Are there theoretical or real world benefits from winding a transformer centre tap in different ways? My preamp’s PSU schematic shows what looks like a centre tap of 22-0-22.
- I’ve seen transformers with this as a single lead to earth.
- However the original trafo (25+ years) has two 0v leads joined to the same PCB earth connection – so, 22-0, 0-22, with no continuity between the pairs when disconnected from PCB and feed (like it’s a separate winding?).
My trafo failed and so am trying to source a new one. Since I'm currently looking to integrate well with the existing PCB and not looking to re-engineer the power supply, it seems that getting a 3-lead centre tap will give me just as much performance as discrete windings with 4 leads. I suppose if I was to reengineer the power supply and put in a separate enclosure, a dual bridge option would be worth looking into. Hmm.
Yes, buy a dual secondary.
It can easily be converted to centre tapped.
Build a mains Bulb tester. Use it to prevent damage to your new transformer if you wire it incorrectly.
What are the advantages of dual bridges versus a center tapped bridge? Audiophoolery reasons OK, just want to know.
I have seen this done in 1960s commercial gear during the the day when good PNP power transistors were not available for the negative regulator.
But is there any advantage today?
Have a look at this explanation Solid State Power Amplifier Supply Part 2. I have also heard it suggested it's better because the charging pulses through the windings are kept separate. The dc output is lower due to the voltage drop across the extra diodes
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I don't necessarily buy the better channel isolation idea. You still have the two supplies tied together through the filter capacitors. I would think that would swamp any crosstalk advantage gained by the dual rectifiers.
The other arguments do have some validity for power amplifiers. Not sure for preamp loads though.
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Thank you for the link to the TNT article on SS Amp power supply. I imagine some of this applies well to preamps as well, though not so much on the stability/load issues.
BTW: I've a Bulb Tester which has saved me a couple of times. Once I forgot and the error fortunately did not make it to the vulnerable bits. In order for a Bulb tester to work, one has to remember to use it! Big sigh of relief on that day.
BTW: I've a Bulb Tester which has saved me a couple of times. Once I forgot and the error fortunately did not make it to the vulnerable bits. In order for a Bulb tester to work, one has to remember to use it! Big sigh of relief on that day.
I have better noise results since I started to use dual bridges. But I'm not very shure of it (that is connected with that fact) - I have made only one experiment with the same power amp: with single bridge power supply board, and dual bridges board - dual bridges looked (I'm not remember exactly) several dB better. (And the whole spectre looked better).
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No. If the two rails take different DC current draw then one bridge shares this load equally between the secondaries while two bridges puts the highest load on one secondary. The total heat dissipated in the transformer will be the same, but it will be slightly more concentrated with two bridges i.e. less optimised.
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