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skouliki 18th December 2012 02:08 PM

AD1865 schematic
 
I am planning to build the following AD1865 and cs8416 schematic from pavouk.org because it includes toner transfer pdf's and this makes it really easy.
CS8416 S/PDIF decoder
AD1865 based audio DAC with I2S input and voltage output

Does anyone have any comments on the quality of layout and circuit?
I intend on using Salas regulators and C0G ceramics instead of x7r
Thanks

Ken Newton 18th December 2012 02:40 PM

1) I notice that the S/PDIF input transformers don't appear to have a D.C. blocking capacitor in series with their primaries. Unless you are sure that your transport's S/PDIF output signal contains no D.C. component, this omission may be distorting (adding jitter to) the received signal.

2) I have some experience with the AD1865 in the Vout configuration. While the sound is okay that way, in my opinion, it's much better in the Iout configuration via a passive resistor I/V (of as high as 330 ohms). The resulting signal voltage can be A.C. coupled (without an intervening active stage) to your linestage input.

skouliki 18th December 2012 03:10 PM

Thanks for the reply Ken.

What value for the capacitor do you suggest?

Pavouk has a schematic for AD1865 with Iout.
Audio DAC with AD1865

I guess i can build both and choose the one that i like best.

Ken Newton 18th December 2012 07:13 PM

10nF to 100nF should be fine for coupling the S/PDIF transformers. Ideally, caps. featuring low parasitic inductance, such as SMD ceramics, are to be preferred since this signal is wideband. Although, I've used both 22nF NP0/C0G ceramics and 10nF film & foil polypropylene with equal success. I must add that I've not before seen a paralleled dual transformer configuration utilized here, I assume there must be a good reason the designer chose to do so. Perhaps, it's an attempt to produce a composite transformer having a wider bandwidth than either one alone, I'm not sure.

The Iout schematic appears fine to me. All one would need then do is A.C. couple (via a quality capacitor) the resulting signal voltage to a linestage. The DAC signal should be large enough that not much gain would likely be required while the output impedence would be just under 200 ohms, together eliminating the need for the usual DAC active output stage.

SSerg 19th December 2012 07:51 AM

Quote:

Originally Posted by Ken Newton (Post 3290076)
While the sound is okay that way, in my opinion, it's much better in the Iout configuration via a passive resistor I/V.

Yes, I agree. The built-in amplifier is mediocre.

marce 19th December 2012 08:14 AM

Single sided design is going to be a compramise, best thing you could do is etch it on double sided PCB material and have a complete ground plane on the other side (clearing where throough holes come through)and wire link ground pins to this plane. The good thing about this design is it allows for this, and would be greatly improved as a double sided layout.

skouliki 19th December 2012 04:37 PM

Thanks everybody for your suggestions.
Creating a double sided version with a ground plane is a very interesting idea (and easy enough for my amateur level).

abraxalito 20th December 2012 05:47 AM

I'm finding these double sided PTH boards excellent for building DIY DACs on. The pads don't lift off when resoldering, they're nicely robust and due to being PTH both sides are usable for SMT components. Makes for very compact layouts :)

2X Double Side Prototype PCB Board 5x7 cm Tinned Universal Board FR4 | eBay

skouliki 20th December 2012 12:43 PM

Didnt know these boards existed. :D They'll be usefull in a lot of projects. Thanks abraxalito

abraxalito 20th December 2012 12:59 PM

You're welcome - I only discovered them this summer too :D They are indeed a great DIY resource.


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