That's with feedback around it, without, it's not a great driving buffer, sound good but it doesn't have balls.
Cheers George
I found the buffer after I/V is most critical. On my OPA861 I/V, the 2nd chip is used as buffer, but I am not happy with it. I simply replaced it with OPA627 and the sound is better.
As there are many PCM1704 users on this interesting thread I want to know your thoughts about this: in a dac I'm working on I only use 120uF per leg between each regulator (muzgdiy V3.1) and the 1704 +-5V pins.
I get very good sound, but maybe a little bit too much on the thin, "anorexic" side...
What do you think? Might more capacitance help?
I get very good sound, but maybe a little bit too much on the thin, "anorexic" side...
What do you think? Might more capacitance help?
As someone whose built quite a few ad844 and opa861 units i think they are both very fine units, i tend to use the 861 now, but its just a matter of taste, the 844 is maybe a bit more "organic" sounding, the best choice is probably more down to what dac chip you use, I'm presently using 1541 but building 1704 now and will try both 844 and 861 to see what suits my taste.
George, for some reason 've never had 1704 before , 1702 in a krell cdp with ian's gear going into i2s lines is closest , I'll have to get the latest refinements for 1704/844 from you.
George, for some reason 've never had 1704 before , 1702 in a krell cdp with ian's gear going into i2s lines is closest , I'll have to get the latest refinements for 1704/844 from you.
With the 1704 chip you mean ?
I believe all those chips are very dependant of the supply typologie and layout (passive parts)
@ supra : did you benchmark ad844 & 861 with the exact same layout & parts ?
I tried one 861 without the second 861 without noticeable change...(tda1541A)
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Hi Mick.
My best so far with the PCM1704k has been
Triple stack AD844 with 2.7k // 470pf at the TZ
From TZ to OPA627 at two times gain, input impedance 200kohm output 50ohms. I know the data sheet say "unity gain stable" but maybe just, so I went two times.
Cheers George
Eldam,
You are right. Last night I skipped the 2nd regulator (TPS7A4701/33) and fed +-13.6V into ADA4627 (OPA861 is still powered by 2nd LDO). The sound changed dramatically (in a good way). I am going to tune my OP amp regulator to +-5V and see what happens. Maybe the OPA861 is best with TL431+follower as Pedja's original design. BTW, my DAC is AD1860N.
Did you try ADA4627? I found it performs better than OPA627, especially the bass is more clear. ADA4267 is my current favorite, followed by Muses02.
I don't want to high jack George's thread, but yes I use the same into my AYA II and I'm interrested by your results as I have to finish a 1862 DAC (powersupply). If you use Pedja's PS topology I have a good mod about the caps to use for a very good improvement with the 861. Well always a mater of taste but many liked it. You can read it on the aya 2 DS edition on Audial website. Tell me what you think about it please after trying it.
Well sorry for this off topîc
Basicly want to try after tda1541, a 1862 (have bought the expensive genuine chips at Rochester) then George's topology, a little like Supra: I share certainly the same front end from IanCanada for my project with pcm dac chips.
Well sorry for this off topîc
Basicly want to try after tda1541, a 1862 (have bought the expensive genuine chips at Rochester) then George's topology, a little like Supra: I share certainly the same front end from IanCanada for my project with pcm dac chips.
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Any better in the bass than it's sounding now? I just couldn't imagine it.
Cheers George
Data sheet looks as good as the opa627. And I think it maybe not fet input, so the input impedance can't be made as high as the OPA627. As the TZ as I use it would preferably like to see 200k or so input impedance.
But the big problem is it's not unity gain stable, only stable at 5 x or higher gain, so this would count it out for me.
Cheers George
The TZ output would have difficulty driving the 10kohm input impedance of the Lightspeed, great idea though, another one is to use a single ldr for an I/V resistor and be able to change it's resistance on the fly while listening.
Cheers George
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Never wanted to design your pcb with all the things you experienced with the 1704K ?
The PCM board from IanCanada to feed the two PCM1704K is good and you have a great idea about this I/V conversion ! Some carefully chosed PS, parts, and clock (AndreaMori, IanCanada) could make it modular....
The PCM board from IanCanada to feed the two PCM1704K is good and you have a great idea about this I/V conversion ! Some carefully chosed PS, parts, and clock (AndreaMori, IanCanada) could make it modular....
Designing with PCM1704's
I built mine up based on the Evaluation board. Used a modular approach. Replaced the input receiver with the WM8804 board from Tekdevices. Considering it went obsolete last year and they never were "cheap" I have my doubts that any one will take on any new boards or kits. Your stuck with whatever is out there now.