white horse optical compressor

Overview

Technical

Demos

 

The White Horse is a clean optical compressor and a whole lot more. The BLEND control allows for blending the uncompressed signal for dynamics & sustain. The unique DRIVE control balances the compression between optical compression and dynamic mosfet drive. The BASS control can EQ higher compression settings to compensate for the perceived treble loss inherent in compression, but also tightens up the drive section for a more natural drive tone.

BLEND:

 

SUSTAIN:

 

LEVEL:

 

RESPONSE:

 

BASS:

 

 

DRIVE:

 

 

 

INTERNAL CONTROLS:

Blends uncompressed & compressed signals.

 

Adds gain/sustain to the compression/drive

 

Controls the output volume of the White Horse

 

Controls the speed of the optical compressor

 

Controls the bass response of the compression/drive section

 

Balances the compression section between a clean compressor (counterclockwise) and a dynamic mosfet overdrive (clockwise)

 

The blue trimpot on the main board affects the pre-gain, and therefore the output volume of the uncompressed side of the BLEND control. The other trimpot adjusts the brightness of the indicator LED.

Click the TECHNICAL tab for a more

"in-depth" analysis of each control

CHECK AVAILABILITY

DIMENSIONS:

 

 

POWER:

 

CURRENT DRAW:

 

INPUT IMPEDANCE:

Enclosure dimensions: 2.37"W x 4.37"L x 1.16"H  (60 x 111 x 29mm)

With knobs & jacks: 2.6"W x 4.4"L x 2.1"H  (66 x 111 x 53mm)

 

Industry-standard 2.1mm, negative-tip 9V to 15V power supply or 9V battery.

 

<30ma continuous, +30ma surge for 4ms during on/off switching

 

1.1M-ohms

Pre-gain & Bass

Compressor & Drive

Mix & Output

 

 

 

 

 

The pre-gain stage serves two purposes. First, it sets the pre-gain for the compressor/drive section, which affects the overall amount of compression available & the dynamic feel of the compressor. Second, it controls the volume of the dry (counterclockwise) side of the BLEND control.

 

 

 

 

 

 

 

 

 

 

 

The BASS control is a very simple passive high pass filter placed just before the compressor/drive stage. The cutoff frequency ranges from about 720Hz all the way down below 20Hz. This does not affect the dry signal path, just the compressor/drive signal path. When adding drive, it's often a good idea to cut pre-gain bass to keep the bottom end tight & punchy.

Pre-gain Stage

Bass EQ Stage

 

The compressor/drive stage uses a standard non-inverting op amp gain stage, where the gain is controlled by an optocoupler and/or mosfet transistors. The SUSTAIN control sets the overall maximum gain of this section. When the DRIVE control is counterclockwise, only the optocoupler controls the gain, yielding clean compression. When the DRIVE control is clockwise, the mosfet transistors have almost all the compression duty, yielding a smooth overdrive. In between, the gain is set by the interaction of the optocoupler & mosfet transistors, yielding a very dynamic compressor/drive that stacks well with other distortion pedals.

 

The range of the SUSTAIN control is way more than is necessary. We just added as much as the circuit could handle, but you don't need to use it all! The maximum amount of gain is over 60dB, which will take the smallest amount of noise & make it very loud!

 

 

The controller section converts the audio signal into voltage that drives the optocoupler. More signal = less resistance = less gain, and vice versa. The speed at which this controller responds to the attack & release of the signal is set by the RESPONSE control. Faster RESPONSE speeds yield a snappier compression, but also can lead to undesirable "pumping" at higher SUSTAIN settings.

 

In order to create a smooth transition when the compressor turns on, the compressor gain is reduced when the pedal turns off. When the pedal is turned on, the gain is increased at the rate set by the RESPONSE control until it reaches the regular compression level. This transition is smooth & brief, even at extreme SUSTAIN settings.

Comp/Drive Gain Stage

Controller Section

 

 

 

 

 

 

The mix stage allows you to blend the dry signal after the pre-gain stage and the compressed signal after the compression/drive stage. When using the clean optical compressor, try blending in some dry signal to preserve natural dynamics, while still adding sustain from the compressor. When using the drive circuit, try using more of the compressor/drive signal for a more natural drive tone.

 

 

 

 

 

 

 

 

 

The output stage offers a small amount of makeup gain (though the gain stages add plenty!), and a passive attenuator control to set the overall volume output.

Mix Stage

Output Stage