Can you adapt a computer power supply for the 5v and 6.3 volt needs? - diyAudio
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Old 24th November 2002, 12:13 PM   #1
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Default Can you adapt a computer power supply for the 5v and 6.3 volt needs?

After reading that some preamp circuits are using a batt power supply for their low voltage needs to get away from hum problems I was wondering if anyone had ever tried a computer power supply. I know the supply is stable and should be well filtered. I went thru all the threads and I didn't see mention of it at all.


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Old 24th November 2002, 12:20 PM   #2
UrSv is offline UrSv  Sweden
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A computer supply is very noisy and is not all suited for a preamp. The supply also need a minimum load to regulate and that is on the order of A not mA.

Let's put it like this: A computer supply would be my very last alternative for a preamp and if it was the only one I would go passive and skip the preamp completely.

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Old 24th November 2002, 12:30 PM   #3
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Quote:
Originally posted by UrSv
A computer supply is very noisy and is not all suited for a preamp. The supply also need a minimum load to regulate and that is on the order of A not mA.
Sometimes to work at all! The mimimum current is very often a couple of amperes.

As Urban says, forget it!
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Old 24th November 2002, 01:22 PM   #4
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I'm sorry here gentlemen a I haven't checked the output of a computer power supply with a scope. I based my question on the fact that I had used the power supply to power a car CD/radio in my garage with no ill effects. I found the supply to be noise free so I assumed that it might be possible to use it to power the heater or filament supply. I made the assumption that it was possible to use the 5volt supply as is and regulate down the 12volt supply to 6.3volts. My voltage checks on this supply in the past have shown it to be stable from a very low draw to a draw of several amps.
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Old 24th November 2002, 01:26 PM   #5
UrSv is offline UrSv  Sweden
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Oh, you are not talking supply to a preamp (SS implied ;-)) but heater and filament in a TUBE pre-amp...

Still the worst possible choice IMO.

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Old 24th November 2002, 09:27 PM   #6
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Yup. Have to agree with above - did try it out a couple of years ago and the sound was horrible. BTW if it's preamp tubes, you can listen to it without modifications @5v, a lot of low power triodes seem to be happy with lower heater's voltage and even become less noisy. Long term effects though may not be great.
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Old 24th November 2002, 11:49 PM   #7
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Default QUIETER TUBES + LONGER LIFE

Hi,

Heater rating voltages are usually given as +/- 10%.

So, when we have a 6.3 VAC heated tube at say 100 mA you can go as low as 5.67 VAC provided the 100mA is delivered.

Conversely you can go up to 6.93VAC under the same conditions.

Good averages for long life: 6V and 12 V at required current.
This a very convenient value for use in hum sensitive preamps since we can then use common voltage regs.
At best stay with the +/- 10% deviation but regulate the current,the tube should never be starved for heater current.


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Old 25th November 2002, 12:27 AM   #8
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You wouldn't beleive the amps a modern PC microprocessor needs Between 50 and 80w dissipation... with 5 volts?

As everyone said before, just use a common regulator, or a passive psu. You'll do much better. Most switchmode power supplies are horrid, both on regulation and noise.
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Old 27th November 2002, 11:07 AM   #9
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Ok, it won't work. You can't blame me for trying.

Joe
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Old 27th November 2002, 11:16 AM   #10
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It may be horrid, but at least it'd be cheap.

$10 AUD for a 200-300W PSU isn't too shabby.
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