Fender DR Vibrato - intermittent fuzzy noise + other noises

[waspclothes]

Hey all,
Thanks for the help getting my Deluxe Reverb build working correctly. After finding a glob of solder bridging 2 terminals of the bias pot, and then after realising I mislabelled the bias current & plate voltage outputs of my weber bias rite clone, I'm happy to say that the amp is finally biased and working properly - for the most part.

I've checked the vibrato circuit over quite a few times, and everything seems correct. However, when I engage the vibrato, it is accompanied by an intermittent white noise. The noise is heard only when there is sound going through the amp, and only at the loud peaks of the tremolo. There's also a 'squeal' that is sometimes accompanies the vibrato - I don't know how to describe this sound, but it sort of sounds like a capacitor charging. it raises in pitch and is high frequency. The volume of both of these sounds is independent of the channel volume. There is also a low frequency "beat" as well.

I've tried a few tubes, all with the same result.

Mike

[soundguruman]

The tremolo shuts down the output tubes with pulses of negative voltage.
every time the tremolo peaks, the amp is under-biased, and distorts. That's the white noise you are hearing.
You may have better luck with the bias adjusted hotter, overall. Then the pulse would not produce so much distortion.

[loudthud]

The amp is a Deluxe Reverb with the opto type tremolo AA763 of AB763, is that correct? The pulsing hiss is normal, there is always some. You may have a noisey resistor in the preamp, what type resistors were used in the amp? Does it go away if you pull V2 or V4?

If there is a thumping sound from the tremolo, that can be addressed. Do a search for "thump" of thumping. I will look for threads that mention this problem.

The squealing is probably an oscillation that is excited by the tremolo. Carefully check for lead dress issues by moving wires around with chop sticks while the amp is making that sound.

Edit: Here's some info I found on the tremolo issue:
http://www.fender.com/community/foru...1afa05434808c5