![]() It certainly has the classic Moog filter sound and it is very stable – one of the notable things about the Sonic Six’s filter is that it can be tuned to track the keyboard surprisingly closely – Once set up correctly you can set the resonance slider to full so that the filter becomes a sine wave oscillator and then use the cutoff frequency slider to tune the filter note so that it is at correct pitch to be played by the keyboard and it becomes a rather haunting “third oscillator”. The image below shows the filter and you can see from the layout of the parts where it gets it’s name. I have only seen transistor type filters in the Sonic Sixes that I have come across, some of the earlier units may have had a diode filter instead. Starting with the VCF we find the classic Moog transistor ladder low-pass filter design. It’s a clever design indeed, very neat and it would have made assembly at the factory quite easy. This board is held in place by some tiny screws and it’s the first place to check if your Sonic Six is behaving erratically – Removing it and treating it with some contact cleaner and re-seating it can clear up any problems caused by tarnished contact pins. All electrical connections to, from and between the two circuit boards are made via a long, thin joiner circuit board that links the two main boards together and connects them to a pair of multicore cables that run down to the bottom case section. In the image below you can see a close-up of one of these clips. Small spring steel clips latch onto these pins and hold the boards in place, these make for quick removal and re-installation of the boards. The boards are held in place by small pins projecting from the rear of the front panel and they can be seen in the photo above. ![]() In the image above you can see the two circuit boards disconnected from the front panel, the rear of which is visible at the bottom of the photo. In the image below you can see the black mains transformer that is mounted behind the action and it is multi-voltage and can be switched for use in different countries by a selector slider beside the mains input socket. Beneath the circuit board are two hefty silver coloured filtering capacitors with solid screw terminals. The rest of the bender module is quite simple – you can see the 4 mains rectifier diodes to the right of the volume slider, between the sliders is a resistor and a couple of other diodes (and an IC and more diodes depending on the version) to provide a centre “dead band” for the pitch wheel to ensure that it cannot pull the synth off pitch if it doesn’t return to centre perfectly. in front of the two sliders is the horiontally aligned bend wheel which has a good, strong return spring providing a definite re-centering action. The bender pot is a good quality closed frame part well protected against dust. Something interesting is immediately seen – The two sliders for the master volume and glissando controls appear to be the same type of sliders that ARP used in their 2600 synth. The story has been well documented already and a search on the internet will reveal more information, Gordon Reid has a very good article on his site on the history of the Sonic Six. This isn’t the place to repeat the story of the synth that Dr Moog didn’t want to make, it was born from a synthesizer called the Sonic Five which was designed by one of his ex-employees for another company and it took the purchasing of RA Moog Music by MuSonics to bring Dr Moog into the Sonic Six story. ![]() The Sonic Six has it’s own story and it was almost not made at all. Moog produced many instruments during their various incarnations throughout the second half of the 20th century and continue to design and manufacture synthesizers to this very day. There were many ups and downs for the pioneering engineer Robert Moog, he was designing circuits and building instruments that had never been seen before at the same time as learning to run a company and a manufacturing production line and as if that wasn’t enough, he and his small team had to convince artists and music stores that these strange electronic devices were practical and useful musical instruments that were worth buying, learning to use and to be early adoptors and to risk taking on stage and into the studio.
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