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Old 6th May 2006, 09:17 PM   #1
alizawi is offline alizawi  Palestine
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Default regulating voltage for preamp

If I want to use the +33 - 33 V rails from my power amp (lm3875) to power my preamp (which uses an lm1458 ) will the lm337 and 317 do the job? and would I have to use the chassis ground to ground my premp and voltage regualtors as well? I think these regulators are more realiable than using zenors, but feedback is appreciated.
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Old 6th May 2006, 10:09 PM   #2
paulb is offline paulb  Canada
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Yes, it will work and ground would be common between the two, but performance will probably be better if the preamp has its own power supply. Ground loops and associated hum may be an issue for you.
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Old 7th May 2006, 01:01 AM   #3
alizawi is offline alizawi  Palestine
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i might eventually build a spearate power supply for it, but for now I just want to use the same supply I'm using for the power amp to see if the thing even works........I need dual 15 V rails, but those regulators are giving me some trouble.....I calculated the resistor values as specified on the data sheet, but I can't get more than 6 V on the ouput for the positive part.....maybe the resistor values i used arent the best, I'm not sure...still haven't tried the negative voltage. Anyone have experience with the lm317/337?
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Old 7th May 2006, 03:42 PM   #4
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LM317:

R1 = 240 and R2 = 2700 would give about 15-15.5V
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Old 7th May 2006, 08:08 PM   #5
Bazukaz is offline Bazukaz  Lithuania
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Hi,
Even simpler is to use fixed voltage regulators - 7815/7915 , for example.
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Old 7th May 2006, 08:52 PM   #6
Khron is offline Khron  Romania
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Yes, it would be simpler, but those regs have a max input voltage of 30V so.. My guess is that itt would be risky, unnecesarily.
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Old 7th May 2006, 08:57 PM   #7
Bazukaz is offline Bazukaz  Lithuania
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Hi,
L79x/L78xx has input voltages up to +/-35V.This is true for 12 to 18 volt voltage regs.
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Old 7th May 2006, 10:04 PM   #8
Khron is offline Khron  Romania
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Oops.. my bad I was referring to the LM78xx/79xx
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Old 7th May 2006, 10:34 PM   #9
Eva is offline Eva  Spain
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Deriving +-15V for the preamp from main amplifier rais is ok as long as the regulators and the preamp are grounded in the proper place to avoid ground loops.
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Old 7th May 2006, 10:58 PM   #10
alizawi is offline alizawi  Palestine
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the lm337 and 317 work just fine im just tryin to get the resistor values for the right voltage......but I think I can wire tthe trhing properly to avoid grounhd loops
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