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Old Today, 03:14 AM   #781
ishizeno is offline ishizeno
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Quote:
Originally Posted by hochopeper View Post
Going back about 10 pages there was some discussion regarding power supplies. I wanted to throw a reference in to the mix - Simple Isolated +/-15V Split Rail



– QuantAsylum
- this page shows a design for an isolated +/-15V from 5V in that could be used for the opamp supplies. May wish to explore different LDOs though. The low power handling would mean a bit of a change of the topology currently proposed (probably won't have enough power to drive the opamps as well as VREF regulator and MVDD). But the isolation may be worthwhile.

Another separate observation on clicking back through the thread is that the OTOBUS pin out looks to have very few ground connections. For all digital signal wires there should be an adjacent pin connected to ground. For signal integrity and EMI it is important to have a return path as close possible to the signal wire, particularly for fast (short rise time) signals. This ensures that the loop area of the signal path is minimised.

Chris

Chris
Chris,

Thanks a lot for this. I really like what QuantAsylum is doing. Very clever stuff...

As far as GND on the OTOBUS™ is concerned, I was worried about that as well. If we feel that we have a real problem there, we'll have to use similar connectors with more circuits. The only drawback is that we'll have to modify our design for the rotary encoder brick, but I don't think that a single brick should drive the design of what is supposed to be a very generic interface. I'll give myself another week of background thinking about the issue before returning to the designs of the OTOBUS™ and the rotary encoder brick: my personal experience is that my judgement is often impaired when I work on the same thing for a long uninterrupted period of time. But when I come back to it after a break, I can sometimes see things through a different angle, and solve a problem that seemed intractable before.

Last edited by ishizeno; Today at 03:30 AM.
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Old Today, 06:30 AM   #782
jan.didden is online now jan.didden  Europe
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Quote:
Originally Posted by hochopeper View Post
Going back about 10 pages there was some discussion regarding power supplies. I wanted to throw a reference in to the mix - Simple Isolated +/-15V Split Rail



QuantAsylum
- this page shows a design for an isolated +/-15V from 5V in that could be used for the opamp supplies. May wish to explore different LDOs though. The low power handling would mean a bit of a change of the topology currently proposed (probably won't have enough power to drive the opamps as well as VREF regulator and MVDD). But the isolation may be worthwhile.
Another candidate that has even lower noise and more output current capability is the diyaudio SilentSwitcher.

It achieves total isolation from the mains as it is powered from a USB charger or, for very sensitive applications, a Powerbank.

Check it out.

Jan
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Old Today, 12:15 PM   #783
hochopeper is online now hochopeper  Australia
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Quote:
Originally Posted by jan.didden View Post
Another candidate that has even lower noise and more output current capability is the diyaudio SilentSwitcher.

It achieves total isolation from the mains as it is powered from a USB charger or, for very sensitive applications, a Powerbank.

Check it out.

Jan
Hi Jan,

The Silent Switcher was explored in detail in that section of the thread along with Frex's new power supply design for the AAPSU01 (from the OSVA development thread). [FWIW I have three Silent Switchers here - 1 in the autoranger, another going to be used for PCM4222evm and another for the Bruno Putzey's preamp - they are really handy!].

I was brief in my earlier post, I should elaborate on my reasoning.

Given that the bigger context of this thread is a complex system with a bunch of ARM SoC and FPGA and hybrid FPGA+Arm CPU SoCs combined with the audio gear. I see no value in over engineering the supply to those devices (in terms of expensive low noise regulators etc).

There is the option to use 5-12V supply in to seperate regulators for that auxillary gear and use that supply in to 1/more silent switchers or AAPSU01 like designs to supply the critical/important parts. With good attention to detail on the layout this will be a really great design and my rational brain is fully satisfied.

My monkey brain can't help wonder what if more/better ideas are left on the table. It has seen lots of folks using galvanic isolation on the i2s / i2c between the DSP/processors/displays. I've seen designs that do that and still use the same upstream supply and still get objectively great results (the best kind of great results). What if we isolated the supply to the audio converter (DAC/ADC) and analogue stuff. A few ideas come to mind:
1. old school, heavy, transformers - you get extra transformers or transformers with more secondaries
2. have a separate battery supplied Silent Switcher/AAPSU01/whatever in addition to the power supply to the other components in the device. (as you point out these solve the mains isolation and ground loop problems - probably the biggest and most important issue that warrants solving)
3. have a single supply to the device and use isolated supplies where it makes sense - similar to what QuantAsylum have used.

In any of the above cases PCB layout is the most important in getting to the performance of a chip like the AKM4499. The complexity, cost, space constraints probably drive the choice between those three options.

Hopefully - that's a more coherent version of my 2c on the power supply at a synoptic level. My earlier post was just to point out that there is a 3rd option that I don't think was considered earlier.

Cheers,
Chris
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Old Today, 12:58 PM   #784
Markw4 is online now Markw4  United States
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Quote:
Originally Posted by jan.didden View Post
Another candidate that has even lower noise and more output current capability is the diyaudio SilentSwitcher.

It achieves total isolation from the mains as it is powered from a USB charger or, for very sensitive applications, a Powerbank.
Been there, done that. Ran into problems both with USB charger and a powerbank device. Both power sources produced switching noise that affected dac sound quality. Could be that CM filtering on the output of the USB charger might have attenuated the ground conducted noise enough. Similar noise from the switching regulator inside the power bank type device, even though it was completely isolated from ground. Some filtering might have helped in that case too. Not a plug and play solution in either case for my dac projects. Ultimately, settled on other power supply solutions.

Also, tried one time to see if I could get an off the shelf line powered switcher to work. Put ferrites in the input and output leads, put the switcher inside a metal box, but not luck. Then lined the inside of the box with copper foil. That helped, but still not clean enough. Wrapped the outside of the box in copper foil completely sealing it. At that point it was pretty close to good, but still not as good as a good linear supply to my ears. Didn't end up using that either.

In addition, I have tried to get LDOs such as used by TP to work with analog circuitry in dacs as well as I can do by other means. It certainly would be more convenient if simpler solutions involving less work for me could suffice. Despite trying some variations powering and loading LDOs I didn't find they could beat or equal the best linear solutions I know of for the most critical analog circuitry in dacs. Of course, still seems likely there are ways to engineer around the problems I have encountered so far, I would like to think so. However, it has bee easier so far to go with what works for me in the way of power supplies, and spend my time trying to solve other types of problems for which I have no good solution at all.

Last edited by Markw4; Today at 01:11 PM.
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Old Today, 02:03 PM   #785
Terry Demol is offline Terry Demol  Australia
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Quote:
Originally Posted by Markw4 View Post
So, people making requests can give their reasons for wanting one in private?
El numero uno was me Mark

Due to circumstances of my other commitments, work, projects etc we
discussed this via PM prior but ishizeno has graciously said OK.

On the plus side
a/ I'm happy to offer any help here with the design side where possible.
b/ I'm happy to offer help tweaking the boards for subjective performance
c/ I have lots of clients/friends with various types of recording studios who
can give valuable feedback.

One owns two Ampex ATR124 machines (this is not him)
YouTube
and Studer C37, 1" 2trk for mixdown. A nice source to test VHQ ADC on.

Some good potential users and beta testers.

Throw your hat in the ring Mark. You're experience would be highly valuable.

T
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