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AliExpress AD1865 R2R DAC
AliExpress AD1865 R2R DAC
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Old 4th October 2018, 05:15 AM   #21
abraxalito is offline abraxalito  United Kingdom
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I don't think they do in fact make any money, probably they're just covering costs. However if you spend much time on Taobao looking at the prices of parts you might be surprised how cheap they are in comparison with Digikey, Mouser etc.
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Old 4th October 2018, 04:26 PM   #22
matt_garman is offline matt_garman  United States
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AliExpress AD1865 R2R DAC
Over on the Head-Fi forums, Jason Stoddard wrote a very lengthy series of posts about how Schiit Audio came to be, along with many of the interesting challenges they've faced. I haven't read all of it, but I found it quite interesting (and I don't even own any Schiit gear).

But one thing that I remember reading (and it's been a while, so I'm quite liberally paraphrasing) that parts sourcing is an on-going challenge. He said that Mouser and DigiKey are actually his last-resort vendors, because even their best bulk pricing is still significantly higher than the huge-volume-only distributors he prefers to use.

To me, it kinda makes intuitive sense that selling small quantities to hobbyists like me incurs a tremendous amount of overhead. I mean, I can go to Mouser/DigiKey and order a single $0.10 SMD resistor. Obviously I don't do that, as shipping alone is at least $5. But I could, and I can't imagine that scenario is at all profitable for them. Even my real orders are usually only $20-50, and they are typically comprised of very small quantities of lots of different parts. Consider how big their warehouse must be given the sheer number of parts they have: they have to pay someone to go pick my relatively small-dollar order (or pay for a really fancy automated picking system). And a large sophisticated database to track their inventories, their own supply chains, etc etc. It's baffling. Not to mention to mention how often I use their website without buying anything, just to see what kinds of parts are available.

There must be 10s of thousands of customers like me. Compare that overhead to a distributor who only deals with customers buying strictly huge lots (10k? 100k? minimum). That's a much smaller customer base, and presumably those people know what they want. The support overhead has to be significantly lower.

Throw currency conversions into the mix, dramatically lower living costs (compared to wealthy western nations), along with "grey market" or potentially fake parts, and I can maybe, kinda-sorta see how these "impossibly" cheap products come to be.

You'd think by now they'd have some detailed case studies of this situation to teach in business school. (Maybe they do, I've never been to business school!) I do find this situation interesting.

While I'm off-topic, another interesting takeaway from Jason Stoddard's book is just how much the case (i.e. chassis/enclosure) costs for a finished product. He spun a lot of prose explaining the lengths he went to to get those (relatively) cheap, simple, utilitarian enclosures.
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Old 5th October 2018, 01:12 AM   #23
Hugh Jazz is offline Hugh Jazz  Taiwan
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I reckon the "not recommended for new designs" parts the seller is using like OP42 op amps and the grey skinned "out of production" Rubycon nonpolar caps would have been even cheaper than usual... to shift old stock.... while I have no issues with old silicon, those caps will come out, get tested, be over 3% voltage loss and hit the bin almost as fast as I typed this message. I noticed the AD1837 board has bypass caps for the coupling electros so it should be possible to get a fairly decent sounding coupling with big Wima MKS and Vishay MKP1837 bypass. The AD1865 has no bypass cap, only the old ectro. I also saw that the AD1865 board has no shunt resistor after the output coupling cap (to draw a little current within the PCB circuit and charge up the cap... with a slight pop?), which I found odd. I think that a small series resistor (isolate the op amp from the cap), then the coupling cap, then a large shunt resistor would create a tight current loop on the PCB so the DAC wouldn't be heavily influenced by any output cable, following circuit etc. Alternatively, the two resistors would do, with the cap after them and before whatever is connected, noting it'll be a high pass with whatever the subsequent input impedance is.

Last edited by Hugh Jazz; 5th October 2018 at 01:40 AM.
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Old 6th October 2018, 10:35 AM   #24
kazap is offline kazap  Australia
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Originally Posted by abraxalito View Post
.....In my lingDAC design I put a 5th order (CLCLC) filter between the DAC and the I/V stage....

Brilliant. Thanks. Did you have to sort out any phase issues that could be heard when listening through two inductors?
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Old 6th October 2018, 11:37 AM   #25
abraxalito is offline abraxalito  United Kingdom
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Whilst the filter certainly has a non-linear phase response, I've not heard any ill-effect from it. Compared to having no filter it cleans up the focus of the 3D soundstage illusion, meaning instruments can be more precisely localized.
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Old 6th October 2018, 12:30 PM   #26
Nisbeth is offline Nisbeth  Denmark
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Quote:
Originally Posted by matt_garman View Post
Throw currency conversions into the mix, dramatically lower living costs (compared to wealthy western nations), along with "grey market" or potentially fake parts, and I can maybe, kinda-sorta see how these "impossibly" cheap products come to be.

You'd think by now they'd have some detailed case studies of this situation to teach in business school. (Maybe they do, I've never been to business school!) I do find this situation interesting.
Definitely plausible - and a big factor would be labour costs. Another factor to consider: When you are close to large-scale manufacturing you can also pick up small volumes of leftover parts quite cheap. I've bought kits from eBay with "fancy" components like RN55 resistors etc. when the components are genuine but the values are slightly off (e.g. 2k15 instead of 2k2) and I definitely think this is what's going on here.
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Old 7th October 2018, 02:44 PM   #27
abraxalito is offline abraxalito  United Kingdom
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Quote:
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Something like AD8065 (with more than 10X the GBW) might well do better.
In the past couple of days I've lashed up an op-amp based DAC output stage using the AD8065s I have. They're 145MHz GBW opamps, and surprisingly cheap on Taobao (about $1 for 3) so I figured it was worth a shot.

I'm using one AD8065 for I/V stage (3k feedback resistor and 5pF across it). I'm biassing the TDA1387 with current sources to GND on its outputs so as to get the opamp output voltage close to mid-rail. The I/V opamp's biassed into classA with a CCS to GND. There's a 3rd order MFB filter after the I/V which does a bit of droop correction. These opamps are powered from the same 6V rail as the DAC chips themselves, albeit with an LC filter between the DACs and the ADs.

The end result is fairly good on simple music, only when there's a lot going on does it become more mental effort to try to separate the strands of musical activity. And while there's an appealing bloom or air about the presentation its not completely a 3D one (as best I can tell on headphones). Still its pretty good for the price and simplicity - only against my experimental MkIII lingDAC does it become clear it has shortcomings. Probably all of it could fit on a 5*5cm PCB. If anyone wants the schematic just ask and I'll rustle it up.
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Old 7th October 2018, 03:53 PM   #28
Shinja is offline Shinja  Japan
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It would be better if the board have MSB trimmer. It must be worth to mod if it can. The seller also have another 2x AD1865 parallel DAC. Interesting, It have a digital filter, but it must be compatible upto 48kHz. The PCB pattern looks not sophisticated than the single AD1865 board.
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Old 8th October 2018, 03:18 AM   #29
Hugh Jazz is offline Hugh Jazz  Taiwan
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Originally Posted by Shinja View Post
It would be better if the board have MSB trimmer. It must be worth to mod if it can. The seller also have another 2x AD1865 parallel DAC. Interesting, It have a digital filter, but it must be compatible upto 48kHz. The PCB pattern looks not sophisticated than the single AD1865 board.

There is an IC before the AD1865 but I can't see exactly what it is. I assumed it was to truncate the bit depth... I am not sure I am capable of an MSB trimmer - i thought they require careful accurate measurement to get right? I don't think I have test gear good enough for this.
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Old 8th October 2018, 03:25 AM   #30
Hugh Jazz is offline Hugh Jazz  Taiwan
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Originally Posted by abraxalito View Post
In the past couple of days I've lashed up an op-amp based DAC output stage using the AD8065s I have. They're 145MHz GBW opamps, and surprisingly cheap on Taobao (about $1 for 3) so I figured it was worth a shot.

I'm using one AD8065 for I/V stage (3k feedback resistor and 5pF across it). I'm biassing the TDA1387 with current sources to GND on its outputs so as to get the opamp output voltage close to mid-rail. The I/V opamp's biassed into classA with a CCS to GND. There's a 3rd order MFB filter after the I/V which does a bit of droop correction. These opamps are powered from the same 6V rail as the DAC chips themselves, albeit with an LC filter between the DACs and the ADs.

The end result is fairly good on simple music, only when there's a lot going on does it become more mental effort to try to separate the strands of musical activity. And while there's an appealing bloom or air about the presentation its not completely a 3D one (as best I can tell on headphones). Still its pretty good for the price and simplicity - only against my experimental MkIII lingDAC does it become clear it has shortcomings. Probably all of it could fit on a 5*5cm PCB. If anyone wants the schematic just ask and I'll rustle it up.

I expect the LC filtered 6V supply has quite a bit of impedance, esp at HF, and that won't be doing the high speed op amps any favours. I would expect that to sound far from its best. I'm sure you know how critical amplifier psu is, even for a little op amp with decent PSRR. Perhaps target that to get the sonics to improve? At the risk of teaching my grandma to suck eggs .... op amps usually perform poorly the lower their supply voltage is, and from what I've seen in datasheets, split rail is often better than single rail, even with class A bias.

Last edited by Hugh Jazz; 8th October 2018 at 03:48 AM.
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