Parts:
P1,P2__________220K Linear Potentiometers (or 250K) P3______________10K Linear Potentiometer P4_______________1M Log. Potentiometer R1_______________1M 1/4W Resistor R2,R3___________68K 1/4W Resistors R4,R5,R6,R7,R8_100K 1/4W Resistors C1,C7___________47µF 25V Electrolytic Capacitors C2_____________220pF 63V Ceramic or Polystyrene Capacitor (or 250pF) C3_____________100nF 63V Polyester Capacitor C4______________47nF 63V Polyester Capacitor C5_____________100µF 35-50V Electrolytic Capacitor C6_____________120pF 63V Ceramic or Polystyrene Capacitor C8______________47nF 63V Polyester Capacitor Q1,Q2,Q3,Q4__2N3819 General-purpose N-Channel FETs J1,J2_________6.3mm Mono Jack sockets SW1____________SPST Toggle or Slide Switch
Circuit modifications:
Marshall Tone Controls Parts:
P2_______________1M Linear Potentiometer P3______________22K Linear Potentiometer (or 25K) R6______________33K 1/4W Resistor C2_____________470pF 63V Ceramic or Polystyrene Capacitor (or 500pF) C3,C4___________22nF 63V Polyester Capacitors
Output buffer Parts:
R9______________10K 1/4W Resistor R10____________100K 1/4W Resistor C9_______________4µ7 63V Electrolytic Capacitor Q5___________2N3819 General-purpose N-Channel FET
Notes:
- A very interesting discussion about Fender and Marshall Tone Controls, showing differences, frequency response graphics and much more can be found at Guitar Amplifier Basics
- Please note that all impedances involved in this circuit are very high (valve like, typically 1M) compared to common transistor circuitry: therefore, to avoid noise and hum pick-up, all connections must be kept very short and if input and output jacks and the pots are not directly mounted on a printed circuit board, all wiring to these parts must be done carefully by means of screened cable.
- In their more recent amplifier types, like '59 Bassman and Blues De Ville/Deluxe, Fender designers have slightly modified the Tone Controls parts values, thus obtaining a sort of compromise between their older models and Marshall Tone Controls. The changes were as follows: C2 and P1 (Treble Control) were left unchanged; C3 was still a 100nF capacitor but P2 value (Bass Control) was raised to 1M (log.) like the Marshall preamp. C4 and P3 (Mid Control) were changed to 22nF and 22K (or 25K) respectively: i.e. the same values and connections of the Marshall preamp modification as shown in the above schematics (left side).
Technical data
- Input Sensitivity @ 1KHz:
- 6mV RMS (Tone Controls set to center position, Volume control set to max.)
- Maximum undistorted output with 6mV RMS input:
- 3V RMS @ 18V supply
- 4V RMS @ 24V supply
- 5V RMS @ 30V supply
Total harmonic distortion @ 1KHz: <0.3% at 1V RMS output
Total current drawing at all supply voltages (18 to 30V): 8.5mA
Source : http://www.redcircuits.com/Page120.htm
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