Good information as dual secondary transformers can be found at any supplier.
However I wouldn't choose 2 x 25V AC for 2 x 24V DC. With 25V there will be approx. 36 to 37V unregulated. This will lead to useless conversion of power into heat.
@Milo66: with careful planning and such low power draw (preamps usually don't consume much power) I would choose 2 pieces 2 x 22V with sufficient VA rating if not overdimensioned somewhat. I take 2 pieces of 15VA each are more than enough but larger ones are OK too if they both fit in the casing you plan to use. Best are R-core transformers which can be found online...
30VA Pure copper R-core transformer 2X 6V / 9V /12V /15V/ 18V/ 24V/ 28V L9-49 | eBay
There are countless old and/or old fashioned designs that work but it pays off to make it the best PSU you can build as costs won't rise dramatically when doing so. If you want optimal results the choice for CLC filtering and ultra low noise LDO regulators is clear. 78xx and LM317/337 based PSU's are therefor not to be recommended. TPS7A4701/3301 are a good choice for optimal results. You might even choose 2 x 20V transformers depending on actual power draw and filter caps.
It helps tremendously when the OP gives usable information for the help he/she wishes. So brand and type number are somewhat essential....Not being familiar with any Naim device I now had to assume stuff. So for correct design you need to know what the device draws in all circumstances/worst case. Multiply by 2 and then choose the right transformer(s).
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After rereading I see you use the phrase "+24v 0 0 +24v" which indicates that you just need 1 transformer 2 x xxV. One winding per positive 24V regulator that is and 2 positive regulators 24V @ xA.
Please ignore my text on TPS7A4701/3301 as they are not only +/- regs but also limited to 20.5V.... You need 2 ultra low noise regulators preferably LDO (often this is a combination nowadays). These need to be able to output 24V at the right current.
Please ignore my text on TPS7A4701/3301 as they are not only +/- regs but also limited to 20.5V.... You need 2 ultra low noise regulators preferably LDO (often this is a combination nowadays). These need to be able to output 24V at the right current.
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You want help/advice but you don’t react or give relevant information.
I think relevant info has been given by members. It would help tremendously if you would read what is written. No further feedback will result in off topic replies eventualy.
Again: if you need 2 x +24V you just need 1 transformer with 2 windings 22V and 2 excellent 24V regulators for your brand X type Y device (which we still don’t know).
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For 2 x +24V no center tap is needed but just a transformer 2 x 22V and 2 rectifiers, filter caps and 2 separate 24V regulators.
This is what the OP asks:
In this unprecise language and native speakers making it even more unclear we try to find our way. Dual rail normally indicates a +/- power supply (unclear/contradictory info nr 1) but OP asks for +24v 0 0 +24v (unclear/contradictory info nr 2) for an unknown type device like someone asking for new tyres for his Toyota. This would mean 2 x +24V so why a center tap (unclear/contradictory info nr 3)? And why 2 transformers (unclear/contradictory info nr 4)?
Exactly like Rayma said except for connecting outputs in series which is plain wrong.
Like on the attached schematic but then such a (preferably better performing) circuit x 2. From what I found out there are many 2 x +24v PSU's for Naim preamps that indeed use 2 x 20V transformers and produce 2 x +24V DC with LT108x LDO regs. No symmetric PSU's so no +/- 24V as thought!!!! OP can buy 1 transformer, 2 if he likes but also 4 with single voltages. In a normal thinking world one would suffice with 1 transformer 2 x 22V.
This is what the OP asks:
In this unprecise language and native speakers making it even more unclear we try to find our way. Dual rail normally indicates a +/- power supply (unclear/contradictory info nr 1) but OP asks for +24v 0 0 +24v (unclear/contradictory info nr 2) for an unknown type device like someone asking for new tyres for his Toyota. This would mean 2 x +24V so why a center tap (unclear/contradictory info nr 3)? And why 2 transformers (unclear/contradictory info nr 4)?
Exactly like Rayma said except for connecting outputs in series which is plain wrong.
Like on the attached schematic but then such a (preferably better performing) circuit x 2. From what I found out there are many 2 x +24v PSU's for Naim preamps that indeed use 2 x 20V transformers and produce 2 x +24V DC with LT108x LDO regs. No symmetric PSU's so no +/- 24V as thought!!!! OP can buy 1 transformer, 2 if he likes but also 4 with single voltages. In a normal thinking world one would suffice with 1 transformer 2 x 22V.
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This is exactly what you need. You already knew. Choose lower AC voltage though as explained earlier on.
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