On the subject of input voltage requirements, I should check my own setup, please:
I'm configuring for +/-13V, 290mA CCS each rail (190mA Legato I/V stage + 100mA shunt) x2
I was thinking to use a 0-15VAC x2 transformer - this would give me 18VDC after the rectifier, correct?
Q1. does 18VDC input provide adequate voltage drop for my target voltage of 13VDC?
Q2. what current rating of transformer should I use? 10VA would be the absolute minimum, right? So for decent headroom I should use 30VA or 50VA?
Thanks
I'm configuring for +/-13V, 290mA CCS each rail (190mA Legato I/V stage + 100mA shunt) x2
I was thinking to use a 0-15VAC x2 transformer - this would give me 18VDC after the rectifier, correct?
Q1. does 18VDC input provide adequate voltage drop for my target voltage of 13VDC?
Q2. what current rating of transformer should I use? 10VA would be the absolute minimum, right? So for decent headroom I should use 30VA or 50VA?
Thanks
Α1. Marginal. Absolute min Vin=(~3.6VDC+R101drop)+Vout for ~300mA CCS. 15VAC are more likely to give you circa 19VDCin though. Measure the real output of your Tx on your own wall power. Your mains could be staying on the strong side, then its passable. If mains duck in your area often, maybe not.
A2. Use 30VA or more.
A2. Use 30VA or more.
I use a 230:15+15Vac transformer for my DCB1, not hotrodded.
I generally have 240 to 245Vac from the mains and I see the DC input to the DCB1 between 21Vdc to 23Vdc.
If you replicate these operational values you will find that you have adequate DC input, even when mains drops to 226Vac for a 10Vdc regulated output.
I suspect that 13Vdc is possible, but at 290mAdc as well you may be a volt, or two, short when mains is very low.
A 16Vac or 17Vac would probably be the safer option, if you want to cater for all worst case conditions.
Now to VA requirement.
A 290mAdc continuous output requires a continuous AC current rating of 580mAac.
If you want the transformer to run cooler than maximum rating then I usually recommend doubling the VA rating.
580mAac * 15+15Vac = 17.4VA, doubling says 30VA is adequate for cooler running. Certainly NOT 10VA.
[290mAdc+5mA(wasted)]*2 * 17+17Vac = 20VA, I'd be looking for 40VA.
I generally have 240 to 245Vac from the mains and I see the DC input to the DCB1 between 21Vdc to 23Vdc.
If you replicate these operational values you will find that you have adequate DC input, even when mains drops to 226Vac for a 10Vdc regulated output.
I suspect that 13Vdc is possible, but at 290mAdc as well you may be a volt, or two, short when mains is very low.
A 16Vac or 17Vac would probably be the safer option, if you want to cater for all worst case conditions.
Now to VA requirement.
A 290mAdc continuous output requires a continuous AC current rating of 580mAac.
If you want the transformer to run cooler than maximum rating then I usually recommend doubling the VA rating.
580mAac * 15+15Vac = 17.4VA, doubling says 30VA is adequate for cooler running. Certainly NOT 10VA.
[290mAdc+5mA(wasted)]*2 * 17+17Vac = 20VA, I'd be looking for 40VA.
Thanks to you both. I've seen 16VAC R core transformers on eBay - that's what I will aim for.
Another question - diodes.
The build guide recommends MUR120 for up to 200mA CCS, and MUR820 for high currents.
With approx 300mA passing through my bridge, MUR120 is under-spec, so I suppose I should use MUR820, such as these by On Semi -
MUR820G ON Semiconductor | Mouser
but this seems overkill for my situation.
I recall someone recommended Vishay BYV27, which I can get as either 50V or 100V -
BYV27-100-TR Vishay Semiconductors | Mouser
Would this be more suitable for me?
Another question - diodes.
The build guide recommends MUR120 for up to 200mA CCS, and MUR820 for high currents.
With approx 300mA passing through my bridge, MUR120 is under-spec, so I suppose I should use MUR820, such as these by On Semi -
MUR820G ON Semiconductor | Mouser
but this seems overkill for my situation.
I recall someone recommended Vishay BYV27, which I can get as either 50V or 100V -
BYV27-100-TR Vishay Semiconductors | Mouser
Would this be more suitable for me?
Done - two of these are up and running:
Not really up to my usual standards in terms of heat sink etc. but it's not really a priority project so it was supposed to be cheap. I'm going to test them in their application later this weekend and report.
Thanks Salas and Teabag.
Sven
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Not really up to my usual standards in terms of heat sink etc. but it's not really a priority project so it was supposed to be cheap. I'm going to test them in their application later this weekend and report.
Thanks Salas and Teabag.
Sven
BTW - this is where it goes:
Cables are may be 4cm. Is it necessary to connect remote sensing at the load PCB? Would be a lot eqasier to just loop it like during the test...
Sven
An externally hosted image should be here but it was not working when we last tested it.
Cables are may be 4cm. Is it necessary to connect remote sensing at the load PCB? Would be a lot eqasier to just loop it like during the test...
Sven
Grounding again
I am sure this has been asked and answered many times, and I'm sure I have read many of the answers, but...
I am building a "2 box" phono preamp powered by a SSLV (BiB) regulator. In one enclosure (let's call it box1) I have a transformer with a center-tapped secondary, feeding a bridge rectifier built from 4 MUR820's, followed by some capacitors and resistors. It is a balanced or dual-polarity supply, so the center tap of the transformer secondary will be the power supply ground.
Box2 holds the phono board and the BiB regulators. The 2 enclosures are connected via a 3-conductors + shield cable.
So box1 has an IEC inlet, and safety ground is connected directly to the chassis. Should I also connect the secondary center-tap to the safety ground and chassis? Should I connect them, but isolated via diodes or other devices?
Either way, the center tap will connect directly to the "ground" side of the filter caps, and on to the "ground" of the cable that carries DC power to box2. How should I connect the shield of that cable? Should it be connected to the chassis at either end? At both ends? Or should it be connected to the center-tap ground reference on one side or both?
*dazed and confused* I want the shield to be effective so I am sure of supplying pretty clean unregulated DC to box2, but I don't want to create ground loops or reference a dirty ground for the phono preamp.
Thanks for any insights.
I am sure this has been asked and answered many times, and I'm sure I have read many of the answers, but...
I am building a "2 box" phono preamp powered by a SSLV (BiB) regulator. In one enclosure (let's call it box1) I have a transformer with a center-tapped secondary, feeding a bridge rectifier built from 4 MUR820's, followed by some capacitors and resistors. It is a balanced or dual-polarity supply, so the center tap of the transformer secondary will be the power supply ground.
Box2 holds the phono board and the BiB regulators. The 2 enclosures are connected via a 3-conductors + shield cable.
So box1 has an IEC inlet, and safety ground is connected directly to the chassis. Should I also connect the secondary center-tap to the safety ground and chassis? Should I connect them, but isolated via diodes or other devices?
Either way, the center tap will connect directly to the "ground" side of the filter caps, and on to the "ground" of the cable that carries DC power to box2. How should I connect the shield of that cable? Should it be connected to the chassis at either end? At both ends? Or should it be connected to the center-tap ground reference on one side or both?
*dazed and confused* I want the shield to be effective so I am sure of supplying pretty clean unregulated DC to box2, but I don't want to create ground loops or reference a dirty ground for the phono preamp.
Thanks for any insights.
I would start with the PSU box grounded to the IEC ground but with the center tap (PSU ground line) yin yang or bridge diodes isolated.
Then about the umbilical cable I would connect its shield to its earth conductor at the phono box only. Not going to the second box metal yet though. Just to the BIBs.
I would refer the phono circuit channels grounds with one wire each to the phono box at the TT ground lug that should have chassis contact. Make sure all chassis panels show continuity with each other and no paint isolates them.
P.S. You got to arrange for the BIBs to have a common so to accept +V-0-V-. Their PCBs are made for separate transformers & bridges. You will need a thick wire from (-) filter cap position of a positive BIB to (+) filter cap position of a negative BIB. Stick the incoming 0 to the mid point of that wire. No diodes on BIB boards when the rectification is already done elsewhere of course. But you can have good electrolytics still used on the BIBs main filter cap positions for incoming raw DC local filtering & decoupling. Incoming + & - goes to those capacitors.
