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Post by johngalt47 on May 14, 2012 17:58:06 GMT
Which brand of transformer do you recommend for preamp power supplies? I like Plitron but they are kinda expensive.
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Post by Deleted on May 15, 2012 12:31:03 GMT
Which brand of transformer do you recommend for preamp power supplies? I like Plitron but they are kinda expensive. Normal toroidal transformers are fine, as long as kept well clear of sensitive areas such as input wiring etc. With a preamp, best results will be with the toroidal transformer(s) in an external case and the secondary windings supplying the preamp, but NOT earthed to the mains at the PSU case.The secondary centre tap could then be connected to chassis of the preamp as well, without any hum loop problems, as done in the Class A preamp project. Alex
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XTRProf
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Post by XTRProf on May 15, 2012 16:56:07 GMT
Not earthing a PSU? That's not good practice for AC PSU. Might as well find the source of the hum and eliminate it.
Btw, I prefer R-Core, as is current amplifier trend, if you can find one of the correct VA over toroidal.
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Post by Deleted on May 15, 2012 22:40:13 GMT
Chong The transformer itself is bolted to mains earth,but the secondary winding's centre tap is not . The inputs and outputs in the preamp's case are not connected to mains earth at any time.There is no hum whatsoever when working with a normal power amplifier, and the prreamplifier poses no safety risks as a high voltage surge that flashes over to the core will blow a fuse or operate an external circuit breaker.Most sources these days are double insulated, and do not use mains earth. Why don't you post a block diagram of how YOU would provide earthing and safety,combined with extremely low mains hum, for a source, preamplifier, and power amplifier combination ? As usual, there is more than one way to skin a cat. I was referring to the secondary windings ONLY. As for R-Core transformers taking over the world of amplifiers? Perhaps in Singapore DIY circles, but not world wide. They are too expensive, an awkward profile for today's slimmer designs,and hard to obtain in suitable voltages and VAs. Alex P.S. These days, in most cases where DACs, preamps etc. use a mains transformer, chassis earth and PCB earth are separate.Some commercial PSU PCBs (Audiowind on ebay, for example) have provision for a capacitor connecting to chassis.
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XTRProf
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Post by XTRProf on May 16, 2012 1:23:19 GMT
Most sources these days are double insulated, and do not use mains earth. Actually, I don't like the present practice of not earthing the equipment as we can definitely feel the minor static like shock when touching the equipment. They do so is just to avoid any possible ground loops thru bad layout and connection as Frans had said. Why don't you post a block diagram of how YOU would provide earthing and safety,combined with extremely low mains hum, for a source, preamplifier, and power amplifier combination ? I don't have Autocad and so can only give a worded projection here. I prefer all METAL chassis to be earthed separately in a Star fashion to one earth point at the AC main socket. The PCB virtual ground will be floated from earth. If the transformer uses a secondary virtual ground connection, that secondary virtual ground is already tied to the pre virtual ground thru the 3 pins PSU connection. So no need to connect secondary virtual ground to pre chassis. That will create possible ground loops. Ground loop is a loop, right? Yeah, I will like to float the pre virtual ground from the earth. So the virtual ground is separate from the earth and so no hum loops any more. As for R-Core transformers taking over the world of amplifiers? That I don't think so. You refering to high quality "highend" systems and not some mid or low budget designs to get the correct alignment of what our reference point of this write is all about? Perhaps in Singapore DIY circles, but not world wide. They are too expensive, an awkward profile for today's slimmer designs,and hard to obtain in suitable voltages and VAs. Oh, even those churned out from China in mass, many of them are using R-Cores. I agreed that it's more expensive for the same VA and harder to find for that special VA though. I'm also having difficulty finding them in Singapore as there are not many AUDIO DIY shops. Now currently looking for one 100 or higher VA R-core 12-0 VAC for my MF X-Can V2. Any suggestion of where I can find one at good price? These days, in most cases where DACs, preamps etc. use a mains transformer, chassis earth and PCB earth are separate.Some commercial PSU PCBs (Audiowind on ebay, for example) have provision for a capacitor connecting to chassis. That's what I like before reaching here. But I don't like we have a cap separating the chassis and virtual ground. Might as well do the full monty of complete separation. Preventing instead of elimination after problem creation is still my motto of KISS. In other words, better design, layout and connection is better than trying to eliminate when noise "problems" arise.
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Post by Deleted on May 16, 2012 1:46:53 GMT
When the power amplifier is earthed, the "earth" side of the RCA connectors of the source is extended via the preamp to the Power amplifier's input earth.In this case via a 10 ohm resistor which is there to reduce the effects of earth loops.In a recent SC design they increased the value of the 10ohm earth lift resistor and obtained a further measurable improvement .
There is provision on my preamp for connecting together the cases of the preamp and power amplifier using the provided earthed banana sockets on both. I have a lead with a banana plug on each end for this purpose.It is quite safe without it plugged in, and does not contribute to lower hum level, as there is none audible or identifiable with a C.R.O. on maximum sensitivity.It MAY be worthwhile using if connected to a P.C. though.
I don't use it. It's not usually needed.
You are living in the past still. Most modern DACs, for example, even when using power transformers, don't have their active area connected to mains earth.The outputs and coax SPDIF inputs etc. are not referenced to mains earth.
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Post by Deleted on May 16, 2012 7:41:29 GMT
Which brand of transformer do you recommend for preamp power supplies? I like Plitron but they are kinda expensive. I would simply buy a transformer that would be suited VA wise, sizewise, is affordable and keep it away from hum sensitive parts if possible or screen it. No particular brands are recommended over other ones IMO. Just select what suits your needs and is available and affordable.
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