AJHSynth

Notes: The Gemini 2412 is a creamy, extremely fat sounding dual filter based on vintage Oberheim SEM circuits. In addition to high-pass, band-pass and low-pass, there is the infamous variable filter type, which allows you to blend between several characteristics. Thanks to its dual concept, serial and parallel modes of operation and an ingenious modulation system, the Gemini 2412 should not only be able to achieve classic, extremely bulbous results, but also wafting stereo effects and lively formant sounds.

Notes: The Low Fat is a new 2hp Eurorack module by AJH Synth, it's a High Pass filter, with frequency control by either manual pot, and/or external CV with attenuator. It's intended to compliment other filters, particularly low pass VCF modules, in practical tasks such as removing excessive low frequencies, for example when the bass is swamping a mix. It can be switched between 6dB (1 pole) response and 12dB (2 pole) response.

By patching a CV signal to the FCV input it can be voltage-controlled and used musically as with any other VCF. When used in conjunction with a LP filter it forms a fully customisable band pass filter, allowing the range of passbands to be cherry-picked. Feeding in a 1V/Oct pitch CV and setting the FCV pot to a suitable level allows it to track an incoming pitch CV, so the amount of High Pass filtering remains constant as the pitch of the incoming VCOs traverse up and down the frequency range. This can be particularly useful in creating percussive sounds, such as snares and hats, but also on sequenced bass lines. Since it is only 2HP it's a great way to occupy one of those frustrating gaps in your eurorack modular case with something that is deceptively useful, and adds another dimension to the classic bass monster that is the Transistor Ladder Filter.

Dimensions:
2 HP
26 mm deep

Current Draw:
9 mA +12V
12 mA -12V
0 mA 5V

Notes: Truly unique one from AJH, based on the sound of NASA's Apollo voice transmissions. Think outside the box and process drums and synths through this thing. Freaky. May or may not allow you to communicate with real astronauts.

Supplier's notes:
Here's a bit of fun for all fans of space missions from the previous century! This module is designed to re-create the ground to space and space to ground transissions from the Apollo era.

To be "Mission Control Houston" the Quindar PTT (push to talk) button adds a short 2,525Hz Qindar tone to the start of the transission, then at the end of the message the PTT button or switch is released and a short 2,475Hz Quindar tone is added to the audio. The bandwidth is slightly reduced in this mode.

For "Astronaut comms" we press the Capsule PTT switch, which allows us to add coloured noise, distortion, bandwidth reduction and either hum or LGM (Little green men space tone) noise to the audio signal. A deep space electret condenser mic is supplied and an be used with the MIC input.

Obviously the Lunar Module can also be used to add noise, hum, distortion, bandwidth reduction and LGM noise tone to any modular level audio too, and if the mic is left attached theremin like sounds can be added too with careful loudspeaker feedback.

Notes: Presenting the new AJHSynth Matrix VCF - this may well be the most versatile Eurorack VCF ever.

This amazing multimode filter and VCA offers sixteen different filter types, and two different resonance models on each, totalling an incredible thirty two assorted resonant filters to choose from. AJH Synth have also included manual and CV control of filter type selection, along with 16 LED's that give a clear visual indication of which filter type is currently selected.

The filter core circuitry is based on that of the rare and highly sought after Oberheim Matrix 12 synthesiser, and of course has an all analogue signal path. The Matrix 12 VCF originally offered fifteen filter types, however AJH Synth have expanded this to 16 with the addition of AP4, a full four pole all pass phaser mode.

AJH Synth have added a unique P-Vox resonance distortion and overdrive circuit that changes the character of the resonance completely, and can force all of the filter modes into self oscillation. This effectively doubles the filter variants and hugely broadens what is already a very impressive sound pallet.

Other features include an inbuilt VCA with Input and Output Level controls, a Peak level LED, CV control of resonance, and of course the legendary AJHSynth build quality.

The Matrix VCF in depth

After two years of development AJH Synth have finally released what they consider to be the most versatile Eurorack VCF & VCA ever. Like many other AJHSynth modules it uses the very best vintage analogue circuitry as the starting point for the design, and in this case, the filter was chosen from the rare and very desirable Oberheim Matrix 12 synthesiser. AJH Synth expanded this from the original fifteen filter compliment to sixteen distinct filter types by adding in a really useful four pole phaser!

So, behind the compact 14hp front panel lies sixteen distinct filter types, including all of the favourites: Low Pass filters with a choice of one, two, three or four poles, Band Pass filtering with two or four poles, High Pass filtering with one, two or three pole options, along with Notch filtering and four complex, combination filter types. Finally, a four stage phaser with two types of emphasis that can be forced into tuneful self-oscillation!

However, this is far from the end of the story. AJH Synth decided to use their design expertise to add in some crazy resonance distortion circuitry, that could be switched on from the front panel. This was inspired by the filter from the Soviet Polivoks synthesiser, but again the implementation used here is considerably changed, improved, and best of all this can be applied to all filter types! This completely changes the filter character when engaged, and it forces all of the filters into self-oscillation at higher resonance settings. Better still, the oscillation waveforms are more harmonically rich than the usual sine waves - everything from gloriously fat to screaming and angry! Best of all, this takes the number of different filters up to a massive thirty two variations!

AJH Synth put a lot of thought into the ergonomics and how to select the individual filter type. Filter type can be changed either with the front panel Mode knob, or by using a control voltage patched to the MODE CV input. The selected filter mode is displayed by the LED next to the filter in use. This is also very helpful when using a step sequencer to change filter mode as it gives a real time display of the filter chosen as you take the step CV voltage up or down, while setting up each individual step.

Lastly, AJH Synth have also included a VCA hard-wired to the output - simply patch an envelope or an LFO to the VCA input, connect a VCO to the audio input and you have a synth voice (with a choice from 32 different filters!) using only three modules!

Thirty two Eurorack VCF's and a VCA would most certainly take up a lot of rack space - AJH Synth have got all of this into 14hp and managed to have a really finger-friendly user interface, without it feeling cramped.


Sixteen distinct filter modes to choose from

Here's a list of the different filter modes that are available:
1 - Four Pole Band Pass
2 - Three Pole High Pass combined with One Pole Low Pass
3 - Three Pole All Pass combined with One Pole Low Pass
4 - Two Pole Notch combined with One Pole Low Pass
5 - Two Pole Low Pass
6 - Four Pole All Pass (Phaser)
7 - Four Pole Low Pass
8 - Two Pole Band Pass
9 - Two Pole High Pass combined with One Pole Low Pass
10 - Three Pole High Pass
11 - Three Pole All Pass
12 - Two Pole Notch
13 - One Pole Low Pass
14 - Two Pole High Pass
15 - Three Pole Low Pass
16 - One Pole High Pass

All of the above filter types can be further altered by switching in P-Vox mode, this doubles the list up to thirty two different filter variants!

P-VOX MODE

Transforming the resonant character of every filter type

This magical switch completely transforms the resonance of the filter core by overdriving it in a similar fashion to the filter from the Soviet Polivoks synthesiser, which was renowned for it's powerful, aggressive character.
In common with the Oberheim Matrix 12 VCF, some of the sixteen filter types will not normally go into self-oscillation, however when you switch on P-Vox mode all sixteen filter types can be forced into self-oscillation at higher resonance settings. But that isn't the only change, the self-oscillation waveform is not the usual sine waveform, it is a rather more interesting and harmonically rich waveform that varies according to the filter type chosen - generally Low Pass modes produce the nearest to regular sine waves, whereas other filter types can produce very much more complex waveforms as can be seen in the diagrams below. It does not require any audio input for this, it can be a stand alone oscillator. Most of the filter types will track 1V/Oct reasonably well over a three to five octave range, so it can be used as a VCO with a few interesting waveshapes!

Of course, P-Vox mode isn't just useful for self-oscillation, it adds lots of character to any audio signal as P-Vox resonance is switched in.

Module Width: 14hp
Module Depth: 29mm (Including power lead)
Current Usage: 56mA Positive, 36mA Negative

Notes: Presenting the new AJHSynth Matrix VCF - this may well be the most versatile Eurorack VCF ever.

This amazing multimode filter and VCA offers sixteen different filter types, and two different resonance models on each, totalling an incredible thirty two assorted resonant filters to choose from. AJH Synth have also included manual and CV control of filter type selection, along with 16 LED's that give a clear visual indication of which filter type is currently selected.

The filter core circuitry is based on that of the rare and highly sought after Oberheim Matrix 12 synthesiser, and of course has an all analogue signal path. The Matrix 12 VCF originally offered fifteen filter types, however AJH Synth have expanded this to 16 with the addition of AP4, a full four pole all pass phaser mode.

AJH Synth have added a unique P-Vox resonance distortion and overdrive circuit that changes the character of the resonance completely, and can force all of the filter modes into self oscillation. This effectively doubles the filter variants and hugely broadens what is already a very impressive sound pallet.

Other features include an inbuilt VCA with Input and Output Level controls, a Peak level LED, CV control of resonance, and of course the legendary AJHSynth build quality.

The Matrix VCF in depth

After two years of development AJH Synth have finally released what they consider to be the most versatile Eurorack VCF & VCA ever. Like many other AJHSynth modules it uses the very best vintage analogue circuitry as the starting point for the design, and in this case, the filter was chosen from the rare and very desirable Oberheim Matrix 12 synthesiser. AJH Synth expanded this from the original fifteen filter compliment to sixteen distinct filter types by adding in a really useful four pole phaser!

So, behind the compact 14hp front panel lies sixteen distinct filter types, including all of the favourites: Low Pass filters with a choice of one, two, three or four poles, Band Pass filtering with two or four poles, High Pass filtering with one, two or three pole options, along with Notch filtering and four complex, combination filter types. Finally, a four stage phaser with two types of emphasis that can be forced into tuneful self-oscillation!

However, this is far from the end of the story. AJH Synth decided to use their design expertise to add in some crazy resonance distortion circuitry, that could be switched on from the front panel. This was inspired by the filter from the Soviet Polivoks synthesiser, but again the implementation used here is considerably changed, improved, and best of all this can be applied to all filter types! This completely changes the filter character when engaged, and it forces all of the filters into self-oscillation at higher resonance settings. Better still, the oscillation waveforms are more harmonically rich than the usual sine waves - everything from gloriously fat to screaming and angry! Best of all, this takes the number of different filters up to a massive thirty two variations!

AJH Synth put a lot of thought into the ergonomics and how to select the individual filter type. Filter type can be changed either with the front panel Mode knob, or by using a control voltage patched to the MODE CV input. The selected filter mode is displayed by the LED next to the filter in use. This is also very helpful when using a step sequencer to change filter mode as it gives a real time display of the filter chosen as you take the step CV voltage up or down, while setting up each individual step.

Lastly, AJH Synth have also included a VCA hard-wired to the output - simply patch an envelope or an LFO to the VCA input, connect a VCO to the audio input and you have a synth voice (with a choice from 32 different filters!) using only three modules!

Thirty two Eurorack VCF's and a VCA would most certainly take up a lot of rack space - AJH Synth have got all of this into 14hp and managed to have a really finger-friendly user interface, without it feeling cramped.


Sixteen distinct filter modes to choose from

Here's a list of the different filter modes that are available:
1 - Four Pole Band Pass
2 - Three Pole High Pass combined with One Pole Low Pass
3 - Three Pole All Pass combined with One Pole Low Pass
4 - Two Pole Notch combined with One Pole Low Pass
5 - Two Pole Low Pass
6 - Four Pole All Pass (Phaser)
7 - Four Pole Low Pass
8 - Two Pole Band Pass
9 - Two Pole High Pass combined with One Pole Low Pass
10 - Three Pole High Pass
11 - Three Pole All Pass
12 - Two Pole Notch
13 - One Pole Low Pass
14 - Two Pole High Pass
15 - Three Pole Low Pass
16 - One Pole High Pass

All of the above filter types can be further altered by switching in P-Vox mode, this doubles the list up to thirty two different filter variants!

P-VOX MODE

Transforming the resonant character of every filter type

This magical switch completely transforms the resonance of the filter core by overdriving it in a similar fashion to the filter from the Soviet Polivoks synthesiser, which was renowned for it's powerful, aggressive character.
In common with the Oberheim Matrix 12 VCF, some of the sixteen filter types will not normally go into self-oscillation, however when you switch on P-Vox mode all sixteen filter types can be forced into self-oscillation at higher resonance settings. But that isn't the only change, the self-oscillation waveform is not the usual sine waveform, it is a rather more interesting and harmonically rich waveform that varies according to the filter type chosen - generally Low Pass modes produce the nearest to regular sine waves, whereas other filter types can produce very much more complex waveforms as can be seen in the diagrams below. It does not require any audio input for this, it can be a stand alone oscillator. Most of the filter types will track 1V/Oct reasonably well over a three to five octave range, so it can be used as a VCO with a few interesting waveshapes!

Of course, P-Vox mode isn't just useful for self-oscillation, it adds lots of character to any audio signal as P-Vox resonance is switched in.

Module Width: 14hp
Module Depth: 29mm (Including power lead)
Current Usage: 56mA Positive, 36mA Negative

Notes: This useful module is a Bipolar Mixer, DC voltage source and Linear DC coupled VCA.

- With no input to channel 1 the Input 1 pot becomes a voltage source with a range of +/- 6V.
- The control pot and input for channel 4 can be switched to become an offset control and/or a second CV input for the VCA.
- Input 3 has 2x gain, so it can amplify lower level CV's too.
- All inputs are bipolar, which means that either non-inverted or inverted version of the input signal can be added to the mix depending upon the Input control being turned clockwise (non-inverting) or anti-clockwise (inverted). The 12'o'clock position is zero.

Notes: Five-channel mixer with mutes, built-in VCA, switchable overdrive and LED level meter. Simple, straightforward, high-quality stuff from AJH.

Supplier's Notes:
The MiniMod Muting Mixer & VCA is a 10HP wide, five channel audio mixer with many useful features. It is available with either a black (Dark Edition), or a silver front panel.

The mixer section has five input channels, and each channel includes a bi-colour tactile LED switch that can instantly mute or un-mute the channel, replicating the oscillator on/off switches on the original Model D synthesiser. This arrangement is more convenient than regular switches as each illuminated switch shows the on/off status of the associated channel and multiple buttons can be pressed at once, making it very useful for live performance.

AJH have also included a four segment LED level meter so that the overall level can be seen at a glance and adjusted to prevent the output from getting too "hot" and causing distortion in other modules further downstream.

It also features a VCA that is integrated into the output section, and this can be switched from linear to exponential response - this allows it to be used as a voltage controlled sub mixer or as a stand alone VCA with five inputs.

Lastly, AJH added a wonderfully soft and warm sounding overdrive circuit that can be switched in to add smooth, tube like distortion. This works in a similar fashion to a master volume guitar amplifier, so the amount of overdrive can be varied widely with different settings of channel and master output levels.

Module Width: 10hp
Module Depth: 26mm (Including power lead)
Current Usage: 55mA Positive, 25mA Negative

Notes: The Tone Science Chance Delay is a unique concept in Eurorack modules as it combines chance and randomness, with pulse delay and pulse conditioning. It is a collaboration between electronic musician/composer Ian Boddy and AJH Synth.

It can perform as a Chance generator, but is also capable of pulse stretching for Trigger to Gate conversion, pulse shortening for Gate to Trigger conversion, Gate Delay, Sub Bass Generation and also "divide by n" clock division.

There is a wide range of control and all functions can be operated manually from the front panel or can be automated using external CV voltages. Chance can range between 0 to 100%. The Gate out can be delayed by anywhere between from 0.5mS to 30 Seconds, and the output Pulse length can also vary from 0.5mS to 30 Seconds.

The TRIG push button allows manual triggering of pulses, also determined by the Chance control, and a green LED shows the output pulse status.

Includes a handy "Gate pass through" mode; when the Length control is set to zero the incoming pulse or trigger will still be determined by the Chance and Delay controls, whilst the outgoing gate length will be the same as the incoming gate length.

Compact 8hp form factor and very low power consumption make this an excellent addition to any Eurorack system.

Key features:

Chance, Gate Delay time and Pulse Length can all be set manually or controlled using external CV voltages.

The 'TRIG' push button allows manual triggering, and Chance will be applied to any manual triggering too.

Fast processing allows operation into the lower audio range, so it can perform sub bass generation on drone type sounds. In this mode the Length pot (or an external Length CV) can be used to change the PWM of the output waveform.

After the initial trigger pulse has been acted on, further incoming pulses are ignored until the current cycle has finished. This useful feature allows it to perform "divide by n" division on gate pulses, so it can be used for clock division, and the delay function can be used to add a "swing" away from the rhythm.

Gate pass through mode - if the Length pot is set to zero, then the incoming gate length is preserved, so in this case the gate has Chance and Delay time applied to it, but the outgoing gate length is the same as the incoming gate length.

By setting Chance to 100% and Delay to zero (0.5mS) it can be used as a Gate to Trigger converter, or a Trigger to Gate converter, depending on the Pulse length set with the LENGTH control. We can also use an external Length CV to shorten or increase the length of the output pulse in real time.

Fast and slow ranges for both DELAY time and PULSE length - Fast range is 0.5mS to 2 Sec and Slow Range is 2 Sec to 30 Sec.

Green status LED shows when the output pulse is high.

Front panel controls

Chance Control and CHA Input

This sets the probability of an incoming trigger or gate being passed through to the Pulse Generator circuit. The chance can be set anywhere between 0% and 100%.

The CHA input allows an external control voltage (CV) to control chance remotely. In this mode the Chance control acts as an attenuator for the incoming CV. With the Chance control fully clockwise a CV of +5V will give 100% chance, and lower CV voltages reduce the Chance accordingly. For example, a +2.5V CV will give a 50% chance. The attenuator function is useful if we are using higher control voltages of for example 0 to +10V. If we set the Chance control to the 12 o'clock position it would then halve the incoming CV signal, so in this case +10V will give 100% chance and +5V will give a 50% chance. Negative CV voltages are ignored and will be treated in the same way as zero volts..

Delay Control and DEL Input

This sets the delay amount that is applied to the leading edge of the incoming Gate or trigger received at the IN jack (or a press of the Manual Trigger button), assuming that the "Chance" has been determined to be positive. With the Delay Time switch set to FAST the Delay range will be from 0.5mS to 2 Seconds. With the Delay Time switch set to SLOW the Delay range will be between 2 Seconds and 30 Seconds.

The DEL input allows an external CV voltage to control Delay Time remotely. In this mode the Delay control acts as an attenuator for the incoming CV. With the Delay control fully clockwise a CV of +5V will give the maximum Delay time of either 2 Seconds or 30 seconds depending on the position of the Fast / Slow switch. Lower CV voltages reduce the Delay Time accordingly, so if we apply a CV of zero volts then we will get the minimum Delay time. The attenuator works on any CV patched to the DEL input in the same manner as described for the Chance control.

Length Control and LEN Input

This sets the length, or rather pulse width of the output pulse. With the LENGTH Switch set to FAST the pulse length can be anywhere between 0.5 mS to 2 Seconds. With the LENGTH Switch set to SLOW the pulse length can be between 2 seconds and 30 Seconds.

The LEN input allows an external CV to control Delay Time remotely. In this mode the Length control acts as an attenuator for the incoming CV in the same manner as the Chance and Delay controls.

Setting the Length control to zero invokes "Gate pass through" mode - in this case the incoming gate length is preserved, so the incoming pulse or trigger will still be affected by the Chance and Delay controls, but the outgoing gate length will be the same as the incoming gate length. Turning the Length control slightly clockwise will then invoke the minimum pulse length around control position 1, and further clockwise rotation will increase the Pulse Length as expected. This behaviour also applies to external CV's patched to the LEN input, where a CV of 0V will enable Gate pass through mode.

Fast / Slow mode switches

These switches allow the selection of Fast or Slow mode for Delay time and pulse length, so these ranges can be selected independently for Delay and Length. Fast range is 0.5 mS to 2 Seconds, and Slow range is 2 Seconds to 30 Seconds.

TRIG Switch

The TRIG push button allows manual triggering, and Chance will also be applied to any manual triggering, so depending on the setting of the Chance control, pressing the button has a chance of not doing anything! Holding the button down keeps the incoming gate high for as long as the button is pressed, however this is only really relevant in "Gate pass through" mode - normally only the leading edge of the input pulse is used.

IN - input jack

Connect your input here - a gate, output from an LFO, or even waveforms from a VCO. Any negative component of the input voltage will be ignored, so unipolar or bipolar signals can be used.

OUT - output jack

This outputs the binary pulse (or stream of pulses) that are generated by the Chance Delay circuitry. The gate low level is 0V and gate high level is +6V. The green status LED shows if a pulse is currently being generated.

Module Width: 8hp
Module Depth: 26mm (Including power lead)
Current Usage: 25mA Positive, 6mA Negative