Parasound HCa 1000a

infiniti52 · 23rd September 2010, 04:08 PM

The repair tech stated the amp is in pretty good shape and the problem with the channel was the two fuses and he replaced them. The only suggetion he recomends is some of the 12 resistors (.33/3w) need to be change. so rather than just changing the (4) just change all of them. He stated that h ewould just cut the leads on the existing resistors and just add the new ones, that way he does not have to take the amp apart. What .33/3watt resistors would anybody recomends. Stay with the same (no brand on them they are just ceramic) or what would be better some one mentioned mills.

Please help

birdyman · 23rd September 2010, 07:49 PM

Why .33ohm/3w resistors need be changed? Are they bad? or just preventive replacement?

texaslonghorn · 23rd September 2010, 09:01 PM

I did the same thing on one of these amps a couple years ago. I think John Curl himself recommends that, although may not be recalling that correctly. I used 5% Sfernice thick films from Newark. To be honest, I sold that amp before things got burned in and I did so much other work on it I can't offer an opinion on the sonic quality of the change. It also doesn't help that I didn't care for the amp (you gits what you pays fer and I think I paid $100 for that one...) John himself said the amp was designed and built for a low end price point.

Mills would be good but at 3W they may not fit cuz aren't they big? Also, I would feel better if the resistors were replaced the "normal" way rather than the "easy" way.

birdyman · 23rd September 2010, 09:17 PM

Low priced amp but pure audiophile topology and lot of good quality parts used. Cutting parts to replace them are not real professional work.

john curl · 23rd September 2010, 09:40 PM

If the .33 ohm resistors test OK, just leave them alone, even if they look a little discolored.

infiniti52 · 24th September 2010, 02:55 PM

they just looked discolored and some of them where tested lower value and some higher. so he suggested might just as well replace them all.

birdyman · 24th September 2010, 03:40 PM

It is tricky to test them right. Did he unmount them to test? I think you said he want to " just cut the leads on the existing resistors and just add the new ones, that way he does not have to take the amp apart." He needs to unmount them or cut them to test exact value of each resistors because insulation sleeves, old soldering rosin, oxidization, attached parts etc....

john curl · 24th September 2010, 05:20 PM

I would still leave them alone. At least, try it, as is. It is difficult to get a precise reading without taking them out, and even a +/- 20% variation would not do much, IN THIS AMP, because the value is so large, virtually twice the JC-1's resistor value, and different values actually help make a smoother transition from class A to class B. The BEST thing to do is to operate the output stage with as much current as possible, before over-heating the heatsinks, and they should run very warm to the touch or 50 degrees C or so.

birdyman · 24th September 2010, 08:09 PM

Hi Mr. John Curl
My hca-1000a has bias set at 10mv and it is not even warm after one hour of normal volume use. What is proper or recommended bias setting ? I am afraid to set it too high and fry the amp.
Thanks

john curl · 24th September 2010, 08:49 PM

Go to 20-25 mV. This is optimum for this amp.

23rd September 2010, 04:08 PM	#1
infiniti52 diyAudio Member Join Date: Oct 2009	Parasound HCa 1000a The repair tech stated the amp is in pretty good shape and the problem with the channel was the two fuses and he replaced them. The only suggetion he recomends is some of the 12 resistors (.33/3w) need to be change. so rather than just changing the (4) just change all of them. He stated that h ewould just cut the leads on the existing resistors and just add the new ones, that way he does not have to take the amp apart. What .33/3watt resistors would anybody recomends. Stay with the same (no brand on them they are just ceramic) or what would be better some one mentioned mills. Please help

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23rd September 2010, 07:49 PM	#2
birdyman diyAudio Member Join Date: Jan 2010	Why .33ohm/3w resistors need be changed? Are they bad? or just preventive replacement?

23rd September 2010, 09:01 PM	#3
texaslonghorn diyAudio Member Join Date: Sep 2009	I did the same thing on one of these amps a couple years ago. I think John Curl himself recommends that, although may not be recalling that correctly. I used 5% Sfernice thick films from Newark. To be honest, I sold that amp before things got burned in and I did so much other work on it I can't offer an opinion on the sonic quality of the change. It also doesn't help that I didn't care for the amp (you gits what you pays fer and I think I paid $100 for that one...) John himself said the amp was designed and built for a low end price point. Mills would be good but at 3W they may not fit cuz aren't they big? Also, I would feel better if the resistors were replaced the "normal" way rather than the "easy" way.

23rd September 2010, 09:17 PM	#4
birdyman diyAudio Member Join Date: Jan 2010	Low priced amp but pure audiophile topology and lot of good quality parts used. Cutting parts to replace them are not real professional work.

23rd September 2010, 09:40 PM	#5
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	If the .33 ohm resistors test OK, just leave them alone, even if they look a little discolored.

24th September 2010, 02:55 PM	#6
infiniti52 diyAudio Member Join Date: Oct 2009	they just looked discolored and some of them where tested lower value and some higher. so he suggested might just as well replace them all.

24th September 2010, 03:40 PM	#7
birdyman diyAudio Member Join Date: Jan 2010	It is tricky to test them right. Did he unmount them to test? I think you said he want to " just cut the leads on the existing resistors and just add the new ones, that way he does not have to take the amp apart." He needs to unmount them or cut them to test exact value of each resistors because insulation sleeves, old soldering rosin, oxidization, attached parts etc....

24th September 2010, 05:20 PM	#8
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	I would still leave them alone. At least, try it, as is. It is difficult to get a precise reading without taking them out, and even a +/- 20% variation would not do much, IN THIS AMP, because the value is so large, virtually twice the JC-1's resistor value, and different values actually help make a smoother transition from class A to class B. The BEST thing to do is to operate the output stage with as much current as possible, before over-heating the heatsinks, and they should run very warm to the touch or 50 degrees C or so.

24th September 2010, 08:09 PM	#9
birdyman diyAudio Member Join Date: Jan 2010	Hi Mr. John Curl My hca-1000a has bias set at 10mv and it is not even warm after one hour of normal volume use. What is proper or recommended bias setting ? I am afraid to set it too high and fry the amp. Thanks

24th September 2010, 08:49 PM	#10
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	Go to 20-25 mV. This is optimum for this amp.

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