Parasound HCA-3500 Bias issue

thejck · 1st February 2012, 06:41 PM

The right side of my amplifier is a lot hotter than the left side after running it for about an hour or so. I am told this might be a bias issue. Is this something that is fairly user serviceable or should I take it in for a repair to a local amp store?

Anyway familiar with the HCA-3500 and the schematic?

john curl · 1st February 2012, 07:20 PM

How technical are you?

thejck · 1st February 2012, 08:14 PM

I am currently modifying a pair of Polk SDA 1.2 speakers. Including soldering and desoldering things from a new PCB. I know how to use a solder gun I know how to use a multimer I can understand basic circuit layouts but I dont know what they mean or do.

If you gave me a PCB board and inductors resistors and caps and a schema i could put it all together.

thejck · 1st February 2012, 08:17 PM

part of the reason why i am concerned is because the upgrade that I am doing to my speaker (well documented on the polk forum) involves replacing a coil with a much lower DCR. this reduces the overall inductance of the speaker. I checked with Richard @parasound and he said the amp would be able to handle it.
So far I got the left speaker done and set up with the lower DCR inductor and the right one is stock. So when I put my hand on the amp I was surprised that it was the right hand side that was hotter than the left

Original Burnedfingers · 2nd February 2012, 11:04 AM

If it were mine I would hook the amp up to a dummy load and put a sine wave into it and monitor it. Take an infrared thermometer reading of each heatsink and check the bias on each channel before jumping to any conclusions.

thejck · 2nd February 2012, 12:37 PM

Last night I had it on for a few hours with no speakers attached to it.
While the amp did not get as hot as the previous night. I did notice that the right side was still a bit warmer than the left. I was using my hand to check this. And I had the wife double check and she concurred.

sgrossklass · 2nd February 2012, 03:08 PM

Depending on bias circuitry, it is possible for bad contact inside the quiescent current setting pot to result in increased current, sometimes dramatically. These pots need to be cleaned and quiescent current readjusted. Should be routine for a hi-fi workshop, otherwise it generally isn't too hard to do as long as you have service docs, a suitable kind of contact cleaner (a bit of a science in itself), a multimeter and suitable test leads.

a.wayne · 2nd February 2012, 05:55 PM

Send it to JC for service and upgrades .......

thejck · 06:31 PM

JC?

nvm John Curl.. yup I know he is. Does he do that?

thejck · 9th February 2012, 02:03 PM

Anyone have the service manual to do this? Can this be done at home by a guy who knows how to use a multimeter?

1st February 2012, 06:41 PM	#1
thejck diyAudio Member Join Date: Jun 2010	Parasound HCA-3500 Bias issue The right side of my amplifier is a lot hotter than the left side after running it for about an hour or so. I am told this might be a bias issue. Is this something that is fairly user serviceable or should I take it in for a repair to a local amp store? Anyway familiar with the HCA-3500 and the schematic?

2nd February 2012, 06:18 PM	#9
thejck diyAudio Member Join Date: Jun 2010	JC? nvm John Curl.. yup I know he is. Does he do that? Last edited by thejck; 2nd February 2012 at 06:31 PM.

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1st February 2012, 07:20 PM	#2
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	How technical are you?

1st February 2012, 08:14 PM	#3
thejck diyAudio Member Join Date: Jun 2010	I am currently modifying a pair of Polk SDA 1.2 speakers. Including soldering and desoldering things from a new PCB. I know how to use a solder gun I know how to use a multimer I can understand basic circuit layouts but I dont know what they mean or do. If you gave me a PCB board and inductors resistors and caps and a schema i could put it all together.

1st February 2012, 08:17 PM	#4
thejck diyAudio Member Join Date: Jun 2010	part of the reason why i am concerned is because the upgrade that I am doing to my speaker (well documented on the polk forum) involves replacing a coil with a much lower DCR. this reduces the overall inductance of the speaker. I checked with Richard @parasound and he said the amp would be able to handle it. So far I got the left speaker done and set up with the lower DCR inductor and the right one is stock. So when I put my hand on the amp I was surprised that it was the right hand side that was hotter than the left

2nd February 2012, 11:04 AM	#5
Original Burnedfingers diyAudio Member Join Date: Nov 2002	If it were mine I would hook the amp up to a dummy load and put a sine wave into it and monitor it. Take an infrared thermometer reading of each heatsink and check the bias on each channel before jumping to any conclusions.

2nd February 2012, 12:37 PM	#6
thejck diyAudio Member Join Date: Jun 2010	Last night I had it on for a few hours with no speakers attached to it. While the amp did not get as hot as the previous night. I did notice that the right side was still a bit warmer than the left. I was using my hand to check this. And I had the wife double check and she concurred.

2nd February 2012, 03:08 PM	#7
sgrossklass diyAudio Member Join Date: Nov 2004 Location: Germany	Depending on bias circuitry, it is possible for bad contact inside the quiescent current setting pot to result in increased current, sometimes dramatically. These pots need to be cleaned and quiescent current readjusted. Should be routine for a hi-fi workshop, otherwise it generally isn't too hard to do as long as you have service docs, a suitable kind of contact cleaner (a bit of a science in itself), a multimeter and suitable test leads.

2nd February 2012, 05:55 PM	#8
a.wayne diyAudio Member Join Date: May 2008 Location: Front Row Center	Send it to JC for service and upgrades .......

9th February 2012, 02:03 PM	#10
thejck diyAudio Member Join Date: Jun 2010	Anyone have the service manual to do this? Can this be done at home by a guy who knows how to use a multimeter?

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