PC-2A

Photo Optical Tube Compressor

Effectrode's PC-2A is an exceptionally musical and smooth sounding compressor pedal. This is achieved by using the same thermionic technology found in highend, vintage studio compressors. The signal path is 100% analogue, class A, based on a vintage Sylvania, U.S.A. made tube and a special design Silonex photo-resistive attenuator. This attenuator has essentially instantaneous gain reduction with no waveform or harmonic distortion for musical, unobtrusive and transparent compression.

The PC-2A is designed for flexibility , simplicity and outstanding sound quality. Audiophile grade components and silver solder are used throughout the circuit with precision metal-film resistors for lownoise and stability , polyester coupling capacitors for their ability to resolve fine signal detail and ground plane layout. The result is a compressor that exhibits a level of purity and natural tone not found in solid state VCA (voltage controlled amplifier) or variable bias pedals.

Additionally , the photocell exhibits a memory effect where the time it takes to recover depends on light duration and intensity. In use this results in a faster release time for short signal bursts and a slower release when the signal remains continuously above the compression threshold. This is analogous to how the human ear recovers from high sound pressure levels and is the reason why the PC-2A sounds so natural and transparent.

Side-Chain Circuit the PC-2A is based on a ‘feedback’ control circuit like the LA-2A studio compressor. With this circuit topology the signal that is used to drive the side-chain is affected by the gain-reduced signal. This type of topology seems to be preferred over ‘feed-forward’ for its more musical characteristics.

There is also some pre-emphasis on the side-chain similar to an “A” weighted filter curve. This curve characteristic approximates the response of the human ear. Here it works to minimize ‘pumping’ normally associated when a compressor is processing low-frequency material

Footswitch utilizes quiet true bypass switching to reduce ‘pops’ or ‘thump’ when engaging the pedal and ensure there is no loss of guitar tone when the pedal is bypassed.

Internal Knee and Attack Trimpots These are factory set, however can be adjusted by the user to tailor the compression characteristic to suit instruments that are challenging to amplify or record such as bass guitars with active high output pickups or acoustic instruments fitted with piezo pickups.

Peak Reduction knob controls both the threshold and the amount of compression. This knob should be set so that the PC-2A exhibits the desired amount of compression or sustain. A good starting point is at the 9 o’clock position, where the subtle compression enhances note detail and creates a fuller, warmer tone. Rotating this knob further clockwise progressively levels out playing dynamics to compress notes that are too loud and boosting quieter notes. This is particularly appropriate for country and funk-style licks.

Gain knob should be used to match the relative levels of bypassed and affected signals. It also provides the capability to boost your guitar signal for solos and even overdrive your amp. To use the PC2A as a tube booster and push your amp into smooth overdrive, simply turn the ‘Peak Reduction’ knob fully anti-clockwise.

Limit/Compress toggle switch alters the transfer characteristic of the compressor input/output curve, enabling PC-2A to operate as a compressor and limiter. When in the ‘up’ position (compressor mode) the curve is shallower, presenting a low compression ratio which sounds subjectively more transparent. In the ‘down’ position (limiter mode) the curve is steeper resulting in a higher compression ratio, creating a fatter, more squashed sound.

The larger the input signal, the lower the gain, resulting in a reduction of dynamic range or compression of the signal. Conversely , an expander increases the dynamic range of a signal.

Gain Reduction Circuit. The photo-resistive attenuator is the heart of the compressor and determines the attack and release characteristics. The photo-resistive device is specially selected for fast attack of less than 1ms. This is important for achieving transparent operation during gain reduction and minimizing undesirable artifacts such as ‘pumping’. The electrical performance of the attenuator is a close match to the electroluminescent (EL) panel used in the Teletronix LA-2A studio compressor. The EL panel was developed in the early 1960s to eliminate attack speed shortcomings of neon and filament photo-optical attenuators. The release time of the compressor is entirely determined by the photocell in the attenuator. The cell has a desirable two-stage decay characteristic where it releases within 40 to 80 ms to approximately half its off resistance when light is absent. The remainder of the release then takes place over as much as several seconds.