LXH2 "Marshall" simulating preamp circuit Last updated
02-04-06

Latest updates:

I have made a few updates and revisions to this circuit.

I have provided for a seperate output level control for the "non cabinet"
output. The cabinet simulator input level control is provoded to prevent
clipping of any of the subsequent filter circuitry. This control can be a
trimpot used only for initial setup and calibration of this circuit. Even though
the "non cabinet" output includes the "chunk" and "damping" circuitry, it is not
considered to be part of the cabinet simulator circuit. This is because I have
found that when using the preamp output into a guitar amp, the cabinet simulator
was largely redundant, as it simulates the frequency response of a guitar
speaker in a cabinet. However, in most cases, I found that the "chunk" and
"damping" sections are a welcome addition to the preamp output, providing a more
chunky bottom end.

Recently I have been informed of several devices currently on the market
that claim to do something similar to the amp and speaker simulators described
here. I have not heard them and will not pass judgement on them.

I have also added a switch in the diode circuit to facilitate a degree of
asymmetry in the waveform. This is a matter of what what suits your ear. I
originally designed this circuit to get as close to the real thing as possible
without getting into digital signal processing. However, you may want to
experiment with using different diodes in different combinations to suit your
taste.

Includes both preamp and speaker/cabinet simulator sections.

The cabinet simulator frequency response sonically duplicates the response of
this graph.

The control called "Chunk" is also referred here as "Cabinet" or "low
frequency boost"

!!!!! IMPORTANT WARNING !!!!!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.

FILTER DATA TABLE:

Notes:

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.

MFB FILTERS FOR PEAKS

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 FILTERS FOR DIPS

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

TECHNICAL NOTES:

1. All op-amps are TLO84.

2. The "chunk" 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.

Click on here for
Disclaimers and copyright info!

Copyright (C) 1997-2006 LXH2. All copyrights are strictly enforced. You are
granted licence to build one for yourself only.