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Can I measure VR1 and VR2 after the dac is powered down, and then use the value that I measure to get fixed resistors in place instead of VR1 and VR2 ?
For an example on VR2 on Placid BP, the value is 700R at 14.8 vdc. So if I replace VR2 with an 700R I will get a stabil 14.8 vdc ?
Is 25w on an 700R ok ? Is 25w ok for the other fixed resistors I am planning to replace the other adjustable VR1 and 2's.
Thx
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Originally Posted by: musicman  Can I measure VR1 and VR2 after the dac is powered down, and then use the value that I measure to get fixed resistors in place instead of VR1 and VR2 ?
yes Originally Posted by: musicman
For an example on VR2 on Placid BP, the value is 700R at 14.8 vdc. So if I replace VR2 with an 700R I will get a stabil 14.8 vdc ?
yes Originally Posted by: musicman
Is 25w on an 700R ok ? Is 25w ok for the other fixed resistors I am planning to replace the other adjustable VR1 and 2's.
It depends on the voltage across. The pots are spec'ed @ 0.5w.
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Thx avr 300
On Placid BP the voltage across CCS- VIN on both rails are 90mV each.
On Placid HD (for the BIIi ) the voltage across CCS-VIN is 640mV.
On the Placid HD (to Exa ) the voltage across CCS-VIN is 180mV.
How do I calculate ? Ohms law ? Or ?
Thx
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Thx again.
Will report after soldering the resistors.
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Ok, all of the VR1's is now replaced with fixed resistors ( 560 R ). I have done this on both of my two Placid BP's
Tha strange thing is that the positive rail is ok but not the negative. 91 and 95 mV, CCS-VIN + and shunt is 60 and 55mV ( pos rail )
The negative rail show 67 and 61mV- shunt is 31 and 27mV
All of the VR1's measured exactly 560R when dac was powered down.
The new fixed resistors measure different when dac is powered down. On the positive rail things look ok with still 560R, BUT on the negative rail the numbers is 450R.
Anybody any idea why ? ( the V-out is 14.80 on both Placid BP )
Will it help to put on resistors with a higher value on the neg rail ? I have 680R I can try.
Thx
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Sorry I missed this. You should measure the values of vr1 and vr2 after removing them from the board. This will prevent other components from affecting their measured value.
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Thanks Brian
Must be something that affect the resistors on the neg rail.
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If you measure VR1 and VR2 now (removed) do you get the same readings?
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The dac sound wonderful as it is now. Maybe it's a good idea to let it play for a while and see if things will change over time.
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Originally Posted by: Brian Donegan If you measure VR1 and VR2 now (removed) do you get the same readings?
Ehhh, I had a hard time removing them ( no expert like you guys ) so I am pretty shure they are broken. The legs snapped of the VR's body.( Maybe it's time to get a desolder iron). The reason I measured them on the pcb ( dac powered down ) was a comment from Russ somewhere in the diy forum. The strange thing is that both of the fixed resistors on the pos rail have fine measurements. But not on the neg rail where the values are a bit lower then recommended. VR1 on pos and neg rails measured exactly 560R. No big deal for me since the BIII works fine now. Any thoughts according the low numbers on the neg rails ? Edited by user Tuesday, April 9, 2013 3:02:04 PM(UTC)
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Done deal !!!
I have finally completed BIII.
The VR1 on Placid BP( have two ) where replaced by fixed resistors in paralell. 820R and 2.2 kohm measured together 597R, and this give me 59mA shunt.
I tried a singel 560R, but that was a bit to low.
The reason that I go for fixed resistors instead of the VR's is that I measured different almost everytime I check the current and shunt. Not anymore.
Thx to TPA for an outstanding dac.
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