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Old 20th May 2009, 01:49 PM   #1
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Default Computer PSU for LM1875

Hi,

I just got 2 LM1875 chip and am looking for a way to power them.

Since i do not have acces to a transformer and am not sure i want to make the whole PSU, i thought about using a spare computer PSU that i have lying around.

i really just want to have you guys opinion. Is this a bad idea from the start ? what other option do i have ?

Also, i was wondering, if i have a wall transformer (those black box things) that gives 24V DC, is there an easy way to get -24V DC to power the chips ? (go from positive to negative tension)

Thanks in advance
Lespoils
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Old 20th May 2009, 02:21 PM   #2
Geoff H is offline Geoff H  Australia
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It is unlikely that the -12v rail of a PC PSU will supply sufficient current.

A simple way of getting the power required is from an old amplifier of about 15 to 20 watts. The Pioneer SA-5500 II is an ideal candidate. A pair of LM1875s will run circles around the original monolithic power IC in terms of noise and distortion.

The main requirement is a spilt supply not exceeding +/- 30 volts unloaded. It is pointless going above about 2x18 volts on the transformer as the overload protection prevents any gain in output power.
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Old 20th May 2009, 03:23 PM   #3
anti is offline anti  Slovakia
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Ha, that makes two of us.

I was also thinking on using an ATX psu for powering a chip-amp. Afaik, the "-12V" rail must be somehow upgraded, because these psu's usually have only 0,3-0,8A current capability on the -12V rail.

One alternative I know is to use two of them, sort-of connected like batteries; in series, so you use only the powerful +12V rails.

Modding an atx psu so that a single one could be used would be neat.

Patiently waiting for the gurus...
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Old 20th May 2009, 07:39 PM   #4
star882 is offline star882  United States
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There's also the option of running two chips in BTL.
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Old 20th May 2009, 08:02 PM   #5
tomchr is offline tomchr  United States
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PC power supplies are incredibly noisy and often requires rather large loads (1 A or more) on either the +3.3 or +5V supply in order to provide good regulation. Typically, the +/-12 V supplies are not regulated. They rely on the tight regulation of the logic supply to work.

Building a linear power supply isn't that hard. I think I was in fifth grade when I designed my own for the first time... But if you really don't want to build your own, I'd suggest looking at one of the many supplies available from Digikey, Jameco, and others. I'd aim for a linear supply that can deliver the voltages at the currents you need. I would imagine that the medical switchers would be fairly decent as well. They are typically switchmode supplies followed by a linear regulator.

~Tom
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