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.


6 responses to “How to wire-up a Dual Mono Bloc Amplifier”

  1. Miroslav Novak says:

    You have nicely done “How to Wire Up a Dual Mono Bloc Amp for Zero Noise and Hum”
    You can draw a similar diagram for dual mono with a mains switch on the front panel (220V) and a volume potentiometer.
    Thank you Mira

  2. Tuan says:

    Hi. I noticed in the image at slide 2, the speaker “-” (minus) wire comes from the power supply unit. While at slide 5, there is no connection between the speaker output and the PSU – or ground.
    Could you please explain?
    Another one, at slide 5 you said to use a heavy duty speaker cable (5mm) for output. Why is that? The speaker cables that run outside the amplifier (to speakers themselves) usually are 1.5-2.5mm. Why should we use 5mm inside? It’s a bit hard to find 5mm speaker cables.
    Also, since the two input signal cable need to be tie together, can i use a 3-wire cable (two signal and a GND) for that instead of two separate cables? Can you recommend a wire gauge?
    Sorry for asking too many question. I’m new to the hobbies with little electrical background so i’m trying to learn.
    Thanks in advance and looking forward to your reply.

    • admin says:

      Hello Tuan, thanks for your questions.

      1. You can take the speaker- wire back to the module and it will then share the module 0V back to the PSU. So both slide 3 and slide 5 will work. What is important is that the wires to the speaker terminals are tightly twisted together, and from the module to the PSU. So, if you decide to run the speaker- wire directly back to the PSU, make sire you route the wire over the module (but no near any small signal areas!) and then twist or bunch it tightly with the PSU cables back to the power supply.

      2. I usually use 4 or 5mm cable for my speakers so it’s quite heavy. I would not go as low as 1.5mm, but 2.5mm is ok.

      3. If you amplifier modules are mounted on opposite sides of the amplifier chassis, I would use two separate cables for the input. See on how to route the input cables and how to mount the input sockets – mount them next to each other and not on each side of the amplifier.

      • Tuan says:

        Hi Andrew,
        Thanks for your reply.
        What’s the pros/cons of wiring the speaker – back to the PSU? Does it offer any noise performance advangtages?
        Also, do i need to make any changes for a 2-prong electricity plug system? In my country, we use 2-prong plug so there will be no earth wire.
        Thanks again for taking your time and replying to comments.

        • admin says:

          Tuan, if you run the speaker return back to the PSU, you will remove high currents from the main 0V cable running to the amp module and this will in many cases offer reduced distortion. However, the radiating loop area can be larger so you really have to keep the speaker return cable tightly bundled with the power supply cables running from the PSU to the amp modules and make sure you route it over the PCB close to the 0V track if possible.

          For electrical systems where you don’t have an Earth or Safety Ground, all of the wiring practises discussed in the presentations on the hifisonix website still apply with respect to reducing radiating and receiving loop areas, twisting wires etc. Obviously in systems where there is a Earth (eg USA, Europe), this must be securely connected to the chassis. In your case, you should follow your local regulations and just make sure the Live or Hot connection is not exposed at any place inside your amp.

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