Thank you for buying LVL by SYNTHFOX. LVL is a dual utility signal summator module capable of signal mixing, offsetting, and even mini matrix mixer action. In this manual, an overview of LVL's features is given, as well as some additional information, such as a flowchart (logic diagram) of the module's insides and some patch ideas. Please, read the safety notice carefully!


  1. Installation / Safety Notice
  2. General Overview
  3. Controls
  4. Flowchart
  5. Patch Ideas

Installation / Safety Notice

Thank you for buying LVL! We at SYNTHFOX want people to have as much fun with and make as much good use out of our gear as possible. But firstly, we want users to be safe and their synthesizer systems to be fully functional. This device is not a consumer piece of electronics. This is a specific part (module) that is to be installed into Eurorack system and interfaced with other parts of it. The user handles the installation process - extra care should be taken!

LVL has a keyed connector. The included ribbon cable is tested to comply with standard Eurorack boards, and it cannot be inserted the wrong way into the module. However, the power distribution boards may vary, and it is up to the user to well understand which way to connect the ribbon to the distribution boards. The red line on the ribbon cable marks the -12 volts line. The module should be connected like in the picture below: on the left side is the bus board connector, and on the right side is the connector on LVL.

image by David Haillant

When installing the module:

The module should now be ready to play. Have you any troubles, feel free to reach out to SYNTHFOX through


The backbone operations of modular synthesis are addition, subtraction, attenuation and inversion of signals. LVL excels at each of these operations, providing two identical manually controlled voltage summators: one on the left half, and the other on the right half of the module.

Each summator has three inputs. The inputs are DC coupled, meaning they will not block the constant component of the incoming signal, making the module suitable for audio, CV and any other type of a signal existing in a Eurorack system. Each input has an associated level control. The knobs follow the order of the inputs, i.e. the topmost knob is associated with the topmost input of the selected summator.

A switch to the right of the input jacks sets the summator's mode. In up position (-+), the level knob will act as an attenuverter. In this mode, the input signal will pass to the output at maximum level if the associated knob is set fully clockwise. As it is turned towards noon, the level is decreased and reaches 0 (no signal passes through) at noon. Then, as it is turned towards the full counter-clockwise position, the inverted version of the input signal will reach maximum. So if the input is a falling sawtooth from 5 to 0 volts and the level control for this input is fully CCW, a rising sawtooth from -5 to 0 volts will appear at the output. If the mode switch is in the down position (0+), the level controls act as simple volume knobs, with no signal passing through when full CCW and maximum signal level at full CW. This mode may be preferrable for audio mixing, since sometimes it's necessary to quickly fade out a particular sound, and it's not always easy to hit the exact middle point in -+ (attenuverting) mode. The attenuverting mode makes sense when summing CVs or trying to tap into more experimental audio summation, e.g. subtracting the filtered signal from the unfiltered.

LVL features clever normalling of signals. Every input of the left summator (Summator 1) is normalled to respective inputs of the right summator (Summator 2). That is, if nothing is connected at a summator 2 input, but something is connected to the same input on Summator 1, a copy of that signal will appear automatically at the corresponding Summator 2 output. This way, one could use LVL as a mini matrix mixer! If only Summator 1 inputs are used, the Summator 2 inputs will simply copy whatever is going on on the first summator inputs. Naturally, the level controls on the two summators are independent, so one can easily achieve two different mixdowns of up to three different signals using this feature. It is, of course, possible to use this feature for just two channels, for example, and put something else into the third input of summator 2: summator 1 will then output its own inputs' sum, and summator 2 will process two inputs of summator 1, and a signal that was patched directly to it.

Finally, a constant voltage of +6v is normalled to summator 1 lowest input (input 3) jack. So, if nothing is patched to summator 1 input 3, its blue knob will effectively become an offset generator of -6...6 (-+ mode) or 0..6 (0+ mode) volts range. Summator 2 will receive this offset into its own input 3 only if nothing is patched into both Summator 1 and Summator 2 input 3. So, if you know you are going to need all three inputs of LVL, it may be logical to start with Summator 2, as to keep the other half's offset functinoality for possible use later on in patch building.


Ⓐ Summ. A Input 1 level
Ⓑ Summ. A Input 2 level
Ⓒ Summ. A Input 3 level
Ⓓ Summ. A Input 1
Ⓔ Summ. A Input 2
Ⓕ Summ. A Input 3
Ⓖ Summ. A Mode Switch
Ⓗ Summ. A Output with indicator LED
Ⓘ Summ. B Input 1 level
Ⓙ Summ. B Input 2 level
Ⓚ Summ. B Input 3 level
Ⓛ Summ. B Input 1
Ⓜ Summ. B Input 2
Ⓝ Summ. B Input 3
Ⓞ Summ. B Mode Switch
Ⓟ Summ. B Output with indicator LED


Patch Ideas

Although LVL provides a very basic backbone set of operations, the usage can be anywhere from extra conventional to extra creative. Here is a couple of ideas on the creative side that can get your patch setup started!

Simple audio mixing with clipping

LVL is a device that can mix up to 3 audio signals with each of its halves. If you intend using one of the summators as a simple audio mixer, it is advised to start with Summator 2, to preserve unit's offset functinoality at Summator 1 for further usage (if you patch something into Summator 1 input 3, summator 2 will receive that signal instead of the 6v offset at its input 3, and the unit will lose the offset at both halves). Set the mode switch down (0+). Patch your audio sources to inputs 1..3 and get a weighted mixdown at the output. With eurorack signal levels, it is advised to keep the knobs below 1 o' clock to evade clipping. If clipping is desired, however, it's possible to leave input 3 unused, and use the associated (blue) level control, now acting as an offset generator, to push the mixture of two audio signals to positive rail clipping!

Creative CV summation

LVL is a DC-coupled module, meaning its inputs do not block DC or slow (relatively to audio) signals. This makes it a perfect CV summator, too. For this, set the mode switch up (-+) and select up to three CV sources for mixing. If input 3 (the lowest jack) is unused, the blue knob of the selected summator becomes a -6..+6v offset control. You can now process your control voltages and use them to control target devices. With precise level control, you can process unusual signals, such as logic (gates, clocks), to achieve creative stepped modulations, that are also melodically tunable. LVL can be used as a 5-input CV mixer by patching Summator 1 output to Summator 2 input 3, and using the three channels of Summator 1 and two of Summator 2 as input. The entire group of three CVs incoming to Summator 1 will appear at Summator 2, along with its own two incoming signals. The group of CVs incoming to Summator 1 can then be conveniently attenuated/attenuverted at once with Summator 2 input 3  level knob. This 5-input trick also works with audio.

Stereo mixdown

You will need a stereo output module for this idea. Put Summator 1's output to the L (left) input of your stereo out module, Summator 2's output to the R (right) one. Set both summators' mode switches to 0+ mode for audio application. Take three sound signals that you like and put them to Summator 1's inputs, leave the other summator unpatched to have all three copied over. Now you have a stereo mixer with separate left/right volume controls per each of the three channels!

Feedback Explorer

This idea works best with delays, distortions, reverbs, filters and so on. You will need two external audio effects and a passive/active signal multiple for this patch. Put both summators in -+ mode. Patch each summator's output to an audio effect's input. Patch audio effects' outputs to Summator 1's second and third inputs. Optionally - patch some audio to Summator 1's first input - although it may as well start noising right off. Mult from any output in the patch (any of the LVL summators' outputs, or from the output of an FX module you used). Now you have a matrix mixer setup perfect for exploring cross-feedback of audio effects, playing extreme textures and such!



v1.0: initial module release, short batch

v2.0: compelte redesign of the module. prototype, never released.

v2.1: redesigned module release .


[20211215] 1.0.0: initial document

[20220926] 2.0.0: remade the document for the revision of the module


Happy patching!