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lingDAC - cost effective RBCD multibit DAC design
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Old 10th January 2019, 07:17 AM   #181
tjstyle is offline tjstyle
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I'm Interested to for the 10-off kit!

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Originally Posted by abraxalito View Post
Here is the BOM.

I'm wondering about the bulk kits idea - I'd like to encourage more ultra-cheap DACs out into the world and Taobao sourcing is the only way I know of to get this DAC to below $3 in components. As PCBs tend to come in quantity 10 minimum to me it kind of makes sense to kit up for a build of 10 DACs. Then shipping costs won't swamp the parts cost. What I don't know is how much labour's involved in putting together kits so at this stage I can only make a rough guess. Would there be any takers for a 10-off kit priced at $50 (including PCBs)? I'd guess this might be attractive for people who'd like to build multi-channel DACs for digital XO'd active speakers. For those who don't need more than a single stereo DAC, they could potentially sell their 9 remaining built-up PhiDACs to those who prefer not to get involved with soldering, more than recouping the cost of their own DAC.
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Old 11th January 2019, 04:14 PM   #182
matt_garman is offline matt_garman  United States
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lingDAC - cost effective RBCD multibit DAC design
I'd also be willing to jump on the 10-lot train.
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Old 14th January 2019, 04:45 PM   #183
miro1360 is offline miro1360  Europe
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Where to get working TDA1387? The one, which is not recycled? Recycled SMD components from the electronic garbage are my worst ebay experience so far, only DIPs components are working because they are not pulled out by overrated hotair (unfortunately TDA1387 is only SMD).
I have strip of 40pcs from ebay and no wonder that they do not work (even though bias from iout is 0.5mA, Vref is 1/6 from Vdd, but there is no reaction on I2S signal - standard I2S (I have not tried LJ - EIAJ, because datasheet says standard I2S)).

Last edited by miro1360; 14th January 2019 at 04:47 PM.
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Old 14th January 2019, 10:09 PM   #184
miro1360 is offline miro1360  Europe
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I found a few working pieces ... time to try something ...
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Old 14th January 2019, 11:31 PM   #185
miro1360 is offline miro1360  Europe
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I tried this combination without any filters:
xmos i2s --> TDA1387 --> basic opamp I/V (lets say best were OPA1688 or ADA4898) --> audioCap --> TPA6120 for headphones (powered from batteries)

... well, the result from this simplicity is not the way (in terms of dynamics and detail) ...

Who knows what would happen if one took abraxalito's filter+I/V and put it forward to the AD1862 or PCM1704 ?)
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Old 15th January 2019, 02:40 AM   #186
abraxalito is offline abraxalito  United Kingdom
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Quote:
Originally Posted by miro1360 View Post
... well, the result from this simplicity is not the way (in terms of dynamics and detail) ...
I'm curious - what does 'not the way' mean? I'd really like to know how that combination you tried sounded.

Incidentally why not use the TPA6120 as the I/V stage, seems simpler to me, omitting an opamp? I'm getting very good results from using AD815 as I/V and according to TI, TPA6120 is an upgrade on AD815.
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Old 15th January 2019, 01:06 PM   #187
miro1360 is offline miro1360  Europe
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Not the way means ...., this simple connection lacks details through the frequency range (compared with similiar simplicity of AD1862 or PCM1704). The most noticeable is the loss of dynamic in low frequency and fewer noticeable, but still be, few details in higher frequency. Perhaps paralleling TDA1387 is a good idea to improve dynamic in low frequencies (but for price of increasing capacitance on the output, adding errors, ... overall it can bring some improvement).

Well, the TPA6120 directly as the I/V is in oscillation. It needs some tuning to get off the oscillation ... I did not get this oscillation completely off (the chip is than slower).

Do you have an internal concept/schematic of AD815?

PS: when you connect your I/V to the AD1862, it can be interesting

Last edited by miro1360; 15th January 2019 at 01:09 PM.
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Old 15th January 2019, 01:22 PM   #188
abraxalito is offline abraxalito  United Kingdom
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Did you delete the feedback capacitor on the I/V when you tried the TPA6120 in that position?

I have no internal AD815 schematic but judging by the DS for the AD8017 its most likely the 'Nelson' architecture : Current-feedback operational amplifier - Wikipedia

What are you powering the TDA1387 from? I don't have any AD1862s to try here.
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Old 15th January 2019, 02:45 PM   #189
miro1360 is offline miro1360  Europe
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Yes, I removed the feedback cap (this slightly decreased the oscillation). I tried a solid plane GND on the PCB and the same result was present. The oscillation is in few of MHz and heats up the chip. The simulation in ltspice is ok, but the reality is not.
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Old 15th January 2019, 02:52 PM   #190
abraxalito is offline abraxalito  United Kingdom
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I found AD8017s oscillated with a few cm of wire between the +ve input pin and my Vref. A 220pF cap between +ve in and -V (on TPA6120 this would be between pin4 and pin1) fixed the oscillation.
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