Manley Compressors

By | August 12, 2015

Compressors (limiters) reduce the dynamic range (also known as the span between the loudest and softest sounds) of audio. And while compressors help control your maximum levels, they often bring a cold, sterile presence to your audio. With lack of warmth comes lack of interest. Thankfully we have Manley compressors, which keep your music from going frigid. The all-tube designs bring warmth and natural, organic sound to the table. All Manley compressors come with high quality components, including hand-wound transformers!

There are five Manley Compressors: Manley Stereo Variable Mu, Manley Stereo Variable Mu Mastering Version, Manley Slam!, Manley Slam! Mastering Version and Manley Stereo ELOP Limiter. Let’s take a look at these tube limiters!

Manley Stereo Variable Mu and Mastering Version

Price: $3960 / $5175 (Mastering Version)

Manley Stereo Variable Mu Compressor Limiter gain face front panel MSLCHP MMSSLCHP

The Manley Stereo Variable Mu is a limiter / compressor that utilizes a unique 5670 dual triode tube design for peak reduction and compression. Compression is achieved by using the remote cut-off (or re-biasing) of the vacuum tube. The vintage Fairchild 670 used this technique. Smooth changes in gain are achieved by the constant re-biasing of the tube sidechain control voltages. The Manley Variable Mu (fancy word for gain) has a compressor setting with a soft knee ratio of 1.5:1, in addition to a limit mode with a sharper knee (from 4:1 to 20:1). What does this mean? It means that the higher the limiter settings are, the softer the knee will be. This Manley compressor has a sidechain high-pass filter (HPF) that can help prevent audible “pumping” in audio on the low end of the spectrum. While the Manley Stereo Variable Mu is ganged, it can process two independent channels with separate threshold and output controls. It operates in true stereo mode when the link switch is engaged, which is great for processing two-track, final mix or mastering limiting and compression.

The Mastering Version of the Manley Variable Mu only has minor differences. All conductive plastic pots are replaced with Greyhill rotary switches. These switches have 1% metal-film resistors that provide recallability and an improved sound quality.

Manley Slam! and Mastering Version

Price: $6660 / $7740 (Mastering Version)

Manley Slam Microphone Preamplifier two channel 2 ch mic preamp pre compressor limiter MSLAM face front panel

The Manley Slam! is a two-channel tube microphone preamplifier with two unique limiters / compressors. One is an electro-optical (ELOP) limiter and the other is a field-effect transistor (FET) “brick wall” limiter. Each channel can utilize the ELOP and FET limiters simultaneously or separately. The ELOP circuit is set before the mic preamp and makes it almost impossible to clip the tube preamp stage. The circuit’s design provides you with a fixed ration, attack and release. Variable control for the ELOP circuit is only available for the threshold. This side of the Manley Slam! is complete with a sidechain high-pass filter with a 200Hz setting. Contrast this with the FET circuit, which acts as a quick, “brick wall” limiter. Variable controls are available for attack, release and threshold. The FET circuit has the ability to color audio in various tones, while still maintaining zero overshoot limiting. Both the ELOP and FET circuits have sidechain inserts available on the rear panel of the Manley Slam! mic preamp.

Visual monitoring is possible thanks to VU meters and LED indicators on the front panel. A source toggle switch is paired with each VU meter and allows you to monitor gain reduction, input and output. The LED peak indicator also has a source toggle switch that can be set for gain reduction, peak and reset & mode. Reset & mode clears out peaks signals and allows you to calibrate the peak LEDs to match the meters of whatever A/D (analog to digital) converters you use. You can link three Manley Slam! units together for a total of six limiting channels. That’s useful when working with 5.1 surround sound. A separate power supply is included and helps reduce heat and electromagnetic fields that could interfere with the signal path.

The Mastering Version of the Manley Slam! eliminates the mic preamps and instrument inputs. They’re replaced with a paralleled tube section that yields lower noise and distortion. All conductive plastic pots are replaced with Greyhill rotary switches and provide improved sound quality and recallability. Other additions include an expanded range for the limiters and transformerless 1/4″ inputs.

Manley ELOP Limiter

Price: $2970

Manley ELOP Limiter Compressor face front panel MELOPB

The Manley ELOP Limiter is a two-channel electro-optical tube limiter / compressor. It has the ability to reduce gain without any increase in harmonic distortion. The all-tube audio path utilizes one 12AU7WA tube and one 6414 tube per channel. This is a great choice for working with voice and individual instruments. The dedicated sidechain high-pass filter causes the limiter to ignore low frequency signals, which is perfect for music on the low end of the spectrum. The Manley ELOP Limiter works by shining an LED on a light dependent resistor. The photo resistor works with a fixed resistor in order to function as a voltage divider. This reduces the audio signal based on the brightness of the LED and gives you natural compression characteristics.

This is the same ELOP limiter that’s found in the Manley Slam! A major problem with photo-optical limiters tends to be that sample accuracy comes at the cost of high frequency loss. This isn’t the case with the Manley ELOP. This Manley compressor can track audio with sample accuracy without high frequency loss thanks to unique technology! The front panel interface gives you control knobs for gain reduction and make-up gain on both channels. Two illuminated VU meters provide visual indication of device parameters. Each VU meter is paired with a toggle switch that you can set between gain reduction and main output levels.

If you have any questions about these Manley Compressors, send us an email at!