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Got my Placid cased up today, and have been having trouble with it. I can adjust the voltage with VR2 to 5.5volts, and then the current to 350ma (0.35 volts across R1) with VR1, but when I adjust the current, the voltage lowers down to around 3.4 volts. If I increase the current with VR1, then the voltage goes up a bit, and I can adjust it back to 5.5 volts.
When I power my Buffalo II, the voltage drops to around 1.8 volts, and it won't go up even if I adjust VR2.
Would shorting current limiting resistor possibly solve the problem? I read in older threads that it was a problem in older versions, but that might have been solved in this version.
I reheated all the solder joints, and I was very careful when I assembled. I'll go through and double check everything, but I thought that if shorting a resistor was a potential fix that I should ask.
Thank you for reading my post.
Aaron.
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What are you using for a transformer?
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Brian Donegan wrote:What are you using for a transformer? I am using the Avel-Lindberg that you offer on your website. I have Blue/Violet primaries to AC 120 hot, and Grey/Brown to Neutral. Then I have Black/Orange and Red/Yellow to the AC input on the Placid. At first I only used one set of wires from the transformer, but when I had the problem with the voltage drop, I put them both together, but it didn't solve the problem. Tomorrow I'll go through and make sure that I put everything in the right spot (already double checked it when I built it, but mistakes can happen). I tried changing the fuse (I had a 1/2 amp) to a 1 amp, no change, and then to a 8 amp fuse, and still no change. I set the output voltage with VR2 to 5.5 volts, then set the current with VR1, and the voltage drops to 3.5 volts. I can't raise it back up again with VR2, unless I increase the current at VR1 to around .60 volts. What rating of fuse should I be using? I am putting the fuse on the hot leg of the incoming AC, before it goes to the transformer. Any suggestions for what the problem could be? Thank you for your help. Aaron.
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Any chance you could post some photos?
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Russ White wrote:Any chance you could post some photos? Here are some photos of my Placid. First time photographing a circuit board and posting it, please let me know if you would like me to take better or different pics. I rechecked the placement of the parts on the board, and everything is in the right place. I even desoldered the QP2 JFET because I couldn't see the part number so I could make sure that I didn't mix them up. I also put some solder on the pads for R1 and R2 to make it easier to measure there without scratching away the masking on the board. I powered it up again and tested it after I checked all the parts and reheated the solder joints again. Still has the same problem. I was able to narrow it down a bit though. The voltage is stable only at or above .5 volts across R1. If I drop the current to even a little below 500ma, the output voltage begins to fluctuate and drop. Is there a particular part that could be failing or malfunctioning to cause this particular problem? Is it possible that I overheated something when I was soldering? I used a Weller variable solder station, set to around 3. Thank you for your help. Aaron  
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and here is the bottom of the Placid board, in case you need to see it. There are a few small areas where the masking on the board was scraped off when I put the board together. I've cleaned the board with alcohol since this photo and removed the solder that was on those spots. Thanks again for your time and help. Aaron. 
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Ok you might have everything right, try measuring your current from, R8 instead of R1. There was an error in the first revision of the Placid 2.0.1 manual.
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Russ White wrote:Ok you might have everything right, try measuring your current from, R8 instead of R1. There was an error in the first revision of the Placid 2.0.1 manual. Thank you for taking the time to help me. I reset everything as it says in the manual, 10k on VR2, 100ohms on VR1. I then powered and set the voltage with VR2 to 5.5 volts. Then I adjusted VR1 and measured with R8 to set the current. At the maximum resistance of VR1 (around 215ohms), I only measured about 285ma of current (.285 volts) at R8. When I added the load of the Buffalo II, the voltage dropped to between 2.1 and 2.2 volts. I checked R3 to see if any current was being shunted, and it came up 0 volts. I checked R8, and I had around 290ma (.290 volts). So, still no go using R8 to measure the current, even though the current is much higher than it was before using R1. Is it possible that one of the parts on the board is bad? Which one would be the most likely culprit to cause this problem? Thank you again for your time and help with this power supply. I am itching to listen to my Buffalo II after spending so many hours building up the boards and cabling. I would love to get this Placid working. I have a wallwart that is a 2amp selectable voltage supply with a 5 volt option. Could I use this just to see if the Buffalo II and IVY III that I have are working? Also, I was planning on using two 12 volt SLA batteries in a +12 -12 configuration. Would it be alright to attach this supply directly to the IVY III board without any caps or anything inbetween the supply and the power input on the board? Best, Aaron.
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I hooked up the Buffalo II to the 5 volt wall wart, and the IVY III to the 12 volt SLA's arranged in +12/-12. It is working, and so far it sounds very good. I'd love to get the Placid working to that I could have a better supply for the Buffalo though. It is great to get to listen to the DAC after spending so much time building it up. I'm enjoying the sound with the wall wart, and I bet it will be improved once I solve the problem with the Placid.
Aaron.
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Hi Aaron, if you are only getting 290ma you can jumper R5. Edited by user Monday, April 19, 2010 4:30:22 PM(UTC)
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Thank you so much Russ! That did it. Jumpered R5 and now my Buffalo II is singing being fueled by the Placid. Let me know if you want me to take any measurements anywhere on the board in case you want to know why my circuit behaved that way. I have a good Fluke DMM, but I do not have an oscilloscope (yet).
Thank you for helping me with the Placid, I really appreciate all the work you do making these kits available to the DIY community. I'm very impressed with the Buffalo II/IVY III so far, and I'm looking forward to building the Counterpoint II and probably a Placid BP when it is available. It is a relief to know that if I run into a problem, you guys will be here to help me out.
Best,
Aaron.
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