User manual

T25 Tube Compressor API Select

1.0 Introduction

Welcome to the API Select line of premium tube-based audio processors and thank you for choosing

the T25 Tube Compressor. The T25 is a classic 2-channel, F.E.T. feedback-style compressor/limiter

with a Class-A tube output stage that utilizes a custom API transformer. Built with 12AT7WC and

12BH7 dual-triode vacuum tubes, the T25 represents the next step in API’s compression technology

and new vistas of tonal shaping while retaining the unmistakable API sound quality. The result is one

of the world’s best sounding tube compressors that’s capable of handling an infinite number of

production applications, including stereo operation. Carefully designed to deliver a wide range of

compression options, the T25 delivers warmth, clarity and punch, whether used for subtle adjustments

or heavy compression effects.

1.1 Features

• Field Effect Transistor (F.E.T.) based gain reduction circuit

• Audio circuit uses 12AT7WC and 12BH7, dual-triode vacuum tubes with custom

transformer output

• 11-step attack time switch

• 11-step release time switch

• 4 fixed ratios

• 31-step input/threshold control

• 31-step output/make-up gain control

• Detented controls for accurate recall

• Patented

THRUST

filter for low-frequency dependent side-chain control

• D-S feature provides high-frequency dependent side-chain control for de-essing

• Link switch for stereo operation

• 10-segment LED gain reduction meter

• LED peak indicator

• Vintage looking VU meters indicate output levels

• IN/out switch

• Full hard-wired relay bypass

• XLR and ¼” TRS input and output connections

The T25 Tube Compressor has several unique features that will allow you to tailor the sound of the

compression in many different directions.

The patented

THRUST

inserts a filter in front of the RMS detector that evens out the energy by lowering

the energy in the low frequencies and increasing the energy in the high frequencies, so each octave

has the same energy instead of each octave having half the energy as the one lower. This creates a

unique compression effect that still reduces the overall gain, but the sound is much more punchy and

the signal actually sounds much less compressed.

The D-S feature accentuates compression of high-frequency content (bell curve w/ 6kHz center) for

use as a vocal de-esser.