The API TranZformer GT is a multifunction pedal that puts two of API's studio circuits in a stompbox: a compressor based on the API 525 feedback-type design, and a guitar-optimized three-band equalizer styled after the API 553 program equalizer12. API, a maker better known for pro audio consoles and rack gear, built the GT to, in the maker's words, "easily and affordably bring the world-famous analog sound of API to your guitar"1. The pedal is fully analog and uses what API calls its traditional fully discrete circuit design1.
The TranZformer GT is discontinued. API lists it as discontinued on its product page and includes it among its discontinued gear13. It was introduced around 2016 to 2017: Premier Guitar describes the original TranZformer GT and LX pedals as "first introduced in 2016"42, while Delicious Audio reported the GT being shown at NAMM 20172.
What it does: a 525 compressor and 553-style EQ in a pedal
The GT combines two studio circuits in one box. The compressor section is borrowed from API's 525 feedback-style circuit2, which the maker describes as an API 525 feedback-type compressor1. The EQ section is an inductor-based three-band design styled after the API 553 program equalizer, which Delicious Audio notes was itself out of production2. Both sections are, in API's description, independent of each other, and each is triggered by its own footswitch, "so you can use them whenever and wherever you want"2.
For a player, that means the GT can serve as a compressor pedal, an EQ pedal, a boost, or any combination of the three. Delicious Audio points out that a separate gain control can act as a clean boost, "which is always useful"2. API describes the pedal as offering "an unsurpassed level of sonic control"1.
The compressor's character is set by fixed timing: attack is less than 5ms, and release averages 100ms, frequency-dependent for what API calls natural envelope tracking1. The ratio varies from 2:1 to 20:1 depending on where the compressor control is set1.
The controls
The GT keeps its control set simple, with one multi-position compressor control and three tone controls doing the heavy lifting1.
| Control | What it does |
|---|---|
| Compressor Control | 6 switchable settings, from 1 for subtle compression to 6 for maximum compression; turning clockwise increases gain reduction (lower threshold) while simultaneously raising output level to match1 |
| Tone Control | 200Hz and 1500Hz peaking bands plus a 5kHz shelving band, each continuously variable for boost or cut over a +/-16dB range1 |
| Level Control | -inf. to 0dB, variable, on the Hi-Z output only1 |
| Gain | Separate gain control that can act as a clean boost2 |
| Footswitches | Separate footswitches for compressor and EQ, so each can be used independently2 |
The compressor also has its own in/out switching1, so the EQ can run on its own with the compressor disengaged, or vice versa.
Power and connections
The GT is not a typical 9V pedal. It runs on +18VDC at 650mA1, which rules out a battery and means it needs its own supply rather than a shared 9V daisy chain.
The TranZformer GT requires +18VDC at 650mA1. Most pedalboard power supplies and daisy chains built for 9V pedals cannot run it, so plan on a dedicated 18V supply.
On the connection side, the GT doubles as a DI. It has a 1/4 inch Hi-Z unbalanced instrument input (~500kΩ impedance, +13dBu maximum input before clipping) and two outputs: a 1/4 inch Hi-Z unbalanced output with variable level control, and a fixed-level male XLR balanced line output1. With the Level control fully clockwise, the balanced line output sits +6dB higher than the Hi-Z output1.
Other maker specifications include:
- Gain range: 9.2dB to 30dB, variable, on the Hi-Z output1
- Maximum Hi-Z output level: +21dBu before clipping1
- Output impedance: 7.5kΩ on the Hi-Z output1
- Frequency response: +0, -0.5, 20-20kHz on both outputs with low-capacitance cable1
- Noise: -75dBu1
- Size: 8″ x 5.5″ x 4″1
- Weight: 4lbs. actual1
History: from the API 525 and 553 studio units
API built the GT by adapting two of its studio products. The 525 is a feedback-style compressor, and its circuit forms the compressor half of the pedal2. The EQ half follows the 553 program equalizer, an inductor-based design that Delicious Audio described as legendary and already out of production when it wrote about the GT in 20182.
The GT was API's move into guitar pedals. Premier Guitar describes the original TranZformer GT and LX pedals as first introduced in 20164, and the GT was shown at NAMM 2017, where, as Delicious Audio put it, "the high end console and pro audio manufacturer introduced a new product called Tranzformer GT"2. A sibling pedal, the API Tranzformer LX, was introduced alongside it4.
When Delicious Audio covered the GT in May 2018, it noted the pedal rested "at a high price point (just under $500 as we write)"2. The pedal is now discontinued13.
Videos
Pete Thorn
Sweetwater
Guitar World
Questions
Can the API TranZformer GT be used as a DI box?
In effect, yes. Alongside its normal 1/4 inch Hi-Z output it has a fixed-level male XLR balanced line output, so it can feed a mixing desk or interface directly. With the Level control fully clockwise the balanced output runs +6dB hotter than the Hi-Z output, which is worth knowing when setting levels at the desk.
Can I use the EQ without the compressor on the TranZformer GT?
Yes. The compressor and the three-band EQ each have their own footswitch, so you can run either one independently or both together. The compressor also has its own in/out switching, and a separate gain control can act as a clean boost on its own.
Is the API TranZformer GT discontinued?
Yes. API lists the TranZformer GT as discontinued, and it appears on the maker's discontinued-gear page. It was introduced around 2016 to 2017, so remaining units are found on the secondhand market rather than new from retailers.
How much did the API TranZformer GT cost?
When Delicious Audio covered the pedal in May 2018 it sat at what the site called a high price point, just under $500. That was the street price at the time; as a discontinued pedal its current value depends on the secondhand market.
Is the API TranZformer GT true bypass?
API specifies a hard wire bypass switch, which passes the signal around the circuit when the pedal is off. Note that the pedal still needs its +18VDC supply at 650mA to run when engaged, so it is not a battery-friendly or typical 9V pedalboard unit.
Sources (4)
- TranZformer GT Guitar Pedal, API: Automated Processes, Inc. (apiaudio.com), 2024-12-09
- API TranZformer GT Compressor + EQ, Delicious Audio, 2018-05-13
- Discontinued Gear, API: Automated Processes, Inc.
- API Announces API Select TranZformer Pedals, Premier Guitar, 2021-12-08
