Harp ringing in 200As

[David68]

I've got two 200As in the shop at the moment, both from 1977. With one, when you hit a staccato chord, you hear a bit of a metallic ring after the note that appears to be coming from the harp itself. You hear it even if you just tap the harp from the side. It doesn't appear related to damper tension, nor is it from the shield. The other 200A produces the same sound, but it's not as noticeable.

Is there any way to treat this issue on the one that has more "ring" after a note?

[Tim Hodges]

I had this recently, whilst it might not be the same issue as yours I found that a reed was too close to the pickup so whilst it had clearance to ring, it was just close enough when hit by the hammer to then induce ringing from the pickup.

To test it I pressed the pickup (whilst the piano was off) when play each note. It seems to happen more on the treble side as the pickup spacing width is smaller that the bass.

[pianotuner steveo]

One other quick test- turn down the trim pit on the pcb and see if that changes anything. I've heard some pianos get feedback if this is turned up all the way- happened more in the treble than the bass

[David68]

Thanks for the replies. I think I've figured out the difference between the two. The 200A with less harp noise has a Retrolinear amp I installed. The one with more harp noise has its original reed bar preamp PCB, and I think that the reed bar preamp is itself slightly microphonic -- and screwed directly to the harp. The Retrolinear amp does not have active components mounted to the harp and is thus more isolated.

[pianotuner steveo]

It could be bad caps, a bad ground connection, or a cold solder joint

[David68]

I rebuilt most of the reed bar preamp to lower noise, including resistors, transistors, and electrolytic capacitors. All soldering was carefully done and double-checked because the goal was to get rid of an intermittent crackle, which was successful.

The 0.022uF film cap and two 100pF ceramics are still original. I guess I can tap on them and see what happens. I know that Class 2 ceramic caps can be microphonic.

[Electrickey]

Just a thought, try to adjust the left screw that holds the metal music rack and see if the metallic overtone disappears. If it's the same problem I have, I find just turning the screw to tighten the lid onto the chassis makes the errant sound go away. Check if your rubber grommets on those screws are full and pliable.