Gates Executive Audio Console Restoration, Part 3: Further Enhancements

The WA-6600 preamplifier is a replacement for the Gates M-6034 transistor preamplifier used in the Executive console (and other consoles of that era). The WA-6600 is intended to address the need for additional preamplifier boards. The original form factor is retained, including the card edge connector and pin-out. The WA-6600 closely follows the design of the Gates M-6600 remote amplifier, produced in the late 1960s, with some important enhancements.

The WA-6600 is a premium quality, low noise module intended for use in audio mixing consoles. The input is balanced, floating, and connected for a 150 ohm source impedance. The output is 600 ohms balanced and floating. The amplifier has a typical gain of more than 60 dB.

In the Executive audio console, the WA-6600 serves as the microphone preamplifier (AP1 through AP6) and the Audition buss preamplifier for monitoring functions (AB1 and AB2). In addition, two spare positions are provided for special-purpose applications (AP7 and AP8).

The WA-6600 is intended to be used with the Gates M-6039 mounting frame, which carries a mating receptacle for the printed card-type connections.

The WA-6600 may be operated in a “legacy mode” that provides plug-in compatibility with the M-6034, or in a balanced and floating output mode that is enabled through additional wiring to the M-6039 mounting frame. Jumpers on the WA-6600 are used to configure the board for the desired mode of operation.

The WA-6600 is capable of more gain than the M-6034 (63 dB versus 45 dB) and the gain is adjustable. This feature is helpful when using dynamic microphones with relatively low output levels.

The ability of the WA-6600 to provide balanced and floating microphone send lines is a significant improvement over the original design as it increases the interconnection flexibility for send/return circuits and reduces potential noise-related issues. This is particularly important when the send/return lines are routed to a patch panel.

The protective elements built into the WA-6600 power supply section prevent a failure in any one board to cause the entire console to shut down. For critical applications such as an on-air console, this is a very important feature. The robust and flexible power supply makes it possible to operate the preamplifier in a variety of applications beyond a plug-in replacement for the M-6034.

The WA-6600 can also serve as the basis for an equalized preamplifier by using the WA-6600EQ add-on board. The WA-6600 is unmodified, except for two connections between the WA-6600 and the add-on PCB: power and output. The equalization board is shown below.

The WA-6600EQ add-on equalization board is based on an RCA design (RCA Transistor Manual, 1966), so it is in keeping with the era of the Gates console. Two forms of equalization are provided: RIAA phono input and NAB tape input. The operating mode is selected through setting on-board jumpers. A jumper is also provided for flat frequency response.

The photo above shows the WA-6600 preamplifier mated with the equalization board.

An aluminum shield can be used on the foil and top side of the WA-6600 PCB for improved noise immunity.

The WA-6107 power amplifier is an implementation of the Gates M-6108 monitor amplifier intended for use in an M-6039 (or equivalent) PCB card frame. The board may be used as a power amplifier to drive a loudspeaker or as a 600 ohm line driver.

While the WA-6107 is designed around the M-6108 amplifier, several enhancements have been included, notably an input buffer stage and optional line-level output daughter board. The input buffer simplifies the gain control function and provides an input impedance that does not vary depending on the setting of the volume control. Safeguards built into the WA-6107 ensure reliable operation under varying loads and unexpected conditions.

The WA-6107 is intended to be powered by a –30 to –37 V dc power supply.

For applications requiring a 600 ohm balanced output, such as a line amplifier or distribution amplifier, an optional transformer output board is available. The PCB mounts directly onto the WA-6107 using the four screw holes provided for the rear-side aluminum shield. The output board is mounted on the component side of the WA-6107 using standoffs. Connections from the WA-6107 to the transformer output board are made using jumper wires.

The WA-6107 and optional transformer output board are shown above. The transformer board provides a direct 600 ohm output plus four bridging outputs.

An aluminum shield can be used on the foil side of the WA-6107 PCB for additional noise immunity.

The WA-6205B dc power supply is intended for use in a PCB card cage of the same dimensions of the M-6039 card frame (used in the Executive audio console). The board is the same physical size and uses the same card edge connector as the other plug-in printed circuit boards described in this blog. The WA-6205B power supply provides two dc outputs: a –37 V unregulated source and a –30 V regulated source.

The power supply is built around an LM337BTG 3-terminal adjustable negative voltage regulator. The device features:

• 1.5 A minimum output current
• Line regulation of 0.01%/V (typical)
• Load regulation of 0.3% (typical)
• 77 dB ripple rejection
• 50 ppm/°C temperature coefficient
• Thermal overload protection, internal short-circuit current limiting protection

A companion aluminum shield may be mounted on the foil side of the board for increased shielding of sensitive adjacent boards.

The WA-6205B requires an input of 28 V ac, which can be provided by the WA-6024 ac power supply, or equivalent.

It is common practice in a live radio environment to repeatedly cue turntables, tape decks, and other audio sources. When the source is cued, the operator typically turns down the monitor volume, and then after the source is ready, the monitor volume is returned to its previous level. It is possible to automate this repeated action by lowering the monitor volume to a preset level (dim) when a signal is present on the cue speaker, and to return it to the normal operating point when the cue signal is no longer present. This is the function of the WA-6111 Monitor/Cue Dim Controller.

The system described here is designed to work with the WA-6107 or WA-6108 power amplifier configured as a line amplifier to feed an external monitor amplifier, and the console cue system configured to drive an external cue amplifier.

There are two basic operating modes:

• In the manual Dim mode, controlled by an external switch, the monitor volume is reduced by an amount determined by the setting of the Dim Output Level control. This control is used to set the dim volume. At the minimum setting, the monitor output is reduced by at about 18 dB.
• In the Auto mode, whenever the cue signal exceeds a certain level (set internally), the dim is initiated for as long as the cue level is above the threshold. To accommodate normal pauses in the cue signal, the delay to “un-dim” is set internally (approximately 2 sec). When activated, the monitor level ramps down in about a second, and when deactivated it ramps back up in about a second. Auto is the normal operating mode.

The monitor output of the Executive audio console is applied to the appropriate input terminals on the controller PCB and the external monitor amplifier is connected to the appropriate output terminals. In addition, the cue output of the console is bridged to the controller before application to the external powered speaker.

Because the WA-6111 Monitor/Cue Dim Controller simply changes the shunt resistance of an H-pad between the output of the Executive console and the input to the external monitor amplifier, the dim function has no impact on audio performance. When in the off mode, it is invisible; when in the on mode, the level is reduced with no other effects on the monitor signal.

The WA-6111 form factor is identical to the other PCBs described on this page. For each device, the pinout is different of course.

Having a readily available audio test signal can be quite helpful in a studio operating environment. The WA-6032 Audio Signal Generator may be used in a variety of applications, including:

• Setting the balance between the left and right program channel outputs on the Executive console.
• Setting levels on studio recording devices.
• Providing a “confidence” signal (tone) for remote feeds.

The WA-6032 circuit is based on the Heathkit IG-18 audio signal generator, produced in the late 1960s and early 1970s. This circuit was chosen to maintain the technology era of the Executive audio console.

The signal generator operates at a fixed frequency of 1 kHz. Other frequencies can optionally be set. The board matches the form factor of the other PCBs described in this blog.

Remote control functions are required in most installations for—at minimum—turntable and cart machine start/stop. Other remote control capabilities may be needed as a facility expands. The WA-6011 PCB provides three possible remote control modes. Jumpers on the board are used to configure the circuit as needed.

As described in a previous blog, remote control functions were added to the Channel 4, 5, 6, and 7 Audition/Program key switches on the Executive audio console. When the key switch is placed in either the Audition or Program position, a contact closure is provided. This is intended as a machine (turntable, cart machine, etc.) remote-start. The WA-6011 remote control serves as the interface between the contact closures in the console and the controlled devices.

A single board can control two audio source machines. For each machine, one of three operating modes can be selected through jumper settings. The operating modes are as follows:

• Momentary On/Off. This mode provides a momentary contact closure when the console key switch is placed in the Audition or Program position, and another momentary contact closure when the key switch is placed in the Off position. This mode is intended for applications where the turntable (or other device) cannot be controlled by switching the input power on or off. Instead, a momentary contact closure is required to start the device, and another momentary contact closure is required to stop the device.
• Momentary On. This mode provides a momentary contact closure when the console key switch is placed in the Audition or Program position. No closure is made when the key switch is placed in the Off position. This mode is intended for applications such as a cart machine, which requires a momentary contact closure to start the device. No facility is required to stop the cart machine, since it will automatically re-cue.
• Always On. This mode provides a sustained contact closure for as long as the console key switch is in the Audition or Program position. This mode is intended for use with turntables where wires from each side of the power switch are brought out from the device, or where a low-voltage logic circuit can be controlled with a dry contact closure.

All control outputs are provided as dry “C” connections.

The WA-6011 board is the same form factor as the other PCBs described in this blog.

In a radio studio there is often the need to condition an input signal to reduce the level and provide isolation in the form of a balanced and floating output. Such an output provides an ideal match for the input of the Executive audio console. The interface board shown below, designated the WA-6030, may be used for this purpose.

The board design is straightforward. The input is applied to a fixed pad, which can be configured for the amount of attenuation required at the input to the console. An isolation transformer provides an input impedance of 600 ohms and an output impedance of 600 ohms. The resistive pad can be wired in a T-configuration for an unbalanced input or an H-configuration for a balanced input.

The WA-6030 includes provisions to feed multiple bridging loads from a single input. The circuit can also be used to combine multiple inputs to produce a single output. A common application for this feature would be to combine left and right inputs to produce a mono sum output.

The WA-6169 phono preamplifier is not strictly a part of the Executive audio console; however, a preamplifier is needed for any turntables used with the console. The preamp is designed to work with any of the popular moving-magnet cartridges (input impedance = 47 k ohms). Output connections are provided at 600 ohm balanced and floating.

The WA-6169 phono preamplifier is designed for use in broadcasting, recording, and general sound applications where low distortion and exacting frequency response characteristics are demanded. Special techniques have been employed to obtain reliability, low distortion, and excellent stability over time.

The WA-6169 is best understood by dividing the preamplifier into the input and output sections. The input section, equalized to the RIAA curve, is based on the M-6169 Stereo Transistor Equalized Turntable Preamplifier, produced by Gates Radio in the 1960s (part no. 888-0706-001). The output section, with flat frequency response, is based in part on the Gates M-6600 Remote Amplifier, with some important enhancements. In the WA-6169, improved components are used throughout, with substitution of certain parts as required based on the availability of modern devices. Substitute transistors are used, but in all cases the match is close enough that performance is not adversely impacted.

The WA-6169 uses the same form factor as the other PCBs described in this blog.

An aluminum shield can be used on the foil and top side of the WA-6169 PCB for improved noise immunity.