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If you are experiencing loud pops when you switch Vibrato on or off, then, dollars-to-donuts, you have an old leaky capacitor in your preamp. The culprits are the feedback coupling capacitors from the first preamp stages of both the vibrato and non-vibrato channels.

Technical Details

When these caps get leaky, they allow some DC voltage to build up on the preamp inputs whenever they are floating. When one of the manuals is switched onto the input, the DC offset is shunted to ground through the output winding of the matching transformer. The sudden change in input voltage results in a pop.

The Fix

You have to replace the leaky caps. Really, it might be time to rebuild the preamp, while you have it out.

In an AO-28 the capacitors in question are C5 and C11. In an AO-29 C3 and C8 are the suspects.

See also: CapacitorReplacement.


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