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Jungson JA-88D crackling and static fixed!
Jungson JA-88D crackling and static fixed!
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Old 27th October 2013, 11:55 PM   #1
chillysalsa is offline chillysalsa  Canada
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Location: T.dot, Canada
Default Jungson JA-88D crackling and static fixed!

No requests or debates, just wanted to share a success:

Over the last year, my Jungson integrated started creating some crackle and noise from the left channel.

Checking the output, measured a dc offset of >200mV, and fluctuating about 50% higher sometimes. It did settle a bit after warning up, but never completely went away.

Found this site with some info on mods and schematics:

JungSonJA88D-09

And located the trim pots top zero the positive and negative offset.

Now the amp is dead quiet! I think one of the protection circuits may have been fighting the output to try and reduce the offset.

Hopefully this may help someone in the future.
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Old 12th July 2014, 12:56 AM   #2
dwong168 is offline dwong168
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Hi Chillysalsa, I have the same problem on my Jungson JA88D. May I ask where the trim pots are located? I visited the link in your post and I wasn't able to find a schematic or a photo of what you're referring to.

The crackling is driving me nuts! Please help.
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Old 8th January 2015, 10:50 PM   #3
chillysalsa is offline chillysalsa  Canada
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Hey there, sorry it took so long to respond, you should have PM me
Here is a picture of the location of the pots.

Be careful adjusting, only make a small change in one, measure the DC offset, then try fine tuning the other.

I see test points shown in the schematic, but I could not locate them I the board, so take care in adjusting it too far so it does not run too far out of range.
Attached Images
File Type: jpg 20140729_013823.jpg (934.9 KB, 176 views)
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Old 12th January 2019, 12:39 AM   #4
TheloniusFunk is offline TheloniusFunk
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I'm also having a problem with static/cracking in my left channel on my Jungson JA-88D.


I see there are 2 pots per channel for this adjustment as per chillysalsa's attached thumbnail. Am I correct in assuming that these are for fine/coarse adjustment and if so, which is which?


Thanks for any help/advice.
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Old 12th January 2019, 08:39 AM   #5
huggygood is offline huggygood  France
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I do not know this amp but logically, it must be a potentiometer for offset and another for bias.
if we act on the offset, we must adjust the bias, and vice versa.
in any case, both, offset and bias must be controlled.
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Old 12th January 2019, 11:23 PM   #6
TheloniusFunk is offline TheloniusFunk
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huggygood...wouldn't logically one pot be for the positive speaker output and the other for the negative speaker output?
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Old 13th January 2019, 03:32 AM   #7
Ian Finch is offline Ian Finch  Australia
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Unless it's a bridgemode amplifier, the negative speaker terminal is returned to ground at the power supply. With conventional power amplifiers, there is no possible adjustment to ground potential, just to the differential DC potential which, like the signal, appears at the output+ terminal.

There are nice pictures but unfortunately, there are no technical details at the link to Troel's site and the OP's description is unclear as to what he did. He could just as easily have solved the fault just by resetting a poor quality 15 turn pot. or temporarily "fixing" a soldering fault by pushing a few parts.
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Old 13th January 2019, 04:17 AM   #8
TheloniusFunk is offline TheloniusFunk
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Hi Ian...it is indeed a bridgemode amp as it runs 4 amplifiers bridged in pairs for the left and right channel respectively.
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Old 13th January 2019, 09:02 AM   #9
Ian Finch is offline Ian Finch  Australia
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Well, if bridge mode, all the more reason to get a service manual detailing the offset setting of each amplifier before playing about with them in bridge. If that's not possible, you still need first hand expertise as opinions don't work when no one really knows what the design is like or how best to set it up for correct operation.

I guess the schematics that the OP referred to were taken down from the site as I can't see anything useful there. Perhaps Troels Graveson who is probably also the same person as a member here, can provide contacts and assistance as it seems the design was developed many years ago and well before Jungson assumed production.
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Old 13th January 2019, 03:12 PM   #10
TheloniusFunk is offline TheloniusFunk
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Thanks for the reply Ian.


Please excuse my ignorance but I am under the impression that DC Offset should be set as close to zero as possible or am I entirely off the mark here? If there is a specific value I should be shooting for and failing any available Jungson documentation could I just measure the offsets (+/-) of the properly working R channel and replicate this for the L when adjusting?
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