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Old 2nd February 2012, 11:54 AM   #1041
UnixMan is offline UnixMan  Europe
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Quote:
Originally Posted by oneoclock View Post
The ideal is with a constant current source. But starting from 5 V. going to be impossible.
that's why I insist that there should be two different branches of the project: one with focus on portable use and another one with focus on SQ, for home use only.

IMHO the portable version(s) should be something like the current designs, particularly George's ones: as good as possible while being small, cheap and "USB power-able" (that is, USB powered with a connector for optional external 5V supply which cuts USB power when plugged in).

I'd make it single board, perhaps with the DAC chip itself (plus a minimal number of components, such as small local by-pass) mounted on a tiny "piggy-back" board to allow for the possibility to "swap in" different suitable DACs such as the ES9023, PCM5102, etc.

The home version(s) must be mains powered. Forget about 5V and single supply, go for as many and as high as convenient supply rails. They should be modular, too. I would split it into several boards as follows:

  1. main AC PSUs board
  2. uC board (USB interface)
  3. galvanic isolation board
  4. DAC board
  5. digital output(s) board
  6. other options board(s)
The PSU board should distribute constant currents to the other boards. With many separate lines, one CCS for each load. Local regulators (or simple Zener+Cap) on the various boards will do the rest.

The interface between 2. and 3 as well as 3. to 4. or 5. should be identical, so that the galvanic isolation board becomes optional: it may be omitted by directly connecting uC and DAC boards or added (even in a second time) just by inserting it in between the two (like in a daisy chain).

The DAC and digital output boards must host the clocks (and clock "switch", etc). Economically it would be more convenient to put the clocks and related circuitry on the uC board (or on the galvanic isolation board), but for best performance (minimum jitter) the clock must be as close to the DAC chip as possible.

Perhaps, also the digital output and DAC boards may be made daisy-chain-able, so that a user may setup a device with both analog and digital outputs.

It would be nice if the uC board might also have connectors for optional input board(s), either digital (S/PDIF, I2S), analog (ADC) or both.

The whole design of the "home branch" should be "future-proof": if you will eventually replace the uC for another one allowing for up to 384KHz/32bit, it must be possible to swap-in the new uC board without changes. And it should also be possible to exploit the new capabilities with no or minimal changes to the other boards.
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Last edited by UnixMan; 2nd February 2012 at 12:05 PM.
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Old 2nd February 2012, 12:10 PM   #1042
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Thumbs-up from me on UnixMan's approach.
The modular home version will be interesting (even to people that have some of the mentioned aspects e.g. DAC covered), better performing and future-proof.
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Old 2nd February 2012, 03:22 PM   #1043
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I can see desire to mix and match with the full size unit where you may want to experiment with PS, capacitor selection etc but there is limited opportunity to experiment with my boards.

I have no problem reworking my design into a 2 part system but I don't see many takers when you will be offering the full buffet of choices with the 'home version'.

George
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Old 2nd February 2012, 06:09 PM   #1044
MrSlim is offline MrSlim  Canada
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Quote:
Originally Posted by UnixMan View Post
The whole design of the "home branch" should be "future-proof": if you will eventually replace the uC for another one allowing for up to 384KHz/32bit, it must be possible to swap-in the new uC board without changes. And it should also be possible to exploit the new capabilities with no or minimal changes to the other boards.
I thought Alex already demonstrated 384Khz/32bit transfers through the existing micro, and were waiting for George's 5102 board to verify 32 capability end to end?
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Old 2nd February 2012, 06:38 PM   #1045
Turbon is offline Turbon  Sweden
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Quote:
Originally Posted by MrSlim View Post
I thought Alex already demonstrated 384Khz/32bit transfers through the existing micro, and were waiting for George's 5102 board to verify 32 capability end to end?
I believe it was 32/192...

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Old 2nd February 2012, 07:36 PM   #1046
MrSlim is offline MrSlim  Canada
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I agree with UnixMan's approach too, but at the same time I would like to see "core modules" that could work on their own and then other modules could be added to upgrade performance as the user sees fit. So, lets say the USB and DAC boards were the core and could operate by themselves (possibly powered by USB), and then the more advanced power supplies, etc could be added as the owner upgrades.. (thinking about playing with that idea myself when I have some free bandwidth.)

Last edited by MrSlim; 2nd February 2012 at 07:39 PM.
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Old 3rd February 2012, 04:08 AM   #1047
rsdio is offline rsdio  United States
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Each separate board adds to the minimum cost of the total solution. It's certainly possible to make boards fairly cheaply, but there is separate overhead for each one and that needlessly adds cost. My preference is a single board which has everything necessary; with sections that can be left blank if the features are not desired and/or connectors that can be used to bypass parts of the basic design for upgrades. In the latter case, stacking connectors can allow multiple outputs, even combined with the default, on-board outputs.

Keep in mind that a single board can have divided power planes just as if there were two or more separate boards, making it pointless to actually build two or more PCBs just for isolation.

I certainly see that it may seem strange for me to complain about price on what hopes to be audiophile quality sound, but it's just too easy to get up to $500, $1,000 or $2,000 just for the populated boards and basic case. I'd rather see the bulk of the money going into high-grade DAC chips rather than just having a pile of boards.
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Old 3rd February 2012, 04:52 AM   #1048
Turbon is offline Turbon  Sweden
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Quote:
Originally Posted by rsdio View Post
Each separate board adds to the minimum cost of the total solution. It's certainly possible to make boards fairly cheaply, but there is separate overhead for each one and that needlessly adds cost. My preference is a single board which has everything necessary; with sections that can be left blank if the features are not desired and/or connectors that can be used to bypass parts of the basic design for upgrades. In the latter case, stacking connectors can allow multiple outputs, even combined with the default, on-board outputs.

Keep in mind that a single board can have divided power planes just as if there were two or more separate boards, making it pointless to actually build two or more PCBs just for isolation.

I certainly see that it may seem strange for me to complain about price on what hopes to be audiophile quality sound, but it's just too easy to get up to $500, $1,000 or $2,000 just for the populated boards and basic case. I'd rather see the bulk of the money going into high-grade DAC chips rather than just having a pile of boards.
But a single board is restrained to grow in 2 dimensions. Multiple boards can be stacked to keep a small footprint.

Brgds
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Old 3rd February 2012, 09:23 AM   #1049
rsdio is offline rsdio  United States
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Originally Posted by Turbon View Post
But a single board is restrained to grow in 2 dimensions. Multiple boards can be stacked to keep a small footprint.
Very true. As I mentioned, the daisy chaining for multiple outputs could be implemented by stacking headers.

However, when the primary motivation for all of this separation is to isolate the various building blocks, stacking introduces the very real possibility of electromagnetic interference from one board to the one above or below. In other words, if you take expensive measures to isolate your DAC from the USB, but then stack the analog section of the DAC board directly above the noisiest USB traces - well, then you've got a whole new problem that is an order of magnitude more difficult to plan for compare to traditional 2D board layout.

In general, compact electronics are not always the highest performance.
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Old 3rd February 2012, 09:28 AM   #1050
Turbon is offline Turbon  Sweden
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True rsdio, but on the other hand you can add ground planes between the cards to minimise the impact of stacking if needed.

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