Forgotten Keys

The Hardware

You may have heard of the Hammond Auto-Vari drum machine, usually called Auto-Vari 64. It had 16 rhythms with four variations each. The model you see here however, wasn’t a stand-alone machine, rather it was the rhythm unit salvaged from an old Hammond Organ. It has only seven rhythms with four variations each totalling 28 rhythms, which is why I call it the Auto-Vari 28!

I’m not going to pretend that the rhythms are going to fill you with musical inspiration; they are typical of a 1970s home organ rhythm unit. Some of the variations are too busy to be used continuously in my opinion. However, if you feed it some nice patterns from your DAW/sequencer there’s far more potential.

Sound-wise there are seven sounds including both high-hat variations, and all are perfectly usable analogue sounds.

Being part of a home organ this unit also supplies the auto-accompaniment, but I haven’t figured out if or how that could be used. Other organ-related features are synchro-start where the rhythm starts when the player touches the keyboard, and reset which just starts the rhythm from the start of the bar/measure when you press it.

To get this drum machine working as a stand-alone unit I had to build a simple -15 volt power supply on strip-board, and fix the auto-vari lights. There was only one bulb left so I decided to replace them with LEDs along with an appropriate current-limiting resistor.

The patterns are provided by an IC rather than a diode matrix board like some of the early machines. Using my scope I discovered that the pulses sent to each voice generator are of different length. Just using a switch to trigger a voice won’t work properly, you’ll get an infinitely long snare for example. The best way to sample the individual sounds was to short out the sounds not required.

I had intended to try and fit this into a 1U rack, but other things came along and I never got around to it.

The Kontakt Library

Details of the Kontakt library and how to purchase it are here. Please ensure that it is compatible with your set-up before purchasing.