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Old 11th March 2012, 08:25 PM   #11
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Gosh, again with that agnostic stuff???
Some people NEED to know what ingredients to use and in what quantity, order to make that pudding.
Your aproach is "pudding is just a miracle, you just have to belive in it. Research is futile". It might work for you, but it does not mean that others cannot try to KNOW more.
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Old 11th March 2012, 09:08 PM   #12
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I was not totally satisfired with the dac:

1. I changed the standard LF 351 to OPA 827, those ones are quite fast but i think noisy. At the output is are two OPA 602.
2. I can hear out humm (and are able to measure it with a simple usb soundcard).

I think 2. depends on the powersuply cables which went in top of the board, but mabe it is the grounding issue.
The Humm has nothing to to with the plug grounding (i tried every possibility), there is no ground loop in general with my stereo (only one device is grounded).

I must look at the datasheet of opa 827 again (with the today knowlage!).
That are the reasions i'd like to search for new alternatives.

For me a dac must be so quiet that with maximum gain of my Revox amplifier there shouldn't be additional noise and humm compared with an open input (and the Revox B251 is really quiet!)

And knowing "whats going on" in my equipment help me to get the feeling of "good sound".

A short look at the quite interesting pdf's let me ask a question:
The guys of AD differ between high current digital and low current digital circuits connected with analogue. The Ad 1955 consumes 22mA is that low current?

I looked at the evaluation module of the WM8740 chip. The analogue ground and digital ground is only connected at the bottom of the chip, this looks like suggested two in the AD pdf (and makes sense in my eyes).

In a few posts ago, i said that i'd like to use little inductors, i meant ferrite's.
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Old 11th March 2012, 09:32 PM   #13
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Quote:
Originally Posted by SoNic_real_one View Post
Gosh, again with that agnostic stuff???
Some people NEED to know what ingredients to use and in what quantity, order to make that pudding.
Your aproach is "pudding is just a miracle, you just have to belive in it. Research is futile". It might work for you, but it does not mean that others cannot try to KNOW more.
Yes, SOME people, but not THIS person. He wasn't asking how to cook up his own meal, he was asking for recipe details as a proxy for the subjective flavor of some untasted dish. The cook needs to know the recipe, not the person eating the dish.

Your thinking often comes across as disappointingly binary. Seriously, how did you become so self-righteous, so deluded in to seeing yourself as a crusader for the one single truth. The truth as you have determined it, of course. While you may fancy yourself as some crusader for the truth, your mindset is quite doctrinaire, dogmatic, and more than a bit hubristic. Haven't I before proven you wrong about things of which you were absolutely certain? Maintaining an open yet critical mind requires much more effort, and dare I say, intelligence, than does maintaining a closed one.
__________________
Ken

Last edited by Ken Newton; 11th March 2012 at 09:40 PM.
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Old 12th March 2012, 12:34 AM   #14
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"My truth" was posted before by engineers. I usually give links to support that. It is maybe a partial truth (as seen by the electronics engineer comunity today), but it has a higher degree of incertitude as compared with the dogma "measurements are useless".
Quote:
Originally Posted by Stefan0815 View Post
In a few posts ago, i said that i'd like to use little inductors, i meant ferrite's.
I hope that they are NOT on the ground. They need to be on the positive power supply, coupled with decoupling capacitors from positive power pin to ground.
When they talk about digital low current, they are reffering to the digital ground lead of the ADC/DAC cip that cannot be separated internally. The switches need to be connected to both digital and analog side. Unless somebody will make internal switches with optical command.

Last edited by SoNic_real_one; 12th March 2012 at 12:42 AM.
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Old 12th March 2012, 12:52 PM   #15
marce is offline marce  United Kingdom
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These days and for several years most of the advice is to lay a board out with digiatl and analogue seperate areas, and have ONE contigous ground for the whole board. The worse sort of connection if you do deciede to have two grounds is one skinny little high impedance star point, the connection needs to be as large as possible.
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Old 12th March 2012, 01:00 PM   #16
qusp is offline qusp  Australia
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ha... opa827 noisy? Stephan0815, i think the noise is much more likely to be coming from your layout and/or implementation, as opa827 is one of the quietest opamps in existence. the noise you measure is much more likely to be induced on the ground reference unless you have done something very wrong with the opa827
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Old 12th March 2012, 01:26 PM   #17
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I looked at the spec's of the opa 827 again yesterday. You are totally right! I had in mind that this opamp was desinged to be very fast, but its lowest noise two.

So my conclusion is that there is something wrong with the DAC layout. The ground mod on the photo was after the first ad 1955 gone to smoke and i never tryed and measured the dac with it.

So what to do? I think i am finished with chinese stuff and don't whant to spend another 100€ for a bad desing. And for spending the nights on an own desing is not possible in the moment.

Last edited by Stefan0815; 12th March 2012 at 01:30 PM.
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Old 20th March 2012, 10:35 AM   #18
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My solution is to order a DAC pcb from Hoerwege, looks really good and is not so extreme expensive (bevcause its an prototype).
Attached Images
File Type: jpg DAC1794_2_Proto_oben.jpg (117.0 KB, 56 views)
File Type: jpg DAC1794_2_Proto_unten.jpg (104.9 KB, 54 views)

Last edited by Stefan0815; 20th March 2012 at 11:00 AM.
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