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SSM2 Mains Soft Start Module

The common use of toroidal mains transformers in audio equipment has solved a great many problems but in doing so, has created others.

One such problem is because the toroid uses a much smaller magnetic core, the high inrush current at power up is liable to blow any mains fuse fitted.

A solution would be to up-rate the mains fuse fitted to the equipment but these are less likely to ‘blow’ under fault conditions and more damage may result.

The SSM2 addresses these problems completely automatically:

Mains Soft Start Module Operation – SSM2

At power-up, the mains supply is connected to the toroidal transformer via a bank of ballast resistors, thereby temporarily restricting the incoming current until the capacitor bank has had the time to gain a charge.

After a specific time, the ballast resistors are removed from the circuit by another high current relay. At this point the mains supply is now connected for full operation, all without any intervention from you and without the need for any power supply other than the incoming mains itself.

Each aspect of the circuit has been well proven for reliable and silent operation. Incorporated in the module are points to which a thermal trip device may be inserted such as the one fitted as standard to Naim Audio amplifiers. This removes the previous restriction to the incoming mains supply as it only carries the low current relay energy.

The SSM2 needs only the addition of a low-current mains switch to complete the installation and have the added advantage of requiring only the equipment manufacturers specified fuse, offering all the protection needed.

This new compact unit may be installed into some models of the Naim Audio range of amplifiers and power supplies such as the XPS models 1 & 2. Eliminating the impact of excess inrush current on toroidal transformers can lead to this component having a longer and quieter service life.

Connections are made by high quality screw blocks so avoiding the need for any soldering.

Maximum load at 240V AC is 1KVA – 1000VA.

No heat is producing during operation.

Impeccably constructed on 2.4mm FR4 substrate with 70 micron thickness tracks which are gold plated to avoid the effects of high impedance and long term corrosion.


83L X 57W X 20H (without stand off pillars) and may be fitted in any orientation i.e. flat or on edge with the fixings and angle brackets supplied


SSM2 Soft Start Module

Mains Soft Start Module SSM2

Mains Soft Start Module SSM2

Mains Soft Start Module SSM2

Mains Soft Start Module SSM2

Mains Soft Start Module SSM2

Mains Soft Start Module SSM2

Mains Soft Start Module SSM2

Mains Soft Start Module SSM2

Mains Soft Start Module SSM2

Mains Soft Start Module SSM2

Please note

The SSM2 is intended to protect the mains supply to your equipment against surge current excesses and is not for the protection of any connected loudspeakers. For this purpose, a dedicated loudspeaker protection circuit would be required.


Installing this unit involves working with potentially lethal voltages and it is crucial that the work is carried out by suitably competent and qualified technicians.

This product is accompanied by our Data CD to gain the best from this unit.