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Old 21st June 2003, 01:48 PM   #1
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Default optimum power supply for power amp

I have a centre tapped toroidal transformer and two large bridge rectifiers. What is the optimum way of connecting them to achieve +ve, -ve and zero volts for a power amp supply. From my research I have found, I think, 2 options:

1. Wire both bridges in parallel taking the +ve from one and the -ve from the second bridge(only using 2 diodes in each) as per Naim. The centre tap providing the Zero reference.

2. Connect one bridge to one transformer secondary and the centre tap and the other bridge to the second secondary and the centre tap. +ve is taken fom one bridge and -ve from the other. Zero is taken from the -ve on the + bridge and the + on the -ve bridge.

Grateful for advice on which is best of these, or any other options.
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Old 21st June 2003, 03:34 PM   #2
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The consensus seems to be that the two-bridge arrangement is best, giving improved flexibility with regard to ground wiring. It's hard to describe circuit configurations in words, so I'm not totally clear on the exact configuration of the Naim circuit you're describing.

There's pretty good coverage of this topic in a nice three-part article here:

http://www.tnt-audio.com/clinica/ssps1_e.html
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Old 21st June 2003, 09:29 PM   #3
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You need two separate windings for alternative number 2 or you'll get a short circuit.
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Old 22nd June 2003, 01:17 AM   #4
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Quote:
Originally posted by andy_c
The consensus seems to be that the two-bridge arrangement is best, giving improved flexibility with regard to ground wiring. It's hard to describe circuit configurations in words, so I'm not totally clear on the exact configuration of the Naim circuit you're describing.

There's pretty good coverage of this topic in a nice three-part article here:

http://www.tnt-audio.com/clinica/ssps1_e.html
I gave that article a read and it seems to have identified a couple of proverbial red herrings. There really isn't a practical advantage to using two bridge rectifiers besides spreading the heat load out between two separate devices, and that costs double the price and voltage drop of a single bridge. Next is making claims about the slew rate of a capacitor in volts/uS when I think the author really meant to say, "the voltage drop resulting from attempting to deliver a certain amount of amps/uS through the capacitor's ESL and ESR." The author seems to think that it is not possible to parallel smaller capacitors to achieve the equivalent "speed" of a single premium capacitor, but that's contradicted by pretty much every switchmode power supply larger than 100W in existence. A stroll through the Digi-Key catalog will prove that two capacitors of x uF have a lower impedance than 1 capacitor of 2x uF. Of course, making the connections between capacitors will render some of this advantage moot, but there are other benefits like reduced internal heating, sharing of ripple current, longer life, etc., to be had from using several smaller capacitors rather than one big one.
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Old 22nd June 2003, 04:04 PM   #5
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In one arrangement both secondaries charge both capacitors, in the other each secondary is devoted exclusively to one capacitor. If the secondaries are not electrically identical then in the former case you could get uneven energy delivery between the two secondaries and increased ripple at the ac frequency.
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Old 22nd June 2003, 04:40 PM   #6
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Default optimum pwer supply

Thank you, but with a centre tap will each secondary charge its own cap independently? Which arrangement do you prefer?
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Old 22nd June 2003, 06:58 PM   #7
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If you have a transformer with a centre-tapped secondary (as opposed to dual secondaries) then I don't think you can use 2 bridges to any special advantage. I'm not sure what you meant in your Naim reference...my understanding is that they use dual secondaries with a bridge on each.
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