Analyze This

GAD

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This is Grot's G1000. It sounds great after replacing the filter caps, but it's still doing this even with all knobs on zero:

 

davismanLV

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Nice little background filler hum with it's own rhythm and everything!! Once it's gone, can you make it do that on purpose? :devilish:
 

GAD

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Nice little background filler hum with it's own rhythm and everything!! Once it's gone, can you make it do that on purpose? :devilish:
If I could vary the tempo I could work with it!
 

GAD

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Aliens? In your guitar amp? The stunning answer may surprise you!
 

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Take it out to the garage and see if it makes the same racket. It might be picking up something like the computer or other electronic device. When I plugged the Realistic amp in at Bill's house, it was far noisier than when you were playing through it at Grot's place o' work.
 

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Sounds like the chorus (does it have trem?) isn't shutting off all the way. Is it footswitchable? Does it still make that pulsing with a switch plugged in?
 

AcornHouse

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From my amp tech:
[FONT=&quot]When he switches the chorus in & out seems to change the problem, that's where I'd start looking. [/FONT]
[FONT=&quot]Never seen or heard one. Probably a bad chip in the chorus electronics.[/FONT]
 

FNG

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Definitely the flux capacitor.
 

beinhard

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Interesting.

Does it sound good even with chorus active?
If it does, and since the noise is there even with the depth control on zero, I would guess that the chorus circuit itself is ok.

There is a part connected to the chorus switching which I assume is an analog switch chip.
Could there be noise injected via its control gate?
Is the capacitor connected from control gate to ground ok?

beinhard
 

GAD

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From my amp tech:
Interesting.

Does it sound good even with chorus active?
If it does, and since the noise is there even with the depth control on zero, I would guess that the chorus circuit itself is ok.

There is a part connected to the chorus switching which I assume is an analog switch chip.
Could there be noise injected via its control gate?
Is the capacitor connected from control gate to ground ok?

beinhard
Thanks guys. I'll take a look there.
 

GAD

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Replaced the cap connecting to the to the analog switch chip and even sourced a NOS switch chip - no joy.

Since the sound is present with all controls off, I have to imagine this is a power supply or power amp issue. Time to break out the oscope.
 

Nuuska

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Hi

Suppose there are higher voltages for the power amp and lower voltages for preamp.

You started with replacing filter caps - assume they were in higher voltage part - +/- 40V or something.

I suspect the +/- 12-15V rails are not stable and get crap from chorus oscillator.

Just guessing - without schematics . . .
 
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