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Old 2nd January 2012, 03:38 AM   #121
gootee is offline gootee  United States
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Old 2nd January 2012, 10:52 AM   #122
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Quote:
Originally Posted by Duwenbleidd View Post
It's just the same as measuring in loopback. A little example follows - LM317 with Vbe multiplier. Maybe I've made a mistake somewhere, but I have calculated that it shows 5,6uV (at 50Hz)... That doesn't seem quite possible with such a simple design...
Tomáš
ok that makes sense, with no input signal (ie the 1Khz signal) it will just show what is actually there.

5.6uV does seem very low (not so much from a point of view of the circuit, but of what the soundcard can actually resolve!!) I haven't tried to do any calcs yet based on the measurements I did last night, but I see that Arta has calibration facilities, so I assume you can set it up to give absolute values.

edit: I won't probably get the measurements for a few days. It takes quite a lot of setting up to get the noise sources eliminated! possibly tomorrow evening if things aren't too busy the measurements earlier were actually done by recording 10 seconds of the PS using audacity and then analysing in RMAA.

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Last edited by wintermute; 2nd January 2012 at 10:59 AM. Reason: added comment on when I can next do measurements.
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Old 15th April 2015, 04:52 AM   #123
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Would this LM317/LM337 variant of the circuit work? The DAC I'm modding has an R-core transformer with a center-tapped secondary, hence the need for a dedicated negative reg.
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Old 15th April 2015, 12:32 PM   #124
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No, it doesn't work.

The last 4 tappings to the +ve side Zero volts and the last 4 tappings to the -ve side Zero volts, must all meet at a star point.

You then need to take a single wire to the junction of the smoothing capacitor and from that junction another single wire to the Centre tap of the transformer.

Electrically this layout looks identical to what your sch shows. The difference becomes apparent when you assign values of Impedance to every wire in your sch. The performance will be very inferior and that's why I said it won't work.
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Old 15th April 2015, 01:34 PM   #125
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Thanks for pointing that out, the layout in my schematic is bad in regard to grounding. It was hastily scribbled down during breakfast... I'll hand in a proper version later.
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Old 16th April 2015, 06:58 AM   #126
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And here it is. I think I'll build a prototype over the coming weekend.
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Old 16th April 2015, 10:36 AM   #127
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YES !
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