Audio Power supply

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Seen this style of power supply to feed aux circuits with 15+15V

Any body cares to explain what is the benefit on using this style of rectifier ?


  • Power supply.png
    Power supply.png
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No this is wrong in most circuits, AC loss detect works just fine by using one single diode from any of the AC winding to provide a reference

The need for one quick information about the AC loss doesn't call for creating a rectifier like that.

Is there a chance that a rectifier like that is more quiet than the standard since power there is to be used for pre op amps and phono stage ???

Never seen that before ..on the other hand schematic is from a Philips amplifier so anything weird is expected ..

Kind regards
Remember production design is cost driven.
Maybe phillips had a transformer already designed that produced 17.5 vac and they wanted 15. So two diodes in series drops 1.2 v. That means no tooling charge for a second transformer for this model. Plus the bridge diodes see half the current, so 1 amp rated 1n4004 costing. $.04 each would do. If they had used another diode after the bridge to drop .7v, maybe it would have to be a 3 amp rated MR802 at about $.35.
Maybe the AC detect circuit needs 14.3 v max and the rest of the linear circuitry needs 15. Tapping off the middle of two bridge diodes is weird but cheap.
Maybe programming the pick and place machine for long bodied fat lead MR802 requires a manual operation and costs $$ whereas using more 1n4004 is just more of the same, done automatically by the cassette change program.
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What's even stranger about this circuit is that despite the dedicated secondary, the +/-15 V regulators are still being fed a whopping +/-29 V (not used anywhere else). Unless that's a misprint (19 V would make a lot more sense) I have no idea why.
Using an existing transformer. It costs $$$ to get a new type transformer engineered, prototype built, and type accepted by VDE, UL, CSA, or CE. How many of this amp were sold anyway? Low volume product, cut your engineering costs to the budget.
Hi Guys

I believe that post-4 and 9 cover the answer to the Q. However, post-15 may be erroneous: It is not usually up to the OEM to worry about family approvals for the PT , rather on his own assembly and wiring. The transformer manufacturer carries that approval and as long as he builds your PT like all the others, then it is covered.

Ignore the extra diodes and use a standard four-diode bridge if you are building such a supply for your own amps. As you already know, it only takes one extra diode to have AC-on/off monitoring circuit for turn-on-control and/or output muting timing.

If you needed a true assessment of whether Philips' choice to do this is good, the rest of the circuit is required.

Have fun
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