hear what ppl has to say
about what high frequency caps sound best. This
is not really the everyday audio frequency
application. It is more like a bypass cap doing
duty as a coupling cap.

Also, as ppl can tell you better than I, Any time
an opamp drive a load, the output current caused
heating degrades the sound. This application
basically has the first opamps driving a 2.7K
load. I think this might be the reason Norman
Tracy and others have reported so-so sound from
AD1853's.


I really suspect that this output network would sound better if each opamp had a buffer.

 

[rickcr42]

Ok,so this thread was locked at HeadWize so I guess I will continue here.Just received the Analog Devices AD1866 DAC chip http://products.analog.com/products/...product=AD1866
Not that the 1861 is forgotten,just on hold temporarily.This DAC chip caught my eye due to the great 10 ma current draw for both channels at +5 volts single supply.Add the fact that it has current outputs allowing bypassing the internal op-amps and it looks like a winner.
Yes it is only a 16 bit DAC,but CD redbook is speced at 16 bit.I am also rethinking the input receiver chip.The Yamaha is maybe not the superchip the crystal receiver is,but it also is not as power hungry.8 ma looks pretty sweet from my perspective.Remeber,this is not a search for the ultimate DAC,it is a proposed REAL portable DAC/Headphone amplifier and so must be usable in the real world.There are always tradeoffs when there are limits,in this case those limits are size,weight,and battery life.
And as far as a gainstage is concerned,remember we do not need the full 2 volts output by a home DAC so we can chose the output voltage of the chip by adjusting the IV resistor and possibly eliminating a gain stage entirely,going directly to output buffers or unity gain parallel op-amps,whatever.
One point-the IV resistor has much influence on the ultimate sound and dynamics of the end DAC.Selecting the proper value is not just a math solution but has to be actually listened to and selected on the basis of output volts/sound/dynamics,as much voodoo as science.
This thread needs to live again so I brought it back to life

Lazarus,I mean, er , um, rick

 

[aos]

Wow, how did this one elude me before? Power consumption is excellent, and performance is acceptable.

I've put the PCB design on hold since I'd need hundreds of dollars to buy yet more and more parts, and now is a really bad time for anyone working in the high-tech to spend money he/she doesn't have. Besides, with air travel being one step away from having passengers handcuffed to their seats for the duration of flight, the value of the whole project is higly questionable, at least for me.

 

[aos]

Rick, this chip requires use of digital filter. That will increase power consumption significantly.

Also, it does not have current outs bypassing the internal opamps. It only has voltage outs from its internal opamps.

Also, bear in mind that jitter characteristics of portable device's digital outs are probably worse than that of stationary ones. Therefore having a good jitter resistant receiver chip will make a bigger difference in sound quality.

 

[aeberbach]

Hey aos, obviously this is an expensive project to undertake. If people were willing to subscribe towards development costs, maybe $50, could you perhaps provide a PCB from the first run? (Or maybe the second if it needs a rev!) IF and only if it comes to something. I wouldn't be asking for the money back if it all proved impossible, just a sharing out of some parts that had been purchased. This should be a community project, we're all going to want one.

 

[aos]

I'd consider ordering a batch of boards once design has been verified & tested & found worthwhile. First board will have to be hand-made but once quirks are out and I'm happy with sound, I could use Eagle's fabrication files to order a batch of boards. But that's all in the future.

I'd consider lending a finished prototype to someone here for evaluation before ordering boards just so that it can be independently verified that the sound is. But as I said, there's a long long way to go before that.

I have to order DAC chips, opamps and voltage references/regulators. I'd also need an optical receiver module. That's 3 different suppliers, 4 if I want to order OSCONs and other good parts for the DAC...

 

[ringtheorist]

If you need to order in quantity, double what you need and I'll take the other half.

b

 

[rickcr42]

Quote:

Rick, this chip requires use of digital filter. That will increase power consumption significantly.

not true at all aos,it just is not mentioned in the data sheet,or any others for that matter

Quote:

Also, it does not have current outs bypassing the internal opamps. It only has voltage outs from its internal opamps.

KEYRECT ! Way too many DAC chips and Data sheets sitting in front of me,they start to blur into one after a while

I still like the curent spec,not that I am giving up the 1861,doing an A/B will be fun.If even close the final design goes over to the more efficient.

BTW-neither of these chips are under consideration as my main home DAC.That duty is my AD!865.Also need to get cracking on the USB DAC since I have had the parts for about six months

 

[aos]

I guess filter is not required as such... However then you need very steep analog filter, or you'll get aliasing. And steep analog filter usually means non-linear phase at higher frequencies...

The chip itself is quite allright, numbers at least are more than fine. AD1853 that I want to use needs a lot more power

.

Oh, AD1865... is one ******VERY****** expensive SOB. I already spent tons of money on PCM-63 and whatever is the latest 24-bit version so I'm not in the mood to pay another US$50+ for just a chip. I can almost buy a portable CDP for that price for God's sake.

 

[rickcr42]

also sitting on an 1853,no idea where that is heading yet.Looks like by the time I am done there will either be a DAC on every single digital audio componantI own,or santa will be coming early this year for someone

 

[ringtheorist]

It occurred to me yesterday that I've only ever seen one portable cd player with an optical digital output ever. I went searching for them yesterday and again came up with only one hit. MIniDisc players also don't have digital output anymore.

So.. is this project just an experiment in excess? (or rather, lack thereof?)
I don't see portability really as the issue with a DAC.

b

 

[rickcr42]

Pretty damn amazing how each generation of player give you less for more loot.The only thing the new players seem to give MORE of is battery life and anti-skip time,but at the expense of output power and REAL features.
But when talking about a digital output there are several reasons behind this.First,the MD has not taken hold in the US as I for one think it should have.And since MD is a niche market here and the main use use for a digital output is to make a copy why bother ?
The second reason could be related to the first reason,copying CDs is becoming taboo,and the manufacturers are in cahoots (knew i would get that word in somewhere,someday) trying to eliminate the practise.
The lack of digital outputs and Cds that will not play in a CDROM plus some of the new copyguard schemes can spell the end of digital copies of a CD.

 

[aeberbach]

cahoots! Good word. Yes, they are. I met people from Sony's Digital Rights Management group in Tokyo recently - they would LOVE to see CD as a format just die, because there is almost nothing they can do to control it. Couple it with MD and they may as well just let us download it all for free, because the MD copy protection is so easily broken...

 

[aos]

Here in Canada we pay about 30 cents per CDR levy "for the artists". Therefore I see any manufacturer trying to prevent copying as breaking the law. I *pay* tax so I expect to be able to copy the thing. Either stop the tax or stop puting unlawful restrictions on the CDs.

Luckily, I listen to classical and I could happily live the rest of my life with just getting the current CDs. Pity those who listen to modern "artists"...

As for Sony, they're almost on the top of the list of companies I'd love to see go broke and dissapear in history books. There are very few things that could make me happier.

 

[rickcr42]

I have been copying my recordings since old enough to know how to do so.I may have exchanged tapes a few time but I doubt if that caused any company or artist to go broke.
It was a ritual to purchase the LP then copy it to cassette for use in my car.
There is the extreme of the copying of copyrighted material but that should not apply to personal use of something I purchased for MY use as i see fit.
What next ? CD liscence to listen ?Pay per play ?
Greedy bastards.