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glt  
#1 Posted : Tuesday, November 3, 2009 9:39:53 PM(UTC)
glt

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Thinking of bypassing the on-board 5v regulator for OPUS VA.
- I think the noise figure of Placid should be orders of magnitude lower than the 30 uV of the regulator and higher PSRR (what is the noise figure for Placid?)
- Is there any benefit of feeding Placid with regulated power from LVDPS?
- Increasing the voltage above 5V should also decrease THD
Russ White  
#2 Posted : Wednesday, November 4, 2009 8:11:13 AM(UTC)
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The PSRR of the placid is already excellent(I mean really excellent), but if you put the LCDPS in front of it it would be even better. :) Enough to worry over? No, but better. :)

Using for the 5V supply should not be any trouble at all. Just remove the on-board reg.

Good luck! :)
glt  
#3 Posted : Wednesday, November 4, 2009 9:35:01 AM(UTC)
glt

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Thanks. What would be the minimum/optimal input DC voltage for Placid?
glt  
#4 Posted : Thursday, November 5, 2009 5:19:53 PM(UTC)
glt

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I ordered the supply.

I found in the diyaudio forum that it requires about 3V above regulation. So 8V input.

Also Russ says "The shunt employs a shaped compensation scheme that keeps the regulator stable even into large capacitances (I have tested 1000uf low ESR Pannasonc FMs). You typically do not want to load a shunt reg with a very high capacitance. It defeats the purpose."

I suppose the 100uf bypass cap after the regulator should be no problem
glt  
#5 Posted : Sunday, November 22, 2009 4:36:46 PM(UTC)
glt

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Some photos of Placid. 9VDC input, 5V Output, Icss=160mA, Iout=100mA. Transistors run cool

UserPostedImage
UserPostedImage
glt  
#6 Posted : Tuesday, November 24, 2009 9:04:23 AM(UTC)
glt

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Voltage Drift

Is it normal to see a voltage drift from dead cold to operating temperature? I measure about -50mV. I set it to 5.13V right after turn-in and it settles to 5.08V


[update]
I found the answer in the diyaudio thread: http://www.diyaudio.com/...ated-power-supply-7.html

So it is normal for the output voltage to drift lower because of the negative temperature coefficient of the led references (I guess that's why you can buy voltage reference ICs that are temperature compensated)

Edited by user Tuesday, November 24, 2009 12:03:10 PM(UTC)  | Reason: Not specified

Beefy  
#7 Posted : Tuesday, November 24, 2009 12:58:56 PM(UTC)
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glt wrote:
So it is normal for the output voltage to drift lower because of the negative temperature coefficient of the led references (I guess that's why you can buy voltage reference ICs that are temperature compensated)


I can't imagine that macroscopic changes in the overall voltage are all that critical. It is instability over very short time periods that is much more important.
Russ White  
#8 Posted : Tuesday, November 24, 2009 5:54:34 PM(UTC)
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very good work as always glt!

The slight tempco drift from the LED VREF is something we chose to live with in order to get very low noise. For all practical applications it won't make any difference at all. The time period for such a change is very large. And once equilibrium is reached it will stay within a few uV over minutes,

Cheers!
Russ
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