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I am powering a Buffalo II, Legato and Amanero/Cronus combo with an older LCBS (the resistors were replaced with the jumper to provide higher current) and a Placid HD BP. It sounds very good but I have always had issues with the voltage supplied to the Buffalo creeping up and I'm not sure why the power supply is shunting so much current feeding the Legato. I'm also not sure if the transformer feeing the Amanero/Cronus and Buffalo is large enough. Measurements are below: LCBSFed by 15VA 9+9v (.83A) transformer 10.34v on secondary into LCBS supplying 5v to Amanero 9.95v on secondary into LCBS supplying approx. 5.4v to Buffalo II Placid HD BPFed by 30VA 15+15v (1A) transformer 16.43v on secondaries into Placid HD BP supplying 15v into Legato 405mA ccs current; shunting 183mA 402.3mA ccs current; shunting 201mA If I adjust VR1 to lower shunt current to the recommended 50-60mA for the Legato, CCS current drops to around 260mA. I thought the Legato should show a constant load of 350mA so would be worried it isn't getting enough power. To supply 350mA while shunting 60mA, I've aimed to adjust CCS to 410mA; however, the below thread seems to suggest that after setting CCS, you should go back and adjust shunt current to 50-60mA - but as I mentioned this then lowers CCS current below 350mA. What is the correct approach? http://www.twistedpearau...um/posts/t3882-HD-BP-2-1Edited by user Saturday, December 14, 2019 8:00:33 PM(UTC)
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Sorry for the delay...
Let's start with the Legato and Placid BP. I think the 350mA in the manual was more of a ballpark early on. Trust what you are measuring and follow the steps you pointed to. Should be fine.
Can you describe the voltage creeping up on the Buffalo? My gut there is that it would benefit from a larger transformer. We now carry a 30VA 9v transformer.
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Thanks Brian. So I understand, should I be adjusting VR1 with an aim to shunt 60mA? As long as the Placid is showing some shunt current, does that mean the Legato is receiving all of the current it needs? I don’t fully understand how the Placid operates. My concern is that if I am adjusting to shunt 60mA, but only reading 260mA of CCS, am I “starving” the Legato by only giving if 190mA (after shunting) or would the Placid shunt 0mA and deliver the full amount if that’s current the Legato was actually drawing? Regarding the voltage drop, I have always set the power supply to deliver around 5.4v, but hours, days or sometimes weeks later when I check voltage again it’s drifted up to 5.8v or higher. I haven’t had any problems with the newer AVCC trident, but, in the past, two older AVCC modules have failed, I believe because voltage drifted higher and was too much for the trident. Oddly, I don't think the other side of the power supply going to the USB module drifts upwards. I will try a higher VA transformer. I am also planning to supply the Legato with an additional bi-polar Placid. Theoretically, would there be any advantage to using say two 50VA transformers, each supplying one bi-polar Placid, vs. one 100VA transformer to supply both? If a transformer has “dual” secondaries, does that mean one transformer can be wired to two bi-polar power supplies (8 wires) or only that it can power one bi-polar supply (4 wires)? Edited by user Wednesday, January 8, 2020 6:03:33 PM(UTC)
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Yes, if the Legato draws more current than is available, you would see the output voltage of the Placid drop.
As for the power supply drift, that is strange. Possibly a bad trimmer pot on the supply (?). Next time you set it, check the resistance across the trimmer (with power off). If it then drifts, check the pot value before correcting it. It could also be a cap leaking (I guess). Strange.
If you are using a single Placid BP now, I would stick with that. 50VA would be plenty. In theory you can gain benefots from full dual-mono, but I personally wouldn't bother.
Dual secondaries means the transformer has two sets of secondary windings (four wires). The transformers we sell have both dual primaries and dual secondaries. This is so the primaries can be wired in parallel for 120V countries or in series for 240V. The secondaries can be wired in serial (center being common connected) for bipolar usage, used independently for two single rail supplies, or in parallel for one single rail supply (with twice the current capability).
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I swapped in a new v2.1 Placid BP and Centaur that I am planning to use for a Buffalo III build and am getting good voltages now. I also used fixed resistors in each to set the voltage. I didn't think to resistor match before soldering the resistors to the Placid and the L/R channels are off by about .15mv. I'm not too concerned about the difference, but if using different resistors in the Mercury, I assume the resistors to match are the corresponding L/R positions of the same resistor ( I believe there are 4 resistors total, 2 pairs). I am looking at the below transformer for the I/V stage. Is a 16v secondary close enough to 15v to feed the Placid and the i/v stage? If this transformer would work, 16v secondaries are available when wiring in series, but then it looks like I would need two transformers for each rail as wiring the dual secondaries in series would only give one secondary per transformer. If I were to wire the secondaries independently, what v would you get on the secondaries? I'm confused because I only see series and parallel specs in the below data sheet, but no details on wiring independently. https://www.hammfg.com/part/266M16
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You would just wire the four secondaries (two pairs) to the four inputs of the Placid. That transformer would work fine, but torroidal transformers are generally lower noise.
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