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The Fender Rhodes Electric Piano / Re: North Facing Magnets
« Last post by sean on Today at 12:44:23 AM »

That video is great!  That shows that the magnets pointing the opposing directions in neighboring pickups do indeed cause enough interaction to be heard.  So that should be corrected by flipping the magnets around so that they all align.

Drill a 3/8" hole in a lump of wood,  stick the pickup tip in the hole, and push the tip and magnet out from the back side.  Use a drill press, arbor, or a dull nail and hammer.  (The nail and a gentle tap works easiest for me.)  Later production pickups seem to have a bigger glob of obstinate glue in there.
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The direction of the winding is important, because we need the induced noise to be generated in a uniform direction across all the pickups (so that we can use the groups-of-threes front-to-back back-to-front method to cancel the noise).

In the discussion below, I am discussing only the current caused by EMI (Electro-Magnetic Interference or Radio waves: undesirable electric and magnetic fields).

Thanks to ├śrsted, Ampere, Faraday, Maxwell, the right hand rule, and the way that electrons like to move in a magnetic field, there is a pretty detailed understanding of what happens in a solenoid (coil of wire) when there is an incident magnetic field.  However, I can't find a satisfying writeup on the web.

See the diagrams at https://en.wikipedia.org/wiki/Solenoid.  The magnetic field causes the electrons to move in a circle around the core of the pickup, but we want those electrons to move in a predictable direction (they do, according to Faraday's law and the right hand rule).  In the diagram showing the magnetic field around the cross-section of a solenoid, the wires with a dot have current flowing OUT of the page toward your face; wires with an X have current flowing IN to the page.  The current is moving in circles around the magnetic field.

We want the current in the wire to move in a predictable direction, so we wrap all the pickup wires in a helix that is uniformly oriented with respect to the tip of the pickup, and also to the wire terminals.  (We do this by always pointing the pickup in the same direction when winding, turning the winder in the same direction every time, and always connecting the start/inner coils to the tail terminal, and the end/outer coils to the tip terminal.)  This way, current moving in a circle around the pickup core will eventually spiral around the helix and arrive at the end of the coil at one of the pickup terminals.

Imagine that at one instant, all the EMI noise is pushing electrons toward the tip of the pickup, we want to have this electron flow cancel itself out.  We do this with the way we connect the pickup terminals.  In the groups-of-threes series connection, half of the pickups have their terminals wired tip-toward-ground, half of the pickups have their terminals connected tail-toward-ground.  So the net current at the RCA jack is nothing.  EMI noise is cancelled.  Nice.

If there is a uniform magnetic field created by an ancient fluorescent light ballast, or a refrigerator compressor, or whatever; and that magnetic field wanders across our Rhodes pickup rail, the magnetic field will cause a current in all of the pickup coils.  This current will travel around the pickup coils headed for the same end of the pickups.  But since we have the pickups electrically connected in a way that this flow of electrons is opposed and cancelled by current from other pickups, we get no noise.  Then an instant later, when the offensive magnetic field points in the opposite direction (the other half of the cycle in the wave), the noise will travel toward the other end of the pickups - where it is again cancelled out.

Groups-of-sixes and criss-cross pickup rail wiring works the same way.

This noise-cancelling strategy is generally very effective, but it can be defeated if the magnetic field is not uniform across the whole harp (or a big enough region of the harp).  If the source of the magnetic field is particulary strong and is particularly close to the piano, then the magentic field can be non-uniform enough to be heard.  If you lay your cell phone on top of the piano, and the phone tries to excite the ringer or vibrator, you may hear the induced noise in the Rhodes output.  If you lay an un-shielded electronic device (maybe a synth, or a fluorescent sheet music light) on top of the piano, you may hear a buzz in the Rhodes output.

That's is the physics as I understand it.

Sean
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Parts, Service, Maintenance & Repairs / Re: Few keys sound problem
« Last post by Ben Bove on Yesterday at 04:56:09 PM »
Just to clarify - are you talking about the sound on attack, or the sound on release? 

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Yes, the round disc cap should be removed.
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The Fender Rhodes Electric Piano / Re: North Facing Magnets
« Last post by Jenzz on Yesterday at 10:14:18 AM »
Look at this vid from Chris at VV:

https://www.youtube.com/watch?v=MozJadTEcsY&t=261s

It shows the importance of having consistend magnet pole direction throughout the pickup rail...

Jenzz
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Parts, Service, Maintenance & Repairs / Re: Few keys sound problem
« Last post by rhodesjuzz on Yesterday at 08:29:25 AM »
I think it might be more than just the damper arms. Sometimes with mixed tines you can have a striking line issue. Try playing around with the harp (start with right side only) and notice what happens with the metal like sound. I had the same issue with different tines and I found a setting that improved the suspected tines without affecting the other tines or at least not too much.

I have found the era right tines that I still need to install....

Hope this helps

--Roy
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Parts, Service, Maintenance & Repairs / Re: Few keys sound problem
« Last post by tjh392 on Yesterday at 06:16:55 AM »
That is the sound of the damper felts "kissing" the tine when dampening. Try adjusting them by bending the damper arm up to give it a bit more force.

Only bend the arm just in front of where the bridal strap holds the damper.
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Parts, Service, Maintenance & Repairs / Few keys sound problem
« Last post by guvech on Yesterday at 04:33:27 AM »
Hi guys,
Can you help me with this issue? There is some sound like on metal. It's most of these three keys Eb,F and F#. The tone bar grommets  and springs were replaced (new). The strike line seems to be OK too. The escapement is good as well.
i made a video in you tube with the sound:
https://www.youtube.com/watch?v=-zr-OJpCjig
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Not sure why they jumped those two leads. They're connected by the trace and I can't see any obvious damage to the board in that area. Here's a photo for reference:



I agree on both of those solder joints, they need reflowing. Also worth posting an image of the pre-amp board too.



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The Fender Rhodes Electric Piano / Re: North Facing Magnets
« Last post by Oliver Sheen on Yesterday at 02:02:39 AM »
Thanks for that detailed reply, Sean. Can you explain again why the winding direction is important?
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Hey pianotuner steveo, what are your thoughts on the attached picture that seems to show a capacitor from the main power input to the chassis of the amp?  Could this be the "death cap" that you wish not to speak?

Dave
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