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Old 2nd October 2012, 02:32 PM   #1301
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That'd be close enough in my book as the 0.47R reference resistor wont be exactly 0.47R, neither will all the relevant connectors/wires be completely accounted for.

I wouldn't mind betting that the temperature at the time, of all the various components, would probably affect the absolute current drawn, as could small variations in the power supply voltage too.

I agree that it isn't perfect, but it's probably safe to say that a 500mA spec'd reg would be more then enough.

I think choosing a reg that could deliver 500mA would be a safe bet.
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Old 2nd October 2012, 04:02 PM   #1302
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0.47 5%, so a 5% in the current measurement must be taken into account, at least.
I agree with you that 500mA is a safe bet.

Last edited by m.massimo; 2nd October 2012 at 04:12 PM.
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Old 2nd October 2012, 10:20 PM   #1303
bismuth is offline bismuth  France
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Hi,
I understand that a regulated PSU is certainly cleaner that the 5V rail from computer USB.
But isn't it overkill to use a shunt reg here ? Isn't the 5V rail only used for feeding onboard three legs regulators in front of the clocks (3V3) and the XMOS chip (3V3,1V8,1V) ?
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Old 3rd October 2012, 04:29 AM   #1304
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Default Very good question!

Quote:
Originally Posted by bismuth View Post
Hi,
I understand that a regulated PSU is certainly cleaner that the 5V rail from computer USB.
But isn't it overkill to use a shunt reg here ? Isn't the 5V rail only used for feeding onboard three legs regulators in front of the clocks (3V3) and the XMOS chip (3V3,1V8,1V) ?
I have often thought about this myself. I use a different (but similar, XMOS based with lots of onboard regulation/filtering) USB card, and am using a shunt to power it, mostly because that is what I had around to easily build, but it does seem to be overkill considering the onboard IC regulators. Perhaps a simpler supply, using a CRC feeding a 1705 followed by a good quality cap would be just as effective...
Usually shunt regulators are applied directly at the point of load, and not as pre-regulators...
What do others think?
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Old 3rd October 2012, 04:53 AM   #1305
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A lot of people have reported subjective positive improvements using salas shunt regs. I've not understood the purpose, though looking at the recent Linear Audio - Vol 4 noise graphs , specifically the one available - here, perhaps it is the salas shunt's low noise that is helping here. I recently got shot down in flames (well that's an exaggeration really) for suggesting that depending on the rest of the system (ie feeding an ebay dac kit) that the WaveIO is feeding a salas shunt may be an overly complex and expensive regulator solution to providing a PSU for this device.

I wonder if the change in regulator that people are using also comes with a new independent tx and rectifier? It may be these other changes that are all adding to the perceived improvement.

I ended up deciding on a LT1085 in a pretty simple reg build (build on one half of of OPC's 'the wire' psu board). It is a good but intelligent PSU design by Owen where I've only changed the regulator IC and set it for a fixed voltage output. It has an Nichicon R7 series FPCAP on the output too which can't hurt.

I haven't compared this to anything yet and am currently waiting on a new DAC board to arrive. I have previously only used my WaveIO on usb power when testing with a TPA Opus. So by the time my new DAC comes I'll have no way of doing any meaningful comparison anyway.

Last edited by hochopeper; 3rd October 2012 at 05:17 AM.
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Old 3rd October 2012, 07:31 AM   #1306
bismuth is offline bismuth  France
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Interesting comparison graph, I think the regulators on the board are LP5900 type with 6,5 uV noise figure. But their PSSR is not very high depending on freq (see datasheet). Maybe it is a good reason for using an 'overkill' shunt pre regulator ?
Or is the 5V used somewhere in the circuit (without additionnal regulator) ?
Aren't noises from clock rail and XMOS chip way higher ? They surely propagate ? Anyone with a good scope to take a look ?

Last edited by bismuth; 3rd October 2012 at 07:39 AM.
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Old 3rd October 2012, 08:08 AM   #1307
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The propagation of noise from each part of a circuit should be minimised in Lucian's design, that's why he uses a multilayer PCB

A shunt pre-reg is not the only way to achieve low noise at the input either.
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Old 3rd October 2012, 08:28 AM   #1308
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Quote:
Originally Posted by bismuth View Post
Interesting comparison graph, I think the regulators on the board are LP5900 type with 6,5 uV noise figure. But their PSSR is not very high depending on freq (see datasheet). Maybe it is a good reason for using an 'overkill' shunt pre regulator ?
Or is the 5V used somewhere in the circuit (without additionnal regulator) ?
Aren't noises from clock rail and XMOS chip way higher ? They surely propagate ? Anyone with a good scope to take a look ?
Yes, interesting graphs! LP5900 has 6.5uV noise figure but it depends in which implementation was measured. I highly doubt that was any XMOS processor around or had common ground with the PC/MAC Even if WaveIO's design has 4 layers, a lot of Vregs and decoupling caps it doesn't mean that there is 6.5uV all over that board! My main goal was to minimize noise as best as possible can but with a 400MHz processor in the center of it and direct GND connection with the host, the goal was (is for newer card) harder to achieve.
Anyway, let's hope that daughter board will have something to say on this as noise will be the first thing to be addressed.
Kind regards,
L
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Old 3rd October 2012, 06:31 PM   #1309
Magsy is offline Magsy  United Kingdom
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Please add me to that list for 1x Daughter card
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Old 4th October 2012, 06:39 AM   #1310
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Done, thank you!
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2. analog_sa
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6. vitalica
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11.12. kp93300 X 2
13. lindamar
14. merlin el mago
15. Reo
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17. jmltinc
18. zibra
19. tagheuer
20. hochopeper
21. hacker
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25. jrling
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28. flocchini
29. ichiban
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