Hammond AutoVari 64 midi with uniPulse

Thanks to Jonas Olesen we now have a comprehensive uniPulse installation manual.
He also installed extra outputs and pitch mods which are of course optional, but recommended modifications.

Note from Tubbutec forum user Cyrano1 :
Note this is only for AV-64 MK-1 boards (->1979).
Auto-Vari 64 MK-2 board (1980) has completely redesigned unit on one single board with various ICs that is totally different.

The Hammond Auto vari 64 – Unipulse installation and modifications

By Jonas Olesen

some more info in this thread.


The power wire in the back goes directly to exposed solder joints besides the transformer, BEFORE they go
into the transformer. This means that 220v is completely exposed – be careful.
I glued a piece of plastic on top of these joints.
The service manual is extremely well written and explains almost all circuits in detail, and combined with
the fact that all connections in the machine are marked with their functions in plain English, makes the
machine very easy to work with.

Installation of the Unipulse:

Very straightforward – simply cut the wires in the voiceboard connector and solder on the unipulse triggers and power. Then reinsert the connector.
[Tubbutec: We believe there is a way to avoid cutting wires, but lacking a machine we can not test this. If you own a machine and want to test this, please get in touch]

I attached the unipulse board to a piece of wood glued and screwed to the chassis.
Trig outputs 1-9 triggers the sounds, except brush and sandblock.

On the front of the Autovari I have installed 10 additional outputs from the Unipulse, so these can be used
to trigger / synch other machines. Please note that the back panel is too thick to attach minijack outputs,
The fron panel is thin metal, and there is a lot of space for outputs and additional potmeters here.
Midi input installed on the back besides audio outputs.

Small corrections to the Tubbutech voice board trigger points:

Bassdrum trigger: differs from the drawing, has to be Bassdrum besides it (has a wire)
Brush has no wire in the connector, it will probably trigger if the trace is followed underneath the voice
board, but I did not implement it. Strangely the Brush plays in the internal rhytems, although no visible wire
is connected to it via the voiceboard main connector.


Low frequency output:

Seperate output for the low frequency content.
Main output contains both hugh and low content – the balance pot located on the back is moved to the
front – from here the balance can be set to only high frequency content.
This way there are a seperate output for low and hugh content.

Pitch mods:

Easy and a must do!
I found the resistors by poking with alligator clips – the online scanned service manual is so low resolution,that the resistor numbers can not be read.
1: Bassdrum: Replace R4 with a 50k log pot
2: Snare drum low frequency: Replace R65 and R55 with a stereo 50k log pot
3: Conga: Replace R14 with a 50k log pot
4: Bongo. Replace R23 with a 50k log pot
5: Claves: R33 + R32 50k log Stereo pot (to obtain a wider pitch range)
6: Rimshot: Replace R40 with a 50k log pot
Cowbell: The cowbell consists of two seperate sounds:
7: Cowbell 1: Replace R50 with a 50k log pot.
8: Cowbell 2: Replace R58 with a 50k log pot.

Not implemented:

Sandblock CV trigger.
Brush trigger.
Decay mods.
Sync clock:
Not tested

Download the config file (you need to extract the pconf file from the zip file).