Not a big effort -- a couple hours spread over a weekend, usually as I'm waiting for dinner to cook.

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Before I forget AGAIN: I was told that on the OS 21-bar 'harps, the buttons are
separate from the bars, allowing you to move a bar readily to any of the three rows, no matter whether it's major or minor or seventh. Anyone know about this??
Though I really like the "open" look of the ChromAharP 21 system, being able to more freely arrange my bars seems like a HUGE plus....
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Though I love the cachet of Oscar Schmidt autoharps, I managed to talk myself into a ChromAharP -- looks like this one:
https://reverb.com/item/3103726-rhythm-band-inc-28-button-chromaharp-trans-cherry-autoharpA boatload of skinny aluminum bars, cork dampers, & more buttons than a calculator.
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FWIW -- Yer D'ness, here's a half-decent OS 21-bar, a mere $145 delivered:
https://reverb.com/item/2769558-oscar-schmidt-autoharp-maple-wood-body...only half because it needs a new string set & some re-felting, but felt is
cheeeep -- $2/bar from AutoHarpWorks.com, or AutoharpStore.com has official US Music Corp strips at $2.90/foot. Opinions differ as to whether it's best to use little bits (as factory original) or just lay down a whole strip & notch it.
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A crafter friend tells me there might be a source for suitable pressed felt in all sorts of groovy colors. My older OS has a couple of bad bars (looks like a Pepsi-related accident

) so I maybe oughta field-test the stuff, right?