What started years ago as a collaboration with another builder eventually resulted in me continuously refining the JCM800 preamp circuit. After designing version 2, I grew tired and started to ask myself what I wanted in a Marshall-style preamp. The first thing was starting to mod my own JCM800 but the added gain still wasn't where I wanted it to go. Soon later I worked with some 8100 builds but that wasn't it either. Following those experiments I set out to just work from scratch and this is the product of those experiments. With nods back to multiple 80s circuits while paving its own path, this is my answer to a high gain British preamp. This MIAB doesn't use any JFETs and instead uses a unique opamp gain staging topology unique to this design but you'll find the slightly modified tone stack to react similar to that of a 2204.
CONTROLS
Name Location Description
Level External Plenty of output to boost your signal or just dial in unity gain.
Gain External Adjusts the amount of preamp amplification. Cleaner sounder at lower gain settings, high gain settings will produce more sustain and distortion.
Treble External This control determines the amount of treble and makes your guitars tone brighter as it's turned up.
The tone network is highly interactive and, because of this, altering the setting of one control can change the way the other controls behave.
Mid External Crank this CW for a fuller more cutting mid tone. Turn it down (CCW) for a more aggressive scooped sound of classic thrash
Shifting away from the classic JCM mid control, I went with an anti-log pot to help with dialing in those more mid focused tones.
Bass External Controls the amount of low-end frequencies in your tone.
Presence External Adjusts the amount of boost or cut in the upper high frequency range.
Bypass LED Brightness Internal Adjust overall brightness of front LED.
Default setting at minimum (full CCW).
POWER - 9VDC ONLY - CENTER NEGATIVE (not included)
This product contains internal circuitry to increase the 9VDC supply to higher voltages for additional headroom.
This product contains THE overvoltage circuit for 9v input only.
CONSUMPTION 77mA
SWITCHING TRUE BYPASS Soft click (1.1KGf) mechanical 3PDT.
