UNVERIFIED. This module is drawn and checked in Copper Bottom - the copper agrees with the netlist below, and the checks come back clean. The board it grew from is the Hive Drone, which I have built and heard; rows 0 to 15, columns 0 to 29 of this layout are that board hole for hole. The rack block has not been built. Every number on this page is a datasheet number, not a measurement. Build it once, fix whatever fought back, and this banner comes off.

Hive Rack

Six drone voices on the rack · The Hive Drone plus a rack block · 10 HP · By Onion Madder · Mess O' Pedals

The Hive Drone is six CD40106 oscillators on one chip, each with a pitch knob, mixed onto one bus. This is that board in a rack: the same copper, the same parts at the same holes, and a block bolted onto the right-hand end that takes the rack's power, makes the chip its 5 V, and puts the six voices out at rack level. No inputs - it is a drone. Six knobs and a jack.

What is the Hive, and what is new

Rows 0 to 15, columns 0 to 29 are Hive_Drone.json hole for hole - same cuts, same parts, same chip at the same place - and the script that drew this page re-derives every net of the Hive from the new copper and refuses to write if one changed. Two things came off: the old output network (C15 and R13, the 10 µF and the 1K) and the two jack pads. That output network was the part of the built Hive that never worked - the sound only came through with the output tapped straight off the bus strip - and it is not missed.

What replaces it is the point of the module. The six 10K-and-1 µF legs still meet on strip 15, the mixing bus, and the bus now runs straight into the inverting input of the TL072 - a virtual ground. So the six voices sum properly instead of loading each other, with a 3K3 feedback resistor setting the level: one voice at full is about ±0.8 V, all six about ±5 V, which is what a rack expects. Out through 1K.

The layout file is the guide

As on every stripboard guide here, the build document is the file itself: ↓ Download Hive_Rack.json - import it into Copper Bottom and the editor gives you the board picture, the placement walkthrough, the electrical checks and a printable build sheet, all from the same file. No coordinates are written out on this page on purpose: the editor is the viewer, and a number typed twice is a number that can drift.

The netlist

Quoted verbatim from the layout file. It was written from the board, so checking the board against it can only pass - what it is for is carrying the circuit somewhere else, and telling you what each strip is supposed to be doing while you stare at it. The bug board's nets keep the names they have on its own page.

The off-board wiring

26 pads leave the board. Ten of them are the power header.

The panel

10 HP, which is 50.8 mm of a 128.5 mm blank - Amplified Parts sells reversible black-and-aluminum blanks in every width from 2 to 20 HP. The template is drawn for 9 mm Alpha pots (7 mm holes), Thonkiconn jacks (6 mm), sub-mini toggles (6.5 mm) and 5 mm LEDs, with the rack's rails kept clear top and bottom and the four M3 mounting holes where Doepfer puts them. I/O along the bottom, controls above, as everything on this site does it.

The rack block, the same on every module

The right-hand end of every board on this shelf is the same idea drawn six times. The 2×5 header takes the rack's power cable, mounted with its pins running down the strips so each pair of pins lands on one strip: -12 V, then three grounds, then +12 V. That is the only way it can go on stripboard - turned the other way, the -12 and ground pins would share copper. The red stripe on the cable goes to H1 and H2. A 1N5817 stands in series with each rail so a cable put on backwards does nothing instead of everything. A 78L05 then makes a 5 V rail for the chip, and a TL072 on the real ±12 V does the rack-level work.

Five volts for the CMOS, not twelve, is what makes these rack-polite for free. A CD4000-series input switches near half its supply, so a +5 V gate from a sequencer clocks a 5 V chip directly but would never reach the ~7 V a 12 V chip wants; a pot across 5 V makes exactly the 0 to 5 V control voltage every rack sequencer speaks; and a hot or negative rack signal into a CMOS input needs only a 100K in series, the chip's own input diodes doing the clamping at well under a tenth of a milliamp. It is also a change from the 9 V these boards were built at - every chip is rated down to 3 V so the circuits are fine, but the oscillators will sit at slightly different pitches, and that is one of the things the bench is for.

The IDC socket on the power cable overhangs the header by about two strips at each end. Nothing tall stands there - the generator that drew this refuses to put anything standing under the socket - so keep it that way if you move a part.

How it works, in one breath

Everything the Hive does, it still does - the six inverters each charge a cap through a 1K and a pot until the input flips, six square waves. Where the old board took the bus through a cap and a 1K straight to a jack, the rack version treats the bus as a summing node: the op-amp holds it at 0 V, each voice pushes its current in through its own 10K, and none of them can feel the others. The feedback resistor turns that summed current back into a voltage and sets how big. It comes out inverted, which a square wave does not mind.

Things to try

• Six outputs. Each voice's 10K-and-1 µF leg could go to its own jack instead of the bus - then the Hive is six oscillators and a patch cable picks one. It costs 10 HP of jacks and the summing stage does nothing
• Quieter. 2K2 in place of the 3K3 brings all six at once down to about ±3.3 V, if your next module clips
• A mix knob. A 10K pot as a divider on OUT, wiper to the jack, gives the whole drone one level control

The Hive is the Hive Drone layout from this site, itself six 40106 oscillators on one chip - the Lunetta idea. The rack block is the standard DIY Eurorack power entry (Doepfer's header pinout, a diode per rail) and a textbook inverting summer. Drawn in Copper Bottom.