HF Feedback - how to stop it

[King Tut]

I'm using a Trace AH200 head (Series 6 GP12) - usually into either a Nemesis 2 x 10 (horn disabled) or an Aguillar DB110.

I like quite a twangy sound so boost the high mids to achieve this - usually playing a Jazz bass.

Quite often when I turn towards the amp (even when facing away sometimes) I get a painful HF feedback. Am I just being greedy with the volume and top end or is something wrong.

I'm using compression from a pedal - but not masses of it - seems worse when using single coil pickups.

Thoughts please.

[King Tut]

Anyone?

[nick]

Sounds like a microphonic pickup to me.

[stevie]

I'd agree with that.

[King Tut]

Seems to happen with more than one bass though . . . . .

[Slipperydick]

Does sound like microphonic pups to me as well.

If you gently tap a pickup can you hear it through the speakers ?

do the pickups 'float' or are they stuck down tight against the body or scratchplate ?

[99mustang]

Can someone explain "microphonic pickup" please.


John.

[Ou7shined]

It happens with very old pickups as the windings loosen off and vibrations of the pickup (rather than metal objects around it) can be amplified. Most modern pups won't do this as they are treated with wax or resin to prevent it the winds from vibrating.
Some old pups were designed to operate like this. I remember years ago having a crappy old pup that you could actually shout into and the amp would amplify your muffled voice.

[Slipperydick]

Microphonic means its acting like a microphone, picking up sound rather than just the magnetic field caused by the string moving past the magnet.

Usually something loose in the pickup itself. Hence tapping it with a fingernail you would hear, like tapping a Microphone.

[King Tut]

OK thanks - will check this out - the pups are floating on sponge - my main bass - the pups are from a Geddy Lee Jazz. One of the others that does it - it's a really old '75 Ibanez pup. Some good info here to work on. Interestingly it doesn't happen with my more up to date Sandberg JM4

[brensabre79]

Yep sounds like microphonic p'ups. Although both my JBs do this too. One with brand new Wizards, the other with stock Fender p'ups (about 10 years old) the only bass that doesn't do it is my Sabre which hasn't been touched electronically since 1979 when it was built!

[King Tut]

Interesting Ben - so is this a fault or something I just need to live with?

[MoonBassAlpha]

I reckon it will help if you can bolt the pickups more tightly to the body. One of my pickups foam had got too compressed and a bit loose and would squeal at volume. A lot better now with more foam jammed in.

[brensabre79]

No I don't think you should live with it KT. Neither should I. But I'm at a bit of a loss myself with this problem. put in extra foam pads - good place to start though MoonBass. Grounded the whole of the cavities with copper tape. The pickups have all been wax-potted and still I have this. The only time I don't get it is when I don't boost the treble on the bass pre-amp.
I have to say though when I turn the gain down on the amp and the master volume up I get the same volume without the squeal - but I don't get the growly sound I like either