Grid stopper resistors - which value?

Discussion in 'Amp Tech Center' started by BigDaddy23, Jun 11, 2019.

  1. BigDaddy23

    BigDaddy23 Tele-Meister

    Jan 4, 2019
    Hey all,

    I'm interested in why we choose particular grid stopper resistor values. You see a pair of 68k resistors commonly used in Fender style amps (1 for each input jack). I've seen various other values in use such as 33k in single and paired inputs, 56k and so on.

    What difference does this make to the tone of the amp and how do we arrive at selecting a particular value? What do you do if there is a single hi input in the amp design?

    I need to do some more reading on this but thought I would put it out to you blokes who have 'the knowledge! '
  2. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    The value of those input resistors control the strength of the input signal. Take that Fender approach. When you are plugged into input #1 of two inputs, the resistance is 34k since that situation has those two 68K resistors in parallel. When you are in input #2, therefor is a single resistor in the circuit for a 68K resistance to the guitar’s signal....and there is a 6db cut compared to the #1 input.
    Looking at a few Fender schematics, we can see a few different approaches than the ‘typical’ 68K resistances. The Pro Sonic uses 47k’s there. The Pro Jr, which has only one input, uses a input, eh?

    And....there are other concerns....
    robrob likes this.
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