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Old 1st March 2012, 12:57 AM   #21
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Supply impedance is over-rated in the digital domain. With traces long of several inches (read inductances), only close LOCAL decoupling can provide that low-impedance needed for high-frequency domain.
There is no point of investing in an expensive regulator for the digital part of a DAC.
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Old 1st March 2012, 03:39 AM   #22
i2k92 is offline i2k92  Indonesia
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Originally Posted by Drweird View Post
Interesting, never thought of it like that. So then modding the card's power section or changing its supply will yield a minimal improvement at best?
Yes I agree that changing out the speakers will be the best improvemnt, but I jus want to get the source outta the way first.


Well its exactly because there are many so dedicated DACs to choose from and their availability in India is iffy.
There are some reliable Chinese DAC seller out there (take hifimediy as example), you can get a good DAC module, power supply including shipping perhaps less than the price of Asus STX. I don't know with India, but in my country where the custom service is not at all reliable, I never had any problem with shipping from China.

And yes, speaker upgrade will be more significant. There's no point in upgrading the source if the speaker cannot reproduce the improvement brought by the upgraded source.
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Old 1st March 2012, 06:11 PM   #23
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Originally Posted by Raj1 View Post
One should strive to keep leads short. There are some nice drop in replacements out there for 3 pins regs by a couple of very clued up power engineers that perform admirably when used properly. Supply impedance variance over the audible range for an analogue circuit can be quite noticeable.
How exactly is it noticeable though?

In a switching circuit one absolutely needs to have local decoupling and the charge carried by the capacitor will provide a low impedance reservoir of energy should it be required, but we're talking about MHz here where rise times are particularly quick.

How exactly does a lower supply impedance or 'flat' supply impedance affect the audio quality? At a very basic level the supply impedance will affect the voltage seen at the power supply pin of the opamp lets say. This will vary depending on the frequency that the opamp is asked to reproduce, but lets say there's a 0.5V difference (a gross exaggeration) between the supply potential for a 1kHz signal vs a 20kHz signal. This wont have any effect on the output wave-form unless we're working with a signal level that's extremely close to the rail limits. Naturally though we've got local decoupling in place so when the high frequency signal comes along it can draw off of the coupling cap for the instant that the PSU and trace internal resistance would act to lower the rail potential.

If the supply and trace impedance were going to have any effect on the signal passed by the device then it should be easily measured as distortion on the output waveform.

Interestingly though, if you look at the measurements performed on super regulators with regards to the reduction in output impedance vs local and remote sensing, the drop is 'considerable'. But we're talking about a drop, at 20kHz, from 0.02 ohms down to 0.0005 ohms. This might sound like a lot, but when you consider that 1cm of PCB trace with a standard thickness of 0.25mm on 1oz copper has a resistance of 0.01ohms...the power supply impedance is going to be completely dominated by the PCBs traces. Even standard 3 pin regs have output impedances of around 0.1 ohm at 20kHz, again the PCB traces are going to be the dominant factor in a multi-chip product. The only real place where the remote sense and therefore very low output impedance feature of a super regulator might prove beneficial is in single chip designs such as some phono preamps etc, where you can remove sense directly to the opamps supply pins.
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Old 2nd March 2012, 07:53 AM   #24
Raj1 is offline Raj1  United Kingdom
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Originally Posted by 5th element View Post
How exactly is it noticeable though?


Because any modulation is imposed on the output. Of course if you're only playing with sine waves, carry on as you are and have fun.
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Old 2nd March 2012, 11:34 AM   #25
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Originally Posted by Raj1 View Post
Because any modulation is imposed on the output.
Did you hear about a thing called PSRR? That makes your supply "modulation" irrelevant.
Plus you didn't say how is a PS impedance helping with the inductrances of the traces/wires. Local decoupling is the only real help you can get, PS is "important" only in the 10-100 Hz domain.

Last edited by SoNic_real_one; 2nd March 2012 at 11:36 AM.
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Old 2nd March 2012, 02:18 PM   #26
Raj1 is offline Raj1  United Kingdom
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Yes, all we ever needed is the 7805 series of regulators - anything else was a waste of time to develop, because they all sound and measure the same and there is no audible change.
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Old 2nd March 2012, 08:17 PM   #27
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Basically yes... for high-frequency digital signals, anything else is overkill. Your super-cool power supply won't do squat for a digital IC situated at the end of 5 inch of wires and traces.
Local decoupling is all you need to do properly:
http://www.analog.com/static/importe...als/MT-101.pdf

Last edited by SoNic_real_one; 2nd March 2012 at 08:19 PM.
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Old 2nd March 2012, 08:26 PM   #28
Raj1 is offline Raj1  United Kingdom
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Some of us like overkill without 5 inches of wire, especially for analogue. "Bit perfect digtial", who cares.
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Old 3rd March 2012, 12:11 PM   #29
marce is offline marce  United Kingdom
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If digital signal tranmission wasn't "bit perfect" then not only would your ananogue output be distorted and not a faithfull reproduction or the origional material, but computers, the internet and most entertainment devices would also not work, or work as reliably as they do. That is the whole point of laying out digital circuits, so that the signal gets there in a state that will allow the reciever to correctly determine the data stream.
That is why when I'm layoing out a digial board I have at hand about 36K of Cad software, as well as all the tools the engineers use. Its more cost effective to simulate all aspects of the design before commiting to a physical PCB and assembly. Having an unreliable product can ruin a company, look at Amstrad in the early days of PC's and their disk problems...Very few Amstrad PC's these days.
Most new PSU development is in maximising efficiency, shrinking the PSU PCB footprint and reducing heat loss. This is being prompted by the ever decreasing size, yet increasing power of mobile devices, and the requirement for longer battery life. Some of the new devices from Ti, Linear etc, in conjuction with some cool FET packaging
http://www.ti.com/lit/ds/symlink/csd16321q5c.pdf
You can get a lot of power density in a small footprint. Then there are the numerous local supplies, that todays digital boards demand, with some chips requireing upwards of 4 seperate supplies, the increasing practice is to cascade local 3 pin LDO devices for local supplies (there can be upwards of 22 supplies on a board) after a main SMPS. Dependant on the design there can be 12V 5V 3V3 and 1V8 (or 1V2) main supplies with chip cores and IO supplies being local to the device. Then AS pionted out, its all down to decoupling, and here very small chip package (0402, 0201) X7R MLCC caps are your best friend, with the odd COG for the local decoupling of a oscillator. Modding any decouling of a digital board is more likely to cause problems rather than improve things IMO. How many refer to Henry Ott, Electromagnetic Compatability Engineering before embarking on their modifications, or the numerous design notes and app notes available for nearly every chip
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Old 3rd March 2012, 06:18 PM   #30
qusp is offline qusp  Australia
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am i missing something, or does that new mosfet linked above have the hugest gfs for a mosfet youve ever seen? is there something about the conditions or the way its specified i'm missing? because 150s is more than 150x the highest gm out of a field of mosfets we chose for the NTD1 reworked Pass D1 IV stage or is gfs a completely different measure to gM? is this just a biproduct of 'designing for minimized losses'?
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