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The Neve 2254 Compressor/Limiter, designed in 1969, builds upon its predecessors, the 2252 and 2253, by incorporating a classic design that utilizes the electrical characteristics of diodes to optimize dynamic processing. This design features two diodes in a bridge structure that significantly reduces distortion, allowing for an ideal compression curve. It can produce various types of compression ranging from subtle and smooth to aggressive and overloaded, quickly becoming a legendary application in recording studios.

Alctron has taken the classic Rupert Neve 2254 diode bridge compressor as a model, reproducing and further upgrading this valuable circuit design. By employing fully discrete transformer-coupled technology with three custom Alctron audio transformers at the input, bridge driver, side chain, and output stages, it achieves both warm and clear analog effects. The standard 1U rack design allows for seamless integration into studio equipment.

Equipment Appearance, Build Quality, Accessories, and Expandability

The Alctron CP540V2 is a single-channel compressor/limiter (as shown in the figure below). It features completely independent compression and limiting circuits, allowing for separate processing or combined activation of both. This enables the device to compress the input signal while simultaneously limiting the output level.

The control panel features clearly defined functional zones, as shown in the figure below.

Both the compression and limiting sections are equipped with independent activation switches, allowing for selective use or combined operation. Additionally, the compression section includes an HPF high-pass filter to compress the signal from the LINK interface.

The rear panel serves as the interface area, providing. The rear panel serves as the interface area, providing LINK, and external power allows for connecting another CP540V2 to form a dual-channel compression/limiting system for processing stereo signals.

Monitoring section supports signal source switching display and can monitor the input, compression and output signals separately. Signal level is displayed on VU meter. VU meter is equipped with backlight to clearly display under any lighting condition. Warm light tone unifies with analog sound color created by it.

In terms of appearance, the Alctron CP540V2 and the original Neve 2254 are quite different. After all, the prototype was a product of the 1960s. However, one can find design elements that correspond to it in the reissue version of the Neve 2254R, as shown in the image below.

Of course, Alctron is not the only one to recreate this classic device. The 10DCF from BAE is also one of the competitors. Its appearance is similar to that of the Alctron CP540V2, and design elements of the Neve 2254R can be found in both. See the image below.

The original Neve 2254 had dual-channel processing capability. The reissued Neve 2254R breaks this rule and designed as a single-channel unit, but it is equipped with a LINK interface. Through this interface, another identical device can be connected to form a dual-channel processing capability. Both the Alctron CP540V2 and the BAE 10DCF adopt this application concept. As can be seen from the front and rear panels in the image above, there are LINK interfaces and activation switches.

In addition, in terms of compression and limiting functions, they both possess the capability to handle these functions independently or in combination. Judging solely from the appearance, the Alctron CP540V2 and the BAE 10DCF have a higher degree of similarity, which is why there are many comparisons made between the two. However, making a judgment based purely on appearance is too superficial. In fact, both have their own internal circuit improvements and manufacturing processes, which are the core of their competition.

In terms of construction quality, the Alctron CP540V2 features an outer shell made of steel plate through stamping, which can effectively shield against magnetic field interference and is sturdy and durable. The surface of the chassis is finished with a paint process, which strongly contrasts with the rugged original-colored shell of the American-made BAE 10DCF, displaying different aesthetics.

In terms of packaging and standard equipment (as shown in the figure below), the Alctron CP540V2 follows the simplicity of rack equipment and only provides the necessary power adapter and instruction manual.

Meanwhile, in order to adapt to desktop use, it is also equipped with four self-adhesive high-density foam pads.

Specification and adjustment

In terms of noise level, the Alctron CP540V2 performs better than the reissue version of the Neve 2254R (with a noise figure of -72.5dBu). Another set of sound quality indicators includes "maximum output level" and "distortion," where it slightly underperforms the Neve 2254R (maximum output level at 26dBu; distortion at 0dBu: 0.03% + 15dBu: 0.2%).

In terms of control precision, the Alctron CP540V2 is identical to the Neve 2254R, but it also adds some additional parameters. For example, the release time for compression/limiting now includes an "auto2" option (which automatically performs compression or limiting based on the attack and release times of the input level), while the Neve 2254R only offers the "auto1" option.

Another newly added improvement is the HPF (High-Pass Filter). This is a high-pass filter with selectable cutoff frequencies at 50Hz, 100Hz, and 7kHz. It can be used to filter and compress signals from the LINK interface. This feature originates from the BAE 10DCF, but the selectable cutoff frequencies were mostly concentrated in the low-frequency range, which had certain limitations. The Alctron CP540V2 has expanded the filtering range. The figure below shows the comparison between the two.

The Alctron CP540V2 is an analog circuit-based compressor/limiter, and in terms of adjustability, it differs from common digital effect plugins. All its controls are switch potentiometers, unable to take continuous linear values, which is an inherent characteristic of analog hardware. As for compressors/limiters, they use electronic components (such as resistors, capacitors, etc.) to achieve compression functions. Their settings are usually more fixed, for example, the attack time may only have one or a few preset positions, such as 6ms, 12ms, 25ms, 50ms, etc., which is what analog mixing commonly refers to as fast (quick) or slow compression. These time settings are determined by the electronic circuit structure, and are not as finely adjustable as digital compressors, but they are more intuitive and easier to control.

Plugin compressors, on the other hand, are software-based processors that rely on digital signal processing (DSP) for their internal controls. Therefore, they can offer very fine-grained control options, such as allowing users to set an infinite number of attack and release time points, and even make continuous gradual adjustments. However, in terms of efficiency, sound quality, and ease of use, analog hardware has the upper hand.

Performance and Audio Characteristics

The reason why the prototype Neve 2254 became a classic is that, in addition to adopting a diode bridge structure, its entire audio signal path uses Class A discrete circuits. This includes a discrete transformer-balanced output that evolved from the early Neve console's line output module.

Those familiar with Neve hardware know that its internal transformer is a closely guarded secret and the core guarantee of its sound quality. Consequently, later reissues have featured various combinations of transformers. For example, the BAE 10DCF uses Carnhill and Jensen transformers. Obviously, whatever approach is taken is a beneficial attempt to achieve good sound.

The Alctron CP540V2 also attempts this in its circuit design. The following diagram shows its internal circuit structure, from which we can explore the origin of its good sound.

As can be seen, its internal circuit is clean, which helps to reduce the heat buildup among components and improves the stability and lifespan of the components. This is especially important in audio circuits because high temperatures can cause sound distortion. Secondly, the layout is reasonable. The control circuits and interface circuits are clearly zoned, effectively reducing signal interference and attenuation during transmission. In addition, it also keeps the wiring as short as possible to reduce noise and signal attenuation, ensuring that the sound quality is not affected.

Three customized transformers (as shown in the red circles in the figure below) are used in the audio link, with the Alctron brand LOGO clearly marked on them.

The following figure shows the circuit of the power supply section.

The VU meter backlight uses seven LED diodes to form a backlight array.

The controls for the compressor and limiter section all use switch potentiometers, and the output level adjustment is a sealed carbon film potentiometer.

The following are several compression tests to understand the audio characteristics of the Alctron CP540V2:

l Test 1 : compress ration 4：1 、ATTACK 0.5ms、RELEASE 800ms

In terms of signal shape, the compressor responds quickly to extremely short attack times. The onset of the sound is effectively compressed, indicating that the compressor has a good transient response speed.

l Test 2: compress ratio 6：1、ATTACK 12ms、RELEASE 1.5s

The compressor handles longer attack and release times smoothly and progressively after reaching the threshold, which is known as the "soft knee" processing. The soft knee processing makes the signal sound more natural and faithful to the original sound characteristics, suitable for most music styles. However, it is less suitable for processing hard-styled sounds such as heavy metal.

l Test 3: compress ratio 4：1、ATTACK 6ms、RELEASE auto1/auto2

Auto1 and Auto2 are two automatic compression options. Under these options, the compression settings are automatically determined based on the signal's input level variation time. Although I specified an attack time of 6ms, it is invalid under the automatic options. As can be seen from the compressed signal shape, both Auto1 and Auto2 can relatively completely preserve the sound tail, and they differ in attack time.

Test

The Alctron CP540V2 has two application methods. It can be connected into an analog hardware system or used in combination with a DAW, and both are very typical use methods. In terms of applications, it can be used in the initial recording stage and is also suitable for the post-production stage.

My production environment is mainly based on DAW. Therefore, I chose to try the combination of hardware and DAW as shown in the following figure.

For equipment connection, just connect the input/output. For equipment connection, just connect the input/output0V2 with the multi just connect the input/output of CP540V2 with the multi-channel input/output of the sound card (as shown in the following figure). If you want to use CP540V2 in the initial recording, you need to add a microphone preamp before the compressor. I don't have a hardware microphone preamp device, so I can only demonstrate the use of this device in post-production.

The software setup is shown in the following figure. The DAW used is Ableton Live. A return track is created, and the signal source is the output end of the connection between the audio interface and the hardware effect unit. The signal source of the second track on the left side of the DAW window is the input end of the connection between the audio interface and the hardware effect unit, and the track monitoring mode is In. The first track on the left side of the DAW window is a pre-processing track. Use the track send knob to send the signal to the return track, and then send it to the CP540V2 from the return track. Adjust the dry/wet ratio of the effect by adjusting the level of the audio track (the compressed signal requires 100% wet signal, and the default level is OK).

Application 1: Percussion Compression (click to listen to the audio).

Audio Player

The screenshots above show the comparison between the compressed signal (yellow track) and the original signal (pink track). This is a compression treatment for the entire drum kit, which can be understood as bus compression. The specific compression settings are: THRESHOLD -4, COMPRESSION RATIO 3:1, ATTACK 6ms, RELEASE 400ms. A medium compression ratio and release time are chosen here. The tail sounds of the kick drum and snare drum in the original signal are reduced, and their volume is relatively decreased. The faster attack time makes the onset of the sound more noticeable.

Application 2: Percussion Compression (click to listen to the audio).

The screenshot above shows the tracks of the entire song. As a demonstration, only the vocals were compressed here. The specific compression settings are: THRESHOLD -4, COMPRESSION RATIO 3:1, ATTACK 12ms, RELEASE 400ms. The compressor settings in this example are also relatively conservative, similar to the previous drum kit. The purpose is to blend the vocals into the mix. The medium attack time allows for a relatively complete preservation of the transients of the vocals, and the medium compression ratio and release time reshape the envelope, resulting in better integration with the accompaniment.

Conclusion

As a replica version, the Alctron CP540V2 has a high degree of correspondence with the original device in terms of performance parameters, and its actual usage performance is also satisfactory. Alctron's full understanding of the transformer at the core of the Neve hardware is one of the successful factors that contribute to its sound quality performance.

In terms of overall performance, the Alctron CP540V2 and the BAE 10 DCF replica version have many similarities, and it can be said that it is difficult to distinguish between the two in terms of superiority. In terms of price, I consulted the quotations on foreign audio websites. The retail price of the Alctron CP540V2 is$500, while that of the BAE 10 DCF is $2339.89. Therefore, in terms of cost-effectiveness, the preferential selling price of the Alctron CP540V2 completely stands out, with its market competitiveness and cost-effectiveness being higher than that of the BAE 10 DCF.