Digitana Electronics Synthi Hi-Fli


press release (May 1st, 2010)

I am pleased to say I have negotiated with Robin Wood at EMS to re-release the Hi-FLi under License. The price for each re-release Hi-FLi unit (including pedals) will be £2000 + shipping. This price is a reflection of the many hours of build time each unit takes (this is not a glorified 'stomp box' and is closer in complexity to a Synthi A or a VCS3 than it is to any stompbox. Don't forget the original HiFLi sold for £350 in the early 1970's which conservatively translates to about £3500 today). They are extremely labour intensive to build. The number of units I will make to sell directly is 15. Any more than that or those units I may build for EMS to sell is not decided yet. I already have a current waiting list of 13 people. If you are interested in putting your name on the build list for one the remaining 6 then please email me. Its hard to predict the exact rate of production but i expect to make about 8-10/year.

Digitana Electronics

The Synthi Hi-Fli was designed by legendary EMS electronics genius David Cockerell (of Synthi AKS/VCS3/Synthi100 fame) in 1973, probably primarily as a guitar effects unit (though it certainly has uses as an analogue effects for synth sounds) and used by the likes of Dave Gilmour (Pink Floyd) and Steve Hackett (ex Genesis) and others. I was intrigued by the air of mystique surrounding this unit. It seems to be regarded by many guitar player out there as the ‘Holy Grail' of vintage analogue guitar effects.

Whether this is because it's also one of the rarest effects in the world, maybe in part explains this. Although guitar playing is not something I am good at... I was also intrigued by its possible uses on synth type sounds. The prototype is an exact duplicate of the circuits of the original mk2 Hi-FLi..down to using the same obsolete transistors and the same opamps. The only 'electronics' difference is my use of a very stable toroidal transformer based internal power supply.

The case design is of course different. The original was in a wonderful white fiberglass (very 1970's style!) console..something that is beyond my skills to easily reproduce. Therefore I opted for a powder coated black steel chassis with iroko end-cheeks and a cnc engraved and machined top panel (I made this myself with my CNC engraver/router) in satin anodized silver aluminium. Part of the project was also to clone the original pedal unit... this being a crucial part of the HiFLi in my opinion.

I used 2 new Moog expression pedals suitably adapted and fitted with a preamp as the original. The audio input (eg guitar or synth) is via a jackplug built into the side of the left pedal. Control voltages and amplified audio go to the main unit via an 8 way umbilical cable with Jones plug on the end (just like the original). The right hand pedal has a convenient pot to control the amount of preamp gain. This scaling pot was part of the original Moog pedal so I made good use of it!

Hi-FLi Main Features

The HiFLI consist of several sections. Those on the left half are Top Boost, Octave Shift (containing Sub-Octave and Ring Modulation features) and Sustain Fuzz. Then a Bypass Mixer (mixing wet/dry signals) divides the left and right parts and the right half consists of probably the most important part as regards sound shaping, a wonderful multi-feature Phase Filter. I also added 2 features that appeared on the original HiFLI mk2 units: a bypass front panel slide switch to bypass the left hand side effects completely and send the audio signal directly into the Phase Filter (very useful!) and an additional ‘Growl' switch that drops down the fundamental note extracted from the audio in by 2 and 3 octaves (The Sub-Octave drops it by 1 octave). These sub-harmonics are not just combined with the original sound but used to modulate the phase filter thus allowing very strange/bizzare new sounds to be created. The pedal unit is a fantastic idea. All the front panels sliders simply provide a control voltage to operate each effect..yes all the effects are voltage controlled! On the bottom of each slider is a 3 way slide switch marked ‘+,0.-‘. In the ‘0' position the pedal has no affect on that effect as you operate it and the slider acts as the effect control. In the + or - position operating the left or right pedal sends a control voltage that swings from +12v to -12v or -12v to +12v as you move the pedal up/down. The left/right pedals control the left/right hand effects when viewing the top panel. Since there is an independent pedal slide switch on every effect..you can imagine the creative possibilities here! There are many many different sounds you can create simply by altering the state of each pedal voltage slider switch. This is a really great idea and is why I said earlier that the pedals unit in my opinion is crucial to getting the most out of the HiFLi.

The Effects

Before we get on to the effects, an important function of the HiFLi is to detect an attack/decay time from the input audio. So for a plucked guitar string the initial attack and the point at which the amplitude drops below a certain level is detected. The attack detection is used to trigger other effects which I'll discuss later. An exponentially decaying envelope is also generated from this attack/decay section. The attack/decay extraction is rather sensitive and its ‘correct function' (ie single rather than multiple triggers as each string is plucked) depends on how you play (solo/strum) and the input level of the audio from the preamp. Thus there is a panel slide switch for flipping between sensitivities, one for ‘solo' and the other for ‘strum' guitar playing. In practice I found you can play as you wish in each mode and you get different responses/sounds!

  • Top Boost

    Audio in from the preamp in the pedal unit is fed to the Top Boost that is basically a treble boost. Makes quite a big change to the sound when you push the slider up ..particularly on fuzz sustain.

  • Octave Shift/Ring Modulation

    This section involves a suboctave generator that extracts a fundamental note form the audio in and drops it by one octave. Rather than simply mix this suboctave with the original signal something more sophisticated is done. A ‘pseudo' ring modulation effect occurs where instead of multiplying 2 waveforms, the RingMod just adds a half wave rectified version of the fundamental to the output of the Top Boost and thus can produce a fundamental that is double in frequency..so a bit like what happens with a standard RingMod where the frequency of eg a sine wave sent in is doubled though waveform multiplication.

    But in the HiFLi RingMod version one doesn't hear the typical metallic/bell like sounds. Rather this pseudo ringmod signal is sent to a pair of FET's which act as modulators..modulated by the suboctave signal. The result is some great deep suboctaves the amount of which are controlled by the ringmod and suboctave levels.

  • Sustain Fuzz

    A fairly standard but nice sounding fuzz section that can be mixed with the output of the Octave Shift. The fuzz input is the from the Top Boost section. The fuzz attack time is controlled from the attack/decay section and is variable. On fast rise times..the fuzz appear instantly a string is plucked. Slower rise times allow the fuzz to ‘swell' in amplitude after the string is plucked. So you get a slewed fuzz effect. Great!

  • Phase Filter

    Here is where the major soundscaping effects occur. The phase filter is in fact 6 filters and FET/bipolar transistor switches that alter the signal path through the filters of audio fed from the left hand effects. The 6 different ‘Treatments'(selected by front panel rotary switch) are Vibrato, Phasing 1,Phasing2, Waa, Waw and Meow are the result of different paths the audio is fed through the filter sections. For any given phase filter configuration above, there is in addition, 6 different modulations you can apply to vary the frequency of the phase filter. Varying the frequency alters the amount of phase shift that occurs in the audio signal. These modulations take the form of ‘transients' ie waveforms that are produced only between the attack and decay sections of eg a plucked guitar string. Outside of this ‘attack/decay' envelope the modulation waveform goes back to a simple sine wave. The 6 transients are slow sine, fast sine, increasing amplitude sine, decreasing amplitude sine, ramp up and ramp down. Modulation speed is controlled via slider (or pedals) and modulation amount by another slider. Here is a great feature. The time taken for transients to appear modulating the phase filter is controllable. So there is a slew option ..controllable via the modulation ramp time slider/pedal. Finally there is a slider/pedal that directly shifts the frequency of the phase filter. This allows you to ‘sweep' the audible range of the filter if you use pedal control.

    The ‘Growl' switch option drops the fundamental by 2 or 3 octaves depending on the switch position. As mentioned above, these sub-harmonoics are used to modulate the phase filter not simply mixed with the orighinal sound. This gives amazing/bizzare new modulations! The amount of growl is controllable via the depth slider and also if the increasing/decreasing sine modulation is selected, by the decaying envelope extracted from the attack/decay section of the input audio.

    My impression of the phase filter is that its the ‘guts' of the HiFLI and produces an astonishing range of phasing effects form subtle vibrato to screeching wah sounds all with transient modulations on top! The Envelope and Fuzz bypass switch allows you to bypass completely the left hand effects section of the HiFLi and send audio directly into the Phase Filter. This was something (along with Growl) that EMS seem to have added in the mk2 version of the HiFLI..so you wont see it on earlier mk1 versions. Its a simple idea but allows for yet more different sounds..'clean phasing' if you wish Finally the bypass mix slider is a simple dry/wet mix control of the audio output.

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