channel distortion

sriegel · 31st January 2002, 01:49 AM

hello all,
well, i finally got my aleph5 up and running, sort of. this is the wierd trouble i have;
i built the class A case/heatsink from 'lottusblossum's' web-site, i.e. the whole case is connected together.

i developed an intermittent static in one channel so i opened that side up to check it out and all measured fine. so i powered up and it worked fine. i "closed" it back up and tightened down the bolts, fired it up and there was that static??? only out of that one channel, the other is fine. and when i power down, it takes a long time for that channel to stop playing music.

i was thinking that maybe i was shorting out the output hexfets somehow, but can't figure it out and i don't know how to go about testing it to see.

any thoughts?

cheers,
scott

R. McAnally · 31st January 2002, 05:37 AM

Quote:

Originally posted by sriegel
... my amp sounds bad ...

Sounds like the biasing isn't right. Since Class A draws more or less the same current all the time regardless of output, the fact that one side takes a long time to "die out" seems to me like a lack of bias. Maybe a bad connection somewhere.

This would also explain the horrible sound you must be experiencing

Good luck

AudioFreak · 31st January 2002, 05:41 AM

i dont think it's biasing....

you say that channel takes a long time to stop playing music after you turn it off ... does it do this while the case is off or only when it's closed and all screwed down.

sriegel · 31st January 2002, 02:45 PM

Well, it's as i thought, sort of. when the heatsinks aren't touching the rest of the case, it works fine. turns off right away and the distortion is gone. so, do i have a comprimised sil-pad? it seems that maybe i'm shorting the outputs to the case somehow. does that seem like a reasonable culprit? what's weird is that it worked fine for ~ 3 days at around 3-4 hours each before this happened. and i didn't change anything during this time. any thoughts as to what would cause the insulating pad to fail over such a short time? they are kapton pads, supposed to be alright.

thanks for any input!
cheers,
scott

GRollins · 31st January 2002, 03:57 PM

Use mica insulators.

Grey

PassFan · 31st January 2002, 08:53 PM

Is there any way that the cover is coming into contact with the power supply caps or anything else inside. Maybe one of the screws is hitting something when it threads all the way in.

jam · 31st January 2002, 09:01 PM

Grey is right. Use mica insulators with silicon grease. It might be a little messy but it works and has better thermal characteristics. I have had a lot of problems with sil-pads.

Jam

sriegel · 1st February 2002, 01:09 AM

any suggestions on where to buy mica insulators? i live in u.s.

thanks,
scott

sriegel · 1st February 2002, 03:15 AM

i found 'em,
thanks for the help and advice to all!!!

cheers,
scott

sriegel · 12th February 2002, 01:38 AM

hey all,
i replaced the insulators with mica and then electrically isolated that channel with electrical tape to be safe. everything seems fine, however, when powering up, there is still some static in that channel and the LED changes intensity, like there are voltage spikes or irregularities. this all seems to die out after a minute or two and all is fine.

any thoughts as to what would cause this weirdness?

cheers,
scott

31st January 2002, 01:49 AM	#1
sriegel diyAudio Member Join Date: Nov 2001	channel distortion hello all, well, i finally got my aleph5 up and running, sort of. this is the wierd trouble i have; i built the class A case/heatsink from 'lottusblossum's' web-site, i.e. the whole case is connected together. i developed an intermittent static in one channel so i opened that side up to check it out and all measured fine. so i powered up and it worked fine. i "closed" it back up and tightened down the bolts, fired it up and there was that static??? only out of that one channel, the other is fine. and when i power down, it takes a long time for that channel to stop playing music. i was thinking that maybe i was shorting out the output hexfets somehow, but can't figure it out and i don't know how to go about testing it to see. any thoughts? cheers, scott

1st February 2002, 03:15 AM	#9
sriegel diyAudio Member Join Date: Nov 2001	mica insulators i found 'em, thanks for the help and advice to all!!! cheers, scott

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31st January 2002, 05:41 AM	#3
AudioFreak Warp Engineer On Holiday Join Date: Oct 2001 Location: Queensland, Australia	i dont think it's biasing.... you say that channel takes a long time to stop playing music after you turn it off ... does it do this while the case is off or only when it's closed and all screwed down.

31st January 2002, 02:45 PM	#4
sriegel diyAudio Member Join Date: Nov 2001	Well, it's as i thought, sort of. when the heatsinks aren't touching the rest of the case, it works fine. turns off right away and the distortion is gone. so, do i have a comprimised sil-pad? it seems that maybe i'm shorting the outputs to the case somehow. does that seem like a reasonable culprit? what's weird is that it worked fine for ~ 3 days at around 3-4 hours each before this happened. and i didn't change anything during this time. any thoughts as to what would cause the insulating pad to fail over such a short time? they are kapton pads, supposed to be alright. thanks for any input! cheers, scott

31st January 2002, 03:57 PM	#5
GRollins diyAudio Member Join Date: Feb 2001 Location: Columbia, SC	Use mica insulators. Grey

31st January 2002, 08:53 PM	#6
PassFan diyAudio Member Join Date: Aug 2001 Location: Central FL	Is there any way that the cover is coming into contact with the power supply caps or anything else inside. Maybe one of the screws is hitting something when it threads all the way in.

31st January 2002, 09:01 PM	#7
jam diyAudio Member Join Date: May 2001 Location: Charlotte,NC,USA	Grey is right. Use mica insulators with silicon grease. It might be a little messy but it works and has better thermal characteristics. I have had a lot of problems with sil-pads. Jam

1st February 2002, 01:09 AM	#8
sriegel diyAudio Member Join Date: Nov 2001	any suggestions on where to buy mica insulators? i live in u.s. thanks, scott

12th February 2002, 01:38 AM	#10
sriegel diyAudio Member Join Date: Nov 2001	hey all, i replaced the insulators with mica and then electrically isolated that channel with electrical tape to be safe. everything seems fine, however, when powering up, there is still some static in that channel and the LED changes intensity, like there are voltage spikes or irregularities. this all seems to die out after a minute or two and all is fine. any thoughts as to what would cause this weirdness? cheers, scott