Need Help With Schematic for Amp

Discussion in 'The Projects Forum' started by bubbagump0, Aug 9, 2007.

  1. bubbagump0

    Thread Starter Member

    Jul 10, 2007
    26
    0
    I am drawing up a schematic for a small 1W stereo amplifier, based off of another schematic (Im doing a few minor changes.) I am fairly new at drawing schematics, and I came across a symbol that I didn't understand. It is an arrow going from a pin of an IC to a resistor. I included the link for the schematic, and attached a picture of what the symbol looks like. I am using ExpressSCH. If anyone can tell me what the symbol means and how to replicate it with ExpressSCH I would be very thankful.
    http://kitsrus.com/pdf/k87.pdf
     
  2. spar59

    Active Member

    Aug 4, 2007
    51
    0
    If you are referring to the arrows at P1A and P1B these resistors are potentiometers - variable resistors the arrow is the sliding contact.

    Steve
     
  3. spar59

    Active Member

    Aug 4, 2007
    51
    0
    In this instance they are the volume controls the 10k means they are 10,000 ohms measured between the 2 non-sliding contact connections. The log means the characteristic of the resistance track that the slider moves along is not linear but logarithmic - so when an input voltage is applied via IN1 for example the voltage into pin 7 when the potentiometer is at half travel is not 1/2 the applied voltage but a lot less - this particular chacteristic is to match the response of our ears which become less sensitive at high sound (power) levels and hence on the final 50% of travel a lot more than 50% more output is required to make it sound twice as load.

    Steve.
     
  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    As already indicated it is a potentiometer or variable resistor. spar59 has described the function of such a component nicely.

    hgmjr
     
  5. bubbagump0

    Thread Starter Member

    Jul 10, 2007
    26
    0
    Thanks, but what I really want to do is replace the potentiometer with two 10K resistors. Once I do that, I don't know how to or if I should connect pin 7 and 6 to the two 10K resistors.
     
  6. spar59

    Active Member

    Aug 4, 2007
    51
    0
    In that case the first resistor is connected between the +ve side of C2 and ground and pin 7 is also connected to the +VE side of C2.

    Similarly the second resistor is connected between the +ve side of C3 and ground and pin 6 is also connected to the +VE side of C3.

    Steve.
     
  7. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
    12
    In my opinion you should replace the pot(s) with two 5K resistors for each pot (in series from C2 to GND & C3 to GND), which then add up properly to equal the 10K pot(s) being replaced.

    The input to the IC, such as IN1+, would be from the center of the two resistors between C2 & GND. This also has the effect, provided the resistors are of equal value and irrespective of their actual value, of dividing the input signal in half.
     
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