The Mega-Phase 12 Multi-Tap Phaser module:

A beautiful sounding phaser based on the original vintage EH "SmallStone" phaser guitar effects pedal. It has been expanded from 4 to 12 stages, with unique switching which allows stages to be individually selected for both the Output and Resonance return paths.

It can be used in Mono IN, Mono Out mode or Mono IN, Stereo OUT mode, with the Stereo outputs taken from the Stage and Emphasis paths rather than the more usual inverted signal only method. We have added CV voltage control of Phasing depth and Emphasis (Resonance) levels, so that these can be fully controlled from other Eurorack modules or external voltage sources.

In addition to a manual Frequency control it includes two separate Frequency CV inputs; FCV1 and FCV 2, and the latter includes an attenuverter function. An inbuilt, wide ranging LFO is normalised to FCV 1 input, and the LFO has its own external output too.

Unique "Wet" output and second Input with level control, which allow external effects to be patched into the Emphasis loop to create a second Emphasis path.



Module Width: 18hp

Module Depth: 24mm (34mm with power cable)

Current Usage: 70mA Positive, 65mA Negative



In Depth

 The AJH Synth Mega-Phase 12 is an all analogue Eurorack format vintage style phaser based on the vintage "Smallstone" Phaser circuit, but expanded to twelve stages, which allows much more complex phasing than the original four stage design, it also includes switchable Output stages and Emphasis stages for a huge variety of phaser sounds.


Wide range of phaser sounds

Usually a phaser only offers one type of phaser sound, which is determined by the topology of the phaser circuit used. However, we have taken the vintage Smallstone phaser, which was a four stage phaser effects pedal for guitarists and expanded it so that it can now be up to 12 stages, and a different stage can be selected for the Emphasis path, which allow manx different sets of phase cancellation to be explored, so rather than just having a single, "fixed" phaser sound a wide range of different sounds are available. We have also modified the Emphasis circuit so that much deeper, more extreme levels of resonance are possible giving an even wider range of possible sounds, and now in stereo too!.

The Smallstone phaser was famously used on synthesisers (rather than guitar) by Jean Michel Jarre on several of his early albums, and of course all of these sounds can be readily reproduced by the Mega-Phase 12, simply by switching the Stage and Emp-Stage switches to stage 4.


Built in LFO and external modulation possibilities

A wide ranging, triangle wave LFO is included, which has an amplitude of 10v p/p, along with a bi-colour LED that shows positive and negatived excursions of the LFO Waveform. The LFO has an external front panel output too, so that it can also be used as an external LFO with other Eurorack modules if desired. The output of the LFO is normalised to the FCV 1 Input, so that LFO modulation can be applied to the phaser core frequency simply by turning the FCV 1/LFO knob clockwise. However, an external modulation source can be used instead of the internal LFO simply by patching it in to the FCV 1 jack so that it defeats the internal normalising.

Manual Control of Frequency is with Freqency control knob, and there is also a second Frequency CV, input FCV 2, and its associated FCV 2 level control; however the FCV 2 control is an attenuverter rather than a regular level control. This means that in the centre (approx 12 o'clock) position, none of the modulation voltage patched to the FCV 2 input will affect the cut off frequency of the filter, however as the FCV 2 control is turned clockwise from centre then the voltage or waveform applied to the FCV 2 input will increasingly affect filter frequency. If the control is turned anti-clockwise from centre then an INVERTED voltage or waveform is applied to the filter cut off frequency. This is much more useful tha a regular level control, as it combines both level control and inverter in one convenient control.This invert function is also very useful if combining two Mega-Phase 12 units for true stereo imaging, the output of the LFO on Megaphase 1 would be fed to the FCV 2 Input and the FCV 2 attenuverter control then turned counter clockwise to invert the incoming LFO signal - in this case the FCV 1 pot on the "slave" MegaPhase 12 should be turned to zero as the "master" MegaPhase 12 LFO is providing all of the modulation.. This would cause one phaser to sweep "up" while the other is sweeping "down" which creases a superb stereo image, particularly when listening on headphones.

FCV1, FCV 2 and the manual frequency control can all be used simultaniously to create some very complex modulations and phase sweeps.


Connect external effects to the internal feedback loop

A phaser module is similar to a chorus module, in that the phasing sound is actually a 50/50 mix of the original "dry" signal and the "wet" treated phasing signal, this is required so that the "wet" signal has something to be out of phase against. However, we have added the "wet" only signal as an output too, so that this can be passed through an external effect such as EQ, reverb, flanger etc and then fed back into the Mega-Phase 12 using Input 2, and the feedback level in this configuration can be controlled with the Input 2 level control. This allows a second feedback path which can be used on its own or in conjuction with the Emphasis loop, to create a whole new range of sounds.



The Mega-Phase 12 Module is available with either Silver or Dark Edition (Vintage Black) fascia panels


Using the Mega-Phase 12 as a stereo phaser

The Mega-Phase 12 uses a clever arrangement to generate a stereo output using a single, mono input. To create a true stereo phaser would require either two Mega-Phase 12 units, or for a single unit all of the circuitry would have to be doubled to 2 x 12 stages, this would dictate a much larger circuitboard to accomodate all of these extra parts, and the module grow from 18hp wide to over 30hp wide! And of course the cost would be higher too because of all of the extra components.

A common "cheat" to create a stereo phaser is simply to add an inverter to the right hand outputs, so that the output is 180 degrees out of phase with the Left output, however this is not particularly convincing or versatile. Because we have added switchable taps to the phaser stages, we are able to connect the Right output to the Emphasis stage rather thant the main output stage, which is the case for the Left channel output. So, if the Emphasis stage is set differently from the Main stage, the output sigmals are as follows:

LEFT OUTPUT - Main Stage output plus (if emphasis control is set above zero) Emphasis added from Emphasis Stage

RIGHT OUTPUT - Emphasis Stage output plus (if emphasis control is set above zero) Emphasis from Emphasis stage

As an example, lets see what happens when we set the Main stage switch to 8 and the EMP-Stage is set to 11

First, with Emphasis control set to zero:

LEFT OUTPUT - Output taken from Stage 8

RIGHT OUTPUT - Output taken from stage 11

Next, if we set the Emphasis control to 25%

LEFT OUTPUT - Output taken from Stage 8 plus 25% resonance added from Stage 11

RIGHT OUTPUT - Output taken from Stage 11 plus 25% resonance added from Stage 11

It can be seen that because we can tap the phaser stages separately this allows is a much more versatile Stereo capability.


What does it do and how does it sound?

Here's an excellent demo video / review from DivKid Ben that gives a really good insight into the Mega-Phase 12

The original Divkid youtube video with timing Index can be found here


All analogue circuitry

The Mega-Phase 12 is an all analogue design, and by expanding the original design from four to twelve stages it means that there is a lot of circuitry that has to be fitted into what is quite a small space. This necessitated the use of a four layer printed circuit board and very tightly packed components. Do bear in mind that this is a vintage style phaser built around what was originally a guitar effects pedal circuit, however with three times the number of stages in circuit (and hence three times the noise floor); this, along with a very aggressive resonance circuit, means that there is a degree of background noise that can be heard even with no input connected, and this increases as resonance is added. It cannot really be compared to modern, digital pro-audio studio effects units, this is raw vintage analogue module. The added noise does help the phasing effect, and its only when the treated signal is removed that it is noticeable. Turning the emphasis down does reduce the noise floor considerably, but if it is still a problem then a noise gate or external cross-fader to dry signal may be required if a total silence is needed..


More Reviews and Demos

Here's a couple of video's from Tiziano at Sonic Voltage, covering more experimental use of the Mega-Phase 12

A MegaPhase 12 unboxing and video review from Sonic Voltage



A MegaPhase 12 quick jam from Sonic Voltage



Mega-Phase 12 history

The Smallstone phaser was first launched in 1975 as a battery powered guitar effects pedal. It's first mainstream use in synthesisers was several years later, on Jean Michel Jarre's early albums, where he cleverly used a modified Smallstone pedal to produce beautiful sweeping phased sounds from noise sources and instruments such as the Eminent 310 organ. The modifications made to the Smallstone pedal by his technician Michel Geiss were principally to adapt the Smallstone to the much higher signal levels of synthesisers rather than the low level, high impedance output of an electric guitar pickup which the Smallstone was originally designed to be used with..

The Smallstone circuitry was first adapted to a modular synthesiser format by Tony Allgood of Oakley Sound, as the 5U format Equinoxe four stage phaser. It was, and still is, available as a DIY kit and, like all Oakleysound projects, is highly recommened for anyone who enjoys soldering and synth DIY.

Around twelve years ago I designed an eight stage expansion board for the Oakley Equinoxe, which expanded it to twelve stages and included stage selection and separate emphasis stage selection too. Less than ten of these expansion boards were ever built, however it was the first incarnation of the Mega-Phase 12! Huge thanks go to Tony Allgood for his generosity, kind words and help with this project.

A modified Oakley Equinoxe / AJHSynth Eurorack format phaser built in 2004, currently owned by electronic musician Richard Quirk.