top of page

API Tranzformer CMP Compressor Review

The API CMP Tranzformer Select is a compressor I've been wanting to try for quite a while now. API is known as a pro audio company specializing in mixing consoles and channel strips and has a reputation for quality gear. Certainly, API knows how to build great studio gear and the thought of a pedal board friendly compressor from API is something I wanted to experience.

The Tranzformer CMP incorporates API’s legendary VCA-type compressor circuit and adapts it to the guitar pedal format. There are four dials and three mini switches on the face of the compressor. At first glance, that might be enough to turn off some potential buyers who may write it off as too complicated. It really is not complicated all though. All of the controls are useful and offer a great range.

Once you understand what they do, the device is probably one of the more simple designs offering this amount of control.

The three dials: INPUT dial: Use this dial to increase the input level of what is connected to the compressor from +9dB to +30dB. As you rotate the dial and increase the gain you are also creating more compression because you are driving the compression engine harder with a stronger signal. Unless you have an instrument with very hot output you will want to run the input dial at noon or higher for sure — most likely around 2:00 or 3:00 on the dial to ensure you are pushing the compression engine. More on that later.

SUSTAIN dial: This dial controls the compression level (gain reduction), perceived loudness, and punchiness. Higher levels provide more compression at a lower threshold. API told me the ratio range is essentially 1:1 to 20:1. With a range that wide you would expect the device to make for a great limiter. While it does offer significant enough squeeze, it is so smooth and natural that it doesn't really make for a good limiter. But more on that later too. BLEND dial: This dial allows you to mix your dry (uncompressed) signal with the wet (compressed) signal. Having tested many compressors at this point I have come to the conclusion that a Dry/Wet blend is one of my most desired features in a compressor. Having this kind of control allows you to run the compression circuit at higher levels of compression/lower threshold while still maintaining natural dynamics by blending in some of your dry signal.

OUTPUT dial: When you need some makeup gain, the output dial is there for you. With the Input dial rotated higher, you will find you need less of the Output dial so all four of the dials are highly interactive. If you want to drive the signal higher downline in your pedal chain the CMP offers plenty of gain to do so. The name of the game here is to set the level of input signal (probably at least noon or more on the dial), then set your desired level of compression, then decide how much of your dry signal you want blended in (comes down to feel and dynamics control) and then set the volume at the end. Simple as that.

API Tranzformer CMP is one of those compressors that lets you feel the compression as much as hear it. It really is something to experience.

I think the knobs look really cool and they are easy to grab and turn.

Now for the three switches.

ATTACK switch: You can set the compressor's attack time to either FAST (1ms) or SLOW (10ms). Compared to some other compressors on the market but of these settings are quite fast. I preferred the slower setting (down position).

RELEASE switch: Select a FAST (300ms) or SLOW (1s) release time with this switch. Both are nice. Depends on how much sustain you prefer.

TYPE switch: This switch allows you to selects between two different compression styles — feedback (OLD) or feedforward (NEW). There is a lot of documentation on the Internet about the differences in feedback and feedforward compression styles and is beyond the nature of this review to highlight in detail. Feedback compression feeds the audio signal into the sidechain just after the gain reduction element. This compressor type reacts to the signal amplitude without anticipating. Feed-forward compression feeds the audio signal into the sidechain before the gain reduction element. This compressor type anticipates the signal amplitude and adjusts the sidechain signal in advance. Using the API CMP in feedback (OLD) mode delivers a smoother, slower, and somewhat more vintage sounding compression style. Feedfoward (NEW) mode delivers a style of compression that is faster, more punchy, more sensitive to input level and level of compression. It might be described as more modern and less colored. More like a VCA compressor. It is fun to experiment with both. Depending on what preamp I was using after the API compressor I sometimes preferred OLD and sometimes NEW.

For example, in front of some tube amps I liked the more punchy, faster feel of NEW. But, it is very nice to have OLD style available for use in front of solid state gear.

The design of the CMP is a buffered bypass so even with the pedal off, the signal is buffered. Input and output jacks are side mounted as is the 9 - 18 volt power input. You can use any DC center negative supply from 9 - 18 volts but do not exceed 18 volts. Running at 18 volts offers more headroom but I had no need for running anything more than 9 volts, even with Sadowsky basses with rather aggressive preamp. I heard no distortion or clipping. There is no gain reduction LED though and that is something I do like seeing in compressors. I contacted API to ask if they might consider a second version with gain reduction meter and they replied saying there really was no room inside to include.

The API Tranzformer CMP compressor also incorporates API's signature output transformer. It must make a difference because its hard to make the CMP sound bad.

No matter how you have it dialed in, it sounds fantastic.

Here's the thing though. This is one of those devices where you might initially feel like not much is happening as you rotate dials and play. But then you turn off the pedal and you immediately want it back on. Its then that you realize the pedal is subtly and gracefully sculpting your tone doing what a studio quality compressor should — adding fullness, feel, and sensitivity to the mix. It's the feel that is so impressive.

You don't want to turn it off because of how alive it feels. How your instrument responds feels more energetic.

Notes up and down the fretboard are more even and forward. You are framing a signal that will sit better in the mix. I found myself running the Sustain level (compression) higher than I expected I would. With the Blend control and Input signal control you can really dial in a highly compressed signal that feels so relaxed and natural. True, you don't have continuously variable control over attack and release. If that's what you require, look elsewhere becuase the API is fairly utilitarion in that regard. If you require clinical control over ratio and threshold, look elsewhere. On the other hand, if you want compression that is easy to use, doesn't squash your lows, feels natural, and simply makes your signal sound rich and vibrant give this one a serious look. A tweak of a dial might seem subtle or insignificant at first. But turn off the device and you'll quickly realize what it was doing.

The CMP is one of the most unobtrusive compressors I've used to date.

It's not that it is highly colored. There is no EQ or obvious bump in certain frequencies when enabled. Don't think of it as something like the Diamond or Lusithand Alma or various tube compressors in this regard. But the API CMP Tranzformer compressor is definitely in this mix of devices that you will not want to turn off. In summary, yes, API gives you classic studio-quality compression right at your feet. The feel, sensitivity, and low noise floor is wonderful. The build quality is fantastic. The device itself is quite heavy. Oh, it is also smaller than you might initial think. See picture below for size comparison with the Becos Stella.

The CMP is incredibly satisfying once you understand how it works and the nuances of the interactivity of controls. It might come off as too subtle for some users.

Frankly, it makes many other pedal compressors seem like toys.

No matter what I plugged in to the CMP and what I connected the CMP to, I preferred the CMP turned on. It some ways it reminds me of the big box Cali76 compressors in sound, feel, and how it responds. The API CMP would make for a good alternative to somebody considering a Cali76 compressor in a smaller package. I really like the API Tranzformer CMP Select compressor. It is not the most versatile compressor but it sounds great, looks good, is built well, and adds that special something to your tone while staying out of the way. Pros: • Sounds fantastic • Quiet

• Easy to use

• High quality build

• Studio quality tone in a small footprint.

Cons: • Might seem to subtle for some (at least initially)

• Not enough clinical control for some

• Side mounted jacks might turn off some with cramped pedal boards

• No gain reduction LED

• Some might say the price, but frankly, this is a serious piece of kit Retail price: $295

bottom of page