API: Select T25 Tube Compressor

API consoles, 500 Series modules, and their underlying technologies have been a staple of professional recording studios for over five decades. In 2021, API unveiled a new sub-brand called API Select, introducing an extended product range, including tube-based gear and guitar pedals. Make no mistake; this new gear maintains the same build quality and sonic integrity as all of API’s gear – this is not “budget API.” I auditioned the API Select T25 tube compressor, which marries a 2-channel feed-back style FET compressor to a Class A tube output stage.

The rounded VU meters and visible glowing tubes may be a surprising look from API, and the updated style of the API Select range is likely to elicit strong reactions from die-hard fans of the brand, but the knobs and blue faceplate are unmistakably API. The T25 weighs in at approximately 14 pounds, thanks to its beefy toroidal power transformer and linear power supply. The unit is well made, with a combination of high-quality through-hole and surface-mounted components, and the circuit board of this 2-channel unit takes up the entire interior. With its Electro-Harmonix 12AT7WC and 12BH7 tubes operating on nearly 300 volts, this unit will run warm, so I would advise leaving an empty rack space above it.

The T25 works as two independent mono compressors or as a stereo-linked unit. The transformerless inputs can be fed via XLR or TRS connectors, and the transformer-balanced outputs show up on parallel-wired XLR and TRS jacks. Power is supplied via a standard IEC power cable. This FET compressor will seem familiar to anyone who has used the API 525 or Universal Audio 1176, while it also provides API’s D-S (high frequency-dependent sidechain control for de-essing) and THRUST® (frequency-dependent sidechain) circuitry. You could reasonably equate the T25 to a 2-channel 1176 with the output stage of a Universal Audio LA-2A and the enhanced features of an API 2500 [Tape Op #52].

Each channel provides controls for IN/THRESH (input level/threshold), OUT/MAKE-UP (output level/make-up gain), Attack, Release, and Ratio. Attack, Release, and Ratio are selectable switches for easy repeatability. The IN/THRESH and OUT/MAKE-UP knobs have 31-step detented positions but can be finessed for values in-between the detents. In typical FET fashion, attack times range from 20 to 800 microseconds, and release times vary from 50 milliseconds to 1.2 seconds. Ratios include 2:1, 4:1, 8:1, and 20:1. The T25 does not provide an “all-buttons-in” mode, but you can run audio through the amplifiers, tubes, and transformers with the compression disengaged.

Push-button controls are provided on each channel for bypass, compression in/out, D-S mode, THRUST, and stereo link. A 10-segment LED meter displays up to 24 dB of gain reduction, while a VU meter displays output level. Peak LED indicates an output level of +18 dBu – approximately where your DAW interface will clip. The VU meters can be set via internal jumpers to better display typical DAW bus levels, where 0 VU = +14 dBu, instead of the more conventional 0 VU = +4d Bu. This feature essentially reduces the sensitivity of the VU meters so that 0 VU represents the RMS level for a mastered song, which is about 10 dB louder than any single audio track. Internal trimmers are provided for meter trim and THD calibration but should only be adjusted by qualified techs.

I used the T25 during a few tracking sessions and several mixes, and the unit’s personality was readily apparent. This is not a box that takes long to comprehend, though its applications are broad. As expected from a FET compressor and API gear, the T25 produces a clean and slightly forward tone. With no compression, it provides a bit more harmonic color than the API 2500, but nowhere near the coloration of an LA-2A. Its tone reminds me very much of the API 1608 console [Tape Op #81] I routinely work on, but the T25 also adds a consistent bit of harmonic saturation. On a piano tracked through API 512c preamps, the same piano processed through the T25 seemed to gain a bit more midrange character, depth, and detail as if the low-level harmonics became more critical.

Lead vocals sounded excellent with a 4:1 or 8:1 ratio, whereas on 1176s I tended to favor a 12:1 ratio. A slow attack and fast-ish release really brought an R&B vocal from Judith Hill to the front of the mix. Even the 2:1 ratio effectively levels out a vocal while adding some midrange presence. On gently compressed picked electric guitar, pushing the output added a nice edge. Overall, I favored running the input low and the output high, but the opposite settings would generate a bit more transistor overdrive from the unit. The T25’s release time feels a bit quicker than other FET compressors, making for some effective ambience manipulation on room mics.

Crushing a mono drum room mic with plug-in FET compressors often results in a bit of sonic splatter. Still, the T25 remained harmonically rich and natural sounding even when the dynamics became almost inverted (slow attack / fast release / 20:1). A T25-compressed drum room track felt louder than the plug-in version with similar amounts of dynamic processing and gain. Basses and instrumental subgroups seemed to tighten up slightly with gentle amounts of compression, and the transformer seemed to lift mid bass frequencies gently.

API’s patented THRUST® mode inserts a sidechain EQ that makes the compressor less sensitive to low frequencies and more sensitive to highs. Use THRUST when a signal’s low-frequency energy is driving the compressor, but you would rather the mids and highs trigger the compressor. The end result can be a sound that doesn’t feel as compressed, even with the same amount of gain reduction. This sidechain EQ works on mixes and drum buses while helping to dial in the right amount of compression on bass and lead vocals. Similarly, the D-S mode triggers the compressor when excess energy exists around 6 kHz, providing effective softening of harsh vocals or squeaky acoustic guitars.

The T25 reminds me why it’s so hard to stay away from analog gear! Very few plug-ins provide such dynamic control while retaining or enhancing the harmonic character of a sound. I wish API (and others) would provide a -6 dB pad on the input of their outboard gear so that it interfaces more easily with typical DAW I/O signal levels. I would also like to see continuously variable input and output level pots, but the knobs on the T25 can be set in-between detents, if necessary, to balance stereo sources. It’s great to see a legacy company like API freshening up its lineup with thoughtful and feature-rich new gear.