General tech questions

What Power Supply do I need?

1

This is the reading on the back of the piece of gear.

2

I bought a power supply online that was suppose to be for this piece of gear that is no longer manufactured... and it causes a TON of hum

3

Have you tried finding the owners manual on line? Just because it's 12v and fits, doesn't mean it's right. The one you show above supplies 2000mA which may or may not be enough, for your piece of equipment. I think you have to have at least the minimum requirement and not sure how much of too much, is too much. If you catch what I mean.

4

this is what the manual says in the "make use of the jacks" section

6

Is this a Casio, Korg, or Yamaha keyboard? The 12V tip-positive setup is a clue that it's some type of keyboard, and those three brands have a history of using tip-positive power adapter jacks. Can you plug in headphones and verify that the hum is actually coming from the instrument itself, and not the amp?

And last, are you running it into any type of effects unit or other outboard unit before sending the signal to the amp? If so, you probably have a ground loop issue.

7

Is this a Casio, Korg, or Yamaha keyboard? The 12V tip-positive setup is a clue that it's some type of keyboard, and those three brands have a history of using tip-positive power adapter jacks. Can you plug in headphones and verify that the hum is actually coming from the instrument itself, and not the amp?

And last, are you running it into any type of effects unit or other outboard unit before sending the signal to the amp? If so, you probably have a ground loop issue.

– Tartan Phantom

Yup it is a yamaha Portasound pss160.

I run out of the keyboard into an allen and heath mixer that has a variety of things hooked up to. None of the other gear gives me ground loop issues and are all plugged into the same Furman power strip. no hum with everything else but as soon as I plug in the yamaha (even when it is not powered on) whole room starts to hum.

Mixer is going into my Audio interface and out of my monitors at the moment.

8

In that case , I'd look at the very last line of the power supply label picured in post #2 above.

"Made In China"

Although country of origin isn't specifically the problem, cheap components and insufficient shielding may be. The fact that it causes hum before you even power on the keyboard is indicative of a grounding issue. Try unplugging everything else from the mixer, and just plugging in the keyboard. Then try other scenarios, such as with an amp, etc until you can trace it down.

If you are plugging the keyboard 1/4" out directly into the mixer, try using a direct box (with a ground lift switch) first to convert the output to low impedance, then use an XLR cable to connect the D/I to the channel input. Then, use the ground lift switch on the D/I box to see if it fixes the issue.

9

Well, you've got the voltage and polarity right, and 2000mA is more than enough power. I'd suspect the low rent power supply doesn't have enough shielding or filtering. Remember, most power supplies deliver pulsating rectified DC, and lack filter caps. Try using batteries and see if your keyboard hums then. If it's OK, then the issue is the power supply.

10

What type of noise? You might need a transformer power supply rather than a switching type supply. The fact that it will run on any source from 100 volts to 240 volts indicates that it's not a transformer type.

11

What type of noise? You might need a transformer power supply rather than a switching type supply. The fact that it will run on any source from 100 volts to 240 volts indicates that it's not a transformer type.

– Billy Zoom

Excellent point, Billy-- I missed the source voltage clue.

12

Somewhere in my shop, I have a box of NOS Yamaha PA3B power supplies. If I can find them, you can have one for the cost of shipping. I'm not promising anything though, I've been in this building for 20 years.

13

Have you tried finding the owners manual on line? Just because it's 12v and fits, doesn't mean it's right. The one you show above supplies 2000mA which may or may not be enough, for your piece of equipment. I think you have to have at least the minimum requirement and not sure how much of too much, is too much. If you catch what I mean.

– Suprdave

No experience with keyboards but with pedals it's usually too much mA's that causes hum.


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