Welcome Guest! To enable all features please Login or Register.

Notification

Icon
Error

Options
View
Go to last post Go to first unread
stewart  
#1 Posted : Saturday, December 14, 2019 7:53:25 PM(UTC)
stewart

Rank: Advanced Member

Groups: Member
Joined: 11/10/2008(UTC)
Posts: 107
Location: New York City

Thanks: 1 times
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:

LCBS

Fed 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 BP

Fed 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-2-1

Edited by user Saturday, December 14, 2019 8:00:33 PM(UTC)  | Reason: Not specified

stewart  
#2 Posted : Monday, January 6, 2020 8:27:00 PM(UTC)
stewart

Rank: Advanced Member

Groups: Member
Joined: 11/10/2008(UTC)
Posts: 107
Location: New York City

Thanks: 1 times
Bump.
Brian Donegan  
#3 Posted : Monday, January 6, 2020 11:47:29 PM(UTC)
Brian Donegan

Rank: Administration

Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 2,782
Location: Massachusetts, USA

Thanks: 2 times
Was thanked: 126 time(s) in 121 post(s)
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.
stewart  
#4 Posted : Wednesday, January 8, 2020 6:00:41 PM(UTC)
stewart

Rank: Advanced Member

Groups: Member
Joined: 11/10/2008(UTC)
Posts: 107
Location: New York City

Thanks: 1 times
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)  | Reason: Not specified

Brian Donegan  
#5 Posted : Monday, January 13, 2020 9:11:11 PM(UTC)
Brian Donegan

Rank: Administration

Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 2,782
Location: Massachusetts, USA

Thanks: 2 times
Was thanked: 126 time(s) in 121 post(s)
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).

Rss Feed  Atom Feed
Users browsing this topic
GuestUser (6)
Forum Jump  
You cannot post new topics in this forum.
You cannot reply to topics in this forum.
You cannot delete your posts in this forum.
You cannot edit your posts in this forum.
You cannot create polls in this forum.
You cannot vote in polls in this forum.