Help and comments wanted on power supply

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Hi all,

I need 32VDC to run the Wiener Pro I ordered from GMARSH's group buy.
Got an old Torodial from a broken Marantz amp, claimed to have two 28VAC outputs. I am totolly new on this and cant find answers in threads for my own thoughts on a layout.

1. Joining the two 28VAC in parallell to have just 28VAC, not 56 VAC to the rectifier :
A, Is the wiring to the rectifier ok for that objective.
B, Any disavantages in this except more Amperes into the curcuit?

2. Regulators bringing the DC down to 32VDC
A, can I use these in parallell to handle more Amperes?
B, Can I use these before the smoothing caps? .. haven't seen it in any plans..and then use 50VDC caps instead of 63VDCs?
Or can I mix? f.ex 1000uF 63V before and 22000uF 50 V after?

3. Grounding. Where in the circuit do I have to ground?
A, Regulators and the circuit after the load.. yes.. but is is it ok with chassi-grounding or should it better go to a real ground?
B, Optimal placing of ground on the Zero-side? Before or after the caps?

4. Will a LC-filter on the +28VDC-side be overkill?
a, if not.. what would be good values for a 8 ohm load?

Kind regards


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You will have 39.6 volts DC to play with. Smooth at the bridge with a suitable reservoir capacitor, say 10,000uF at 50volts. Regulate down to 32volts and place a low value capacitor after the regulator. I have no idea what current you want so cannot comment on the type of regulator. More current usually requires a power transistor not parallel regulators.
Don't use an LC circuit after the regulator as there is no ripple to remove. Don't use a ridiculous amount of smoothing, 10kuF is adequate. It is not needed and a waste of your money for any more.
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Your diagram is basically OK. 28 volts AC will actually give around 40 volts DC across the main reservoir cap. Paralleling the windings allows you to maximise the current available. Make sure you phase them correctly... if in doubt use a bulb tester.

Regulators... you can parallel many type of regulator but you often need to include small balancing resistors on the output of each to ensure the load is shared equally. How low these are depends on the currents involved and the regulators used. Your diagram is correct for the location of the regulator.

An LC filter after the reg probably isn't a good idea. Its impedance will seriously impair the final regulated output stability under varying load.

Grounding... is a huge subject.

Just remember the regulator has only one point of reference, its own ground connection, and so normally this would become part of a star ground such that the load current/s are returned to this point. Return them anywhere else and the regulation and noise factor is impaired. You can tie the star ground to chassis if you wish, but the chassis should not normally be used as a ground path in its own right.
The TPA3250 is claimed for max output of 2*175 watts. 350 watts/ 32 V = 10 Amps

In a realistic perspective.. living in an apartment.. everything above 6 Amps should be considered as a misuse ;-)... so maybe a fuse @ 6A before the regulators is the right belt and suspenders if my kids turn the volume knob to 11?
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175 watts RMS into 8 ohms is around 37 volts RMS across 8 ohms. That's around 4.6 amps RMS in the load. Class D, not 100% efficient by any means, so you are probably looking at 6 amps per channel I would guess.

Most domestic listening takes place in the one to two watt region (at most given high-ish sensitivity speakers).
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