Hi,
I just recabled my setup, which contains an old hifi where the speaker connectors were broken so I soldered some cable with a Crocodile clip to the end (the speakers were correctly attached) , the Hifi was set to aux and I had the line in cable in my left hand while searching for anther cable with the right hand. Then I accidentally touched the middle contact of the line in cable with my right hand and a end of the speaker cable. Suddenly I heard a sine like wave which I could modulate (in pitch but almost not in volume) by applying more or less pressure to either of the both cable ends.
This is no problem for my as I hardly do this, but It really got me curious how this could happen. Usually to regulate the pitch of an oscillator circuit you have to change the Capacitance of a capacitor, but to my knowledge, by applying more or less pressure I only changed the connecting surface area and therefore the resistance of the feedback loop.
So any help in finding the nature of this (at least to me) strange phenomenon would be appreciated.
Thanks in advance,
JJ
Edit: I might add that the Hifi was not grounded (just two main connectors) and I (through the floor) was.
Very strange just hardware feedback loop.
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- KVRist
- 270 posts since 15 Jun, 2004 from Munic
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- KVRAF
- 16803 posts since 8 Mar, 2005 from Utrecht, Holland
The connection surface changes the resistance. Apart from capacitance this is also an ingredient of a RC circuit that changes the frequency. Both resistance and capacitance affect the frequency.
We are the KVR collective. Resistance is futile. You will be assimilated. 
My MusicCalc is served over https!!
My MusicCalc is served over https!!
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- KVRAF
- 12615 posts since 7 Dec, 2004
in fact, capacitance is almost never changed in audio frequency oscillators - only resistance is changed. the capacitors in the circuit are generally of a fixed value.
capacitance is often changed in high frequency oscillators into the VHF-UHF ranges and above. in the highest frequency circuits a diode's junction capacitance is used as it changes with changing voltage applied across the junction.
in oscillator circuits like the typical VCO or VCF, a current-path is modulated, generally using a OTA circuit. this is very close to changing resistance.
capacitance is often changed in high frequency oscillators into the VHF-UHF ranges and above. in the highest frequency circuits a diode's junction capacitance is used as it changes with changing voltage applied across the junction.
in oscillator circuits like the typical VCO or VCF, a current-path is modulated, generally using a OTA circuit. this is very close to changing resistance.