My impression is that such ATX power supplies where made to be cheap, usable for a limited load range, used self-oscillating configurations with rather poor dynamic properties and did not bother much about noise and ripple.
In other words, I believe this to be a poor starting point for making an audio power supply.
The notebook charger type of supplies are useful because they are intended to look into a rechargeable battery (similar to a large decoupling capacitance) and can handle (limit) the surge current for initial charging of decoupling capacitors. Thus, by letting the charger-supply feed a solid decoupling capacitance, it is the decoupling capacitance that ensures rather stable supply to the amplifier while the charger-supply is only an energy source with doubtful dynamic performance.
In other words, I believe this to be a poor starting point for making an audio power supply.
The notebook charger type of supplies are useful because they are intended to look into a rechargeable battery (similar to a large decoupling capacitance) and can handle (limit) the surge current for initial charging of decoupling capacitors. Thus, by letting the charger-supply feed a solid decoupling capacitance, it is the decoupling capacitance that ensures rather stable supply to the amplifier while the charger-supply is only an energy source with doubtful dynamic performance.
Atx were never free running, always fixed frequency around 50 kHz, regulated by controller like TL494, KA7500, SG6105, LPG899 a.s.o.
Ripple noise was not relevant but regulation was, loads one amp to ten amps + no problem
Modifying transformer however is almost impossible, they are potted and cannot be rewound without breaking them. Building new transformer diy not recommended because of safety issues with mains voltage.
Notebook power bricks may be used. Outputs are not earth referenced as in atx but floating.
Therefore two 12v bricks could be connected in series to get +24v. Another pair to get -24v.
There are also bricks with higher voltage like 14 or 17v. These would allow for linear post-regulation down to 22v to remove any noise or ripple.
Ripple noise was not relevant but regulation was, loads one amp to ten amps + no problem
Modifying transformer however is almost impossible, they are potted and cannot be rewound without breaking them. Building new transformer diy not recommended because of safety issues with mains voltage.
Notebook power bricks may be used. Outputs are not earth referenced as in atx but floating.
Therefore two 12v bricks could be connected in series to get +24v. Another pair to get -24v.
There are also bricks with higher voltage like 14 or 17v. These would allow for linear post-regulation down to 22v to remove any noise or ripple.
There are dummy loads on all outputs of atx to keep regulation even under no load conditions.
Some require a minimum load on the 12v or 5v rail to start, in most cases a pilot light will do.
I mentioned 1A just because I cannot see why one would want to use atx ps for anything less.
By the way, the regulation feedback is taken from all output voltages combined to the controller and the common mode choke on the outputs also improves cross regulation when currents between outputs vary.
There is also over and under voltage detection implemented which shuts the ps down when voltages go a half volt or so out of bounds.
Schematic examples can be found here: AT and ATX PC computer supplies schematics
You are very competent on these ATX supplies.
I understand, it is not exactly 1A as the lower load limit. My point is, these supplies have a lower load limit (unless loaded with dummy loads) in order to keep in regulation because a computer constantly has a consumption. For an audio power supply, the load current ranges from perhaps 100mA (quiescent current) to several amperes, and the changes can be very rapid (depending on the dynamics in the music). On top, the ATX supplies have a number of protection and start-up/shut-down controls that is of no use for an audio supply.
We both agree, for various reasons, turning an ATX supply into an audio power supply is very difficult and not a fruitful project.
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I've never had an issue with regulation.
I use a re-purposed ATX supply for model building & general hobby use. Half the weight of my old Transformer.
For one of my models, the 5V output directly powers an Arduino and low consumption motors are switched on and off in sequence. Output never varies.
I have heard of old ATX supplies needing huge power resistors to stabilize the output.
Evidently this doesn't apply to all.
I use a re-purposed ATX supply for model building & general hobby use. Half the weight of my old Transformer.
For one of my models, the 5V output directly powers an Arduino and low consumption motors are switched on and off in sequence. Output never varies.
I have heard of old ATX supplies needing huge power resistors to stabilize the output.
Evidently this doesn't apply to all.
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