Underglow Preamp

Description

The Underglow Preamp is a Class A discrete all-analog transistor circuit inspired by the vintage electronic design of classic British studio consoles such as the EMI REDD 47, but adapted for electric guitar. Utilizing a transformer-coupled intermediary stage and two independent negative feedback paths, the circuit transitions from transparent amplification to harmonically dense console fuzz. The input signal can be attenuated and/or low passed similar to vintage consoles for extra control. The dedicated GAIN foot switch is also configurable via a three-way toggle that controls the centre frequency of the overdriven transistors and transformer, yielding super heavy distortion tones to octave-like fuzz effects that cut through the mix with odd order harmonics (responsible for a key part of the "console fuzz" sound) and plenty of mid-range frequency content. The fuzz focus of this circuit and the interaction of the dual feedback paths are what truly set it apart from other console-style guitar pedals.

• SMOOTHEN:

  At its most counter clockwise position, this control makes the signal overdriven and distorted and saturates the transformer. As the control is rolled clockwise, the feedback loops start to take over the signal and the peaks are grabbed and attenuated naturally and gradually more aggressively, resulting in a continuous warm and smooth signal amplification. It feels sort of like a ghetto op-amp "laziness" control. This is a very pure preamp at cleaner low gain settings (i.e., the least lazy setting) and very heavy at high gain (i.e., most lazy). The overall design of this internal stage functions as a discrete variable 2 transistor gain block that is only allowed to correct itself (i.e., get cleaner) at higher SMOOTHEN settings, resulting in a beautiful punchy weight and compression.

• HPF (High Pass Filter):

  This three way toggle lets the user cut bass and also attenuate the input signal which has the effect of increasing or decreasing the impact of the SMOOTHEN control and extra GAIN mode.

• LPF (Low Pass Filter):

  This is a pre-amplified low pass that shapes the input signal for the main gain stages. Darker settings give tones that sound great for jazz, and may also be used for cutting or emphasizing the octave effect of the extra GAIN mode when engaged.

• GAIN HPF:

  Active only in GAIN mode, this switch selects the frequency response of the overdriven console fuzz sound. Sometimes overdriven consoles can sound thin and weak or brittle (e.g., the Beatles' sound engineer famously had to run two mic preamps into each other to get enough "body" for the "Revolution" guitar tone), but by lowering the cutoff frequency of this filter, the Underglow Preamp maintains weight and depth and adds lots of odd order harmonics to cut through the mix.

• MASTER:

  Controls the output volume of the pedal.

Input Z: ~300K
Output Z: ~5K
Gain:~+25dB (at max settings)
Current Draw: ~15mA

True Bypass
Requires a centre negative 9V power supply
Dimensions: 4.7 in x 3.7 in x 1.34 in
(119 mm x 94 mm x 34 mm)
No battery option. If user wants to use a battery, they must buy an external adaptor.