Wurlitzer electric piano interference - diyAudio
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Old 9th November 2015, 11:00 PM   #1
cancon is offline cancon  Canada
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Join Date: Mar 2011
Default Wurlitzer electric piano interference

I've been working on Wurlitzer pianos for about 5 years now. Mainly the 200 and 200A pianos. I've got a good grasp of their limitations and beneficial mods.

Sometimes I hear a funny interference specifically in the 200 models, where the reed-bar shielding is not as good, also this era of design featured the entire preamp/amp circuit on one PCB, as opposed to the later 200A series where the preamp was mounted directly to the reed bar. I always mod the older pianos with tin foil glued to the lid and grounded to chassis for a great improvement in hum reduction.

I have rebuilt the circuit on the piano in question and as always, I get bit of the odd interference. Until now it was always intermittent, sometimes it would play great for an hour. However, tonight I can't get it to go away at all. I say "interference" because if I pull the reed-bar connection from the board the amp output is virtually silent. This particular noise starts a few seconds after power-up. Regardless of when it starts, it always makes a "revving up" type sound. I was able to capture it tonight. Does anyone have any clues?

15 sec mp3 clip of the noise on startup:

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Edit - I've tried unplugging everything else in the room, removing my cell phone from the room, unplugging the modem. I've tried a ground lift and polarity reversal. The power supply is plugged into a new outlet, dedicated grounded line off a new electrical panel, properly wired, with nothing else on the circuit.

Last edited by cancon; 9th November 2015 at 11:02 PM.
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Old 10th November 2015, 09:28 PM   #2
Enzo is offline Enzo  United States
diyAudio Member
Join Date: Sep 2004
Location: Lansing, Michigan
haven't worked on one in years. Seems to me ther was some issue with the 150v on the bar that could cause noise. I am REALLY hazy, but maybe something like dirt accumulated causing some sort of leakage?

By the way, I have sets of tines in my drawer, and they are looking for a new home. if interested, send me a PM.
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Old 10th November 2015, 09:51 PM   #3
cancon is offline cancon  Canada
diyAudio Member
Join Date: Mar 2011
I've been messing with the piano in the last hour and I am in complete agreement that dirt is causing the issue. Light taps against the harp with a hammer made the noise go away entirely, it also brought on a world of reed alignment problems and much harsher noises!

The reedbar screws do work loose over the years, so I'm thinking that a simple removal, cleaning, alignment and screw tightening should make this piano happy once again.
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Old 11th November 2015, 03:05 AM   #4
Enzo is offline Enzo  United States
diyAudio Member
Join Date: Sep 2004
Location: Lansing, Michigan
That is reasonable. In guitar amps, a loose nut on a transformer mounting screw will make static noise.
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