Have you ever wondered how to generate rhythm on a patchable drum machine that has neither buttons, nor a programmable sequencer? We have and turns out you gotta discover it!

Kastle was originally released in Fall 2016 and gained instant popularity as an affordable, pocket-sized modular synth. We processed a lot of feedback and introduced a much improved version v1.5 a year later. Now we’re revisiting the concept once again with an alternative way to operate the same hardware.

The design process gave birth to a seemingly limited, but in fact an innovative and quite playful take on a rhythm box that is using some novel concepts, like the dynamic acceleration envelope to build “a lot of dynamic rhythm” out of very little modulation.

The Kastle Drum is a special edition of Bastl’s classic mini modular synth focusing on algorithmic industrial glitchy drums.

Drum sound synthesis with a unique dynamic acceleration charged envelope makes this rhythm box surprisingly versatile and extremely fun to play. The built-in VC clock generator with a stepped pattern sequencer can either run on its own or it can be synchronized to analog clock, while retaining the triangle LFO for parameter modulation.

The Kastle Drum is a mini modular synthesizer with a headphone output, 2 in/out ports for interfacing other gear, and it runs on just 3 AA batteries. It is ideal for beginners in modular synthesis, but it will add some quite unique functionality to any modular synthesizer system. It delivers the fun of modular synthesis at a low price and fits into your pocket so you can play it anywhere!

Kastle is an open source project with all resources obtainable from GitHub. Given that anyone can do anything with the code, we cannot provide any support for user upgrades from Kastle v1.5. All information is easy to find online for curious users, but please understand that we do not have the capacity to help you with that process.

Features

• 8 drum synthesis styles
• ”noises” output for less tonal content
• DRUM selects drum sounds
• acceleration charge dynamic envelope
• decay time
• PITCH control with offset and CV input with attenuator
• voltage-controllable clock with square and triangle output
• stepped voltage generator with random, 8 step and 16 step loop mode
• 2 I/O CV ports that can be routed to any patch point 
• the main output can drive headphones
• 3x AA battery operation or USB power selectable by a switch
• open source
• durable black & gold PCB enclosure

Technical details

• dimensions: 70 x 60 x 50 mm
• powered by 3x AA battery or Micro USB
• GitHub repository
• PDF user manual

What’s in the box

• Kastle synthesizer
• 10 patch cables
• sticker
• batteries not included