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Howdy tubophiles,another question from the Fisher 500c problem child.
Soft crackling noises are coming from my Klipsch Cornwalls/Fisher 500C. It happens when any source is selected and volume is low or hi. It does not get louder as the volume increases. Any ideas?
thanks in advance,
eric
Follow Ups:
I also had a crackling noise - more like soft static. I swapped the tubes on my pre-amp from the left to the right channel and the noise followed. Turned out it was a noisy tube.
Cut-Throat
nt
EC,Check the solder job your amp tech did in the power supply and bias supply portions of your amp. Maybe a cold solder lingers about...
El C,Sounds like a bad contact or tube going South. If you are comfortable with the idea of looking under the hood of your baby and its 500+ volts DC (LETHAL range)... Then, you might try the old "chopstick" test. You need the amp connected to the speakers. No input. Low volume, amp on.
Take an pair of cheap chopsticks (the kind you need to split)---they MUST BE ALL WOOD. Use ONLY one stick and probe the sockets and all solder points from left to right in your amp. All resistors and caps. LEAVE YOUR LEFT HAND IN YOUR POCKET (if you are right-handed) while probing. You do not want to test the "path of least resistance" theory.
If you can exacerbate or induce the popping and crackling more by probing one section or component---you've probably isolated one of the culprits. Turn off amp. Drain the filter caps (use a draining resistor). Replace the culprit or resolder the bad solder point.
Now, try the test again---until you've rid yourself of the bad seed.
Diodes, caps, resistors can all dry out or crack. This can lead to crackling noises. So, I'd replace most resistors and caps in high heat areas. All ALL of the diodes in the PS circuit---just as preventative measure. Cause if they don't make noise now---they soon will.
All electrolytics caps (including cathode bias bypass caps) should be replaced. These are closest to the heat and often are way off OEM values, after 10-15 years of service. Go to a higher voltage rating, on the cap, if you want---it'll give you longer service. Eg: go from say 50 mfd/25 volts cap to a 50 mfd/50 volt cap. KEEP the mfd value the same.
interesting suggestion. I'll try that (after i read it a couple more times!) I actually had the thing fixed up by a tech back in may. He replaced a bunch of caps, i am not sure about what else. I've misplaced the receipt detailing what was done. kind of frustrating. I'm becoming weary of this thing, although the music still sounds good. I'm contemplating a 70s HK receiver..
Well then, have you looked inside your speakers? If there are old electrolytic caps there in the crossover, this might be your problem since your amp has had a recent going over. These old caps will have + marks on both ends to indicate bi-polarity, and they tend to dry out after many years. If so, then replace these with near same capacitance value modern polypropylene ones.
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