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Portable DAC prototype 2: mission accomplished

post #1 of 15
Thread Starter 
Second prototype is finished and is working just fine:



It draws 69.7mA when optical in is used, but that can be reduced by another 12mA by using another optical receiver (which I still don't have).

At any rate, >20hours on 6 NiMH batteries is satisfied even now (and it could be closer to 30 hours with less power hungry receiver) so I can say mission accomplished. I can now work on optimizing the analog stage to sound even better, do opamp rolling etc.

(Edited for better closeup)
post #2 of 15
Wow. Very cool and involved project. Must feel great to have it up and running! I would like to know the results of some chip rolling when you get to it. Please let us know the results.
post #3 of 15
Aos, let me get this straight...

PCDP -> DAC -> HeadAmp -> Cans

That's one HUGE portable setup!

What would rock would be to make a desktop DAC/Headamp combo. Are you gonna share the plans when done?
post #4 of 15
So what PCDPs are available that you could actually use an external DAC with?
post #5 of 15
I was sort of skeptical when the whole portable DAC project started, simply because of the seeming lack of portable transports. However, it was pointed out to me that almost all portables overseas have an optical output. If you want to get ahold of such a player in the states, check out www.minidisco.com.

And.. if you already dearly love your portable player, open it up and check the circuit board. As was pointed out to me a while back, most portables have a spot on the pcb for an optical transmitter. It doesn't look to hard (I've never done it) to wire up a jack.

As for the details of the project, Andrija posted some schematics for it a while back on head-fi. I'm sure in due time he'll let us know which parts work best, as I think he's toyed with every combination under the sun

b
post #6 of 15
aos: COOL I was Hoping for you to do a portable dac. can you supply PC Board Files? Anyway thanks alot for sharing this design with us. I was Hoping to Build this before Spring. BTW any sonic evaluations yet?

ringtheorest: hav hoy Heared if the Pannasonic SL-SW860 has sutch a Provision on it's PC board?
post #7 of 15
Thread Starter 
ppl: the sound is marvelous, comparable to all my other rigs. I'm hoping some of our local HeadWizers/HeadFizers with audiophile tendencies will want to meet to evaluate it as I'd like some independent opinion; advantage is that I can easily take it with me in the pocket .

I've had some thin sound and clipping initially, but later I discovered some unsoldered joints that I've fixed, and I was also using OPA2604 instead of 2228 (hard to say which is which when markings are barely readable). I also found out that headphones don't like resistors in series when there's a capacitor there as well - some low pass filter effect happens? It sounded a little like AM radio before I bypassed resistors, but when using high impedance load (read: connected to headphone amp or receiver/speakers) the sound was good. I've put a ferrite bead in parallel with resistor so now DAC can power headphones as well. After these changes situation is good. Volume on HD580 and DT931 is somewhat higher than I tolerate listening to, definitely at least as loud as a normal headphones (low impedance) when connected to your average cd player. One could install a potentiometer on the rear panel (no space left on front) and have volume control and eliminate need for separate headphone amp.

As line out, the level is about the same as from my
Panasonic SL-SW851C portable, and it could be made even higher if output is going to be used exclusively for driving high impedance. Conversely, if low impedance cans are to be used, feedback resistors should be lowered to avoid clipping. Output buffer is close to rail-to-rail performance when load is in the kiloohm range but drops to 2.5V to 3V below 100 Ohm.
post #8 of 15
yeah,never follow a cap with a resistor in "series" (unless in the 100 to 220 ohm region).Rather follow with say 10K after the cap.One pole to signal,other pole to ground
post #9 of 15
Thread Starter 
Yes, this is the portable rig:



I just picked that D-EJ915 from Future Shop as "open box". It was $149 Canadian, but it is missing too many things - headphones, which I couldn't care less, but it probably came with the remote and I didn't get that, and neither I got gumstick battery (?!#$@$) and manual. And on top of it, it has some scratches. Should've been much less I recon. Oh well. I'll try to get the battery tomorrow and see if they have remotes as well. At least it's slim and light, I assume it was one of top models generation ago.

I must say, now that I fixed some minor issues, this DAC turns out to be my favorite. So it maybe doesn't have as much "air" as my biggest one (it's not a big difference) but considering the design of analog amp (all discrete zero feedback) and the price of parts in that one (Vishay bulk metal foil, Caddock, Black Gate, MultiCap...) it better be. However it is more musical, in line with my modified Marantz CDP - they both sound warmer without giving away any of the detail. Rendering of treble is the best I have so far, and all strings sound more natural - probably the consequence of zero oversampling and especially use of Bessel filter (which probably has taken away some "air", seeing how it has -3dB at 20kHz and starts slowly rolling of already before 10kHz), because Bessel filter preserves linear phase and thus group delay (so different frequencies get to the output at the same time).
post #10 of 15
aos,

opamp rolling? What, no tube output stage? Way to go champ! btw, Safeway Select rules.
post #11 of 15
Thread Starter 
You mean this?

post #12 of 15
Lol, I was just doing this earlier today with those same model yellow-gripped chip pullers - testing different op amps in a higher power/voltage Szekeres. If I had a digital camera, I could make an immitation of that picture.
post #13 of 15
I don't know how you can afford this hobby considering all the DIY gear you have. I do my shopping at SMI, and they're convenient, but do you think I could do better price wise? Thanks,


jamf.
post #14 of 15
Thread Starter 
zoboomofo, what is SMI? Electronic parts shop?
post #15 of 15
Yup. I think they have several locations in the Lower Mainland.
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