Reed Bar Shields turned Wurli microphonic....

[bobfridzema]

Right, so I have a '69 Wurlitzer 200 that's been upgraded with a 200a amp - but it never had reed bar shields. So there's always been some hum. Recently I ordered the reed bar shields and proceeded to install em. Fairly simple, and as far as i can tell there's no shorts. it was a bit of a puzzle to make sure they're level and not bulging but I managed.

Anyway, i put it back together and the whole piano is now very very microphonic, and just as noisy as it was before, even more possibly. It kind of sounds like ac hum, but also like open single coil pickup picking up hum. It is affected by vibrato, and by volume.
By microphonic i mean that everything on the piano is alive - playing it, tapping it anywhere, it all comes through the speakers like it never did before. It's almost like the gain on the wurli is times ten. I did play around with the gain trimpot, but that is at it lowest setting. Any higher leads to distortion of the speakers.

Any ideas? I've been tapping caps and resistors, but I'm clueless at the moment.

[Allenm]

Did you figure it out?

[bobfridzema]

Not really...it's also not really a problem anymore. Here's what i replied on instagram:
"I have not actually, but it's also not really a problem anymore. I checked all the connections again, removed a ground cable that a previous owner installed, even replaced all the components on the preamp with new low noise bits (not much different).
Something I did helped though coz even though it's still a bit microphonic, it's only noticeable when it's amplified really loud so it's very useable. Perhaps raising the gain on the amp (little red/black pot on the board) makes the gain needed later on lower so less microphonics...?"

I am wondering now whether reflowing all the components on the board might help, and replacing all the ceramic components with modern film ones - they're known to become microphonic. But to be honest, i got so sick of it that when i got to a point where its virtually hum free, silent, and sounds good, i lost track of the microphonic issue. Wrote it off as being part of the beast, like my clavinet