Casio CT-6000 mains hum - problem / question

[Helfried]

hello, I have a question about the Casio CT-6000, so to all owners of this keyboard here 🙂
My specimen is in good condition and was obviously rarely used, inside and outside everything looks like new. It works perfectly, however I notice a relatively strong mains hum from the speakers. The hum depends on the settings of the volume controls of each section, it is strongest when I turn up the "Rhythm" control. It also varies in strength with different sounds, so it is also affected by the different filters and thus is generated before - or everywhere.
I have already checked and measured the electrolytic capacitors in the power supply, they all have the specified capacitance (at least as accurate as can be reliably measured in their built in state) and look good.

So I think, it doesn't seem to be a problem with the power supply and its hum filtering. All connectors seem to be OK, too. 
Could it be that this hum is simply normal for this device?
And now I would be interested if someone can confirm this.
Then I could stop researching for any fault 🙂

 

What else I noticed, I a leaking of the drums with closed "Rhythm"-slider, and indeed "chirping".
Are maybe both effects related - or are both normal ?
These would be my questions.

If both also occur with other CT-6000, I would be appeased:-)

It also comes from the line outputs and from the headphone output (there it is particularly disturbing, since it is already very loud with completely closed volume control).

I'll attach an audio recording from the headphone output - first the basic hum , then drum leaking with the drum slider closed, some knob movement and some playing.

 

Thanks!
Helfried

Casio CT-6000 hum etc.

Edited January 23, 2023 by Helfried

[pianokeyjoe]

ground loop issue which is common on audio equipment, may be one of the issues. The hum, I mean, not the buzz. The drums leaking means the sliders need cleaning and the audio amp section may be acting up due to the grounding loop. I know this from my DOD flanger pedal which had the same thing happen.

[Helfried]

OK, thanks so far,  I think I'll give up researching it for now.

In the meantime I have a second CT-6000 here, also in very good condition and everything works. However, the noise (hum, crosstalk drums etc..)

are EXACTLY the same.

It seems now as if this is normal for this device - which I find surprising for an instrument from 1984,

I know other devices from this time and from earlier, which meet significantly higher "audiophile" standards.
But ok, if it is so, then it is so 🙂.

If someone here owns a CT-6000 , which sounds cleaner or absolutely free of such noise and hum, I would still be interested to know ....
Until then, all the best!

 

[pianokeyjoe]

Hello again. So you have another CT6000 with the same issue? So you can play the rhythms louder on this new unit? Same volume as the melody? Or is it also too low a volume like the first sound example CT6000? The hum is going to be a grounding issue. Chances are your electrical system in your house or at least in that room is without a ground(Earthing or earthing pin?). In the USA, if the Casio is 3 pins mains and the socket is only 2 pins with an adapter to fool the 3 pin plug into a 2 pin, that is part of the hum issue there. As for the rhythm section I would need a sound example with the rhythm section playing at normal volume as the melody to hear if it is the same as the first unit. If it IS, I suspect electrical mains issue! Ok in PUERTO RICO, my native land, the not so bright electricians, will wire up the poles of the wiring backwards AT THE ELECTRIC MAINS PANEL!! In other words, here in the USA and Puerto Rico the mains line wiring is BLACK is LIVE 125VAC, WHITE is NEUTRAL or 0V, and ground or Earthing, is bare wire or green and is ideally also 0V. IF the socket is wired backwards with the LIVE wire hooked up to the side that is supposed to be NEUTRAL?, then the electronic device will NOT work or will not act right. Case in point: I plugged my microwave into the socket in the kitchen in the house in Puerto Rico, I was renting, and the microwave would not work but I plug a light in and it works.. I found out after removing the faceplate that the socket was wired reversed. As such, the Microwave which is POLARIZED and requires the live wire to be live and the neutral to be neutral, also requires an earthing or grounding pin to be wired properly in order to function correctly and safely if at all. I reckon your Casio needs this same strict but sensible electrical connection as it is a 3 pin device and as such like a computer system, needs the same live to live, neutral to neutral earth to earth setup. Check your sockets wiring. It sounds stupid I know, but trust me, I had to fix my electronic devices not working right by doing the electrician's job for him, correctly.. and then? It worked! YAY!

[Helfried]

thank you
the two CT6000 behave in every respect exactly identical, sound exactly the same and also the hum is at the same level and identical. It is mains hum with predominantly the frequencies 50/150/250/350...Hz , so slightly distorted towards squarewave.

I've also run the keyboard in different rooms in our house to rule out such things (and they are on different phases of our house power supply), no difference. And here in my studio no other device (and that's a lot of synthesizers , effects units a lot of audio equipment ) makes any hum problems. Ground loops through audio wiring I have been able to successfully fix with several DI boxes and the AC power seems clean. Protective earth is also connected correctly (3pin connector) and there have never been any problems with that here.

My first guess was possibly a capacitor in the power supply of the device, but there I had already replaced some and it has not changed anything. It hums also already on a certain level, if the main volume control is on zero, so it is also already in the power amplifier - and can therefore only come over the power supply or from ground connection with voltage offset or similar.
A ground problem within a device, and that in two devices identical? 
Or actually insufficient filtering/smoothing of the different supply voltages?
Meanwhile I also have an oscilloscope here and may measure again - but my suspicion is that it may actually be a "property" of the synth.
I know some organs from the 70s that hummed similarly and more, my old Hammond tonewheel organ and the Leslie also hum, more than the Casio, high impedance tube amps also hum - but I don't really expect something like that from a mid 80s synth with ICs and transistors 🙂

 

[Helfried]

oh, one more thing, the rhythm is not too quiet - in my example I only show how much of the rhythm is still audible when the Rhythm knob is set to zero. 
That's not the sound the drums actually make, it's a kind of crosstalk from digital chirp noise.
And this happens even if the cable to the Rhythm Volume pot is disconnected, so this "chirp" comes into the power amp via other paths (ground, Power VC+, VB+, whatever).

 

[CYBERYOGI =CO=Windler]

If it hums, there may be bad electrolytic capacitors in the power supply. We in Germany have mains plugs those always fit in both direction. (The blue and the yellow wires can be 230VAC and 0V or vice versa. The ground wires is always yellow/green striped.)

[Helfried]

9 hours ago, CYBERYOGI =CO=Windler said:

If it hums, there may be bad electrolytic capacitors in the power supply. We in Germany have mains plugs those always fit in both direction. (The blue and the yellow wires can be 230VAC and 0V or vice versa. The ground wires is always yellow/green striped.)

Hi CO-Windler, as far as I know, you also have a CT-6000 and know it well. Does yours have no hum like my two specimen? see mp3 example above, clearly audible in the speakers, but also in the headphone and line-out, where I recorded it. 

[pianokeyjoe]

@HelfriedOk thankyou for clearing it all up. Hmm.. that is a strange thing indeed! I have one unit myself, and I never thought to explore the rhythm bleeding through at 0 volume thing and the hum? YES!! The CT6000,CT6500(see the comments on THAT keyboard in this forum), and some other models with CHORUS analog chip installed, DO hum! You are correct, the CT6000 and other MAINS LINE built in Casio keyboards of that era did hum! LOL! Sorry I was so slow to remember 😛 But yes, I even posted a question like yours but about the CT6500 which also smells of electronics when turned on. I reckon if we could back engineer these boards, we can find a way to sum up the voltages into a nice clean 12VDC to power up the instrument with and use an external Mains to 12VDC regulated power supply instead... So it seems, the mystery, as far as we know, is solved, YES, these built in power supply Casio keyboards DO hum and the rhythm bleeding in at 0 volume, may or may not be a after effect from the power amp inside and the mains power all mingling real nice and crunchy in there..

Edited March 29, 2023 by pianokeyjoe
corrections

[Helfried]

Ah , thank you very much, that is enlightening ! Now I have great certainty that nothing is defective in my devices, but quite simply all CT6000 (and maybe some other Casios with built-in power supply) have this noise. 
It's not that dramatic, but once you've got it into your head that there must be a defect, you want to fix it 😉
I think I can stop researching now.
Many thanks !

Edited March 29, 2023 by Helfried

[Helfried]

I don't think it's worth the effort to design a new power supply for these keyboards. It's certainly possible, but it's enough for me to know that there is no single problem with my device. With this knowledge I can live with the hum 🙂