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Headphone output low-level hum
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KJandKT
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Joined: 04 Feb 2013
Posts: 80

PostPosted: Wed Apr 17, 2013 12:28 am    Post subject: Headphone output low-level hum Reply with quote

Does anybody have a good pair of closed-back headphones in a quiet room that they can check something...?

No matter what position the volume is in, there is a low-level hum/noise that I can hear coming from the headphones. Does anyone else have that problem with their keyboard? I checked it both with Sony 7520's and AKG's.

Also, I have heard this on two PA600's. I want to see if this is possibly a quality control issue or defect in this model. My Motif XS and Kawai digital piano have absolutely no noise from the headphone output.


Thanks and God bless
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charlie67
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Joined: 19 Aug 2007
Posts: 180
Location: Bristol uk

PostPosted: Wed Apr 17, 2013 2:07 am    Post subject: Reply with quote

Very silent except at full volume. Even then it is difficult to hear. but there is a small sound. It is not a hum, more like the sound of a slight breeze. Like a shush. I can only hear it by twiddling the volume knob a few times and concentrating.
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Thoraldus
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Joined: 28 Nov 2010
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Location: Rocky Mountains - SE IDaho

PostPosted: Wed Apr 17, 2013 7:13 am    Post subject: Reply with quote

This is normal. See this ... http://en.wikipedia.org/wiki/Noise_floor
_________________
”It’s easy to play any musical instrument: all you have to do is touch the right key at the right time and the instrument will play itself.”

Johann Sebastian Bach

----------------------------------------------
Rick Stirling - Retired Electrical Engineer - Erstwhile Photographer
Korg Kronos2, Casio MZ-X500, PA600, AKAI MPD32, M-Audio Oxygen 25, ZOOM H6, Cakewalk Sonar
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KJandKT
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Joined: 04 Feb 2013
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PostPosted: Wed Apr 17, 2013 12:08 pm    Post subject: Reply with quote

Thoraldus,

I can appreciate a noise floor but this is more like the sound that you would get from unbalanced cable hum. Like I mentioned...same 2 pairs of headphones....0 hum from the Motif XS or Kawai...doesn't sound normal at all.

Thanks and God bless
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Thoraldus
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Joined: 28 Nov 2010
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Location: Rocky Mountains - SE IDaho

PostPosted: Wed Apr 17, 2013 3:34 pm    Post subject: Reply with quote

KJandKT wrote:
Thoraldus,

I can appreciate a noise floor but this is more like the sound that you would get from unbalanced cable hum. Like I mentioned...same 2 pairs of headphones....0 hum from the Motif XS or Kawai...doesn't sound normal at all.

Thanks and God bless


What exactly is connected to your keyboard? You might have a ground loop.
_________________
”It’s easy to play any musical instrument: all you have to do is touch the right key at the right time and the instrument will play itself.”

Johann Sebastian Bach

----------------------------------------------
Rick Stirling - Retired Electrical Engineer - Erstwhile Photographer
Korg Kronos2, Casio MZ-X500, PA600, AKAI MPD32, M-Audio Oxygen 25, ZOOM H6, Cakewalk Sonar
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KJandKT
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Joined: 04 Feb 2013
Posts: 80

PostPosted: Wed Apr 17, 2013 5:20 pm    Post subject: Reply with quote

I thought about that...nothing elase is connected. It is just plugged into the wall. I also tried another plug. Also as I mentioned I don't have this issue with the Motif or Kawai. Of course those have grounded plugs. Could there be any issue because the Korg is only two-prong (without grounding)? Anyway to test/fix that if it is?

Also the hum does not occur out the left/right outs.

Thanks and Blessings...
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Thoraldus
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Joined: 28 Nov 2010
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Location: Rocky Mountains - SE IDaho

PostPosted: Thu Apr 18, 2013 2:21 am    Post subject: Reply with quote

Any chance you could record this 'noise'? Then we could do a Fourier analysis and determine the frequency components. This would tell us whether it's power line or digital noise.
_________________
”It’s easy to play any musical instrument: all you have to do is touch the right key at the right time and the instrument will play itself.”

Johann Sebastian Bach

----------------------------------------------
Rick Stirling - Retired Electrical Engineer - Erstwhile Photographer
Korg Kronos2, Casio MZ-X500, PA600, AKAI MPD32, M-Audio Oxygen 25, ZOOM H6, Cakewalk Sonar
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KJandKT
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Joined: 04 Feb 2013
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PostPosted: Fri Apr 19, 2013 5:47 pm    Post subject: Reply with quote

Thoraldus,
I will try to figure out something. I have my recording equipment packed away but might be able to put together something. Can you do that test even if the level is really low or do I need to increase the gain of it in a DAW?

Thanks and God bless
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Thoraldus
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Joined: 28 Nov 2010
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Location: Rocky Mountains - SE IDaho

PostPosted: Fri Apr 19, 2013 6:11 pm    Post subject: Reply with quote

KJandKT wrote:
Thoraldus,
I will try to figure out something. I have my recording equipment packed away but might be able to put together something. Can you do that test even if the level is really low or do I need to increase the gain of it in a DAW?

Thanks and God bless


Try recording through the MIC input vs LINE input.
_________________
”It’s easy to play any musical instrument: all you have to do is touch the right key at the right time and the instrument will play itself.”

Johann Sebastian Bach

----------------------------------------------
Rick Stirling - Retired Electrical Engineer - Erstwhile Photographer
Korg Kronos2, Casio MZ-X500, PA600, AKAI MPD32, M-Audio Oxygen 25, ZOOM H6, Cakewalk Sonar
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KJandKT
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Joined: 04 Feb 2013
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PostPosted: Sat Jun 29, 2013 8:21 pm    Post subject: Reply with quote

Thoraldus...sorry it took me so long to send this. I had no way of recording stuff easily (studio is down). I used a quarter inch cable out the headphone output of the Pa-600 and put it into the left input of the Yamaha Motif XS and recorded it (that's why you'll only hear the sound from the left).

I do not believe it is a ground loop or my headphones. To test this, I took the left and right outputs of the Korg and put them into my Motif XS. I then put the headphones into the Motif XS to listen to the left/right of the Korg. It was crystal clean (minus of course some expected low-level noise if you turn the gain up to high). My headphones are Sony 7520's.

Thanks!

(Please see the private message that I sent to you with the link to listen to it).

Thanks!
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Thoraldus
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Location: Rocky Mountains - SE IDaho

PostPosted: Sun Jun 30, 2013 12:13 am    Post subject: Reply with quote

I did an analysis and it's all digital noise. There are no AC line hum components I could identify. The largest spike is at 748HZ at -60db ~F#5.
_________________
”It’s easy to play any musical instrument: all you have to do is touch the right key at the right time and the instrument will play itself.”

Johann Sebastian Bach

----------------------------------------------
Rick Stirling - Retired Electrical Engineer - Erstwhile Photographer
Korg Kronos2, Casio MZ-X500, PA600, AKAI MPD32, M-Audio Oxygen 25, ZOOM H6, Cakewalk Sonar
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KJandKT
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Joined: 04 Feb 2013
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PostPosted: Sun Jun 30, 2013 12:45 am    Post subject: Reply with quote

Hmmm...can you explain to me what that analysis might mean? I don't know enough about the analysis you made to understand what is happening. When I play through my AKG 240 headphones I don't hear it. When I play through my Sony 7520's I can hear it (when no music is playing) and it is enough to be disconcerting for me. The Sony's are so much richer sounding so I like to use them (plus they're closed). Also that noise is there regardless of how high the volume is. So if I want to play the keyboard softly it interferes with the sound. Do you know what might be causing it?

Thanks so much for taking the time to analyze it Smile

God bless
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Thoraldus
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Joined: 28 Nov 2010
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Location: Rocky Mountains - SE IDaho

PostPosted: Sun Jun 30, 2013 1:15 am    Post subject: Reply with quote

KJandKT wrote:
Hmmm...can you explain to me what that analysis might mean? I don't know enough about the analysis you made to understand what is happening. When I play through my AKG 240 headphones I don't hear it. When I play through my Sony 7520's I can hear it (when no music is playing) and it is enough to be disconcerting for me. The Sony's are so much richer sounding so I like to use them (plus they're closed). Also that noise is there regardless of how high the volume is. So if I want to play the keyboard softly it interferes with the sound. Do you know what might be causing it?

Thanks so much for taking the time to analyze it Smile

God bless


Sure. There are some possibilities here.

1. Digital noise is being coupled to the power supply circuitry. Noise on the power leads to an audio amplifier can appear at the output.
2. Digital noise is being coupled electromagnetically between circuit traces in the keyboard.

My guess it is #2 as noise coupled by #1 would probably show up on both left and right channels.

You can fix #1 by liberally using some very low ESR decoupling capacitors between power and ground all over the digital circuit cards.

Fixing #2 is a bit more difficult, requiring analysis of the circuit card layout.

See ... http://en.wikipedia.org/wiki/Decoupling_capacitor
_________________
”It’s easy to play any musical instrument: all you have to do is touch the right key at the right time and the instrument will play itself.”

Johann Sebastian Bach

----------------------------------------------
Rick Stirling - Retired Electrical Engineer - Erstwhile Photographer
Korg Kronos2, Casio MZ-X500, PA600, AKAI MPD32, M-Audio Oxygen 25, ZOOM H6, Cakewalk Sonar
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KJandKT
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Joined: 04 Feb 2013
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PostPosted: Sun Jun 30, 2013 3:04 am    Post subject: Reply with quote

so, since I have had the exact same issue w 2 of theae (Sweetwater sent me a new one because of this problem) do you think it could be a desin flaw¿
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Thoraldus
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Joined: 28 Nov 2010
Posts: 2060
Location: Rocky Mountains - SE IDaho

PostPosted: Sun Jun 30, 2013 3:38 am    Post subject: Reply with quote

KJandKT wrote:
so, since I have had the exact same issue w 2 of theae (Sweetwater sent me a new one because of this problem) do you think it could be a desin flaw¿


At -60db I wouldn't call it a flaw, just an issue. What is the impedance of the headphones that you can hear the noise in? Korg recommends 50 ohm headphones with the PA600
_________________
”It’s easy to play any musical instrument: all you have to do is touch the right key at the right time and the instrument will play itself.”

Johann Sebastian Bach

----------------------------------------------
Rick Stirling - Retired Electrical Engineer - Erstwhile Photographer
Korg Kronos2, Casio MZ-X500, PA600, AKAI MPD32, M-Audio Oxygen 25, ZOOM H6, Cakewalk Sonar
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