The Sonobeat Custom Mixers

From 6 to 16 inputs in 3 years
KAZZ-FM's chief engineer, Bill Curtis, designs and assembles KAZZ's production room console in 1966; it serves as a model for the Sonobeat 6-input mixer he designs and assembles at the beginning of '67
Rim's 2016 elevation drawings, to the best of his memory, of the 6-channel mixer; from top: front view (pan pots on top row, volume controls on bottom row), back view (with line level 1/4" phone jacks and XLR microphone jacks), left side view, right side view (showing line level 1/4" phone jacks that feed the Ampex tape deck inputs)
The mask used to etch the printed circuit boards for the 10-input suitcase mixer's microphone/line input modules
The 10-input suitcase mixer at a recording session; five microphone/line inputs are mounted on each side of the suitcase along with output jacks, on the right side, to feed the Ampex tape deck. Note the VU meters, which help monitor audio levels to prevent circuit overload.
Rim Kelley works on schematics for Sonobeat's 16-input custom mixing console (1970)
There are few surviving photos of the Sonobeat 16-channel mixing console, particularly showing its control surface; this grainy shot shows the main console unit and the sub-mixer side unit

At the beginning of 1967, when Sonobeat co-founders Bill Josey Sr. and Bill Josey Jr. are planning the launch of their Austin, Texas-based record company, they have no recording equipment of their own, so they arrange to borrow professional ElectroVoice microphones and Ampex 350 and 354 tape decks from KAZZ-FM, where both work. Although KAZZ has a small production room mixer used to record local commercials, it's not easily portable nor designed to mix multiple microphone channels. As they're starting out, the Joseys can't afford to buy a professional mixer, so they ask KAZZ chief engineer Bill Curtis, who designed and assembled the station's production room mixer, to design a compact, battery powered stereo mixer that can handle multiple inputs. Thus sets in motion Sonobeat's decision to build its own custom mixers rather than buy commercially-available mixers (although it does purchase a professional mixer-in-an-attaché-case in 1968); in all, Sonobeat builds three progressively more complex mixers, culminating in 1970 with a large, sophisticated 3-piece, 16-input, 4-bus console.

The Curtis 6-input stereo mixer (1967)

Bill Curtis' design for Sonobeat's first mixer is amazingly clean and simple, using only metal-oxide semiconductor field-effect transistors (MOS-FET), capacitors, and resistors. Although field-effect transistors have been around for years, it's only in the mid-'60s that the metal-oxide variety is invented, and they're revolutionary. Curtis chooses the new-fangled MOS-FETs because they're inexpensive, need no audio transformers (because they're high impedence like vacuum tubes), use very little current (so the mixer can be battery powered), and are easy to configure into both audio pre-amp and line driver circuits. And, this new type of transistor is the first to beat the "quietest" vacuum tubes, introducing no perceptible thermal or shot noise – hiss usually associated with transistorized audio amplifiers – into the audio chain. It's because Curtis uses MOS-FETs for the mixer that Rim decides to prominently feature the alliterative "Solid • State • Stereo" – a reference to semiconductors, such as transistors, as distinguished from vacuum tubes – on Sonobeat's record label.

Curtis' approach to assembling each input circuit is as simple as the circuits themselves: he just twists the transistor, capacitor, and resistor leads together and adds a drop of solder to each twist, creating a small open-air ball of components for each input circuit.

Bill Sr. builds a small wooden box – about eight inches high, six to seven inches deep, and 16 inches wide – to house the circuits and dresses it with a brushed aluminum faceplate into which he drills two rows of six holes each to mount the volume and stereo pan potentiometers. He mounts XLR microphone connectors and quarter-inch line input and output phone jacks on the back of the box. Curtis then solders his preamp circuits into place, leaving the balls of transistors, capacitors, and resistors dangling inside the box. He's careful to separate the components so they don't short out. To make it easy for Curtis to tweak the circuits as needed, Bill Sr. leaves the bottom of the box open. Although we haven't found photos of the little mixer in the Sonobeat archives, nor Bill Curtis' schematic drawings, it's modeled on – and looks very similar to – the KAZZ-FM production room mixer. In 2016, Rim recreates a set of elevation drawings from memory.

Bill Curtis' portable mixer gets its acid test in May '67 in a series of practice recording sessions with Leo and the Prophets. Those sessions lead to circuit tweaks before the first "formal" recording sessions Sonobeat holds, in July 1967, first "redo" sessions with Leo and the Prophets, followed by sessions with the Lee Arlano Trio, an acoustic instrument jazz combo, and, a week later, the Sweetarts, an amplified rock band. If there's one failing of the little mixer, it's that it lacks VU meters to gauge when the input volume is too high and, therefore, Rim can't tell when the mixer's circuits are overloading, and creating distortion, during recording sessions. By the time Sonobeat holds the Sweetarts' session, Curtis has worked out a clever calibration method using a small portable audio frequency generator that he runs through one input of the mixer and from its stereo outputs into the Ampex 350 and 354 inputs; this way, Rim can monitor recording levels during recording sessions using the VU meters on the Ampex decks. Although a good solution, it's not perfect, and many of Sonobeat's early recordings indeed are distorted from circuit overload. Nonetheless, Sonobeat continues to use the Curtis 6-input mixer until March 1968, when Bill Sr. and Rim build a new 10-input mixer.

The 10-input suitcase mixer (1968)

By the end of 1967, Sonobeat has outgrown the 6-input mixer, although it provides yeoman service in recording the first group of 45 RPM singles and album that Sonobeat releases. But now Sonobeat wants to use more sophisticated microphone techniques as well as "direct injection" – plugging guitars directly into the mixer, bypassing the guitar amp and speaker box altogether – so more inputs is the number one priority. Rim begins researching audio amplifier circuits early in 1968. Using plans sourced from articles in Popular Electronics and Radio Electronics magazines, he lays out printed circuit board matrices that Miller Blueprint in downtown Austin turns into high-contrast negatives. The negatives are then used with Radio Shack printed circuit etching kits to create the actual copper-clad epoxy boards onto which all the components are mounted. Bill Curtis' 6-input mixer used field effect transistors, but for the new mixer Rim chooses Motorola audio integrated circuits that offer more powerful features. Other components rounding out the circuits include standard transistors, capacitors, resistors, and audio transformers. This mixer also will be battery powered, but will take a bigger battery pack than the Curtis mixer.

Now, how to house the new printed circuits boards and control surface? Another wooden box, but bigger than the Curtis mixer? Bill Sr. sees a Samsonite or American-Tourister TV commercial for luggage that can withstand being run over by a truck. This triggers an idea: since Sonobeat has no studio facility and generally records at a variety of rented locations around Austin, such as Swingers Club , Vulcan Gas Company, and the First Cumberland Presbyterian Church auditorium, the Joseys have to cart their equipment all over the place. So, Bill Sr. decides to mount the new mixer in a suitcase with a detachable lid. He cuts a piece of black acrylic plexiglass to precisely fit flush at the surface of the bottom half of the suitcase, then drills holes into the acrylic for the volume and pan controls. This time, he adds VU meters to more accurately gauge and control input and output levels. He installs XLR connectors and quarter-inch phone jack inputs on each side of the suitcase and mounts suction cups to the bottom to hold the mixer in place when in use. Meanwhile, Rim assembles ten identical sets of the printed circuit boards, each containing a microphone pre-amp, line input, and line-level output, plus one printed circuit board that combines the outputs of the ten input circuits to feed the VU meters and the Ampex 350 and 354 tape decks.

Somewhat surprisingly, when the printed circuit boards are assembled and mounted under the plexiglass control surface and mikes and tape decks are are all plugged in, everything works. The new 10-input mixer is in service by the time Sonobeat records Lavender Hill Express's second single, Watch Out! and Country Music's Here to Stay in March '68. This mixer stays in service until Bill Sr. and Rim build an even more powerful and sophisticated mixing console early in 1970.

The 16-input 3-piece mixing console (1970)

In late summer 1968, Sonobeat acquires a Scully half-inch 4-track recorder, which gives the Joseys the ability to undertake more elaborate, layered recordings. Although the 10-input suitcase mixer is serviceable throughout 1968 and into 1969, it eventually can't handle ever more complex recording sessions. As 1969 comes to a close, Rim begins researching a modular approach to combining audio circuits that can provide an array of functions – including compression and equalization – separately for each microphone and line-level input channel. Again, he turns to db: The Sound Engineering Magazine but also buys a book filled with audio circuit designs that he finds in the Electrical Engineering section of the University of Texas bookstore. Armed with an array of potential circuits, in January 1970, he begins laying out circuit designs for each input channel and eventually creates larger and more sophisticated printed circuit boards using the same process he has used for the printed circuit boards in the suitcase mixer.

Because the new console includes an ambitious professional-level feature set, Rim creates separate printed circuit modules for the various functions, including a PC board that allows each of the mixer's 16 individual input channels to be assigned to any of the sub-mix busses feeding the Scully 280 and newly-acquired Stemco half-inch 4-track tape decks. Bill Sr. decides the console itself also should be modular and builds three separate units that neatly fit together to form an "L". The main unit is five feet wide and houses the 16 side-by-side individual input channel "strips". Each strip features a linear slider volume control; knobs for microphone trim, high and low equalization, reverb and effects send and receive, compression functions, and headphone send; and switches to assign the strip's output to one of the sub-mix busses. On the right side of the mixing surface are 16 linear sliders stacked vertically; each provides stereo pan for its corresponding input strip. Running the full length at the top rear of the main unit is a panel housing VU meters for each channel strip. All printed circuit boards and electronic components are mounted inside each console unit. Although all three units are framed and covered in wood, the surfaces, onto which all the controls are mounted, are black acrylic plexiglass. The back of the main unit includes XLR microphone jacks and quarter-inch phone jacks (for line level inputs) for the 16 input channels. Each of the two side units is about 30 inches wide. One houses the four-channel mixing busses, with a VU meter for each of the four channels. The other houses a patch bay that assigns output channels to the half-inch 4-track Scully 280 tape deck, half-inch 4-track Stemco tape deck, or Ampex AG350 quarter-inch 2-track tape deck as well as to outboard processing equipment, such as Sonobeat's Blonder-Tongue Audio Baton 9-channel stereo equalizer and Fairchild Lumiten stereo optical compressor. Eventually, because it takes up too much space in the small studio, Bill Sr. abandons use of the unit housing the patch bay, which is largely superflous since there's also a patch bay on the equipment rack that holds the tape decks.

The 16-channel main console unit is completed just in time for the complex Mariani Perpetuum Mobile album recording sessions in March 1970, initially recorded in open-air at a 100 acre ranch near Austin, where Bill Sr. and Rim haul their Scully 280 4-track tape deck, the main mixing console unit, and microphones and cables.

The quad modifications (1972)

At the end of 1969, Rim sees an article on "tetraphonic" sound in db: The Sound Engineering Magazine. Electronics companies anticipate this as the next "big thing" in consumer audio but decide to use a friendlier term to describe it: "quadraphonic", in which the listener uses four speakers – front left, front right, rear left, and rear right – to deliver an encircling sonic experience. It's almost like being in the middle of an orchestra or band. Although Rim puts the magazine away, a year or two later Bill Sr. recalls it, anticipating quadraphonic recordings will be a big consumer trend. In 1972, about a year after Sonobeat has relocated its studios to 705 North Lamar in Austin, Rim designs a new set of sub-mixing printed circuit boards that make it easier for Bill Sr. to create quad mixes that literally surround the listener in 360°. These new printed circuit boards are designed to connect to joysticks that position the instruments and vocals anywhere in the quad audio spectrum, but Bill elects to use two pan pots for each quad module: one pan pot moves the audio image from left to right and the other from front to rear, which accomplishes the same feat as the joystick but at much less cost. Bill begins experimenting with quad recording techniques, initially using Austin musicians he brings together into a studio session group he calls Base. His first commercial attempt at quad recording, in early 1973, is with Austin band Vita.

In August 1973, the 16-input console moves from Sonobeat's North Lamar studio to Bill Sr.'s new Blue Hole Sounds studio in Liberty Hill, Texas. The console remains serviceable into 1976, when Blue Hole Sounds shutters on Bill's death in September. Within weeks after Bill's death, his son visits Blue Hole Sounds to recover his dad's belongings, only to find cardboard boxes filled with Sonobeat's master tapes crammed into Bill's station wagon. But all the recording equipment, including the mixing console, is missing from the studio. Where the equipment went remains a mystery to this day.

Rim's early schematic drawings of the input, compressor, and EQ module of the 16-input mixing console; the "effects send" is used to assign an input, such as a microphone covering a drum kit, to Sonobeat's steel plate reverb unit
Detail of a portion of the mixing console schematics Rim draws up
The mask used to etch printed circuit boards for the 16-input mixing console's equalization modules
The mask used to etch printed circuit boards for the 16-input mixing console's submixer module
Rim's schematic for a 10-input quadraphonic mixing console; Bill Sr. adds these modules to one of the two smaller units of the 3-piece mixing console in 1972
A commercial quad panner module featuring a joystick inspires Rim's design of the Sonobeat quad mixing modules; in the end Bill Sr. decides against expensive joysticks in favor of a simple set of left-right, front-rear pan pots