the easy way to select a transformer is to aim for VA to be between 1times total maximum output to 2times total maximum output power.
If you have two channels of 50W, i.e. 100W of total maximum output power, then use a transformer selected from 100VA to 200VA.
The amplifier will work with less than 1times Power but is likely to sound poor.
The amplifier also works with more than 2times Power, but it costs more.
I find that very small transformers have a very high regulation. This results in sagging voltage on the power supply and gives poor sound quality.
I recommend using no smaller than 160VA for small output powers.
Regulation? Two bridge rectifiers (8 diodes) are going to do a better job for that, right? For +/- 28vdc that would be this transformer http://www.antekinc.com/pdf/AN-2222.pdf right? (22x1.25) as in less reliance for charging caps up to a peak voltage when that peak is smaller, right?
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Please clarify.
Two bridge rectifiers (8 diodes) as in a dual secondaries transformer for better regulation than a one bridge rectifier (4 diodes) with a center-tap transformer.
Gosh, I'd hate to be wrong on that, even though it would save me some cash.
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Cool, but I was talking about the DC power at the power supply board as it applies to transformer voltage selection.
In the example of 22+22vac with 8 diodes and several caps resulting in about 28 volts, this power is more steady than. . . getting 20-0-20 with 4 diodes and several caps, resulting in about 28 volts.
I was looking for some support and confirmation for transformer selection. That would be more seemly.
this data is useless.
You have given us no way to replicate your results.
not speaking of amperage, but rather voltage fluctuation.
1 rectifier power supply board and a center tap = ac x 1.43 to find dc
2 rectifier power supply board and a dual secondaries = ac x 1.25 to find dc.
The voltage will fluctuate less with the 2 rectifier dual secondaries setup at the expense of some of the voltage. <statement doesn't end in a question mark.
daniel, we have the following voltage possibilities for a rail:
Dual bridge => current passes through two diodes per each rail
One bridge => current passes through a single diode per each rail
So the voltage is actually like this:
Udc = Uac * 1.4142 - n * Ud
where Udc is voltage after filtering without any load, Uac is the voltage in the secondary and Ud is the voltage drop over a single diode.
1.4142 is the square root of 2. In practice this 1.4142 is more likely 1.40
Dual bridge => current passes through two diodes per each rail
One bridge => current passes through a single diode per each rail
So the voltage is actually like this:
Udc = Uac * 1.4142 - n * Ud
where Udc is voltage after filtering without any load, Uac is the voltage in the secondary and Ud is the voltage drop over a single diode.
1.4142 is the square root of 2. In practice this 1.4142 is more likely 1.40
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Awesome!!!!!! The maths! And they're readable! THANK YOU!!!
Dual bridge power supply board makes for less dc voltage. This has a slight effect on transformer voltage purchase selection.
I'm no expert, but it's obvious that is a nonsense. I think that Daniel believes that single bridge = half-wave rectification, which is not true.
Awesome!!!!!! The maths! And they're readable! THANK YOU!!!
Dual bridge power supply board makes for less dc voltage. This has a slight effect on transformer voltage purchase selection.
Everything in electronics implies math and everything is readable. You only need to want to understand it
yes, sense at last.
It increases the transformer voltage requirement by about half a volt.
Now go and try to source/buy transformers in half volt increments.
At the scale we're using, it increases transformer voltage required by approximately two volts. This is the difference between antek model 2220 versus antek model 2222.
Please don't forget the spike system--even two volts can matter, so I'd rather have the 2222 and spend less time listening to spike-caused clipping.
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no, it doesn't.
The single bridge drops a nominal 1.4Vdc across two series diodes.
A dual rectifier drops a nominal 2.8Vdc across four series diodes.
For each half of a dual polarity supply that is a drop of 0.7Vdc vs 1.4Vdc, i.e. the dual bridge rectifier drops an extra 0.7Vdc.
Using the AC to DC conversion (sine rms;peak) we need just 0.5Vac to make up the voltage difference.
The single bridge drops a nominal 1.4Vdc across two series diodes.
A dual rectifier drops a nominal 2.8Vdc across four series diodes.
For each half of a dual polarity supply that is a drop of 0.7Vdc vs 1.4Vdc, i.e. the dual bridge rectifier drops an extra 0.7Vdc.
Using the AC to DC conversion (sine rms;peak) we need just 0.5Vac to make up the voltage difference.
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That makes for a good question on why the voltmeter would show a different result.
EDIT: OH! It shows your figures exactly, if when ordinary diodes are paralleled with small value polyester capacitors or RC's (shows your figures exactly, when using snubbed rectifiers as seen in radio).
EDIT: OH! It shows your figures exactly, if when ordinary diodes are paralleled with small value polyester capacitors or RC's (shows your figures exactly, when using snubbed rectifiers as seen in radio).
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