Janelectro
01-16-2005, 08:53 AM
I'm going to start a series of articles about passive circuitries.
In this part I will explain how the common elements of passive instrument circuits work.
Potentiometers:
http://img.photobucket.com/albums/v421/Janelectro/pot.jpg
On the picture we see a sketch of a potentiometer.
The ring we see has two contacts (1 and 3), one on each end. It consists of conductive material with a rather high resistance (normally coal)
Contact 2 is connected to a turnable piece of metall which slides on the ring and is turned by dialing the knob of the pot (shown in the picture in red, yellow and green at different positions: full open (red), randomly in between (yellow) and fully closed (green). There are only three connectors in the picture to explain different settings.
Volume potentiometer of a precision as example for the function of a potentiometer:
In a precision with only one pickup the in phase/hot wire from the pickup is connected to contact 1, conntact 2 is soldered to a wire that leads to the tone pot. Contact 3 is grounded.
On the position of the red connector contact 1 is directly connected to contact 2 so the signal is running through the potentiometer with practically no resistance (=losses).
On the yellow connector position the signal has to make some distance on the highly resistant ring, thus the signal is already weakened (=less loud)when reaching contact 2. As the ring has a much higher resistance than the connector, it won't go past the connector's position on the ring.
Green connector position: the signal is weakened by the full ring and then goes direclty to the ground wire: the signal dies.
Shortly said, by turning down the potentiometer you increase the value of the resistance of the pot thus weakening the output.
There are two kinds of potentiometers:
linear pots: on linear pots the value of the resistance is proportional to the turning travel of the knob. That means if the knob is turned open 1/3, the output of the pot is 1/3 of the original signal. Linear potentiometers have a B stamped on the back of their housing.
logarithmic pots: Due to the human ear lacking the ability to hear a linear swell of the output as linear volume increase, logarithmic pots have become the standart on musical instuments. Because the ring doesn't have one value of resistance on its full lengt it the resistance now varies in two ways, thus sounding more linear to the human ear. they have an A stamped on the back.
Potentiometers are used to control volume and tone in passive circuits.
There are also some special versions of them:
The stacked/concentric pot which has practically two different pots one one axis that are nor connected electrically nor manipulating each other, each has it own control knob. built in for example in the Fender '62 reissue Jazz Basses.
The balance pot consists of two potentiometers controlled by the same knob.
Push/pull or push/push potentiometers have a feature a dpdt switch dialed by the vertical movement of the knob.
In this part I will explain how the common elements of passive instrument circuits work.
Potentiometers:
http://img.photobucket.com/albums/v421/Janelectro/pot.jpg
On the picture we see a sketch of a potentiometer.
The ring we see has two contacts (1 and 3), one on each end. It consists of conductive material with a rather high resistance (normally coal)
Contact 2 is connected to a turnable piece of metall which slides on the ring and is turned by dialing the knob of the pot (shown in the picture in red, yellow and green at different positions: full open (red), randomly in between (yellow) and fully closed (green). There are only three connectors in the picture to explain different settings.
Volume potentiometer of a precision as example for the function of a potentiometer:
In a precision with only one pickup the in phase/hot wire from the pickup is connected to contact 1, conntact 2 is soldered to a wire that leads to the tone pot. Contact 3 is grounded.
On the position of the red connector contact 1 is directly connected to contact 2 so the signal is running through the potentiometer with practically no resistance (=losses).
On the yellow connector position the signal has to make some distance on the highly resistant ring, thus the signal is already weakened (=less loud)when reaching contact 2. As the ring has a much higher resistance than the connector, it won't go past the connector's position on the ring.
Green connector position: the signal is weakened by the full ring and then goes direclty to the ground wire: the signal dies.
Shortly said, by turning down the potentiometer you increase the value of the resistance of the pot thus weakening the output.
There are two kinds of potentiometers:
linear pots: on linear pots the value of the resistance is proportional to the turning travel of the knob. That means if the knob is turned open 1/3, the output of the pot is 1/3 of the original signal. Linear potentiometers have a B stamped on the back of their housing.
logarithmic pots: Due to the human ear lacking the ability to hear a linear swell of the output as linear volume increase, logarithmic pots have become the standart on musical instuments. Because the ring doesn't have one value of resistance on its full lengt it the resistance now varies in two ways, thus sounding more linear to the human ear. they have an A stamped on the back.
Potentiometers are used to control volume and tone in passive circuits.
There are also some special versions of them:
The stacked/concentric pot which has practically two different pots one one axis that are nor connected electrically nor manipulating each other, each has it own control knob. built in for example in the Fender '62 reissue Jazz Basses.
The balance pot consists of two potentiometers controlled by the same knob.
Push/pull or push/push potentiometers have a feature a dpdt switch dialed by the vertical movement of the knob.