HVM - Human Voice Module

Constructional Difficulty: Easy but with many surface mount parts.

The 8HP wide Oakley Sound Human Voice Module (HVM) is an all analogue audio signal modification unit that replicates some of the sounds made from a classic electronic keyboard first seen and heard in 1979. The VP-330 is often thought of as a string synthesiser and vocoder but some of its most ethereal sounds utilise its four human voice settings.

The human voice sounds of the VP-330 were created by using seven fixed frequency band pass filters - each of its four preset voices using differing mixes of the seven filters and different octaves from the keyboard's oscillators.

The HVM recreates these filter sections and arranges them in a flexible fixed filter bank format. All seven filters are presented with the same input signal, its level controlled by a single pot, Level. The output of each filter is sent to its own level pot and then mixed with the other six filter outputs to make one single output. Each filter section consists of two narrow band pass filters of slightly differing frequencies in series. The operating frequencies are 220Hz, 330Hz, 600Hz, 910Hz, 1300Hz, 2800Hz and 3300Hz.

Any type of signal can be processed either single notes or, if you have the polyphony, full chords can be used. It is best to use an harmonically rich waveform, such as a sawtooth or square wave, to give the filters something to work with.

The original design used seven bandpass filters with the lowest two bands having very similar operating frequencies, 185Hz and 220Hz. In the suggested build of the HVM I have made them further apart, 220Hz and 330Hz, extending the usefulness of the module. However, an alternative build is possible that recreates the original behaviour if needed.

Current consumption is +/-40mA at +/-12V.

Sound Samples

Just noodling with a single sawtooth VCO going into an Oakley HVM. The added vibrato is under aftertouch control. Reverb added courtesy of Valhalla Vintage Verb.

A polyphonic set. This is the Nord Lead A1 played through the HVM while the HVM's settings are wiggled manually. The A1 is used to generate a single sawtooth waveform and using delayed vibrato as well as the A1's internal chorus setting.

The PCB Set

The HVM comprises of two printed circuit boards (PCBs) connected together with five 0.1” (2.54mm) single in line (SIL) headers and sockets. The main board on the rear of the module houses the seven filters and the power supply inlet. The pot board has the pots and sockets that are attached to the front panel, as well as the input and output circuitry. The main board is a four layer design, while the pot board is a two layer design. Each board is the same size; 40 mm x 107 mm.

The majority of the components are surface mount parts. The ICs are SOIC, while the resistors and capacitors are 0805. All components are standard parts.

One side of the Pot Board showing the input and output circuitry. The pots and sockets are mounted on the other side of the board. The SIL headers connect to the HVM's main board which simply fits on top.


Click here for how to order.

HVM (Euro) main board issue 1 PCB........................................... 12GBP

HVM (Euro) pot board issue 1 PCB ............................................... 6GBP

Both boards are required to build the Oakley HVM project.

All other parts can be purchased from your usual electronic component supplier.

All prices include VAT at UK rates. Shipping and postage is additional to these prices. Click here for full price list and ordering details.

Project Downloads

HVM (Euro) Builder's Guide

Construction Guide Our handy guide to building Oakley DIY projects

Parts Guide Our handy guide to buying parts for Oakley DIY projects

Schematics are available to purchasers of the PCBs and will only be sent via e-mail when the board(s) are shipped.

Front Panel database

A Schaeffer front panel can be made for this module. The databases can be found by downloading the following links:

8HP panel with 220Hz as the lowest frequency

8HP panel with 185Hz as the lowest frequency

To read, edit and print this file you will need a copy of 'Frontplatten Designer' from Schaeffer. Panels can be ordered via Schaeffer's website.

Schaeffer are based in Berlin, Germany and can send panels to anywhere in the world. Delivery to the UK normally takes around ten days. For North American users you can order your Schaeffer panels from Front Panel Express.

A close up of four of the seven filter sections on the HVM's main board. Each filter section comprises of two Deliyannis resonators in series.

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Copyright: Tony Allgood.
Last revised: August 06, 2020.