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My CP136 has a very large and solid transformer inside.

Switching power supplys where not used in quality audio devices for a long time, because they all where a strong source for interference.
Only in newer time it was possible to use them, because it was possible to rise the switching frequency to 100kHz and more, using modern semiconductors and coils.

But even today linear supplys with transformers are in use.
There is a physical phenomenon, named "magnetostriction" that causes every transformer to produce some hum, regardles how solid it is build. Normally this is not audible, but if the transformer has direct mechanical connection to a resonance board, wood or else, it can become audible.

Don't worry Stephen, it got a laugh at this end.

Cheers,
James
x

Thanks for all the feedback. It's a shame that you'll never notice this in a shop, but only once you got the piano and turn it on in the evening.

If you not mind me asking, how much did you pay for your HP 307?

Can you tell us where it's coming from? Thanks. It sounds like you've accepted it as a, errr,,, 'design' limitation? I can't hear any hum from my cheaper DP in a quiet room.

I know about a hum in Yamahas CVP509. Some customers hear it, others do not.
If a customer complains, then Yamaha sends a technician. He/she will cut a trace on the PCB and this will fix the problem.

That said, doesnt mean that it is a similar problem. It could be as simple as a loose screw at the transformer that has to be tightened.

If it disturbs you, ask the dealer, maybe he has technicians that know about it or ask at Rolands service.
If you are unsure about it, test if other people hear it.
/
Peter

Yes, other people hear it as well. The hum comes from the slits on the left and right side above the keyboard. I assume they are speakers? I will go to the dealer again once I have time to do so and see if the piano they have on display also hums. I didn't pay attention at all since in the shop it obviously is not dead silent like at home in the night.

@Mr Romance: I got a 305 and paid €2000 here in Vienna.

Yes, those two slits (at the top of the piano) are where two 5cm speakers are located (one on each side).

the power connector has no ground. so can the hum still be a ground loop? I am a total newbie when it comes to audio equipment, but I read that ground loops are the main source for hum in audio equipment.

Do you have anything else connected? PC, amp, headphone, etc.

No the piano is the only thing in the wall socket. I've also tried a different wall socket with no change.

From the manual:
Using the unit near power amplifiers (or other equipment containing large power transformers) may induce hum. To alleviate the problem, change the orientation of this unit; or move it farther away from the source of interference.

After this I'm out of ideas, other than it's a defect.

conclusion: I went to the dealer and looked at the unit on display. it hums as well. then I asked Roland tech support and they said that this is due to 50hz transformator hum and not a defect.

I also listened to all other digital pianos at the dealer (who had only another roland 201 and the rest were yamahas). none of them hums . anyway I guess I will just live with it. it's just a shame that roland made a really good digital piano and then put in such a bad sound system. I compared with e.g. the Yamaha 330 and the Hp 305 feels definitely more natural to me as a piano (this is the first digital I really play on, before I played on an upgright and a grand that my mom owns).

Still puzzled. Isn't the power supply connector into the HP305 DC?

For example with my DP there is an AC power adapter that plugs into the wall socket, but the output from that adapter is 12V DC which drives the DP. Unless it's poorly smoothed there shouldn't be that much 50/60Hz ripple getting into the audio system. Try a new adapter if that's the case.

Smaller DPs and keyboards have outboard power supplies, like yours.

Larger consoles have inboard supplies, like most other appliances. The HP305 has no adapter ... just an AC power cord.

That's right. The Power supply is internal.

Hmmm...bummer. Thanks for the info though. The HP305 was under my consideration, although slightly out of budget.

I went to my local dealer today, turned the volume full up on the HP305 there and could hear a hum. I did the same thing on an HP307 and no hum.

It's a pity and I think that for my use I have to strike it from my list. Maybe I'm just being too picky and the hum would go unnoticed amongst the other hummers in my home: fridge, sub-woofer, audio, surround sound, etc. Mainly just the fridge it's really loud.

spanishbuddha,

Would you ever play a digital piano at full volume, though?

In my opinion, at this volume level the instrument would be uncomfortably loud.

Cheers,
James
x

Hi KawaiJames

No not even my old ears would want to have the piano at full volume.

It's just that, as the OP said, at normal volume in the store you can't hear the hum, and I was looking for more proof that there really was one.

I have to say I am surprised at this on one of Roland's new DP's, and for the price being asked I would be disappointed to get it home and hear an annoying hum in the silence of a room. Sometimes I think we're picky about things that are perhaps quite unimportant, but I worked hard for my money :-)

I actually have exact the same hum in my piano, so perhaps it's a Roland thing... It's a 2005 Roland HP-7e. Just as being described here, the hum is discrete yet distinctive and since I noticed quite annoying too.

The hum originates from the inside somewhere on the top left, right where the power cord is plugged into the piano. I am very sure, reading here, that the topic-starter's hum is the same as what I am experiencing. Also the sound is NOT coming from any of the speakers, nor is it audible on the headphones, nor has the volume switch any influence on the presence or intensity of the hum.

I am btw living in Holland (The Netherlands, Europe) , we have 230V @ 50hz here, can that perhaps be of any influence?

Topic-starter, have you found a solution yet or a definitive answer to this?