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Old 26th February 2013, 10:27 PM   #1
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Question Single PS powering several boards

I have several boards (chip amp, preamp, and phono preamp) that need power inside an integrated amp. I could get a separate transformer and power supply for each board, but that takes up a lot of space and ends up being pretty expensive. Ideally, I'd have a single transformer and a single power supply that splits up the voltages / currents accordingly.

Do prefab PCBs with multiple power outputs exist? If so, where would I find such a great thing?
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Old 27th February 2013, 02:12 AM   #2
gootee is offline gootee  United States
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If you must use only one supply, one way that's done is with "decoupling capacitors". You would have one main set of reservoir/smoothing caps for the central power supply and then you would have an additional set of electrolytics for each board, to decouple the local supply from the rest. These would need to be wired in parallel, not "daisy chained".

In your case, I would just make a separate supply for the chipamp, since the other two will be very low power, compared to the chipamp.
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Old 27th February 2013, 02:16 AM   #3
DUG is offline DUG  Canada
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Star ground point. (ONE)

This is so that the speaker current does not appear in the power path to low level boards or low level signal paths.
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Old 27th February 2013, 02:18 AM   #4
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A common approach is to get a transformer with multiple secondary windings. You might for instance have a couple of 30V secondaries, and a couple of 15V secondaries. The 15V ones being used to feed a powersupply for the preamp circuitry and the 30V windings for the main amp rails.

This solves the problem of multiple transformers, and the preamp PS (rectifier smoothing caps and probably regulator) won't lilkly be as physically large as the main amp psu due to the fact it is unlikely to need the same amount of capacitance.

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Old 27th February 2013, 02:43 AM   #5
JMFahey is offline JMFahey  Argentina
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What everybody does is to provide for the "largest" PSU, which is the one feeding the power amp, and derive all other voltages from that main one.
Multiple transformers is messy and expensive and *only* justified if you want to feed some tubes inside that amp, which need filament and very high voltages to work.
Pleast post voltage and current needs for each part of your amplifier.
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Old 27th February 2013, 05:11 PM   #6
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Thanks very much for the feedback. Here are the voltage requirements for my (overly ambitious?) integrated amp project:

Chip Amp
Audio Sector LM3875
Power Requirements: 25—35V

Phono Preamp
Twisted Pear Retro RIAA Stage
Power Requirements: 12—15V

DAC
Twisted Pear Opus DAC
Power Requirements: 7.5V

Preamp
Twisted Pear Legato I/V Stage
Power Requirements: 15V

VU Buffer
JLM Stereo VU Buffer
Power Requirements: +12—36V (or split 6v—18v power rails)

I might end up deciding not to wire all these together depending on how complex the power supply wiring gets, but this would be an ideal setup.

And, just for clarity, can someone tell me if all of these expressions equivalent: "15V", "bipolar 15V," and "15V + 15V?" Also, what's the difference between a bipolar supply and a dual supply? Thanks!

Last edited by fingersoccer; 27th February 2013 at 05:18 PM.
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Old 28th February 2013, 10:28 AM   #7
AndrewT is online now AndrewT  Scotland
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Choose your transformer for the chipamp voltage.
add on a dropper resistor from +ve rail to feed a +15V regulator. LM7815 or LM317
add on a second resistor from -ve rail to feed a -15V regulator. LM7915 or LM337
add on a third dropper resistor from +ve rail to feed a +7.5V regulator. LM317
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Old 28th February 2013, 10:30 AM   #8
AndrewT is online now AndrewT  Scotland
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The added resistor will probably need to be power wire wound to dissipate the heat. That heat will depend on the average current draw of the low voltage circuits.
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Old 28th February 2013, 08:19 PM   #9
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Thanks, AndrewT. Would I be correct in thinking that I can use this voltage regulator schematic to determine the correct resistor values? This almost seems too easy!
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