The API Audio TranZformer CMP is a compressor pedal that translates the circuitry of API's 527 VCA studio compressor into a pedalboard-friendly format. It belongs to the API Select series, which adapts the company's high-end studio technology for live performance, and it features the proprietary API 2510 OpAmp and a signature output transformer that RockBoard's PedalPedia says deliver iconic, punchy studio-grade compression1.
The CMP is a fully analog pedal, and it was designed to fit easily on a pedalboard and run off standard 9V power supplies2. Premier Guitar's press coverage of the TranZformer line described it as incorporating key elements of API's legendary VCA-type compressor circuit, along with "of course the classic API sound"3.
Controls and compression modes
The pedal's headline control is the Blend knob, which provides parallel compression by setting a wet/dry blend between the compressed and uncompressed signal23. That lets a player dial in studio-style parallel compression, keeping some untouched pick attack under the squeezed signal.
The CMP also offers selectable compression styles. Premier Guitar's coverage lists selectable feedback/feedforward compressor styles3, and Delicious Audio describes the two modes this way:
"NEW mode uses feedforward compression and gives a more modern compressed tone."
The feedback style is the other side of that switch, in the tradition of API's earlier feedback-type compressor designs1.
Power and bypass
The TranZformer CMP runs on 9V DC, center negative, and draws 100mA1. API's press release for the Select range notes that both TranZformer pedals use standard 9 volt power supplies4.
The CMP uses a buffered bypass, not true bypass2. The buffer remains in the signal path when the pedal is off, which suits long cable runs but is worth knowing if your board is built around a strictly true-bypass chain.
Where it came from
API, a pro audio company long associated with studio consoles and outboard gear, brought the TranZformer name to guitar pedals as part of the limited edition API Select range, announced with Larry Droppa and Jeffrey Richards speaking for the company1. The CMP adapts the company's VCA-type studio compressor circuit, the same approach behind the 527, to the compact pedal format12.
The TranZformer family
The CMP has a sibling in the line: the API TranZformer GTR, an EQ/overdrive pedal2. The two pedals share the API Select approach and both run on standard 9 volt power4, but they do different jobs: the CMP handles compression, while the GTR covers EQ and overdrive.
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Questions
Is the API TranZformer CMP true bypass?
No. The TranZformer CMP uses a buffered bypass, according to Delicious Audio's coverage of the pedal. A buffer stays in the signal path when the pedal is off, which can help drive long cable runs, but players who want a strictly untouched signal path when the pedal is disengaged should know it is not true bypass.
What power supply does the TranZformer CMP need?
The TranZformer CMP runs on a standard 9V DC power supply with center negative polarity, and it draws 100mA. API's press release notes that both TranZformer pedals were engineered to run off standard 9 volt power, so a typical pedalboard supply will run it, though the 100mA draw should be checked against the supply's available current.
Is the API TranZformer CMP analog?
Yes. The signal path is fully analog. The pedal adapts API's VCA-type studio compressor circuit to the guitar pedal format rather than modeling it digitally.
What does the Blend knob do on the TranZformer CMP?
The Blend control sets a parallel compression mix, blending compressed and uncompressed signal. Premier Guitar's press coverage describes it as a wet/dry blend control, which lets you keep some of the dry pick attack underneath the compressed signal.
What is the API Select series?
The API Select series is API's line that adapts high-end studio technology for live performance, translating the company's studio circuit designs into pedalboard-friendly formats. The TranZformer CMP is part of that series, alongside the TranZformer GTR.
What is the difference between the TranZformer CMP and the TranZformer GTR?
The TranZformer CMP is a compressor, built on API's 527 VCA compressor circuitry. The TranZformer GTR is an EQ/overdrive pedal. Both belong to the API Select series and both run on standard 9 volt power.
Sources (4)
- TranZformer CMP by Api Audio, RockBoard PedalPedia, 2026
- API Audio TranZformer CMP Compressor, Delicious Audio, 2021-10-18
- API Announces API Select TranZformer Pedals, Premier Guitar, 2021-12-08
- API Announces Limited Edition “API Select” Range of Products, API: Automated Processes, Inc., 2021-08-02