LXH2 "Marshall" Simulating Preamp Schematic

Includes both preamp and speaker/cabinet simulator sections.

Do NOT connect this circuit to the speaker output jack on your amp. Serious damage can occur to both your amp and this circuit and can cause a fire hazard. This is a line level device. Use only with preamps, effects processors, and other line level equiptment. Line level refers to the output level of most mixers, preamps, and effects processors.

1. Connect all [peaks] MFB filters together in paralell where shown.
2. Connect all [dips] MFB filters together in paralell where shown.
3. Keep all leads as short as possible to prevent oscillations.
4. All power supply connections are not shown in this drawing.

In all MFB filters below, C represents C1 and C2.
MFB FILTER     320 HZ     800 HZ      1.2 KHZ     1.8 KHZ      2.5 KHZ

    R1                      270k          270k          180k            120k            330k
    R2                      4.3k            3.0k          2.2k              1.2k             5.1k
    R3                      110k          150k           82k               68k            180k
    R4                      12k              12k           12k               12k             11k
    C                      .022uF          .01uF      .01uF            .01uF         .0022uF

MFB FILTER     5 KHZ     8 KHZ      11 KHZ

    R1                      247k        390k           68k
    R2                      5.4k          4.4k          1.15k
    R3                      202k        270k          570k
    R4                      18k          16k             15k
    C                      .001uF      560pF       560pF


MFB FILTER     600 HZ     1.45 KHZ      2 KHZ     7 KHZ     9 KHZ

    R1                      220k           120k            330k         220k          56k
    R2                      6.8k            1.2k              1.5k            9k           8.2k
    R3                      120k           100k             180k        202k          39k
    R4                       11k             10k                22k          10k          5.6k
    C                       .01uF           .01uF          .0047uF    560pF     .001uF


1. All op-amps are TLO84.
2. The "cabinet" and "damping" circuitry in the lower portion of this schematic provides an adjustable resonant boost around 100 Hz for use with guitar speakers powered by high damping factor solid state amps. The total low frequency response is more like the resonant response of a sealed 4-12" guitar cabinet powered by a low damping factor amp such as a distorting tube amp.
3. For best results, all potentiometers should be audio taper except the 250K treble control which should be linear. For best results, the 10k "damping" control should be audio taper, using the "low" and wiper leads (left two leads if you view the front of the pot with the leads pointing down). This makes the resistance increase more slowly as you increase it, for best taper in damping. Counterclockwise rotation decreases damping (increases bass resonance). Otherwise, make this potentiometer linear.

marshprb.gif (7401 bytes)

celvint1.gif (27603 bytes)

greenb.gif (18452 bytes)

Copyright (C) 1997, 1998 LXH2.