EM Theremin - Headphone noise

Hi,

I just built my second EM theremin and ive got a strange problem.

When i connect it to my mixer -> monitor loudspeakers it works just fine but when i connect a pair of headphones I get some strange buzzing noise in the signal.

No when i connect to ground of my mixer to the ground of the headphones the noise is away.

It seems that the mixer is is connected to the same power line as the wallwart plug and so they have a common ground or something...

Do you have an idea how to get rid of this problem? if it is a groundloop problem what can i do?

regards,

Flo

The wall plug transformer has normally no grounding. Thus the theremin (which needs to be grounded) is normally grounded via the audio cable's shield and the amplifier. If you connect only a headphone directly to the theremin without connecting the latter to a grounded device, you will have problems like buzz, distortion, ghost tones etc.

thanks for your quick answer.

then it is not my fault. it is just strange that it sounds like  headphones will work in the pdf about the em theremin.

and that ive never seen anything saying that there is a problem.

regards,

Flo

The noise in your headphones is also a symptom of a (IMO) more important problem..

Without being grounded, the theremin will not behave in the same way as when it is grounded.. In particular, I believe the linearity will change, probably hugely.

Even when playing through 'phones, make sure there is some ground connection - If not connected to a grounded amplifier or whatever, Connect a wire to the ground (screen) on a jack plug, and wire this to ground, even if you do nothing else.

Fred.

Okay,

arent there any wallwart transformers or power supply solutions with a third contact for real ground

can it be that the grounding via audio cable is not as good for the theremins performance as another option to ground the machine?

"can it be that the grounding via audio cable is not as good for the theremins performance as another option to ground the machine?" - Flub

Yes, IMO it can be.. As in, its always IMO best to have independent centralised grounding for all audio equipment.. But this is a complete subject on its own.

Back in the days of real Hi-Fi, all quality seperates had a ground terminal for this purpose..

These days one needs to hack a ground connection by having a ground wire coming from the audio plug - Chop off the moulded mains plug on your PSU and replace this with a plug where one has access to the ground connection, then run the ground lead to this..

Or, If you know what you are doing (or if you have a wall wart and cannot chop then plug off) , get a quality extention strip, open it up and insert some banana sockets into it wired to the ground bus... You can then plug banana plugs into this ground bus.. Or you can go straigt to the mains plug and carefully add a ground wire here..

Warning! - If you are not absolutely sure you know what you are doing.. As in, ABSOLUTELY - There is no question, and you understand every word fully and know this will be easy for you and you have no possibility of making an error.. Dont mess with mains!!  If you wire it up wrong, if you connect Live or even Neutral to your ground output, it could do damage and could even be fatal!

If  setting up a "studio", I would get inside all the equipment and put banana sockets in them connected to their ground, and this way have pluggable leads to facilitate grounding ..

But its a lot of effort - For the theremin, I believe the effort is worth while - For most other gear, possibly not.

Fred.

Funny how things crop up! A few weeks back I was playing with the grounding issue of mini amps (battery powered) and the loss of the grounding issue with these. I found a banana plug fits well into a yellow ring terminal end as a cheap removable receptacle!

I just took a saw and cut the 2 pole wallwart plugs away then i wired the cable of a 3 pole plug into the plastic housing of the transformator.

The safety earth pole of the plug is connected to the transformers output which later is connected to earth in my circuit.

Thank you for your advice,

FLo

" I found a banana plug fits well into a yellow ring terminal" - Chris

That is one tasty looking banana !  - Nice 'n ripe  'n  yellow!   ;-)

" I found a banana plug fits well into a yellow ring terminal" - Chris

That is one tasty looking banana !  - Nice 'n ripe  'n  yellow!   ;-)

And it's a European Union approved straight banana too!!!