Synthi AKS KS Expander (Sneak Preview)

The Synthi AKS KS Expander is an expansion add-on for the Synthi AKS Keyboard Sequencer (KS) that is under development.

The Synthi AKS KS Expander interfaces with the Synthi AKS via the male/female 8-pin Jones connectors on the main Synthi unit and KS, and the special EMS pin cable. The standard connecting cable is removed between the KS and Synthi and the unit’s own cables are used instead.

Pricing is TBD. Technical details below.

KS Expander Features:

  • Two VCO’s each built around the high spec Exar XR-2206 waveform generator IC. Each VCO features Sine and Triangle waves and ‘wave-folding’ (voltage controlled) that adds higher harmonics/distortion to each waveform for amazingly rich and varied timbres ..even unfiltered. Each VCO’s frequency is controllable via CV from either the Keyboard (which is also available to the matrix via Input Ch1) or the Sequencer CV (also available via matrix row 16) of the KS or ‘free running’, selectable via a 3-way toggle switch. Frequency range of the VCO’s is very wide, from LFO to high frequency audio.
    • High spec matched transistors are used (MAT02) for the exponential converters in each VCO circuit. Synch of VCO1 to VCO2 is also implemented in a unique fashion based on a clever property of the XR-2206, that of ‘phase sensitive amplitude modulation’. Effectively this gives a synching of the wavefolding of VCO1 by VCO2 rather than hard synching the core oscillator in VCO1. Front panel pots control initial frequency, amount of wavefolding (‘shape’) and level of each VCO.
    • A modulating triangle waveform is available (speed controlled by the S&H clock speed pot..see below) via toggle switches, to modulate the wave-folding of VCO1 and VCO2. Furthermore VCO1 can also act as a source of Vibrato which can be applied independently to either keyboard or Sequencer pitch CV from the KS.
    • The mixed VCO1/2 combination is available via Input ch2 of the matrix. These additional VCO’s mean that 4-oscillator (if we include Synthi OSC1/2) patches tracking chromatically over several octaves can be created for fat sounds. Even 5-oscillator patches are possible if your Synthi has the hi/lo mod on OSC3. The additional VCO’s can be used as LFO modulation source(s) via input ch2. The unit allows, eg, the KS keyboard to control the pitch of Synthi Osc1 and 2 via Input ch1 and at the same time play CV sequences back just through the additional Expander VCO’s 1 and 2.
  • Slew Limiter (SL) with separate control over the amount of slewing applied to a rising or falling input voltage (‘attack’ / ‘decay’) by front panel pots. Slew limiters like this are very versatile processors. Input/output to the SL is via a (blue pin) cable pluggable into the matrix, the matrix row being the input source and matrix column being the output destination. Thus any source voltage/waveform from the matrix can be slewed before being routed to an output.
    • The slew rate is switchable between linear/logarithmic response. The latter allows for long slew times. Obvious applications of the SL are adding portamento (glide) to pitch CV, or to an LFO to get long attack/decay modulation envelopes, slewing of the trapezoid envelope generated by the Synthi Envelope Shaper etc. The SL also has an invert toggle switch that inverts as well as slews the input. With attack/decay levels set at zero the SL can also thus act as a standard voltage inverter.
    • There is also a toggle switch that disconnects input into the SL via the pin cable and instead feeds a gate pulse triggered by the KS into the SL input. The subsequent slewing of the pulse gives a basic variable attack/decay envelope (with inversion option) as a useful additional modulation source for the Synthi. This envelope is available via the tip of the blue patch pin and can be applied to any destination matrix column.
    • Finally there is a toggle switch that allows direct linking of the SL output to the Sample and Hold circuit which is described below. Two bi-coloured leds monitor the attack/decay voltage levels of the SL with colour change triggered by voltage inversions.
  • Sample and Hold (S&H). Standard LF398 based S&H with variable clock (panel led shows rate). Input/Output is again via a pin cable (red pin) plugged anywhere into the matrix to select a source and destination.
    • In addition there is a toggle switch that links the output of the Slew Limiter into the input of the S&H. This effectively produces a S&H with variable slope slew/invertible input. Insertion of both the SL and S&H pins into the matrix is needed to operate in this mode, with the input source chosen by the row the blue SL pin is inserted and the output destination the column the red S&H pin is inserted into. This is a very useful comination to produce ‘staircase’ waveforms for modulation eg the filter or producing chromatic pitch steps, from eg pitch CV (up or down staircase using inversion) or OSC 3 triangle (up/down staircase) or joystick CV generated stairacse etc.
    • The S&H rate pot also doubles as a frequency control for the modulating triangle wave that can be applied to VCO1 and VCO2 wave-folding, as discussed earlier.
    • Additional pin cable (red pin with white dot) that inverts the S&H output. Very useful feature eg it allows S&H of envelopes like the Envelope Shaper Trapezoid and then applies voltage inversion to the output.
  • Octave Shift via two front panel rotary switches giving octave shifts up to +/-3 octaves which greatly expands the pitch CV range of the KS. Can be applied independently to either Keyboard CV or Sequencer CV from the KS. A toggle switch allows slewing of either the KS Keyboard or Sequencer voltages in addition to octave shifts. This allows portamento to be easily applied to sequences in real time as well as fast octave shifting.
  • Inverter available via the white EMS pin cable. Straightforward operation of inserting the pin into the Synthi matrix. The voltage source from the matrix row where the pin is inserted is inverted before being routed to the destination column. Given that the Slew Limiter can also act as an inverter (see above), 2 inverters are available for use at any one time.

Interfacing with the Synthi AKS

The Expander interfaces with the Synthi AKS via the male/female 8-pin Jones connectors on the main Synthi unit and KS, and the special EMS pin cable. The standard connecting cable is removed between the KS and Synthi and the units own cables are used instead.

11 thoughts on “Synthi AKS KS Expander (Sneak Preview)

  1. As you require one expansion kit for each Synthi that you own, a simple calculation coupled with an informed estimate suggests that it is probably within your means to completely fulfil your expansion kit requirements within an acceptable time frame.

  2. My question is: if I don't have a Synthi can I still use this thing as a little table-top synth? If so, that would be great, and I'd buy one in a heartbeat.

  3. hi guys..sorry its not a 'standalone' unit..only works with and was only designed for use with an AKS.
    Digitana Electronics

  4. Steve, your post allowed me to find Digitana Electronics's website, and all the work you guys are doing with EMS products. It's a shame the Synthi AKS KS Expander doesn't have stand-alone operation. It's also a shame your prices and limited runs cater to a small market, but I suppose at the moment that's what works for your company. I'm sure your recreation of the EMS HiFLi would appeal to a ton of people (myself included), if priced a little differently. Regardless, it's good to see someone is doing the work you guys are doing.

  5. Hi Andrew. Its the usual problem ..I 'am' Digitana Electronics..just 1 person ;0) I do have a friend helping with the HiFLi's but still I am not in a position to mass produce anything and so it takes me many hours to built something like a HiFLi or even smaller units like the Synthi Midi-CV interfaces. Indeed it is a small/niche market..I am not unhappy because I couldnt cope with hundreds of orders..the waiting time would be decades! I think you'll find the same story with other hand built stuff (Buchla and Serge comes to mind. Wonderful things they produce but at a price)
    All I can say is that my units sell for a price that takes into account the number of hours build time. Labour cost far outstrips parts cost in this market. The prime example are the new VCS3 and Synthi A's from EMS. The parts cost is not that high ..the reason why they will be £4k or whatever is simply down to labour costs.

  6. Oh, I'm not disputing your reasons for the high prices. I assumed as soon as I saw the low production runs you had a small operation, and thus prices would be much higher for the labour costs. It would be great if you could work out something more stable like Tom Oberheim has now in terms of production, but then you'd need the equity to start a larger operation like that and a guaranteed client-base (the latter of which I think you could get with some well-placed advertising by the way). I just think it sucks that your products are out of my price-range!

    As a side-remark, I know Buchla and Serge are pretty expensive, but for about £4k you can get a Buchla 200e System #1, or a Serge Animal and Serge Gator. They're different sorts of products than what you're offering, but there's a lot of versatility and flexibility in them. They do cater to wider audience than it seems Digitana does at the moment, although I can certainly see the value and merit in your products as well.

  7. Hi again ..yes you got to the point about bringing costs down = expansion = many many thousands of £ of investment which i just don't have nor do I want the responsibility of people working under me and having to pay their wages etc. Frankly that would put me right off doing what I am doing! I am sorry if my products are not affordable to you…I have enough orders from current Synthi owners to keep me me busy for years, so I think the question of what's affordable is always going to be relative.
    But as a one man operation selling custom designed products their prices are never going to be on the level of mass produced synth products.

  8. Isn’t it time that EMS line be outsourced to China or Korea and manufactured at a more affordable cost? Korg just re-issued the MS20 mini at a $600.00 price point and from all pro reviews it sounds like a pretty close re-make. I just think it’s a shame that EMS is so scarce and the price points are ridiculous for what you get. I think the synth players, and audiences who don’t get to hear enough of Synthi music because of it’s lack of availability would greatly benefit.

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