Oakley Human Voice Module

Constructional difficulty: Easy, but it's a big project with many parts.

A completed HVM module fitted into a 1U 19" rack alongside the Oakley SE330. The front panel legending is created by using two 1.5mm thick Scheaffer panels attached to the plain front panel of the rack.

The Oakley Sound HVM is an electronic audio signal modification device that attempts to replicate some of the sounds from two classic keyboards first seen and heard in 1979. The module consists of three sections, two band pass filter networks and one parametric equaliser. It is possible to use each section independently if built that way but the suggested panel design has them wired together so as to allow maximum flexibility with the smallest number of front panel controls.

The design of the bandpass filter network takes its inspiration from the beautiful haunting sounds of the Lambda's chorus ensemble and the VP-330's human voice presets. In the suggested panel design of the HVM these are labelled Chorus and Vox respectively. A simple toggle switch on the panel allows the user to switch between the two modes. The chosen output then goes to a wet/dry mixer control pot. This sets the mix between the untreated audio input and the affected sound. The output of this control is then fed to a parametric equaliser circuit that can boost (maximum +20dB) or cut (maximum -20dB) a selected frequency band between 50Hz and 11kHz. Bandwidth, Q, can be controlled with the emphasis pot and can be varied from around 1 to 25.

A completely populated HVM PCB awaiting its case.

A simple render of the suggested front panel layout.

Input and output level control pots are also provided to allow maximum flexibility in dealing with a variety of input signal levels. Both the input and output connections are balanced but can be used with unbalanced connections if desired.

The power to the unit should be a regulated split supply of +/-12V to +/-17V. Power is admitted onto the main circuit board via a four way 0.156” (2.96mm) header of MTA or KK type. The module can be powered by our own Rack Power Supply Unit (RPSU) or any other MOTM compatible supply such as the Oakley PSU.

The board size is 198mm (width) x 131mm (depth). Power consumption is +/-80mA at +/-15V.

A version of the Oakley HVM with just the VP-330 parts that is designed to fit into Oakley/MOTM and MU modular synthesisers is available here.

All components, with the exception of the input and output sockets, are board mounted for ease of construction and reliability. Here was can see the voice selection switches and above them the 2-way headers that can be used to access the individual parts of the HVM circuitry if so desired.

Sound Samples

These were all created using a single VCO voice from a Jupiter-6. A little delayed vibrato is applied. The output of the JP-6 goes straight into the HVM and then out to be recorded.

This is me just playing about. The HVM is used in Chorus mode first, then Vox, firstly in Lower 4" and then in Upper 4" . A four stage ensemble is used on the output of the HVM to give the final sound a lush texture.

This one is a simple series of notes, firstly the raw sawtooth output from the JP-6, then the Chorus mode of the HVM, then the Vox mode with Lower 4" and finally the Upper 4".

This one is a chord being processed by the HVM's parametric equaliser. The first half is the gain pot at full boost and the frequency swept up and down. The second half has the gain pot at full cut.

The prototype Oakley HVM and SE330 modules side by side in a 1U 19" rack from Bryant Broadcasting. The power is supplied to a single RPSU module with an external Yamaha PA20 line lump for safety reasons.


This board has now sold out and is discontinued.

HVM issue 1 PCB .................................................................... 25GBP

HVM Pot Bracket Kit .............................................................. 1.50GBP

The HVM pot bracket kit contains six special pot brackets. The brackets are used to hold the PCB mounted Alpha and ALPS pots safely to the PCBs. They are not required if you are using different types of pots or hand wiring any pots to the board.

Most of the other parts should be able to be purchased from you usual electronic component supplier. Please see the Builder's Guide for more details.

See the Oakley Sound ordering page for ordering information, shipping charges and payment methods.

All prices include VAT at UK rates. Shipping/postage is additional to these prices. See also the FAQ page.


Builder's Guide

User Manual

Construction Guide Our handy guide to building Oakley DIY projects.

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

hvm.fpd Frontplatten Designer file. You can edit this to suit your own front panel design or print it out to use as a drilling template.

The schematic is provided only to purchasers of the printed circuit board. This will be sent to you as a PDF file with your shipping confirmation e-mail.

For technical support on all Oakley projects please refer to the knowledgeable and helpful Oakley Sound Forum which is hosted at Muffwiggler.com. Tony Allgood and Paul Darlow do not provide building support for Oakley projects, but both and many others are usually available for help via the forum.

This is me playing with a modified Roland RS-101 which now includes the filter bank of the VP-330 using the same circuit as used in the HVM. This is a stereo recording but heavily compressed due to the video encoding.

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Copyright: Tony Allgood
Last revised: September 07, 2017.