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<!-- #thumb --> <p>Controlling the volume level in your stereo system is an obvious and important function. *The element used to turn the level up and down is important as well.</p>
<p>If you look inside a preamplifier you’d discover it’s one of the simpler devices in your chain. *Most consist of only three blocks in the signal path: an input selector, a volume/balance control and a gain stage.</p>
<p>The input selector is nothing more than a switch that connects the input you wish to listen to into the signal chain. *This switch can be a mechanical one requiring you to turn the knob to choose or a series of relays that act like switches. *Relays are simple switches that use a small electro magnet to open and close their switch contacts. *This allows designers to send a tiny electrical signal to control the relay, rather than relying on mechanical force to move the switch from one position to another. *There are even electronic versions of switches that use a transistor as the switch (usually a MOSFET).</p>
<p>Once selected, the source you want to listen to is connected to the preamplifier’s volume control; the subject of this post. *Most preamplifiers use what is known as a pot to control the volume. *”Pot” is short for potentiometer and is a simple device consisting of a resistive element and a contact point (known as a wiper). *The resistive element sounds fancy but it too is simple and made from a material that resists electricity like carbon or certain types of metals that don’t conduct too well; also known as a resistor (because it resists electricity). *The contact point is a simple piece of good conducting metal that touches the resistive element (like silver). *When you turn the pot up or down, you are moving the contact point (wiper) along the resistive element in a wiping motion.</p>
<p><a href="http://www.pstracks.com/wp-content/uploads/2013/10/potentiometer1.jpg"><img class="alignleft size-medium wp-image-12201" alt="potentiometer1 300x205 Stepped attenuators" src="http://www.pstracks.com/wp-content/uploads/2013/10/potentiometer1-300x205.jpg" width="300" height="205" title="Stepped attenuators" /></a></p>
<p>The sound quality of this device is dependent entirely on the quality of the resistive element and the contact material of the wiper, once implemented properly. *A good pot can be extremely expensive.</p>
<p>If you look closely at the picture you’ll note that the wiper is dividing the resistive element in two. *In the example I show, A is a smaller area than B as divided by the wiper. *This means that A has a smaller resistor value than B. *If we were to actually measure these values we’d see that A is probably 25% of the whole and B the remaining 75%. *If the pot is a 10k value (10,000 Ohms) then we could say it can be modeled with two resistors, the A resistor measuring 2,500 Ohms and the B resistor measuring 7,500 Ohms (the two resistors will always add up to the 10,000 value of the pot).</p>
<p>I mentioned the sonic performance of this device depends on the quality of that resistive element and the contact material of the wiper. *There’s no doubt the best resistive elements can be found in individual resistors and the best contact materials can be found on expensive switches – none of which is true of potentiometers. *Thus, if we decide to use discrete resistors and a quality switch to select those resistors, instead of a pot, we would have a better sounding volume control. *This arrangement is known as a stepped attenuator.</p>
<p><a href="http://www.pstracks.com/wp-content/uploads/2013/10/Stepped-attenuator.jpg"><img class="alignleft size-medium wp-image-12202" alt="Stepped attenuator 300x163 Stepped attenuators" src="http://www.pstracks.com/wp-content/uploads/2013/10/Stepped-attenuator-300x163.jpg" width="300" height="163" title="Stepped attenuators" /></a></p>
<p>You can see in the picture such a device. *The switch is nothing more than a series of contacts and, as you can see, there are four sets of resistors: two to make up the A and B combinations of our pot for one channel and another set for the other.</p>
<p>The advantages of a stepped attenuator are the possibility of better sound because of the parts quality. *The downside of this arrangement is the volume is controlled in a series of fixed steps and you may or may not like the step level.</p>
<p>There are pots that can come close to the performance of a stepped attenuator, but rarely do they.</p>
<p>Most high end preamps of today use an electronic version of the stepped attenuator, replacing the mechanical contacts of the pictured switch with either relays or electronic relays.</p>
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[Source: http://www.pstracks.com/pauls-posts/stepped-attenuators/12199/]
<p>If you look inside a preamplifier you’d discover it’s one of the simpler devices in your chain. *Most consist of only three blocks in the signal path: an input selector, a volume/balance control and a gain stage.</p>
<p>The input selector is nothing more than a switch that connects the input you wish to listen to into the signal chain. *This switch can be a mechanical one requiring you to turn the knob to choose or a series of relays that act like switches. *Relays are simple switches that use a small electro magnet to open and close their switch contacts. *This allows designers to send a tiny electrical signal to control the relay, rather than relying on mechanical force to move the switch from one position to another. *There are even electronic versions of switches that use a transistor as the switch (usually a MOSFET).</p>
<p>Once selected, the source you want to listen to is connected to the preamplifier’s volume control; the subject of this post. *Most preamplifiers use what is known as a pot to control the volume. *”Pot” is short for potentiometer and is a simple device consisting of a resistive element and a contact point (known as a wiper). *The resistive element sounds fancy but it too is simple and made from a material that resists electricity like carbon or certain types of metals that don’t conduct too well; also known as a resistor (because it resists electricity). *The contact point is a simple piece of good conducting metal that touches the resistive element (like silver). *When you turn the pot up or down, you are moving the contact point (wiper) along the resistive element in a wiping motion.</p>
<p><a href="http://www.pstracks.com/wp-content/uploads/2013/10/potentiometer1.jpg"><img class="alignleft size-medium wp-image-12201" alt="potentiometer1 300x205 Stepped attenuators" src="http://www.pstracks.com/wp-content/uploads/2013/10/potentiometer1-300x205.jpg" width="300" height="205" title="Stepped attenuators" /></a></p>
<p>The sound quality of this device is dependent entirely on the quality of the resistive element and the contact material of the wiper, once implemented properly. *A good pot can be extremely expensive.</p>
<p>If you look closely at the picture you’ll note that the wiper is dividing the resistive element in two. *In the example I show, A is a smaller area than B as divided by the wiper. *This means that A has a smaller resistor value than B. *If we were to actually measure these values we’d see that A is probably 25% of the whole and B the remaining 75%. *If the pot is a 10k value (10,000 Ohms) then we could say it can be modeled with two resistors, the A resistor measuring 2,500 Ohms and the B resistor measuring 7,500 Ohms (the two resistors will always add up to the 10,000 value of the pot).</p>
<p>I mentioned the sonic performance of this device depends on the quality of that resistive element and the contact material of the wiper. *There’s no doubt the best resistive elements can be found in individual resistors and the best contact materials can be found on expensive switches – none of which is true of potentiometers. *Thus, if we decide to use discrete resistors and a quality switch to select those resistors, instead of a pot, we would have a better sounding volume control. *This arrangement is known as a stepped attenuator.</p>
<p><a href="http://www.pstracks.com/wp-content/uploads/2013/10/Stepped-attenuator.jpg"><img class="alignleft size-medium wp-image-12202" alt="Stepped attenuator 300x163 Stepped attenuators" src="http://www.pstracks.com/wp-content/uploads/2013/10/Stepped-attenuator-300x163.jpg" width="300" height="163" title="Stepped attenuators" /></a></p>
<p>You can see in the picture such a device. *The switch is nothing more than a series of contacts and, as you can see, there are four sets of resistors: two to make up the A and B combinations of our pot for one channel and another set for the other.</p>
<p>The advantages of a stepped attenuator are the possibility of better sound because of the parts quality. *The downside of this arrangement is the volume is controlled in a series of fixed steps and you may or may not like the step level.</p>
<p>There are pots that can come close to the performance of a stepped attenuator, but rarely do they.</p>
<p>Most high end preamps of today use an electronic version of the stepped attenuator, replacing the mechanical contacts of the pictured switch with either relays or electronic relays.</p>
<center><a href="http://www.pstracks.com/pauls-posts/stepped-attenuators/12199/emailpopup/" onclick="email_popup(this.href); return false;" title="Forward to a friend and help us engage more readers" rel="nofollow"><img class="WP-EmailIcon" src="http://www.pstracks.com/wp-content/plugins/wp-email/images/email.gif" alt="email Stepped attenuators" title="Stepped attenuators" /></a>*<a href="http://www.pstracks.com/pauls-posts/stepped-attenuators/12199/emailpopup/" onclick="email_popup(this.href); return false;" title="Forward to a friend and help us engage more readers" rel="nofollow">Forward to a friend and help us engage more readers</a></center><br /><!-- // MAILCHIMP SUBSCRIBE CODE --><center><a href="http://eepurl.com/eSzBY">Get new and fresh stories like this each morning by joining the folks reading Paul's Posts. Click here </a></center>
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[Source: http://www.pstracks.com/pauls-posts/stepped-attenuators/12199/]