Placing regulator chip close to amplifier

terranigma · 6th June 2010, 07:20 PM

I'm gonna place LM338's on same heatsink with LM3875 chips in my dual-mono setup. Transformer will be placed into its own box. I will use 60-70cm power cable between amp and transformer box.

In this case, which option below will you recommend for me? Or any advise?

Transformer + rectifier + filter cap + 100nf bypass cap --CABLE--> LM338
Transformer + rectifier + filter cap --CABLE--> 100 nf bypass cap + LM338
Transformer + rectifier --CABLE--> filter cap + 100 nf bypass cap + LM338

RJM1 · 7th June 2010, 06:03 AM

To quote the LM338 data sheet "Normally, no capacitors are needed unless the device is situated more than 6 inches from the input filter capacitors in which case an input bypass is needed." Go with #2 because your 60-70cm is more than 6 inches. You don't want #3 as your cables would radiate all the high current spikes between your rectifiers and your filter caps.

terranigma · 7th June 2010, 10:19 AM

Thank you RJM, I have checked LM338 manual but I could not determine which section to read to find this information. I will go with #2..

RJM1 · 7th June 2010, 11:51 AM

Page 1

terranigma · 8th June 2010, 08:47 AM

I just noticed that without any negative opinions about your directions.. Thank you again..

6th June 2010, 07:20 PM	#1
terranigma diyAudio Member Join Date: Feb 2007	Placing regulator chip close to amplifier I'm gonna place LM338's on same heatsink with LM3875 chips in my dual-mono setup. Transformer will be placed into its own box. I will use 60-70cm power cable between amp and transformer box. In this case, which option below will you recommend for me? Or any advise? Transformer + rectifier + filter cap + 100nf bypass cap --CABLE--> LM338 Transformer + rectifier + filter cap --CABLE--> 100 nf bypass cap + LM338 Transformer + rectifier --CABLE--> filter cap + 100 nf bypass cap + LM338

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7th June 2010, 06:03 AM	#2
RJM1 diyAudio Member Join Date: Jan 2010 Location: Titusville, Fl.	To quote the LM338 data sheet "Normally, no capacitors are needed unless the device is situated more than 6 inches from the input filter capacitors in which case an input bypass is needed." Go with #2 because your 60-70cm is more than 6 inches. You don't want #3 as your cables would radiate all the high current spikes between your rectifiers and your filter caps.

7th June 2010, 10:19 AM	#3
terranigma diyAudio Member Join Date: Feb 2007	Thank you RJM, I have checked LM338 manual but I could not determine which section to read to find this information. I will go with #2..

8th June 2010, 08:47 AM	#5
terranigma diyAudio Member Join Date: Feb 2007	I just noticed that without any negative opinions about your directions.. Thank you again..