I have build a pre-amplifier and it is very quiet, no hum or noise even with my ears close to the speakers.....but...
When I touch the volume control a buzzing sound comes in both speakers....and only when volume is turned up.....not in minimum.....
It is not very loud, but it puzzels me and is a little annoing.....
When I touch the volume control a buzzing sound comes in both speakers....and only when volume is turned up.....not in minimum.....
It is not very loud, but it puzzels me and is a little annoing.....
This is the 50hz field of power being picked up by your body and injected into the preamps inputs.
Is your case grounded to mains safety ground? If not, you should do this. If it is, you should have your house wiring checked in case you have a bad safety ground connection
Does the input stage of your preamp circuit include filtering?
Is your case grounded to mains safety ground? If not, you should do this. If it is, you should have your house wiring checked in case you have a bad safety ground connection
Does the input stage of your preamp circuit include filtering?
it's about time we did the humanitarian thing and moved the whole population out of Denmark. 
The rules are very different here.
We have to ensure that all exposed conductive parts are connected to safety earth.
If you at least connect all the exposed conductive parts to audio ground then some measure of interference attenuation will accrue.
The metal case around the pot is probably electrically connected to the adjusting knob and to the front panel. Earthing the panel AND the pot case AND the adjusting knob will probably solve the problem.
The pot track and it's three/six terminals should be isolated from the pot casing.
BTW,
how do you make a 220Vac system safe to the user if there is normally no safety earth?
The rules are very different here.
We have to ensure that all exposed conductive parts are connected to safety earth.
If you at least connect all the exposed conductive parts to audio ground then some measure of interference attenuation will accrue.
The metal case around the pot is probably electrically connected to the adjusting knob and to the front panel. Earthing the panel AND the pot case AND the adjusting knob will probably solve the problem.
The pot track and it's three/six terminals should be isolated from the pot casing.
BTW,
how do you make a 220Vac system safe to the user if there is normally no safety earth?
Don't worry about. If there is a "Residual Current Operated Circuit Breaker" in the mains electric distribution panel - box of your house, in practice there is no need for earthing the ground cable into the earth. But we may say goodbye to the shielding of our audio metal boxes. A practical solution maybe it is the connection of the mains earthing cable in a metal water-pipe of our house provided that this water-pipe extended down to earth.AndrewT said:
Fotios
An RCD/RCBO/GFCI/GCI/whatever is NO substitute for a safety earth at all! After all, the current has got to flow out of phase in the live wire with respect to neutral for it to trip... and where's it gonna flow if not to a safety ground ? Oh, thats right.. through the poor user.
Over here, safety earthing on anything metal is MANDATORY... this includes all plumbing, and gas fittings...
They should, at the very least, employ a TN-C-S style system.. if I lived in .dk i would definitely be fitting my own earth rod at the very least!
http://en.wikipedia.org/wiki/Earthing_system
Over here, safety earthing on anything metal is MANDATORY... this includes all plumbing, and gas fittings...
They should, at the very least, employ a TN-C-S style system.. if I lived in .dk i would definitely be fitting my own earth rod at the very least!
http://en.wikipedia.org/wiki/Earthing_system
Shielding and earthing aren't the same thing. You can build a perfectly quiet audio system with proper shielding (and connection of the frame and shaft of the pot, to the shield), but no earthing. Is the preamp completely enclosed in metal, and if you measure from the pot shaft to the case, do you have a connection? I've seen test equipment where they actually put a bronze spring tab against extended pot shafts to insure they remain grounded when turning. Given your earthing situation, I'd be sure and use plastic knobs for everything!
Jaycee your remarks are generally correct. I don't know the conditions of the mains electric distribution network in UK or in Denmark but in Greece the neutral conductor it is connected to the earth rod into the wattmeter of the electric company in each house. This method called neutral-earthing in Greece and exists only for economical reasons in conductors. Thus the earth conductor considered as individual from the neutral conductor only after the RCCB. And this is true, you can check it with an ohmmeter before the RCCB and after the RCCB. For this reason the human protection from shock it is far most better by the use of RCCB. But no one serious person (including myself, because except electronic i am also electrician engineer) recommends the cutting of the earth conductor from the earth rod! I remembered in the past, when i worked as sound engineer in a live music hall, that i maked a seperate earthing with 3 rods in triangle arangement and in this i connected all of the sound equipment earths to isolate them from the noisy dimmer packs etc. And much more tricks to avoid the damned RFI.jaycee said:
Regards
Fotios
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