regulating voltage for preamp

alizawi · 6th May 2006, 09:17 PM

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.
Thanks

paulb · 6th May 2006, 10:09 PM

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.

alizawi · 7th May 2006, 01:01 AM

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?

tobias_svensk · 7th May 2006, 03:42 PM

LM317:

R1 = 240 and R2 = 2700 would give about 15-15.5V

Bazukaz · 7th May 2006, 08:08 PM

Hi,
Even simpler is to use fixed voltage regulators - 7815/7915 , for example.

Khron · 7th May 2006, 08:52 PM

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.

Bazukaz · 7th May 2006, 08:57 PM

Hi,
L79x/L78xx has input voltages up to +/-35V.This is true for 12 to 18 volt voltage regs.

Khron · 7th May 2006, 10:04 PM

Oops.. my bad

I was referring to the LM78xx/79xx

Eva · 7th May 2006, 10:34 PM

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.

alizawi · 7th May 2006, 10:58 PM

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

6th May 2006, 09:17 PM	#1
alizawi diyAudio Member Join Date: Feb 2006 Location: California	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. Thanks

7th May 2006, 10:34 PM	#9
Eva diyAudio Member Join Date: Oct 2003 Location: Near the sea	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. __________________ I use to feel like the small child in The Emperor's New Clothes tale

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6th May 2006, 10:09 PM	#2
paulb diyAudio Member Join Date: Jun 2001 Location: Calgary	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.

7th May 2006, 01:01 AM	#3
alizawi diyAudio Member Join Date: Feb 2006 Location: California	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?

7th May 2006, 03:42 PM	#4
tobias_svensk diyAudio Member Join Date: Jan 2004 Location: Hudiksvall	LM317: R1 = 240 and R2 = 2700 would give about 15-15.5V

7th May 2006, 08:08 PM	#5
Bazukaz diyAudio Member Join Date: Nov 2005 Location: Vilnius	Hi, Even simpler is to use fixed voltage regulators - 7815/7915 , for example.

7th May 2006, 08:52 PM	#6
Khron diyAudio Member Join Date: Jul 2005 Location: Finland	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.

7th May 2006, 08:57 PM	#7
Bazukaz diyAudio Member Join Date: Nov 2005 Location: Vilnius	Hi, L79x/L78xx has input voltages up to +/-35V.This is true for 12 to 18 volt voltage regs.

7th May 2006, 10:04 PM	#8
Khron diyAudio Member Join Date: Jul 2005 Location: Finland	Oops.. my bad I was referring to the LM78xx/79xx

7th May 2006, 10:58 PM	#10
alizawi diyAudio Member Join Date: Feb 2006 Location: California	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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