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Old 3rd September 2011, 12:20 AM   #1
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Join Date: Nov 2008
Default help fixing a tone control circuit

evening all!

i'll cut straight to the chase:

just recapped the final bits in a pioneer A-8, speaker protection output and the loudness section (which is completley seperate from the tone control section) now i have a very loud pop when switching to the bass/tone controls,and strangely enough, no tone controls.. or mono/stereo/balance controls for that matter,checked the volatge at the opamp +/- 15v steady. replaced the opamp with a 5532 i had lying around.. no change

lots of hiss in the background when the tone controls are engaged,which may point to an earth problem, but im not sure.

quite gutted at the moment as ive steadily recapped this amp over a period of about a year,and its just got better and better.

everything else except tone/balance/mono/stereo works fine.. im listening to it right now with the loudness circuit engaged and it sounds quite nice

i dont have access to a scope anymore so thats out of the question, hopefully theres someone out there who can help

thanks guys,for any help

amp schematics (ignore the ver no,as it applies to power/pre only)

Download Pioneer-A8 amp.rar from - send big files the easy way
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Old 3rd September 2011, 05:11 PM   #2
Twaksak is offline Twaksak  South Africa
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Join Date: Apr 2005
Location: Mpumalanga South Africa
Hi lensmanMk2,
Check out the soldering of the pcboard. If it did work before I am sure you can fix it.
If you think you can, then you can!
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Old 3rd September 2011, 05:21 PM   #3
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thank for the reply, just fixed it..

after messing with the multimeter turns out it was a dry solder joint on the balance soon as its switched from line straight the signal goes through the balance control> mono switch > tone controls.

also the slight hiss ive had on the left channel since owning the amp has the dry joint must have been loosened when i was recapping.

i think that calls for a beer
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