How to wire-up a Dual Mono Bloc Amplifier

A few people have asked about wiring up a dual mono amp aka dual mono bloc. In a dual mono bloc there are separate power supplies and lots of opportunity for cross channel ground loops and ordinary ‘classic’ ground loops as well.

This wiring scheme addresses the situation were unbalanced connections between the source equipment and the dual mono bloc is used and should allow a dual mono amp to be wired up that is quiet – i.e. no hum.

The trick it to ensure that there is one and only one connection between the two amplifiers, and that is accomplished by bonding the input connector signal grounds together in this approach.

The wiring scheme uses two ground lifters, although you could cheat and just lift one of the amps, and ground the other directly to the chassis, but I suggest you just spend a little extra effort and use two ground lifters.

A major issue here, as in any DIY amp, is safety. Kindly note the chassis (assumed to be steel or aluminium) is bonded directly to the incoming safety ground (earth) on the IEC receptacle. You cannot under any circumstances omit this connection – it is the most important connection in DIY any amplifier. Using the ground lifters, the two amplifiers and their associated power supplies 0V then float +- 1.4V around the safety ground (earth). For the ground lifters, I always recommend you use a decent 35A 400V bridge rectifier – details in the presentation, although you can use large diodes with a high surge rating.

For the transformers, use a Toroidy (based in Poland) audio grade device with a GOSS band to minimize the radiated mag field, or if specifying custom devices, ensure your order your transformer with a GOSS band. An interwinding screen will also help to minimize mains conducted common mode noise.

One final point: there is a tendency for builders to mount the RCA input connectors on opposite sides of the rear panel. This creates a huge loop area inside the amplifier and the opportunity for a cross channel ground loop. Mount them next to each other and run the input wiring around the edge of the chassis in order to minimize the inter-channel loop areas – again, details in the presentation.