In Depth

This module is a five channel audio mixer with many useful features.

The mixer section has five input channels, and each channel has a switch that can instantly mute or enable the channel which replicates the on/off switches on the original Model D synthesiser which were used to switch the three VCOs, Noise and External input channels. However, the switches on this module incorporate a bi-colour LED (Green for enabled, Red for muted) and have a very tactile feel making it easy to mute or enable channels during a live performance, either singly or several at the same time with one hand, with instant visual feedback of each channel’s status.

The CV controlled VCA incorporated in the output can be switched from a linear to an exponential response allowing it to be used as a voltage controlled sub-mixer or as a stand-alone VCA with five input channels. The module can be used anywhere in the signal flow and as the VCA can be CV controlled, it can serve as an alternative to the MiniMod VCA. The mixer makes it a simple matter to feed the output from several VCOs into a filter that only has a single input like the AJH Sonic XV, Matrix VCF and Gemini 2412 filters.

 

Distortion Characteristics

A wonderfully soft and warm sounding overdrive circuit is included which can be switched in to produce  tube like distortion. The overdrive is based on the MiniMod VCA circuitry but it can be pushed to produce much higher levels of distortion adding mainly even harmonics and soft distortion. Applying different settings of individual channel and master output levels can widely vary the amount of overdrive available in a similar manner to the master control on a traditional guitar amplifier.

 

 

Blue trace is the original oscillator signal, yellow trace is the mildly overdriven signal.

 

 

 

 

Blue trace is the original oscillator signal, yellow trace is the heavily overdriven signal.

 

The oscilloscope traces above show both a mildly overdriven signal and a more heavily driven signal.

The mixer is capable of producing a fairly ‘hot’ output signal so it is useful to see at a glance what the output level is and for this, the four LED Level Meter is used to get the correct balance of overdrive using the channel level control knobs while taming the final output to avoid causing unwanted clipping distortion in other modules further downstream.

A Low Input level and a High Output level results in a lower level of overdrive whereas a High Input level and a Low Output level results in a higher level of overdrive. To achieve a pleasant overdrive effect without introducing clipping, start by reducing the Master Output Level control to zero. Next increase the levels of the individual input channels to push them into overdrive and then increase the Master Output Level to a point where the very highest output transients just stop short of illuminating the orange LED thus achieving the desired overdrive level without driving other subsequent modules in the chain into overloading.

 

Signal level LEDs

As with any audio mixer, the Muting Mixer sums the input channels and as a result the output increases in volume with increasing numbers of inputs. It is therefore important to keep the output level at a maximum of 10v p/p so that we don't overload any modules further down the signal chain. The Orange LED illuminates when the output reaches a level of 10.5v p/p and the Red LED illuminates when the output reaches a level of 12.5v p/p making the signal too high to be useable,

This provides a quick and convenient visual indication of the Output level, if it is running too high then simply rotate the Output Level control anti-clockwise until only the green LED's are illuminated.

 

Using the onboard VCA

The output level of the Muting Mixer can also be controlled by connecting an external control voltage to the CV IN input, and in this configuration the Output level control attenuates the effect of this external CV voltage. When using an external CV the LIN / EXP switch selects whether the internal VCA responds to incoming CV voltages in a Linear or Exponential manner.

The internal VCA feature is a very useful addition as it allows the Muting Mixer to be used as a voltage controlled sub mixer or as a substitute for the MiniMod VCA

 

Demo Video

Here's a short introduction video by Dreams of Wires that covers the features and use of the Muting Mixer and VCA Module.

 

Availability

Both the Dark Edition and Silver variants of the Muting Mixer & VCA module are now in production and available from stock.

 

 

Many thanks to Steve Richards for writing the Muting Mixer and VCA user guide and also creating the "In Depth" section and oscilloscope capture images above.

 

 

 

 

 

 

 

 

 

 

 

Copyright © 2014 AJH Synth