LM338's for one channel getting way hotter than the other

markiemrboo · 26th November 2006, 07:54 PM

Each channel is regulated separately, on totally separate boards. The only difference between the two channels is that one is using Panasonic FC's before the regulators, and one is using "R.M" caps pulled from an amp. The one with the FC's gets FAR hotter than the "R.M" board. The heatsinks are identical and before I put the FC's on I really don't remember either getting that hot at all.

So really, I am just curious as to why it's getting so hot? Could it actually be something to do with the FC capacitors? There doesn't seem to be any issues, even playing with the volume on the pre all the way up, and both boards are giving the same voltage outputs (+/-28.5v) and have the same voltage being fed to them (~35v after the bridge rectifiers).

I'm confused [ again ]

Leolabs · 26th November 2006, 11:56 PM

Voltage rating of the caps????

markiemrboo · 27th November 2006, 12:35 PM

50v

head_spaz · 29th November 2006, 01:13 AM

You stated that you are using two regulator boards, so I assume both regs are running hot on one channel.

Have you tried disconnecting the amplifiers to see if the regs run hot without a load?

Perhaps one of the amplifiers is oscillating.

markiemrboo · 29th November 2006, 09:36 AM

That's right, only one of the boards is running hot.

I will try disconnecting the amp board from it hopefully later and let you know if it cools down, though I wouldn't have thought oscillation would have been a problem. The two amp boards are identical, and the other regulator board doesn't get hot. Along side that the amp board connected to the regulator board that is getting hot.... isn't getting hot at all, which is supposedly a sign of oscillation

head_spaz · 29th November 2006, 08:20 PM

Swap the amps... with their respective PSU boards.
Amp-A to PSU-B, and Amp-B to PSU-A.
See if the same PSU runs hot, or when switching, the other PSU shows the same symptoms. This way you can isolate whether or not it's the PSU or the AMP.

Simple diagnostics.

markiemrboo · 2nd December 2006, 06:20 PM

Quote:

Originally posted by head_spaz
Swap the amps... with their respective PSU boards.
Amp-A to PSU-B, and Amp-B to PSU-A.
See if the same PSU runs hot, or when switching, the other PSU shows the same symptoms. This way you can isolate whether or not it's the PSU or the AMP.

Simple diagnostics.

I put the other amp board on the hot channel, still gets hot. Doesn't seem like the grounding made any difference after all either!

Maybe it's just this capacitor "burn in" doing it? I could swear with the old caps it didn't get this hot... hm...

CarlosT · 2nd December 2006, 06:54 PM

Put in some new caps? Re-check the polarities?

markiemrboo · 2nd December 2006, 08:11 PM

Quote:

Originally posted by CarlosT
Put in some new caps? Re-check the polarities?

The caps on that board are brand new

Or did you mean put the old caps back to see if it is the caps doing it?

Polarities are OK, they haven't exploded

26th November 2006, 07:54 PM	#1
markiemrboo diyAudio Member Join Date: Mar 2006 Location: Great Yarmouth, UK	LM338's for one channel getting way hotter than the other Each channel is regulated separately, on totally separate boards. The only difference between the two channels is that one is using Panasonic FC's before the regulators, and one is using "R.M" caps pulled from an amp. The one with the FC's gets FAR hotter than the "R.M" board. The heatsinks are identical and before I put the FC's on I really don't remember either getting that hot at all. So really, I am just curious as to why it's getting so hot? Could it actually be something to do with the FC capacitors? There doesn't seem to be any issues, even playing with the volume on the pre all the way up, and both boards are giving the same voltage outputs (+/-28.5v) and have the same voltage being fed to them (~35v after the bridge rectifiers). I'm confused [ again ]

29th November 2006, 01:13 AM	#4
head_spaz diyAudio Member Join Date: Mar 2004 Location: Arkansas	You stated that you are using two regulator boards, so I assume both regs are running hot on one channel. Have you tried disconnecting the amplifiers to see if the regs run hot without a load? Perhaps one of the amplifiers is oscillating. __________________ Writing is good exercize for the texticles!

29th November 2006, 08:20 PM	#6
head_spaz diyAudio Member Join Date: Mar 2004 Location: Arkansas	Swap the amps... with their respective PSU boards. Amp-A to PSU-B, and Amp-B to PSU-A. See if the same PSU runs hot, or when switching, the other PSU shows the same symptoms. This way you can isolate whether or not it's the PSU or the AMP. Simple diagnostics. __________________ Writing is good exercize for the texticles!

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26th November 2006, 11:56 PM	#2
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	Voltage rating of the caps????

27th November 2006, 12:35 PM	#3
markiemrboo diyAudio Member Join Date: Mar 2006 Location: Great Yarmouth, UK	50v

29th November 2006, 09:36 AM	#5
markiemrboo diyAudio Member Join Date: Mar 2006 Location: Great Yarmouth, UK	That's right, only one of the boards is running hot. I will try disconnecting the amp board from it hopefully later and let you know if it cools down, though I wouldn't have thought oscillation would have been a problem. The two amp boards are identical, and the other regulator board doesn't get hot. Along side that the amp board connected to the regulator board that is getting hot.... isn't getting hot at all, which is supposedly a sign of oscillation

2nd December 2006, 06:54 PM	#8
CarlosT diyAudio Member Join Date: Oct 2006	Put in some new caps? Re-check the polarities?

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