ADDAC System: ADDAC215 Dual S&H+

This is an introduction to the ADDAC215 Dual S&H+ by ADDAC System, available at Takazudo Modular.

The ADDAC215 Dual S&H+ is a dual Sample & Hold module. In addition to its core S&H functionality, this module offers a diverse set of features including sum/difference/average outputs, noise generation, Track & Hold, and Slew.

This product is available as an assembled unit as well as a DIY kit from ADDAC System.

Both are available for purchase below.

• Product Photos: Assembled
• Product Photos: DIY Kit
• What Is Sample & Hold?
• How to Use S&H
• The “Plus” Features of the ADDAC215
• Reference Videos
• Manual
• Technical Specifications
• Included Accessories
• DIY Guide

Product Photos: Assembled#

Product Photos: DIY Kit#

What Is Sample & Hold?#

Let me start with a brief explanation of what Sample & Hold (hereafter S&H) is.

A basic S&H module has two inputs — a CV input and a Gate input — and one CV output. Imagine you have such a module in front of you, and take a look at the diagram below.

This diagram shows a long-period sine wave LFO being fed into the CV input, while the Gate input periodically receives gate signals from a sequencer or similar source.

What happens is that the CV output jack continuously outputs the voltage of the sine wave at the exact moment a Gate is received. This output voltage is then updated the next time a Gate input is detected.

This is the fundamental behavior of S&H — both the process itself and modules that perform this process are referred to as S&H.

On this ADDAC215, you can see that these three jacks exist in two pairs. Below is that section, with the Gate input (TRIGGER) at the top, CV input (INPUT) in the middle, and CV output (OUTPUT) at the bottom.

How to Use S&H#

Now that you know what S&H does, the question is what to do with it. From here, it is really up to the modular user to explore freely. As one common example, S&H can be used to create melodic lines from a continuously varying CV source such as an LFO or white noise.

Imagine a slow sine wave. It undulates continuously, always changing. If you feed that sine wave into the S&H’s INPUT and send a periodic clock gate into the S&H’s TRIGGER, the OUTPUT will produce a voltage that updates at each clock cycle. Since you are sampling a slow sine wave, the result is like turning a smooth slope of CV into a staircase-shaped CV.

Because the original CV is a gentle sine wave, the resulting CV is not completely random — it gradually rises and gradually falls in a repeating pattern. If you pass this CV through a quantizer and into an oscillator’s 1V/Oct input, you can create an endlessly gently rising and falling melody that follows a musical scale.

Of course, the destination for this CV is not limited to a quantizer — you can use it to control various parameters such as filter cutoff or resonance. Regardless of the original CV source, the existence of S&H allows you to transform a continuously changing CV into one that only updates at the timing you provide a Gate.

Controlling melodies and parameters by segmenting CV changes with S&H feels fundamentally different from the MIDI concept where pitch and note timing are bundled together. This kind of CV control is, in my opinion, one of the important approaches to sound creation when using a modular synthesizer. The method introduced here should be thought of as just one of many possible ideas.

The “Plus” Features of the ADDAC215#

The ADDAC215 S&H+ combines two S&H circuits with a variety of additional features. Below is a list of those extra functions.

• Slew function (smooths CV changes between triggers)
• Shared trigger for both S&H sections
• Track & Hold function (holds CV only while a 5V signal is received at the trigger)
• Difference output of the two INPUT signals
• Average output of the two INPUT signals
• Sum output of the two INPUT signals
• Noise signal output

In the previous section, I introduced creating a melody from a sine wave. By mixing in another sine wave of a different period and summing the two, you can create more complex melodies that still retain the characteristic of rising and falling in pitch.

Additionally, the slew function smooths CV changes. This can be used to recreate the glide function commonly found on bass synthesizers.

S&H works well in combination with other CV processing functions, so the ADDAC215, packed with these extra features in just 6HP, is a remarkably versatile module. Personally, I find that just adding, subtracting, sequencing, and mixing S&H with CVs provides virtually endless creative possibilities.

For anyone looking for an S&H module, the ADDAC215 is an excellent choice that will help you expand the ways you use Sample & Hold.

Reference Videos#

Below are official tutorial videos from ADDAC System. Please check them out for reference.

Manual#

The manual is available on the official website below.

• ADDAC System: ADDAC215 Dual S&H+

Technical Specifications#

• Width: 6HP
• Depth: 40mm
• Power consumption: max +50mA / -50mA

Included Accessories#

• Power ribbon cable
• Screws

DIY Guide#

The DIY kit includes the panel, PCB, all components, a power ribbon cable, and mounting screws.

ADDAC System provides detailed DIY guides on their website. Please refer to the following guide when assembling your kit.

• ADDAC215 Dual S&H+ Assembly Guide (PDF)

The DIY guide for this module includes instructions for attaching many very small parts (SMD parts). However, upon inspecting the contents of a kit we received, the component set appears to be prepared so that the module can be completed by soldering relatively larger, hand-solderable parts (through-hole parts) such as jacks and buttons.

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