Wurlitzer 200A Grounding hum stops when removing IEC ground

[btiems]

So I've been having a hum issue with my Wurlitzer that seems to be grounding related. So I removed the IEC ground which is screwed into the amplifier board, and it seems to have fixed it, but I feel like this is not a long term solution.

Should this be placed somewhere else to actually ground the power? or should I just leave it removed.

[Jenzz]

Hi :-)

Is the Piano connected to any other gear / Amp?

There sometimes connections that will form an internal ground loop. Avoid the connection on the right end between the chassis plate and the harp. This connection is already established by the shields of the wire harenss going to the preamp PCB on the harp.

Jenzz

[btiems]

Hey!

It's connected to amp as it's mostly used for recording and the speakers are unplugged.

the ground is right next to the speaker connection(middle screw, wire with black tape)was thinking of attaching it one of the leg mounts as that seems pretty ground, and doesn't cause any hum

Bobby

[Jenzz]

Hi :-)

What happens when the amp is disconnected?

On a Wurlitzer, signal ground is connected to earth. On most guitar amps, its the same. As a result, both grounds are connected via the earth wire.

If you plug the Wurlitzer into the amp via audio cable, the shield inside the cable will close the ground loop, causing probably hum.


Jenzz

[btiems]

When the amp is Disconnected it doesn't Hum, the Speakers don't seem to have any hum at all.

I also can have the Wurli unplugged with the amp on and as soon as I plug it in with the IEC it just hums away.


Bobby

[velo-hobo]

Ground loop hum is common with solid state Wurlitzers, in my experience. The intensity can vary depending on the particular scenario - what it's plugged into (and what else is plugged into that as well that shares a ground plane) single vs. multiple mains supply circuits for various gear involved, etc.

Doing some troubleshooting as discussed in thread here is good to sort out, for example if there are particular scenarios that are worse than others. Recently I was getting a lot of noise on a new recording setup, and it turns out the source of noise was a mixer I was using to submix the drums mics going to another mixer feeding a tape machine. I had to put a ground lift on that piece of gear to quiet things down, but it required making changes one-at-a-time to narrow in on the noise source and solution.

With Wurlitzers, I typically just deal with it in live settings, and if I need a lower noise floor for a recording, I use a ground lift plug. From a standpoint purely accounting for electrical safety, this is not recommended. However, my personal assessment is that there aren't really that many grounded/conductive bits on a Wurlitzer 200/200A that are exposed to the player, other than the sustain pedal. It's not quite the same risk, IMO, as a microphone or guitar strings that come into direct contact with skin.

Caveat: I am not an electrical engineer nor licensed electrician, but I do work with electrical safety design and assessment as part of my job. Do not follow my example without first carrying out your own assessment and decision-making process.

[Jenzz]

Hi :-)

Safest way is to leave the Piano and amp grounded and use a Line-iso-box for the audio connection. This way, both grounds keep sepatated.  Palmer 'Wupper' or Radial 'StageBug' will do.


Jenzz

[btiems]

Hey Jenzz

I'm trying to remove that :/ . The DI box did work with a ground lift but I want it to function without. I'm thinking of attaching the ground to the leg socket.

There it makes no hum, and seems to a good place to ground?

Bobby