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Hi, I'm new to digital pianos since I've only played acoustic pianos in the past. Now I got myself a HP 305 and am quite happy with it.

But I noticed that when it's quiet in the room in the evening that the piano when turned on is humming. Basically when you turn it on it starts to emit a silent hum. When playing it's obviously not audible because of the piano sound itself, but when not played there is definitely a hum.

Is this normal for a digital piano or might this be a defect?

My Technics PR604 used to do that. It was SOOO loud to me, I had to use headphones all the time, although no one else ever seemed to be able to notice it. I hated it (though loved the Technics itself). Just getting back into DPs (have been out for a few years), so don't know your instrument - has it got an LCD screen? It could be the screen emitting that noise.

How's the house wiring? could be the outlet's not properly grounded..

Hmmm... I do not have this problem on an HP-307 that I have.

Regards

Does the level of the hum change when you change the volume, or is it constant?

Had this with my Kawai CP136. Finally I found, it was not the piano, it was the piano lamp that I had on top of it.
If it has a transformer it can make noise also when switched off.

Peter

I had the same problem with my CLP330. But the hum was heard only when setting volume to max (which is too loud to play in room).

The hum is constant independent of the volume setting. Really odd, couldn't hear it in the store obviously since there it's never 100% quiet. Also tried plugging it into the wall socket as the sole device without a multiplug - still humming. Any 305 owner who can comment on this?

Similar question, can you still hear it with headphones plugged in - from across the room with headphones off (your ears), and also in the headphones? So the question is it coming from the sound system or somewhere else?

I think the Rolands hum because they don't know the words...

The hum is there when the headphones are plugged in, but it's not audible in the headphones (the piano itself is humming independent of headphones plugged in or not). It is not audible across the room (it's not that loud). Basically it fades afer 3 metres.

After some research I think it is transformator hum which is 100hz since here in Austria we have 50hz AC. Also it sounds exactly like this (http://www.youtube.com/watch?v=4Ufa4bXViA4). Unfortunately it seems that this a physical phenomenon, so I assume all digital pianos should have this problem more or less except if the manufacturer somehow isolates the transformator.

Any hum should be at a level that is un-detectable by human hearing - in other words you should never hear it underany condidtion.

Somehow noise from the AC main power line is getting into the piano and being amplified. Actaully it takes a bit of enginerring skill to design an audio system that does not hum. You might notice that cheap, low cost audio equipment will hum. The piano shouldn't. Either the unit is defective, something wriog inside the power supply or yu have a BIG source of noise in your house, one strong enough to get past all the tricks the engineers use to keep it out.

One way to diagnose this is to turn off everything else in the house. And I mean everytrhing, TVs lights and even unplug every wall transformer, cell phone charger Note that to turn some many devices (TVs, stereos, refrigerators) off you must unplug them.

If that does not solve the hum then it is something inside the piano.

Typically transformers are "varnished" After they are made they are placed in vacuum to remove the air from between the coils of wire then dunked in varnish then baked. The goal is to make them silent and not vibrate. What you've got is either a defective transformers or a cheaply made one. It should not make any noise. Yes isolating it by mounting it on rubber might help but they should not vibrate.

Many manufacturers do isolate the transformaer. My Yamaha DP uses an external transformer that connects to the piano with a long DC power cable.

So you only hear it when the piano is actually turned on, correct?

Is the power connector two conductor (as it shows in the HP-307 US owner's manual) or three conductor (w/ ground)?

Quite right. If a nearby noise source cannot be identified, then I'm guess the piano is defective. If so, let it be Roland's warranty issue rather that your own headache. Get it fixed.

As for transformers ... do these pianos even have them anymore. Transformers are so 1950's. Most equipment these days use switching power supplies. No hum. (A very high pitch squeal, maybe. A dog might hear it. But no hum at all.)

Oh, I was wrong. That's not hum from CLP330. It was rather "white noise".

Do you think this could be to do with reliability and cost? For example, I find that the new electronic (switching) ballasts for fluorescent lighting don't seem to last as long as the less expensive magnetic ballasts.

I can't speak about that kind of equipment. But for consumer electronics ... the use of switching power supplies cuts the size and weight (by eliminating the transformer), and it improves efficiency.

With a regular transformer-based linear power supply, about 5% of the device's total power consumption gets wasted as heat in the power transformer. That energy loss is largely eliminated when using a switching power supply.

All power supplies have transformers. The switching supplies use smaller transformers working at higher frequency but still it's a transformer

Most high end audio equipment still uses linear power supplies. Most of the cheap wall wort supplies are linear too.