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Old 1st June 2013, 05:20 AM   #2271
Salas is offline Salas  Greece
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Quote:
Originally Posted by nezbleu View Post
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.
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Old 1st June 2013, 05:31 AM   #2272
Salas is offline Salas  Greece
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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.
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Old 1st June 2013, 08:19 PM   #2273
nezbleu is offline nezbleu  Canada
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Yes, I installed 4700uF electrolytic on the BiB boards. The DC will connect to the usual AC input locations, with a small value resistor carrying over the usual diode locations. That part has already been tested outside the enclosure.
Point taken about the common ground though.
Thanks.
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Old 28th June 2013, 10:05 AM   #2274
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Hi Salas,
May i use +-60VDC 150 ma for my preamp power supply?
Thanks.
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Old 28th June 2013, 10:32 AM   #2275
Salas is offline Salas  Greece
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No, the Q102 Jfet for the 3-4 leds won't take it. It would need to botch a resistor in its place. 15k 1W from R102 & leds node to ground.
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Old 28th June 2013, 11:04 AM   #2276
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Thank you for prompt reply.
May you write some schematic ?
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Old 28th June 2013, 03:19 PM   #2277
Salas is offline Salas  Greece
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Old 29th June 2013, 02:14 AM   #2278
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Thank you very much for your kindly.
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Old 29th June 2013, 03:13 AM   #2279
Salas is offline Salas  Greece
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Also use BC546 Q104 for its higher voltage max.
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Old 29th June 2013, 06:10 AM   #2280
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Salas

Vref setting string on above schematic Is consisted from 3 various types components
I have read that best Is to use only leds If possible because of low impedance
second best low noise reference element
third place - include resistance
could you please confirm
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