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I successfully built my Placid HD, adjusted VR1 and VR2 on this one without problem.
I am trying to trouble shoot my Placid HD BP. I narrowed the problem down to my VR1 and VR2. I think I managed to over-turn three of the VRs on the Placid HD BP and messed them up, so I ordered six 10K VR pot (PN: T93YA103KT20) more from Mouser.
I have been trying to adjust the resistant (by measuring the outer pins of the trimer) to 500R-600R for VR1 and 1k for VR2. However, I cannot get to the specified value. The value stayed around 10.3k Ohm on all six of them.
Am I doing something wrong or I just got bad parts? Can I used fixed value resistor in place of the VR1 and VR2? I bought this kit for about a year now but have not been able to finish this DAC and enjoy some music. Thank you all for your help.
Justin.
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Hi Justin.. You have to measure between the middle pin and one of the outer pin. If done so you'll see the value changing. Next up is to determine where to measure. Look at the attachment #1. This is the two pins which between the placid is measuring the resistance. Likewise for the other side. Or, if you are to insert fixed resistors, you can use the outermost pins, see attach 2. avr300 attached the following image(s):  cut.JPG (25kb) downloaded 19 time(s). cut2.JPG (21kb) downloaded 9 time(s).You cannot view/download attachments. Try to login or register.
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 1 user thanked avr300 for this useful post.
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Thank you so much for the quick reply AVR300. I was able to adjust the positive rail on the Placid BP HD to around 15V at the output, but unable to get the negative rail to that value. Negative rail only measures around 3.9V at the output. All LED's are on, green. I noticed that the heatsink on negative rail gets very hot, barely can put my finger there for 3 sec. D1B is in right rotation, I re-flowed all the joints on negative rail. Can you guys help? Thank you. Justin. Edited by user Monday, April 29, 2013 1:15:27 AM(UTC)
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This is typically cause by misplaced transistors. Double and triple check the small transistor placements.
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Does anyone know the adjustment procedure for VR1 and VR2 for Buffalo III and what are the R values (approx.), once VR1 and VR2 are adjusted? Also what is the purpose of having a current limiting diode D1 (5mA) in the Placid HD circuit. Can this diode be replaced with a fixed resistor or a J-FET connected as a diode?
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Yes, it's all in the integration guide, page 68 Now since you asked here are the values of my Placid HD powering a Buffalo II with Tridents. VR1= 1k5 VR2= 5k6 ALWAYS check the actual V_out with a DMM before connecting the DAC. Why will you substitute the CLD ? It's a part of the circuit. Edited by user Thursday, October 31, 2013 4:35:04 PM(UTC)
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Thanks avr300. The values for B III will be slightly different but it is good to know what bulk figures to expect. When you say Integration Guide p68, what guide are you referring to. B III Integration Guide says nothing about how to adjust Placid HD for Buffalo III, and this info should be in there.
Could you please describe the VR1/VR2 adjusting procedure for output current and voltage in this thread, I am sure I am not the only one wondering about this.
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..and to answer your question why to replace 1N5314 CL diode, it costs about $5.50 a piece, which is a lot for a diode. So why not put a suitable J-FET connected as a diode instead, which would cost about 20c.
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Here is what I got so far, for Placid HD for Buffalo III:
RF = 1K5
RG = 4K7
VR1 = shunt current adjust to approx. 50mA
VR2 = output voltage, adjust to 5.25V
CCS = 440mA for B III with Tridents
This is how I am going to adjust my Placid HD.
Does anyone know what the voltage drop should be on D1 when Buffalo III is powered on and playing and Vout = 5.25V?
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If your using the supplied pots, voltage_out is just a matter of turning the pot. So is the current_out. You look in the manual the needed current of the consumer (the DAC, that's why I refereed to the integration guide). 5.25V and ~500mA - Adjust Vout (VR2) to 5.25V - Measure CSS across R1 (mV equals 1:1 mA), adjust VR1 for ~500mV - Connect the DAC - Measure shunt current across R2 (mV equals 1:1 mA), adjust VR1 for ~50mA - Re-check V_out - Play music . Edited by user Friday, November 1, 2013 5:48:32 PM(UTC)
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Aha, perhaps I misunderstood what you were asking.
Was the question: "Could you please describe the R1/R2 adjusting procedure for output current and voltage in this thread, I am sure I am not the only one wondering about this."
meaning the calculation for substituted resistor ?
If so - what I have done is first using the pot to achieve the requested V_out and I_out. Then measure the resistance across the pot - and you have the value for the resistor.
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