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Old 5th August 2005, 05:20 PM   #21
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Default Regulator problem

The LM317 circuit as shown by Tripath and connected as per Jan at 41Hz would be your best solution. But you do need to heatsink it using the TO220 case style part. This is just too much heat for the small part. The dropping resistor shown in the 41Hz circuit won’t be necessary for the 317 part.
Roger
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Old 5th August 2005, 05:38 PM   #22
soongsc is offline soongsc  Taiwan
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I've used LM317's in preamps before, and they never got warm. I never even added heat sinks. It also seems using the LM317 has more components. Is a sonic difference expected between the LM7805 and LM317? Also dropping 48VDC to 7.5~9V somehow that seems a lot. There is a limit the difference between input and output voltages these devices can handle, I don't recall LM317 can handle 48V to 5 V difference.
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Old 5th August 2005, 09:07 PM   #23
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Default LM317

Yes, you are right, the 317 is maxed out at 40 volts. You would also be dissipating quite a bit more power with this much voltage across it. A substantial heat sink will be necessary. Not the same thing as when you use it in a preamp with 5-10 volts drop. A 2 watt 250 ohm resistor in series will take care of this.
I would expect better sound from the 317 as it is a better regulator.
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Old 6th August 2005, 01:21 PM   #24
soongsc is offline soongsc  Taiwan
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The LM317 does have somewhat lower output impedance, but this seems to mak a difference when supplying analog circuits. I'm not sure what part of the AMP2 the 5V is supposed to supply, but if it's just digital (discrete) portion, then the difference might not be that significant. I'll look into it when I get the kit.
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Old 6th August 2005, 03:16 PM   #25
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I just finished the first of the three 5v supplies I need and I am very satisfied with how it turned out. Under a full load of 1.5 amps it only drops 10 millivolts.

The space between the input wires on the left and the small white cap is for a 47ohm resistor if I decide to use one. I didn't have any laying around so its jumpered with wire for now.

soongsc, the 5v is for the analog input section for both AMP1 and AMP2.
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