Volume pot initially scratchy then not

hnash53

AK Subscriber
Subscriber
I've got a Realistic STA receiver that shows these symptoms:

When I turn it on (it turns on with the same knob used for volume), it's loud and scratchy. But within 10 seconds, all the scratchiness disappears. Sound production is equal out of both channels.

What's going on? Something warming up quickly that dissipates the scratchy noise?

Thanks.
 
I had a similar issue with a volume control and it took a heck of a lot of shots before it stopped but, even now, every so often it will have a slight scratch when turned in the first couple of minutes. If I do not touch the control, there is no problem. On mine, the power switch is a toggle so, I do not have to turn the control. I suspect the only solution would be to pull it,.soak it and hit it with some pressed air to make sure all the crud is cleaned out. I have a toggle on the same unit that is a similar pain in the butt. Happily it is not one needing to be moved often. After a couple of minutes it too quiets down or when I spray it and use it before it dries.
 
My SS Sansui did that both turning on and off,,, turned out to needing a recap,,, Clean the pots first, as suggested,,, if it doesn't help, look at caps/resistors/transistors...

Regards,
John
 
Sometimes pots need to be cleaned two or three times, before that last little bit of troublesome crud is gone. I've cleaned them before and thought, any problem now has to be something else, bur there was still a problem.....but then I cleaned them again and the problem finally went away.
 
My homemade amplifier does this very same thing even though I used a new POT for the volume control. What I concluded is the initial coupling capacitors between the volume in/out and circuitry coming up to bias on amplifying stages cause this..
When the caps are not fully charged to a steady biased voltage (upon turning on) you get offset voltage on the POT and preamp transistors/opamps causing you to hear it pass DC through the POT until all the capacitors in the preamp get to their normal operating voltages.
I think some amps protection timer circuitry even doubles as a timer to cancel out this effect as most amps you notice with this problem almost have an instant on for sound rather than a delay relay circuit.
 
Pretty much a certainty you have leaky caps (electrically leaking, not physical) passing some DC. A recap may not change that characteristic.
 
Back
Top Bottom