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Audio Grade Solid State Relay

Introduction

The audio grade solid state relay is the answer to the problem of reliable loudspeaker protection. The relay is unlike typical solid state relays which use triac switches, these kind of devices are unsuitable for audio as they switch off at zero crossings (and even a few hundred millivolts before) and introduce distortion.

My relay has been designed to be compact and easy to use, and most importantly to pass audio signals both large and small without introducing switching or distortion. There are no moving contacts to create arcs or weld together so it has a long life and will actually protect your loudspeakers, as it has a high DC breaking capacity.

Because there is no wetting current requirement, it can even be used as an output muting relay for pre-amps.

Designed with DIY audio builders in mind, the trigger will accept any DC voltage from 3V to 16V and pulls less current than any power relays coil - less than 15mA - and does not have any back EMF. It can drop in any circuit where a relay coil of 3.3V, 5V, or 12V is used. The drive requirements are ideal for the latest generation of microcontrollers and single board computers such as Arduino and Raspberry Pi.

 

Performance

The relay is rated at 13 amps continuous, 80V DC or 57V AC.

Overview

Overview

Frequency response

Frequency response. Green trace is system baseline, white is relay. Roll off at low frequency is due to measuring system, the relay is good down to DC.

THD

Total harmonic distortion. Green trace is system baseline, white is relay. Bump at 50Hz is just mains pickup due to unshielded wires.

IMD

Intermodulation distortion. Green trace is system baseline, white is relay.

 

What You Get

The module features high quality screwless terminal blocks, accepting 24-20 AWG signal wire and 24-12 AWG power wire.

A PCB mounted LED will light up when the relay is triggered, this however limits the lowest trigger voltage to 5V. A version without the LED is available for 3.3V systems. Please contact for more details.

Also included is a transient voltage supressor, which should be connected across the speaker (or speaker terminals of the amp if using inside an amp). This has no impact on the sound and is just for protection of the relay.

The module comes fully built, tested and burned in.

Higher voltage versions are available at extra cost. Please contact for more details.

Front and rear images

 

Safety and Compliance

The module is fully RoHS and REACh compliant.

Creepage and clearance distances are no less than 2.5mm between trigger and power switching, or between power switching connections. Also between power switching and mounting spacers.

 

Mounting Details

The PCB is 40mm wide by 39mm high. The mounting holes are 3mm diameter, 32mm apart in the x-axis and 31mm apart in the y-axis. There is sufficient clearance around the holes to utilise M3 hex spacers.

For demanding applications mount the module up against a metal panel in your box. The two bigger devices on the bottom will get warm and need to be heatsinked by mounting against a metal surface. For lighter applications (such as gainclones with 8 ohm speakers) you can simply mount the module on spacers and no extra heatsinking is required.

 

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