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Words by Julian Edgar Circuit & PCBs by John Clarke Remotely switch up to six pairs of speakers connected to a single amplifier – or up to 18 pairs connected to three amplifiers! Remote Speaker Switch S peaker switches have been around for many years. Typically, they comprise a box with interlocked switches and connections to an amplifier and multiple pairs of speakers. To select one pair of speakers, you press the appropriate switch. However, these speaker switches have some major disadvantages. The first disadvantage of a conventional speaker switch is that nearly all use terminals that accept only lightgauge wiring. If you want to maintain thick wiring connections all the way from the amplifier to the speakers, for maximum sound quality or high power use, you can’t. The second disadvantage is that all the speaker and amplifier wiring connections need to be routed to where the switch is located – and that can be awkward. For example, if you want a wall-mounted switch that selects between three pairs of speakers, you need to find space inside the wall cavity for eight dual-conductor cables – six for the speakers and two for the amplifier. Especially if you are using heavyduty cable, that can be nearly impossible! Such a wiring approach also often requires overly long cable runs, reducing sound quality and limiting the power handling. The third disadvantage of a conventional speaker switch is that it works with only one amplifier. This is a significant problem if, for example, you 56 Silicon Chip are using one amplifier to power the main speakers and a second amplifier to power subwoofers in the same system. Operating the speaker switch will swap the main speaker output (eg, to a different room) but the subwoofers in the first room will continue operating, and those in the new room won’t start working! To do this changeover with a conventional speaker switch, you would need two switch boxes – one for each amplifier – and press two switches each time. Our new Remote Speaker Switch overcomes all those shortcomings – and gives more benefits besides. Firstly, in our system, the wallmounted speaker selection switch is remote from the main switching box. This means that the main box can be placed right next to the amplifier(s) – it doesn’t have to be anywhere near the selector switch. This approach greatly simplifies the speaker wiring. The connection between the speaker selector switch and the main box is via a plug-in Cat 5/6 cable. You can easily fit this single cable inside any wall cavity. In fact, thin white Cat 6 cables are available that can even be run down the inside corner of a room, while being nearly invisible. Secondly, while the Remote Speaker Switch PCB has the facility to switch two pairs of speakers, by using multiple daisy-chained PCBs, it allows you to select between up to six pairs of Australia's electronics magazine speakers. For example, you can have a pair of speakers in: • two outside areas • the lounge room • the games room • a home office • a bedroom Then, at the turn of the knob, you can select any one of these speaker pairs. Or, more simply, you can use one PCB to switch off an interior pair of speakers and switch on an exterior pair! Thirdly, the Remote Speaker Switch PCBs can be linked to allow the single wall selector to control multiple amplifiers, each working with their own speakers. For example, this will allow bi-amped speakers to be switched, or, as touched on earlier, systems with a second amplifier driving subwoofers. It is possible to switch up to three amplifiers and their associated speakers, so up to 18 speakers can be controlled! In our system, the wall selection switch uses LEDs to show the system status. One LED shows that the power is switched on, while another shows which pair of speakers is selected. The faceplate can be configured to match the number of speaker pairs you are switching. For example, while the switch has positions for six pairs of speakers, if you are switching only three pairs, you can configure the switch for three speaker positions siliconchip.com.au How the Switch is organised Let’s look now at how the Remote Speaker Switch can be organised. The building blocks of the system comprise the Relay Switching PCB and a Control Panel PCB, joined by Cat 5/6 cable. The simplest use of the Remote Speaker Switch is to switch between two pairs of speakers. To do this, you will need one Relay Switching PCB and one Control Panel PCB, as shown in Fig.1. To switch a single amplifier to more than two pairs of speakers requires more Relay Switching PCBs, with one more PCB for every two pairs of additional speakers. In all versions, only one Control Panel PCB is used. These additional Relay Switching PCBs are each configured slightly differently to suit their role. The selection of which speakers they will handle is made by positioning two siliconchip.com.au SILICON CHIMP LEFT SPEAKERS 2 RIGHT Ultra-LD Mk.3 Stereo Amplifier 2 x 135W RMS POWER INPUT 1 INPUT 2 INPUT 3 R + – VOLUME MUTE ACK L + – ON + LEFT AMP+ AMP– – 1, 3 O R 5 SPK+ SPK– + + – + – – 2 , 4 OR 6 SPK+ SPK– CON1 _ A NO NC NC NO CO M D2 4004 CO M COIL COIL 4004 2.2kW RLY2, RLY4 OR RLY6 2.2kW RLY1, RLY3 OR RLY5 D1 + _ A CON2 LED8 R1 100nF Q1 SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 1.5kW R3 FUSE TO SUIT PLUGPACK BC337 R5 D3 4004 CON3 AMP+ AMP– RIGHT A POWER LED1 S1 2 A 3 1 4 LED2 12 5 11 6 10 9 REV.A © 2025 7 8 CON5 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 SPK+ SPK– 2 , 4 OR 6 R2 1.5kW Q2 100nF R4 R6 BC337 CON6 © 2025 (RJ-45 SOCKET) A LED7 SPK+ SPK– 1, 3 OR 5 REMOTE SPEAKER SWITCH 2.2kW GND +12V LED9 CON4 2.2kW and have only three speaker selection LEDs visible. The system can easily be expanded in the future. Extra relay boards can be plugged in, and the faceplate is easily removed and extra LEDs added for more speaker switch positions. Finally, because we are using heavyduty relays to do the switching, there is no audio degradation. We believe the Remote Speaker Switch has sufficient versatility to work in even complex home and commercial systems. LEFT SPEAKERS 1 RIGHT + > Versatile speaker selector with a wall-mounted rotary switch > Modular design is expandable to up to three amplifiers and 18 pairs of speakers > Simultaneously switches main and subwoofer amplifiers/speakers > Wall switch is configurable for the number of speaker pairs that can be selected > Uses standard household wall plate > LED indicators on Control Panel for power and selected speakers > Quick and easy plug-in Cat 5/6 cable connections > Terminal strips allow for heavy-duty speaker cables > Suitable for amplifiers up to 400W (4Ω) or 800W (8Ω) per channel > Can also switch 70/100V public address speakers > No signal degradation 01106252 REMOTE SPEAKER SWITCH resistors appropriately on the PCB – you can think of them as moveable links. Let’s call the two pairs of speakers that the relays switch Speaker Pair 1 and 2. To achieve this switching, the two 1.5kW resistors are positioned at the ‘Speaker 1 and 2’ positions on PCB 1. PCB 2, that will switch the next pair, needs to be configured to switch what we will call Speaker Pair 3 and 4. This is achieved by instead installing the two 1.5kW resistors at the ‘Speakers 3 and 4’ positions. These two PCBs will then work together, the first PCB switching speaker pairs 1 and 2, and the second PCB switching speaker pairs 3 and 4. As you’d then expect, to switch Speaker Pair 5 and 6 requires a third PCB, with this one configured with Australia's electronics magazine (RJ-45 SOCKET) (RJ-45 SOCKET) 01106251 REV.A FITS IN UB1 BOX The lead photos show the wall-mount rotary switch and Relay Switching board. The LEDs on the rotary switch show its position and power status. Also, the RJ-45 connectors on the Relay Switching board make connecting it to the Control Panel easy, and can be used to daisy-chain multiple boards to handle more speakers or amplifiers. ◀ Fig.1: the simplest use of the Remote Speaker Switch is to select between two pairs of speakers driven by a single amplifier. The Control Panel PCB is mounted on standoffs with the LEDs positioned through the drilled holes in the grid and face plates. The vertical RJ-45 socket is different from those used on the Relay Switching board. January 2026  57 L SPEAKERS 1 R L SPEAKERS 2 R L SPEAKERS 3 R L SPEAKERS 4 R L SPEAKERS 5 R L SPEAKERS 6 R AMPLIFIER 1 SILICON CHIMP Ultra-LD Mk.3 Stereo Amplifier 2 x 135W RMS POWER INPUT 3 MUTE ACK L + – ON + RIGHT CHANNEL CONNECTIONS NOT SHOWN FOR CLARITY. LEFT AMP+ AMP– 1, 3 OR 5 SPK+ SPK– + – + – 2, 4 OR 6 SPK+ SPK– LEFT AMP+ AMP– 4004 CON3 GND +12V SPK+ SPK– 1, 3 OR 5 SPK+ SPK– 2, 4 OR 6 CON5 CON6 (RJ-45 SOCKET) (RJ-45 SOCKET) (RJ-45 SOCKET) 1.5kW CON3 SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 REMOTE SPEAKER SWITCH © 2025 01106251 REV.A GND +12V FITS IN UB1 BOX L SPEAKERS 1 R A LED9 AMP+ AMP– RIGHT SPK+ SPK– 1, 3 OR 5 SPK+ SPK– 2, 4 OR 6 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 R2 Q2 100nF 4004 A CON5 CON6 (RJ-45 SOCKET) (RJ-45 SOCKET) (RJ-45 SOCKET) NO BC337 R5 1.5kW CON3 SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 REMOTE SPEAKER SWITCH © 2025 L SPEAKERS 2 R 01106251 REV.A GND +12V FITS IN UB1 BOX L SPEAKERS 3 R NO COM D2 + R3 R6 BC337 NC NC A CON2 R1 D3 CON4 COM LED8 100nF Q1 R4 1.5kW _ COIL 2.2kW 4004 COIL 2.2kW 4004 R3 BC337 R5 D3 CON4 + R1 R4 R6 BC337 COM CON2 LED8 100nF Q1 4004 FUSE TO SUIT PLUGPACK D3 AMP+ AMP– RIGHT A NO RLY2, RLY4 OR RLY6 FUSE TO SUIT PLUGPACK _ R3 BC337 R5 Q2 100nF NC NC D1 D2 4004 A LED9 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 NO FUSE TO SUIT PLUGPACK + SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 COM 2, 4 OR 6 SPK+ SPK– RLY1, RLY3 OR RLY5 _ COIL R2 CON2 LED8 100nF Q1 2.2kW COIL 1.5kW 4004 COM 2.2kW 4004 COIL 2.2kW 1.5kW NO RLY2, RLY4 OR RLY6 _ + R1 NC NC D1 D2 1, 3 OR 5 SPK+ SPK– – CON1 RLY1, RLY3 OR RLY5 + A NO LEFT AMP+ AMP– + – _ RLY2, RLY4 OR RLY6 _ COM 2, 4 OR 6 SPK+ SPK– CON1 RLY1, RLY3 OR RLY5 D1 1, 3 OR 5 SPK+ SPK– + – + CON1 + – 4004 R + – COIL INPUT 2 2.2kW INPUT 1 VOLUME L SPEAKERS 4 R LED9 AMP+ AMP– RIGHT SPK+ SPK– 1, 3 OR 5 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 SPK+ SPK– 2, 4 OR 6 CON4 CON5 CON6 (RJ-45 SOCKET) (RJ-45 SOCKET) (RJ-45 SOCKET) R2 Q2 100nF R4 R6 BC337 1.5kW REMOTE SPEAKER SWITCH © 2025 L SPEAKERS 5 R 01106251 REV.A FITS IN UB1 BOX L SPEAKERS 6 R AMPLIFIER 2 SILICON CHIMP Ultra-LD Mk.3 Stereo Amplifier 2 x 135W RMS POWER INPUT 3 MUTE ACK L + – ON + RIGHT CHANNEL CONNECTIONS NOT SHOWN FOR CLARITY. LEFT AMP+ AMP– 1, 3 OR 5 SPK+ SPK– + – + – 2, 4 OR 6 SPK+ SPK– LEFT AMP+ AMP– GND +12V Q2 100nF CON5 CON6 (RJ-45 SOCKET) (RJ-45 SOCKET) (RJ-45 SOCKET) R4 R3 R6 BC337 1.5kW BC337 R5 CON3 SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 REMOTE SPEAKER SWITCH © 2025 01106251 A REV.A GND +12V FITS IN UB1 BOX L SPEAKERS 1 R LED9 AMP+ AMP– RIGHT SPK+ SPK– 1, 3 OR 5 SPK+ SPK– 2, 4 OR 6 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 R2 Q2 100nF 4004 A CON5 CON6 (RJ-45 SOCKET) (RJ-45 SOCKET) (RJ-45 SOCKET) NO BC337 R5 1.5kW CON3 SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 REMOTE SPEAKER SWITCH © 2025 L SPEAKERS 2 R 01106251 REV.A GND +12V FITS IN UB1 BOX L SPEAKERS 3 R NO COM D2 + R3 R6 BC337 NC NC A CON2 R1 R4 1.5kW COM LED8 100nF Q1 D3 CON4 _ COIL 2.2kW 4004 COIL + CON2 R1 D3 CON4 COM 2.2kW 4004 A LED8 100nF Q1 4004 FUSE TO SUIT PLUGPACK 4004 CON3 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 SPK+ SPK– 2, 4 OR 6 NO RLY2, RLY4 OR RLY6 FUSE TO SUIT PLUGPACK _ R3 BC337 R5 D3 SPK+ SPK– 1, 3 OR 5 NC NC D1 D2 4004 A LED9 AMP+ AMP– RIGHT NO FUSE TO SUIT PLUGPACK + SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 COM 2, 4 OR 6 SPK+ SPK– RLY1, RLY3 OR RLY5 _ COIL R2 CON2 LED8 100nF Q1 2.2kW COIL 1.5kW 4004 COM 2.2kW 4004 COIL 2.2kW 1.5kW NO RLY2, RLY4 OR RLY6 _ + R1 NC NC D1 D2 1, 3 OR 5 SPK+ SPK– – CON1 RLY1, RLY3 OR RLY5 + A NO LEFT AMP+ AMP– + – _ RLY2, RLY4 OR RLY6 _ COM 2, 4 OR 6 SPK+ SPK– CON1 RLY1, RLY3 OR RLY5 D1 1, 3 OR 5 SPK+ SPK– + – + CON1 + – 4004 R + – COIL INPUT 2 2.2kW INPUT 1 VOLUME L SPEAKERS 4 R LED9 AMP+ AMP– RIGHT SPK+ SPK– 1, 3 OR 5 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 SPK+ SPK– 2, 4 OR 6 CON4 CON5 CON6 (RJ-45 SOCKET) (RJ-45 SOCKET) (RJ-45 SOCKET) R2 Q2 100nF R4 R6 BC337 1.5kW REMOTE SPEAKER SWITCH © 2025 L SPEAKERS 5 R 01106251 REV.A FITS IN UB1 BOX L SPEAKERS 6 R AMPLIFIER 3 SILICON CHIMP Ultra-LD Mk.3 Stereo Amplifier 2 x 135W RMS POWER INPUT 3 MUTE ACK L + – RIGHT CHANNEL CONNECTIONS NOT SHOWN FOR CLARITY. LEFT AMP+ AMP– 1, 3 OR 5 SPK+ SPK– ON + + – + – 2, 4 OR 6 SPK+ SPK– LEFT AMP+ AMP– 4004 CON3 CON5 CON6 (RJ-45 SOCKET) (RJ-45 SOCKET) (RJ-45 SOCKET) 2.2kW LED1 S1 A 2 A 3 1 4 LED6 LED2 12 5 A 11 6 A 10 LED5 REV.A © 2025 9 A LED4 7 8 1.5kW BC337 R5 CON3 LED3 01106252 REMOTE SPEAKER SWITCH Silicon Chip 01106251 REV.A FITS IN UB1 BOX GND +12V SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 A LED9 AMP+ AMP– RIGHT SPK+ SPK– 1, 3 OR 5 SPK+ SPK– 2, 4 OR 6 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 R2 Q2 100nF CON5 CON6 (RJ-45 SOCKET) (RJ-45 SOCKET) (RJ-45 SOCKET) BC337 R5 1.5kW CON3 © 2025 REV.A FITS IN UB1 BOX NC NC NO COM D2 + REMOTE SPEAKER SWITCH 01106251 NO A CON2 R1 R3 R6 BC337 D3 CON4 COM LED8 100nF Q1 R4 1.5kW 4004 A RLY2, RLY4 OR RLY6 _ COIL 2.2kW 4004 COIL 2.2kW 4004 COIL R3 R6 BC337 © 2025 A POWER R4 D3 CON4 A LED7 SPK+ SPK– 2, 4 OR 6 COM + R1 REMOTE SPEAKER SWITCH 2.2kW GND +12V SPK+ SPK– 1, 3 OR 5 NO CON2 LED8 100nF Q1 4004 FUSE TO SUIT PLUGPACK D3 AMP+ AMP– RIGHT A NC NC GND +12V SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 FUSE TO SUIT PLUGPACK _ R3 BC337 R5 Q2 100nF NO D1 D2 4004 A LED9 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 COM 2, 4 OR 6 SPK+ SPK– RLY1, RLY3 OR RLY5 _ FUSE TO SUIT PLUGPACK + SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 2.2kW R2 4004 COIL 1.5kW CON2 LED8 100nF Q1 58 COM 2.2kW 4004 COIL 2.2kW 1.5kW NO RLY2, RLY4 OR RLY6 _ + R1 NC NC D1 D2 1, 3 OR 5 SPK+ SPK– – CON1 RLY1, RLY3 OR RLY5 + A NO LEFT AMP+ AMP– + – _ RLY2, RLY4 OR RLY6 _ COM 2, 4 OR 6 SPK+ SPK– CON1 RLY1, RLY3 OR RLY5 D1 1, 3 OR 5 SPK+ SPK– + – + CON1 + – 4004 R + – COIL INPUT 2 2.2kW INPUT 1 VOLUME LED9 AMP+ AMP– RIGHT SPK+ SPK– 1, 3 OR 5 SPK+ SPK– 2, 4 OR 6 CON4 CON5 CON6 (RJ-45 SOCKET) (RJ-45 SOCKET) (RJ-45 SOCKET) SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 R2 Q2 100nF R4 R6 BC337 1.5kW REMOTE SPEAKER SWITCH © 2025 01106251 REV.A FITS IN UB1 BOX Fig.2: up to six pairs of speakers can be driven, one pair at a time, by a single amplifier; as shown in the dashed box. This approach is ideal for switching between speakers in different rooms. If fewer than six sets of speakers are used, some relays and/or boards can be omitted, and the number of LEDs fitted to the Control Panel would be reduced. This whole diagram shows the outputs of three amplifiers, with each able to be switched between up to six speaker pairs. This is ideal for speaker bi-amping (or tri-amping!) and can also be used with systems using separate amplifiers for the main speakers and subwoofers. The input signals to the amplifiers can be different. Australia's electronics magazine siliconchip.com.au the two 1.5kW resistors at the ‘Speakers 5 and 6’ position. Refer to dashed box in Fig.2 for these configurations. Note how in Fig.2, all the Relay Switching PCBs and the Control Panel are connected by Cat 5/6 cables. The amplifier is connected to each Switching PCB. The interconnecting cables supply power to the extra PCBs, so separate power connections don’t need to be made. As you can also see in this figure, in this configuration, not all the RJ-45 connectors need to be installed on the PCBs. Furthermore, on the PCBs powered by the Cat 5/6 cables, you do not need to install the input power terminal strip or the fuse holder. You only need to have those on one of the boards. What about driving multiple pairs of speakers from multiple amplifiers? If running more than two pairs of speakers from each amplifier, the resistor positions on the PCBs are configured just as was described above. That is, the PCB for Speaker Pair 1 and 2 use resistors placed at the ‘Speaker 1 and 2’ positions, the PCB for Speaker Pair 3 and 4 use resistors at the ‘Speakers 3 and 4’ positions, and PCB for Speaker Pair 5 and 6 use resistors positioned at ‘Speakers 5 and 6’ positions. As before, the PCBs are linked by Cat 5/6 cables, with one of PCBs connected to the switch. However, in this configuration, each set of PCBs is fed by a separate amplifier, as shown in Fig.2. As you can also see in Fig.2, not all the RJ-45 connectors need to be installed on the PCBs – the exception is the PCB that also connects to the switch. It uses all three connectors. If you are switching two amplifiers that each drive two pairs of speakers, you need just two Relay Switching PCBs. This would be the case if you were switching a system that, for example, used two amplifiers to drive inside and outside main speakers and subwoofers. In this case, on each PCB, the ‘Speaker 1 and 2’ resistor positions would be used, as shown in Fig.3. Incidentally, while we have been talking about switching from one pair of speakers to another, there are also switch positions where no speakers are connected. You will need one Relay Switching PCB to handle 1-2 speakers, two PCBs to handle 3-4, or three PCBs for 5-6 speakers. This applies regardless of whether you are using one or more amplifiers. siliconchip.com.au Parts List – Remote Speaker Switch 1 12V DC plugpack (100mA+ for each Relay Switching board) 1+ Relay Switching boards (see below) 1 Control Panel board (see below) various Cat 5, Cat 5E or Cat 6 patch leads with lengths to suit the installation Relay Switching board (per board) 1 double-sided, plated-through PCB coded 01106251, 132 × 80mm 2 DPDT 12V 10A cradle relays (RLY1, RLY2) [Altronics S4311, Jaycar SY4008] 2 6-way barrier terminals with 8.25mm pin spacings (CON1, CON2) [Altronics P2106] 1 2-way PCB screw terminal, 5/5.08mm Pitch (CON3) ♦ [Altronics P2038, Jaycar HM3172] 3 8P8C RJ-45 Ethernet PCB sockets (CON4-CON6) [Altronics P1448A] • 2 M205 PCB fuse clips (F1) ♦ 1 M205 fuse, current rating to suit plugpack (F1) ♦ 2 BC337 45V 0.8A NPN transistors (Q1, Q2) 3 1N4004 400V 1A diodes (D1-D3) 2 3mm or 5mm red LEDs (LED8, LED9) 2 100nF 63/100V MKT polyester capacitors 2 2.2kW ¼W axial resistors 2 1.5kW ¼W axial resistors 1 UB1 Jiffy box (optional) 4 6.3mm M3-tapped spacers and short M3 machine screws (optional) • can be reduced to 1 for a single Relay Switching board or 2 for the first and last boards in a string ♦ only required on one board Control Panel board (one required) 1 double-sided, plated-through PCB coded 01106252, 43 × 61mm 1 standard electrical wall plate 1 Clipsal Classic blank grid and plate [C2031VX-WE] 1 single-pole, 12-way PCB-mounting rotary switch (S1) [Altronics S3021, Jaycar SR1210] 1 knob to suit S1 (6.35mm/¼in shaft) 1 8P8C RJ-45 vertical top entry socket (CON7) [Altronics P1468] 7 3mm or 5mm standard brightness LEDs (LED1-LED7) • 2 2.2kW 1/4W axial resistors 4 20mm nylon M3-tapped spacers 4 M3 × 10mm countersunk head machine screws 4 M3 × 10mm panhead machine screws • reduce quantity if switching fewer than six pairs of speakers The Clipsal grid plate with the Control Panel PCB mounted on the rear (left). Note the use of countersunk screws to hold the board in place. These are needed so that the cover plate (right) will correctly slip into place. The drilled grid plate is used as a template to drill the cover plate. Australia's electronics magazine January 2026  59 In the above example, we used two amplifiers, each driving main speakers and subwoofers, and we used the Switch to change from inside to outside speakers. But what if you don’t have outside subwoofers? In that case, you’d simply connect nothing to the ‘outside’ output of the Switch connected to the subwoofer amplifier, so that when you switch from inside to outside, all the inside speakers switch off, but only the main outside speakers switch on. It’s also easy to switch off all the speakers from the remote panel. In fact, there is an ‘off’ switch position between the detent for every pair of speakers. This approach has been taken for two reasons. First, the ‘off’ position is only ever one click away – you don’t need to rotate the switch all the way back to the starting point to switch the speakers off. Second, providing an ‘off’ position between every speaker selection setting ensures that two pairs of speakers can never be momentarily operating. It gives time for the relay to switch off before the next one switches on. Finally, the Remote Speaker Switch LEFT SPEAKERS 1 RIGHT SILICON CHIMP can also switch 70/100V public address (PA) speakers. In this application, the Switch’s wiring connections are just as they are for 4/8W speaker systems; with 70/100V systems, many more speakers can be on the one circuit. Circuit details The circuit is shown in Fig.4. It is divided into two sections: the Control Panel that has the rotary switch, and the Relay Switching section, where the relays are powered on or off for the speaker switching. Both the Control LEFT SPEAKERS 2 RIGHT Using the Switch with a remote amplifier Ultra-LD Mk.3 Stereo Amplifier 2 x 135W RMS One reason we included a power-on LED on the Control Panel (LED7) is for use with remote amplifiers, ie, where the amplifier is inaccessible (eg, mounted in an equipment cabinet or roof space). In this case, you likely have the ability to remotely switch the amplifier’s power on and off. By powering the Remote Speaker Switch from the same source, the power indicator LED on the Control Panel will also tell you when the amplifier is (or amplifiers are) on. POWER INPUT 1 INPUT 2 INPUT 3 R + – VOLUME MUTE ACK L + – ON + LEFT AMP+ AMP– + – 1, 3 OR 5 SPK+ SPK– + – + – – 2, 4 OR 6 SPK+ SPK– CON1 _ NO NC NC NO COM D2 4004 COIL 4004 A COM COIL + 2.2kW RLY2, RLY4 OR RLY6 2.2kW RLY1, RLY3 OR RLY5 D1 + A _ CON2 LED8 R1 100nF Q1 SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 1.5kW R3 D3 FUSE TO SUIT PLUGPACK BC337 R5 4004 CON3 GND +12V LED9 AMP+ AMP– RIGHT CON4 SPK+ SPK– 1, 3 OR 5 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 SPK+ SPK– 2 , 4 OR 6 CON5 R2 1.5kW Q2 100nF R4 R6 BC337 CON6 REMOTE SPEAKER SWITCH © 2025 (RJ-45 SOCKET) SILICON CHIMP 01106251 (RJ-45 SOCKET) (RJ-45 SOCKET) REV.A FITS IN UB1 BOX LEFT SUBWOOFERS 1 RIGHT LEFT SUBWOOFERS 2 RIGHT + + Ultra-LD Mk.3 Stereo Amplifier 2 x 135W RMS POWER INPUT 1 INPUT 2 MUTE ACK L + – A + – + – – 2, 4 OR 6 SPK+ SPK– RLY2, RLY4 OR RLY6 11 _ COM NO NC NC NO COM D2 4004 5 2.2kW LED2 12 COIL D1 4 2.2kW RLY1, RLY3 OR RLY5 A 3 COIL 2 4004 S1 1, 3 OR 5 SPK+ SPK– CON1 LED1 1 6 A 01106252 REMOTE SPEAKER SWITCH Fig.3: a common use for the Remote Speaker Switch is to switch the output of two amplifiers, one powering the main speakers and the other powering one or two subwoofers. For example, the same amplifiers can be used to drive inside or outside speakers. + LED8 100nF Q1 R1 1.5kW R3 BC337 R5 D3 A CON2 CON3 GND +12V SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 FUSE TO SUIT PLUGPACK REV.A © 2025 7 8 4004 9 _ 10 Silicon Chip – + LED7 LEFT AMP+ AMP– A POWER 60 ON 2.2kW 2.2kW INPUT 3 R + – VOLUME LED9 AMP+ AMP– RIGHT CON4 SPK+ SPK– 1, 3 OR 5 CON5 SPK+ SPK– 2, 4 OR 6 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 R2 1.5kW Q2 100nF R4 R6 BC337 CON6 REMOTE SPEAKER SWITCH © 2025 (RJ-45 SOCKET) (RJ-45 SOCKET) (RJ-45 SOCKET) 01106251 REV.A FITS IN UB1 BOX siliconchip.com.au Are Cat 5/6 cables necessary? We chose to use 8P8C connectors and RJ-45 cables to link the boards because they are inexpensive, easy to use, available in a wide range of lengths, and make the system modular. However, if you want to do the extra work, there is nothing stopping you from soldering any multi-core cable with eight conductors (or more) directly between the boards. This allows the use of suitably terminated old multi-core telephone cable etc. However, we don’t think the small cost saving is worth the extra work. If you decide to do this, make sure they are all soldered pin 1 to 1 through to pin 8 to 8. Note that, with the Cat 5/6 network cables, you must use straight-through cables rather than crossover cables. Panel and the Relay Switching sections include indicator LEDs. This split matches the separation of components between the two PCBs. The Control Panel uses a single-pole 12-way (SP12T) rotary switch (S1) to select the speakers you require. Relays in the Relay Switching section handle the actual switching between the amplifier and speaker. On the Control Panel, one LED indicates each switch position. None are lit in the off positions, but one (from LED1 to LED6) will light when a set of speakers is selected. The rotary switch can be limited to positions 1 to 4, allowing the selection of either Speaker 1 at position 2 or Speaker 2 at position 4. Positions 1 and 3 are off positions. For more speaker selections, the switch can be set to operate up to position 6 for an extra speaker selection (Speaker 3), or to position 8 for another selection (Speaker 4). Similarly, position 10 selects Speaker 5 and position 12, Speaker 6. The wiper of switch S1 is connected to a 12V supply, and when the switch is in one of positions 2, 4, 6, 8, 10 or 12, the LED connected to these terminals (LED1 to LED6) will light due to the current flowing through the 2.2kW resistor to ground. At the same time, the switched 12V is connected to a terminal on CON7, an RJ-45 socket. Power is also supplied to this socket at pins 1 and 2. This socket is connected to the Relay Switching board(s) via a Cat 5/6 cable. LED7 lights via a current limiting 2.2kW resistor that’s connected to the 12V supply. This indicates that there is 12V supplied from the Relay Switching board through CON7. The relay switching circuitry mainly comprises two relays, RLY1 & RLY2, for switching two sets of stereo 62 Silicon Chip speakers. To switch extra speakers, another board with identical circuitry can be built. The first circuit is for Speaker 1 (RLY1) and Speaker 2 (RLY2), the second for Speaker 3 and Speaker 4, and the third circuit for Speaker 5 and Speaker 6. These boards are interconnected using daisy-chaining 8-wire Cat 5 or Cat 6 leads between CON6 on one board and CON4 on the next. The relay coils are not directly driven from the switch contacts because the switch contacts are only rated for 150mA, and each relay draws 75mA when powered. Since more than one relay could be driven at the one time, the contact current will reach or exceed the switch rating, reducing the switch’s life. Therefore, an NPN transistor is used to drive each relay coil (Q1 or Q2) and only the base current (just under 3mA) used to drive that transistor is passed through the switch contact. Transistor Q1 is used to drive RLY1, while transistor Q2 drives RLY2. In the first circuit for Speaker 1 and Speaker 2, the bases of Q1 and Q2 will be driven via resistors R1 and R2, respectively. When building the second circuit for Speaker 3 and Speaker 4, the transistor bases are driven via resistors R3 and R4 instead. The third circuit, for Speaker 5 and Speaker 6, has the bases of Q1 and Q2 driven via R5 and R6. Each relay coil has a normally reverse-biased diode (D1 for Q1 and D2 for Q2) across it. This shunts the back-EMF from the coil when the transistor switches off. The 100nF capacitor across the 12V supply provides a reservoir for this charge, so the 12V rail’s voltage doesn’t increase much each time the relay switches off. There is also one LED across each Australia's electronics magazine Fig.4: the Control Panel (left) uses a 12-position rotary switch with indicator LEDs. The Relay Switching board (right) uses two transistors to drive the relays that switch the speaker connections. The RJ-45 sockets allow easy connection to the Control Panel and other relay boards used to expand the system. relay coil that lights when the relay is on. The Altronics relays include an internal indication relay, but other, compatible relays may not. In addition, the internal LEDs require the coil to be connected with a specific polarity, while the external LED orientation is designed to suit the drive arrangement, regardless of the coil orientation. Power for the circuit is via a nominally 12V DC plugpack. Fuse F1 adds protection if a short circuit occurs, while diode D3 is connected in reverse across the supply so that if the supply is connected with the wrong polarity, the diode will conduct and the fuse will blow. The current requirement is up to 100mA for each set of two relays. So if you use three relay circuits, a 300mA plugpack is required. You can use a higher-rated plugpack. Each relay is used to drive a stereo pair (left and right) speakers from an amplifier, switching the positive (+) amplifier terminals. The negative terminals (−) of each stereo amplifier are permanently connected to the outputs, but the channel negatives are not joined. This allows siliconchip.com.au the use of bridge-mode amplifiers, which are increasingly common. In that case, the negative output terminals are not at ground, but actively driven to swing in the opposite voltage polarity to the positive terminals. Construction Both boards are straightforward to assemble. The Relay Switching board is built on a double-­sided PCB coded 01106251 that measures 132 × 80mm – see Fig.5. Fit the low-profile components first – the resistors, capacitors, diodes, LEDs and transistors. The position of the two 1.5kW resistors depends on whether this board will switch the first, second or third pair of speakers. The diodes, LEDs and transistors must be inserted the right way around – follow the markings on the PCB and in Fig.5. The longer lead of the LED is the anode (marked with an “A” on the PCB). Insert the terminal blocks for the power supply and speaker connections next. The speaker terminal blocks can go either way around, but the power supply terminal block’s openings must face the bottom of the PCB. Next, solder in the fuse clips, ensuring the tags that hold the fuse in place are on the outside at each end. The RJ-45 sockets can be soldered into place next. The solder pads are fairly close together, so check after soldering that you have not made any bridges – use a magnifying glass to do that if necessary. Finally, solder the two relays into Fig.5: the Relay Switching PCB is easy to build. The diodes, LEDs and transistors must be inserted the right way around. After soldering, check for bridges between the RJ-45 socket pins – these are quite close together. siliconchip.com.au Australia's electronics magazine January 2026  63 place. You will have to push down firmly to get the relay terminals to project sufficiently through the PCB. The number of RJ-45 sockets each board requires depends on the amplifier and speaker configurations you are switching – see Figs.1-3. Also, only one board requires the fuse holder and input power terminal strip – the remaining linked boards get their power feeds via the Cat 5/6 cable connections. Having said that, we chose to insert all these components on every board – it gives more versatility, should the system requirements change in the future. Building the Control Panel Making the Control Panel and mounting it takes several steps. We will assume that you are using the specified Clipsal Classic blank grid and cover plates. Copy or print out the drilling template (Fig.6) at actual size (100% scale) and position it on the grid plate. Ensure the position you have chosen on the grid plate will allow the PCB to fit within the wall opening. Use clear adhesive tape to hold the drilling template in place and then drill the four 3mm holes for the PCB standoff mounts. Countersink these holes by hand with a larger drill bit – the screws that mount the standoffs must be flush with the outer surface of the grid plate. Next, drill the holes for the power LED and switch position LEDs. Remember that you need to drill holes to match the number of speaker pairs you are switching; they can be either 3mm or 5mm holes, depending on what size of LEDs you have chosen to use. Now drill the 10mm hole for the Fig.6: the drilling template for the Control Panel. All dimensions are in millimetres, and this diagram is shown at 100% scale. shaft of the rotary switch. It is not held in place with its shaft mounting nut; instead, it is held by the PCB. If you are switching fewer than six pairs of speakers, the nut & washer will need to be removed, and the switch rotated fully anti-clockwise, before you can access the tab washer that sets the number of positions the switch can move through. You will also likely have to shorten the shaft of the switch to suit the knob you are using. This is easiest done by placing the shaft in a bench vice and using a fine-tooth hacksaw to cut the plastic shaft to length. Clip the faceplate over the grid plate and, using the drilled grid plate as the template, drill the faceplate holes from the rear – that is, the holes for the shaft and all LEDs. Do not drill the four holes for the PCB mounts through the faceplate! Deburr all the drilled holes in both plates with a larger diameter drill bit by hand. Now it’s time to assemble the Control Panel PCB, which is coded 01106252 and measures 43 × 61mm – refer to Fig.7. Solder the two 2.2kW resistors to the PCB, then mount the rotary switch. Attach the nylon standoffs to the PCB. Insert the leads of one of the LEDs into the holes in the board, then offer the PCB up to the rear of the grid plate. You can then easily push the LED through the appropriate grid plate hole before soldering the LED leads into place, making sure the longer lead goes into the hole for the anode (“A”). Repeat the process for each of the LEDs. Doing it this way means the LED leads are all precisely the correct length (LEDs with short leads may need tinned copper wire extensions). The switch rotates clockwise, as viewed from the front. Insert the first LED in the upper-most PCB position – this is, for the first pair of speakers. Install the LED for the next pair of speakers in the next clockwise PCB position – and so on, for the number of speaker pairs you are switching. Note that the power LED is optional – if you don’t want it, you can leave it out. Now solder the RJ-45 socket into place, noting that it is placed on the underside of the PCB and is a vertical (top-entry) socket, unlike those on the Relay Switching board. Mount the PCB to the grid plate using the previously attached nylon standoffs and countersunk head 3mm screws. Remember to feed the LEDs through their appropriate holes as you mount the PCB. Check that the drilled cover plate neatly fits over the grid plate and clips into place. Testing When you have finished building the switch and relay boards, check the soldering carefully with a magnifying glass. You are looking for cold joints (dull finish), incomplete soldering or solder bridges. Connect the Control Panel and Relay Switch boards with a Cat 5/6 cables. You can connect one at a time for testing if you’ve fitted the power supply Fig.7: there are just a few components on the Control Panel board so it shouldn’t take long to assemble, but prepare the switch plates first, as described in the text. You only need to install the LEDs that you want or need, ie, one per set of speakers switched (LED1-LED6), plus the power indicator (LED7), if desired. 64 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.8: the cutting details for the optional Jiffy box enclosure for a Relay Switching board. The hole positions shown suit a PCB attached to the base using 6.3mmtall standoffs. components to all of them; it doesn’t matter which connector the cable goes into on the Relay Switch board. Otherwise, connect the Control Panel to the Relay Switch board that has the power supply input. Apply 12V power and rotate the speaker selection knob. One relay (and its associated LED) should activate with the switch knob at the uppermost (12 o’clock) position, then switch off at the next clockwise switch click. Another relay and LED should activate at the next clockwise click. If all is well and you are using multiple Relay Switching boards, switch off power and use another Cat 5/6 cable to daisy-chain the next Relay Switch board. Switch the power back on and check that this works as required – depending on your switching arrangement, either the second board will mimic the behaviour of the first, or its relays will activate at further switch positions. Continue the testing until you’ve verified that all the boards are working. Mounting it The rotary switch is designed to mount behind a standard wall plate. However, if you wish, the Control Panel could be mounted in a box. The relay board fits in a UB1-sized Jiffy box using 6.35mm standoffs. If you are using multiple Relay Switch boards, multiple Jiffy boxes can be used, side-by-side or on top of each other. Fig.8 shows the template for cutting holes in the box sides to allow access to the RJ-45 sockets. However, as the boxes are likely to be hidden from view, round holes could instead be drilled at each of these positions – this will be quicker and easier. To allow the speaker and amplifier connections to the terminal strips, cut a rectangular hole in the appropriate wall of the box or drill a hole. Installation We’ll initially assume that you are Driving speakers in parallel switching one amplifier between two pairs of speakers. Connect one pair of speakers to the Relay Switching board. Using the “Spkr 1,3 or 5” terminals, make both the left and right speaker connections. Then connect the amplifier’s outputs to the board, again to the left and right inputs. Power up the switching system and amplifier. The speakers should work when the switch is set to position 1, and be muted with the switch in other positions. When that is working, power it off and connect the second pair of speakers, using the “2,4 or 6” terminals. You should then be able to switch between the two pairs of speakers. For more complex switching, start with the simplest switching and then build the system from there, checking each step by playing audio and confirming that the speakers are working properly. With complex systems, there are a lot of wires to connect, so always test the system step-by-step rather than SC connecting everything at once. Only the ‘master’ board needs the input power terminal strip and the fuse – the other boards will receive power via the interconnecting Cat 5/6 cables. The Remote Speaker Switch does not allow the operation of multiple pairs of speakers at once. That is, it can connect Pair 1 or Pair 2 to an amplifier, but not Pair 1 and Pair 2 at the same time. This means that, assuming all the speakers have the same impedance, the impedance seen by the amplifier does not change, irrespective of the selected speakers. However, if the amplifier is wired to drive two pairs of speakers, the Remote Speaker Switch can switch between multiple sets. For example, let’s say the speakers are all 8W and the amplifier is happy with a 4W load. You can wire two pairs of speakers in parallel, so that each channel has two speakers (four in total), and each channel gives a 4W load to the amplifier. Then, you can use the Switch to alternatively select another four speakers, wired in the same way. So, while we have shown only one pair of speakers connected to each Remote Switch output, if the impedance doesn’t become too low, you can use two pairs of paralleled speakers on each amplifier output. siliconchip.com.au Australia's electronics magazine January 2026  65