Ampeg J12-B Tremelo Whoosh

[KingCameron]

Howdy from Austin!

I am repairing an Ampeg J12-B for a local musician.

The amp functions fine, except it has a "whoosh whoosh" pulsing sound that can be adjusted with the tremelo speed knob.

Obviously, the tremelo is somehow getting through to my output signal.

I have replaced the multi-section cap so the amp is completely silent when volume is turned to 1. As the volume increases, so does the "whoosh whoosh"

This amp is largely vintage and contains most all original Astron caps. I don't want to butcher its sexy circuit by replacing too many of these.

Any ideas on what I should focus on?

[52 Bill]

The amp functions fine, except it has a "whoosh whoosh" pulsing sound that can be adjusted with the tremelo speed knob.

I don't understand what you are describing. If you turn off the tremolo does the whooshing stop?

Are you only concerned about the whoosing sound when there is no guitar signal being played?

[KingCameron]

Whooshing Ampeg (Tremolo)

Sorry for the unclear description...Let me try again

(Multi-section cap is new)

[B]First[/B]
[no guitar being played]
Volume ~5, Tone ~5, Tremolo = 0 (Tremolo is able to be switched off)
Scratchy sound as volume is increased.

Second
[no guitar being played]
Volume ~5, Tone ~5, Tremolo ~1
Scratchy sound, whooshing begins, and can be adjusted in speed by changing the tremolo setting

Have tried switching the 6SL7 pre-amp tubes to ensure that it is not a noisy pre-amp tube.

Otherwise amp sounds killer..

[52 Bill]

Scratchy sound as volume is increased.

The volume control may be dirty. Try spraying a little Deoxit or tuner wash in it and see if it clears up. If it doesn't check to see if there is any dc voltage on the terminals. If there is any dc on the control, you may have a leaky coupling cap.

...whooshing begins, and can be adjusted in speed by changing the tremolo setting

The whoosing sound that you describe is caused by the power amp being biased on and off by the tremolo oscillator. What you hear may be normal. Is the sound louder than the background noise/hiss that the amp makes when the trem is turned off?

Otherwise amp sounds killer..

Cool!

[KingCameron]

Ampeg Caps

Thanks for the feedback... You rock!

I have decided to order some Mojotone oil filled caps and do a replacement of the old Astrons.

My friend is recording with this amp, and needs it to be silent, other than the intended signal.

So, I am gonna start replacing all of the old Astrons, with the Mojotone caps.

I will most likely replace the resistors with metal oxide resistors too.

It will basically be a rebuild, but should go a long way toward cleaning up the overall hiss, and maybe a smidge of the whoosh.

Any other cool recomendations I should consider?

[juniorbrando]

ampeg j-12 rebuild

Just wondering as I'm considering recapping my j-12D, how'd it turn out? how did it affect the sound?

At the moment my tremolo doesn't work at all, so Im looking around the forums for advice.

Best-
Jr