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Contents > Vox Public Address Equipment > Vox Microphone Mixers

Vox Public Address Microphone Mixers

A detail from the JMI dealer catalogue of 1964. The catalogue as a whole is avaliable here.

Preamp mixer

An account by David of the early units

"The first mixers I made were like the one in the brochure as picture 2. I first made these in my front room at home and they were built on small veroboard panels for each channel. Jennings supplied all the parts but not the case which they had made by their usual case makers and fitted at their works. May have been Glocks in Crayford that made the wooden boxes. The front panels were made of Traffolyte engraved by Dartford Engraving Company who had a small workshop unit behind a house almost opposite the Jennings music shop. Don't know who made the chassis and brackets. I think I made about 50 but may have been less as they wanted to test the market."

"The parts were "cheapest they could find" with germanium transistors at the time. I built these for a company called EvT who had a camera shop in Bexleyheath and they also did film striping and made, under license, a film sound adapter for adding sound to 8mm film. I got involved building/repairing the electronics for them. I then went full time with them and we made the later mixers in a grey metal case and a proper printed circuit board this time for each channel. We had problems as the channels had to be selected to have the same gain and noise levels. Subsequently I found that there was a capacitor fitted the wrong way round that caused the problem. We just copied the sample supplied and I pointed this out to Derek [Underdown]. An investigation showed that the circuit that they "copied" from a Japanese mixer was wrongly drawn. After that they worked properly. Not sure how many we made over a probable 2 years. It was at this time that the "works" moved to Erith. I discovered that most of their circuits were borrowed and sometimes modified to suit."

In 1964 Jennings joined the "Association of Public Address Engineers", attending the annual exhibition in March (and also that of March 1965). See the pages linked here. It seems possible, in light of what David recalls, that the circuit for the mixer was picked up either from the 1964 meeting, or via one of the adverts for such units in the Association's journal. Transistorised mixers were an increasingly popular thing in '64.

"Journal of the Association of Public Address Engineers", 1964. Detail of an advert for a transistorised mixer.

Vox Precision in Sound newspaper catalogue, 1964, the Microphone Mixer

Detail from the JMI "Precision in Sound" newspaper format catalogue of late 1964. Image repeated from the earlier JMI dealer's catalogue (at the top of this page).

It is likely that the Mark 1 mixer of 1964 had seven controls (as illustrated above), and the Mark 2 (Mark II) eight. The Mark 2 unit was two inches longer.

A detail from the JMI pricelist of September 1964. Note that the Mark II is over £3 more than Mark I.

Mark 2

The JMI circuit diagram for the Mark 2 (II) is sheet OS/058, dated 23rd October 1964, drawn by Albert Hogben.

Much as the Mark I, the Mark II had three high gain inputs for microphones, and three low gain for music. Each had its own volume control. There was no "master" volume. Overall Treble and Bass controls were provided instead. An ON/OFF switch was provided underneath the Treble. Transistors were the OC44 and OC71, both germanium. Cases were wooden (also as the Mark I) with latching fronts.

Above, an old picture of a Mark II unit with black traffolyte panel. Note the separate Treble and Bass controls (JMI circuit diagram OS/058), and the presence of an ON/OFF switch. The box front latches differently from the Mark I mixer illustrated in the "Precision in Sound" newspaper-format catalogue.

A detail of the front end of the "Mk II Mixer Unit" from OS/058.

Detail from the Thomas Organ "King of the Beat" Vox catalogue, autumn 1965. Still the first style wooden case with latching front, produced for JMI by P.A. Glock in Crayford, a mile or so up the road from the Dartford Works. Clearly represented - two sets of three inputs, low gain and high gain.

Mark 3a (Mark III) - summer 1965

4 screws on the front panel; the letters of "VOX" in white outline

A new circuit - OS/082 dated 3rd June, 1965 - and a new all-metal housing to match the new-style housings of the Vox Metal Clad PA amplifiers. There are now five high gain inputs (for microphones) and one low gain input (for "music").

Detail from the JMI flyer for the BMII Trade Fair at the Russell Hotel, August 1965.

This mixer has OC44 transistors for its main tone circuit and "music" input, and either OC71s or AC107s on the five microphone input boards.

Mark 3b (solid state range) - late 1966

8 screws on front panel; "VOX" in solid letters.

The JMI circuit diagram for this version is likely to be sheet number OS/082, dated 30th November 1966, drawn (as the earlier sheet was) by Albert Hogben.