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VA rating needed for 2x60W
VA rating needed for 2x60W
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Old 20th March 2009, 09:39 PM   #1
Knorr is offline Knorr  Denmark
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Default VA rating needed for 2x60W

I'm in the process of designing a power supply for a stereo amplifier.

My head is quite overwhelmed with calculations and such, and searching some forums haven't made me less confused.

I have a toroid rated at 160VA with 230V prim and 2x22V secondary.


22Vrms would make about 60W in 8 ohms per channel. I doubt the amplifier will be reaching 60W consumption very often, if at all.

Now, the thing that confuses me is, that the secondary windings is only rated 80VA each.

If I connect the secondary windings in series to make +/- ~30Vdc rails, would that power rating be sufficient, or do I need each of the windings to be more like 160VA? Making the need toroidal twice the size?

Also when selecting filter caps for smoothening, how should I relate to their ripple current rating? How much is needed?
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Old 20th March 2009, 09:47 PM   #2
richie00boy is offline richie00boy  United Kingdom
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VA rating needed for 2x60W
You need to wire the secondaries in series to get the rails you need. This means you are using the whole transformer, which is rated at 160VA. This should be sufficient for a 120W (2x60) amp playing music.

Ripple current is hard to know what you need. Just aim for 10000uF per 100W of amp power and you should be ok.
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, modules and more.
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Old 20th March 2009, 10:59 PM   #3
mjf is offline mjf  Austria
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the electric power (here 160va) of the transformer should be greater than the power of the amp (120w max) needed.......
10000uf per rail (or more) is a good choice..........
do not use a tiny (4 amp or so) rectifier........8 or 10 amp is better....
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Old 20th March 2009, 11:03 PM   #4
454Casull is offline 454Casull  Canada
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Old 21st March 2009, 02:12 PM   #5
AndrewT is offline AndrewT  Scotland
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160VA transformer can support between 80 and 160W of total output power.
You're 60+60W target is right in there. Perfect for the job.

22Vac will not get you a guaranteed 60W of output power. The normal voltage from this 22Vac is too low for that.
At highest mains supply voltage it will get you very close to your target.

I recommend that you use +-20mF for each channel feeding an 8ohm speaker, i.e. 80mF (0.08F) for two channels or 160mF (0.16F) for two 4ohm channels. Very few builders do this. Any that use smoothing capacitance approaching this amount usually report excellent bass power and depth.
Those that skimp on smoothing capacitance prefer their MID and treble performance usually to the exclusion of bass reporting. Some even criticise the bass performance of all chip amps when they have never tested a chipamp with adequate smoothing capacitance.
regards Andrew T.
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