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Old 5th December 2011, 05:53 PM   #511
1audio is offline 1audio  United States
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I posted a really good regulator circuit here:Asynchronous I2S FIFO project, an ultimate weapon to fight the jitter
Less than 1 nV/rt Hz noise and simple and cheap to implement. The output impedance is not as low as some other designs but the source isolation is really high. It can be "mapped" to negative use and even as a shunt with a little fiddling. Its ideal for crystal oscillators and works well in other applications as long as you understand its limitations.

I'm starting to implement it in some commercial products with good success.
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Old 5th December 2011, 06:01 PM   #512
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Yes Demian - why not as long as the design is out in public domain.

Brgds.
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Old 7th December 2011, 06:06 PM   #513
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Quote:
Originally Posted by alexlee188 View Post
Are there "standard" drivers with rate feedback for Ethernet soundcards?
is there any such thing as a standard Ethernet soudncard at all?

For a network-based option I was suggesting an embedded MPD server, thus using a "de facto standard" protocol (sort of).
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Old 7th December 2011, 06:33 PM   #514
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1audio, Damien!

I believe I understand which connections that are connected to ground in your schema for it to make sense but could you write them down so I can be certain... Intersecting 90deg lines in schemas can be hard to understand.

Brgds
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Old 7th December 2011, 08:11 PM   #515
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Quote:
Originally Posted by alexlee188 View Post
So, what we want to achieve for a future version of audio-widget are:
some more free suggestions besides the already mentioned good points...

* provide a "DACless AW" board (I2S + S/PDIF + Clock outputs) to ease integration with existing DACs!

This would be very easy to do and IMHO would pay back a great deal in term of project widespread and popularity. People who have recently spent big money on some DIY or commercial DAC would hardly be willing to buy "another DAC"... but they may be more than happy to integrate a state-of-the-art UAC2 interface such the AW with what they already have!


* design a truly "no-compromise", hi-end AW DAC. Use top-of-the line DAC chip (such as ES9018), possibly two of them (one per channel, "dual mono" design) with best possible clocks, indipendent PSUs, etc. No USB power or wall-wart! Use as many internal linear PSUs as required for best SQ.


Quote:
Originally Posted by alexlee188 View Post
3. As discussed previously, we are not keen on SPDIF or HDMI unless there is a standard way to implement rate feedback.
Agreed. But, as already suggested some time ago, a few auxiliary (no special efforts, just bare functionality) spdif/toslink I/O ports for integration with existing "mid-fi" consumer devices (such as DTVs, etc) would be a nice plus. Of course no one would/should expect "top SQ" from that, but being able to easily integrate common devices with the main audio system would be a nice and useful feature. Needless to say, such a "commodity" feature should only be considered if its implementation does not compromise in any way the overall SQ of the AW when used in its "primary" way (USB-to-analog).
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Old 7th December 2011, 08:45 PM   #516
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Quote:
Originally Posted by borges View Post
Any takers on the analog power supply?
my take would be as follows.

On a dedicated PSU board, put:

* schottky diodes bridge, with R-C (or CCS-C) filter to minimize rectification noise (including current peaks in the power transformer, diodes and first filter cap).

* a simple, low noise voltage pre-regulator

This parts may be common to more than one load (of course you'll need at least two of these with dedicated power transformers if you use galvanic isolation).

Now you have to distribute the power. Use one separed, indipendent supply line for each indipendent load!

Rather than trying to supply costant voltage, having variable currents running all around (=noise, undesired interactions, etc), do distribute constant currents instead!

That is, use CCSs. Use simple but effective ones, based on cascoded high-impedance depletion devices (depletion MOSFETs or JFETs). One CCS for each supply line (that is, one for each load).

Then, on the board(s) where the loads are, as close as possible to each of them (e.g. right on each supply pin of the ICs), convert back to voltage supply using a Zener in parallel with plenty of capacitance (use A LOT of capacitance!).
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Last edited by UnixMan; 7th December 2011 at 08:51 PM.
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Old 7th December 2011, 09:59 PM   #517
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Quote:
Originally Posted by Turbon View Post
1audio, Damien!

I believe I understand which connections that are connected to ground in your schema for it to make sense but could you write them down so I can be certain... Intersecting 90deg lines in schemas can be hard to understand.

Brgds
I understand your concern. Long ago I learned to never connect at a cross for the reasons you mentioned.

The TL431 was added to get a higher accuracy and more stable voltage long term which is why its below the ground.

I need to redraw it so its more understandable. I'll also fold it into a shunt version. I don't have the time to do the spice stuff.

I have attached a quick LTSpice schematic. They did not have a TL431 or equivalent so I used another device to show the connections.
Attached Images
File Type: png lnreg.PNG (22.9 KB, 281 views)
Attached Files
File Type: zip Low Noise series regulator.zip (822 Bytes, 23 views)
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Old 7th December 2011, 10:35 PM   #518
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I found the LT1431 under opamps but its so different I'll pass on revising the drawing for now.

This regulator is optimized for static loads that need really good low noise DC. It may not be ideal for an opamp that has high dynamic loading (driving a headphone). It may not be possible to meet both requirements (low source impedance and low noise) in one circuit.
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Old 7th December 2011, 10:45 PM   #519
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Quote:
Originally Posted by UnixMan View Post
my take would be as follows.

On a dedicated PSU board, put:

* schottky diodes bridge, with R-C (or CCS-C) filter to minimize rectification noise (including current peaks in the power transformer, diodes and first filter cap).

* a simple, low noise voltage pre-regulator

This parts may be common to more than one load (of course you'll need at least two of these with dedicated power transformers if you use galvanic isolation).

Now you have to distribute the power. Use one separed, indipendent supply line for each indipendent load!

Rather than trying to supply costant voltage, having variable currents running all around (=noise, undesired interactions, etc), do distribute constant currents instead!

That is, use CCSs. Use simple but effective ones, based on cascoded high-impedance depletion devices (depletion MOSFETs or JFETs). One CCS for each supply line (that is, one for each load).

Then, on the board(s) where the loads are, as close as possible to each of them (e.g. right on each supply pin of the ICs), convert back to voltage supply using a Zener in parallel with plenty of capacitance (use A LOT of capacitance!).
In my experience the radiated noise from the rectifier/cap/transformer network is the hardest to deal with. My best experience uses a complex network in front of the transformer to limit the rate of change of the current through the network (power factor correction). But this requires heavy iron. Buy or make a pick up coil and watch the noise with a scope as you try variations on bypassing and arranging the wires. There is more technique than circuit involved ultimately.

JFet current sources are great but they have gotten more expensive. Linear Systems still sells them. Please use them liberally so they can justify making them still.
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Old 7th December 2011, 11:11 PM   #520
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Quote:
Originally Posted by 1audio View Post
In my experience the radiated noise from the rectifier/cap/transformer network is the hardest to deal with.
that's why I was suggesting to limit and slow down the charge currents adding a series R after the diode bridge (before the first filter cap). In principle using an inductance (inductive input filter) would be even better, but in practice there are also drawbacks. Fortunately in this project we are dealing with relatively little power and can afford to waste more power than we actually use. In higher power application it would be a really hard to solve problem...
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