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MU524 from Sound Skulptor

DIY Vari-Mu compressor kit

Sound Skulptor MU524 Vari-Mu Compressor DIY 500-series analogue outboard valve tube transformer vintage style compressor

Sound Skulptor have announced the availability of the MU524 Vari-Mu Tube Compressor, the latest addition to their growing range of DIY 500-series modules. Employing a pair of transformers and a NOS (new-old-stock) valve in its signal path, the unit promises to deliver the characterful sound of a vintage compressor at a surprisingly affordable price point. As with all of the company’s devices, those who would like to get their hands on an MU524 but don’t fancy putting it together themselves can instead opt for a pre-built module at an additional cost.

Based on compressors such as the Altec 436 and Abbey Road’s RS124 units, the MU524 is said to offer a smooth and natural compression with a soft knee, and can be pushed into distortion if driven hard. The device is recommended for use on a wide range of sources, and it is also possible to link two units in order to process stereo buses or entire mixes.

An In parameter sets the input level into the compressor, which also defines the threshold, with the amount of gain reduction applied displayed by an illuminated SIFAM meter. A Limit button placed to the right of the control increases the ratio, allowing the unit to function as a limiter. A Rec knob provides continuous adjustment of the compressor’s release time, whilst a button labelled Fast Attk serves to shorten the attack time. A HPF button engages a high-pass filter in the compressor’s side-chain, helping to prevent low-frequency content from causing pumping effects, and an Out control allows users to adjust the amount of make-up gain applied.

The Kit

An MU524 kit contains the following parts:

  • Passive components (resistors, capacitors, inductors)
  • Transformers
  • Active components (valve, diodes, transistors, ICs),
  • Control elements (meter, switches, potentiometers, knobs),
  • Connectors, relay
  • PCBs
  • Front panel and side panels
  • All hardware

Sound Skulptor say that the kit is of a medium difficulty, and can be undertaken by anyone who is able to make a clean solder joint! The setup process is said to be a little more complex than with some of the company’s other devices, however, and will require a good quality digital multimeter.

Key Specs

  • Frequency response: 20Hz to 20kHz (±0.2dB)
  • Attack time: Slow/Fast = 10mS/1.2mS
  • Release time: 50mS to 1 second
  • Ratio (Limit off): 1.2:1 to 3.5:1
  • Ratio (Limit on): 1.5:1 to 7:1
  • Idle current draw: +125mA / -125mA

Pricing & Availability

The MU524 Vari-Mu Tube Compressor is available now, with kits priced at $435.02£351.02 / €399. A pre-built unit can be bought for an additional €270, with a four week wait time.

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