MMSR77

Thank you for your purchase of a Boscoe Music MMSR77 Control Plate Kit!

This kit combines a reproduction of the preamp used in late-1970s Music Man StingRay basses with the period-correct potentiometer values, output jack, and wiring, fully assembled on a control plate.

Each control plate kit is individually tested before shipping and is designed to help recreate the classic StingRay tone in your bass.

Pickup Selection

The MMSR77 will work with many different pickups and wiring configurations. For the closest approximation of a vintage StingRay tone, however, a vintage-style Music Man humbucker is recommended.

The original preamp was designed around an Alnico V humbucker wired in parallel, with approximately 1750–1950Ω DC resistance and approximately 700mH inductance. Early StingRay pickups varied somewhat in winding count and specifications.

Some examples of third-party vintage-style humbuckers include:

• Aguilar AG 4M and AG 5M

• Nordstrand MM4.2 and MM5.2

• Seymour Duncan SMB-4A and SMB-5A

A pickup wired in series can still be used with the MMSR77, but its higher resistance, inductance, and output will produce a different response from the original parallel-wired StingRay pickup.

For additional pickup models, coil identification, magnetic polarity, and series/parallel wiring information, see the Pickup Wiring Reference.

Power

The MMSR77 is designed for normal operation at 9V and is safe to operate at up to 18V.

Higher voltage may provide additional headroom, but does not necessarily improve the sound.

For normal operation, use a standard 9V battery.

The supplied TRS output jack automatically switches battery power when a standard mono instrument cable is inserted.

Unplug the instrument cable when the bass is not being used. Leaving a cable inserted keeps the preamp powered and will discharge the battery.

Before You Begin

Before disconnecting any existing wiring, take several clear photographs so you have a reference during installation.

Pay particular attention to:

• pickup wiring

• bridge ground

• battery wiring

• output jack wiring

• cavity shielding

• and any existing ground connections

Disconnect the battery before beginning installation.

Complete all wiring before connecting the battery.

The included import-spec control plate is intended for Sterling by Music Man Ray4 and OLP basses.

Screw-hole spacing can vary between instruments, so minor adjustment of the mounting holes may occasionally be required.

Before installing the control plate permanently, test-fit the complete assembly in the bass.

Make sure:

• the preamp and wiring fit comfortably inside the cavity,

• wires are not pulled tight,

• the output jack has adequate clearance,

• and the underside of the preamp cannot contact conductive shielding, potentiometers, or other metal.

Installing the Control Plate Kit

The control plate, potentiometers, output jack, and preamp are already wired and tested.

For a normal installation, you should only need to connect:

• the pickup

• the bridge ground

• battery positive

• battery negative

Carefully insert each wire into the appropriate screw terminal.

Before tightening the terminal, make sure the stripped conductor is positioned inside the terminal's internal box clamp.

It is possible to accidentally insert a wire underneath the clamp. In that situation, the screw may feel tight even though the wire itself is not securely held.

After tightening each terminal, gently pull on the wire to make sure it is actually secured.

Make sure no loose strands of wire are exposed where they could contact an adjacent terminal.

Do not overtighten the terminal screws.

Connect:

Pickup hot lead(s) → PICKUP INPUT

Pickup ground/shield → GROUND

Bridge ground → GROUND

Battery positive, normally red → 9V+

If reusing an existing battery box, connect battery negative, normally black, to the output jack Ring connection using the supplied WAGO Lever-Nut.

Make sure the contacts on the underside of the preamp cannot touch conductive shielding paint, copper foil, the potentiometers, output jack hardware, or other metal.

Use the supplied self-adhesive insulating pad as needed.

Pickup Wiring

Sterling by Music Man Ray4 basses have been produced with several different pickup and wiring configurations.

Many are wired with their pickup coils in series from the factory, while the original StingRay used its humbucker coils in parallel.

For the Sterling by Music Man H-1 pickup configuration tested by Boscoe Music, parallel wiring is:

Red + White → PICKUP INPUT

Black + Green + Bare → GROUND

Do not rely on wire color alone.

Pickup wiring can vary by model and production run. If you are unsure, identify the pickup coils with a multimeter before connecting them.

Some vintage-style pickups may also require additional attention to grounding and shielding.

For example, the Nordstrand MM4.2 is built to vintage specifications and does not ground its pole pieces. Additional shielding or grounding may be useful depending on the installation.

For tested pickup wiring, coil identification, and additional information, see the Pickup Wiring Reference.

Control Plate Wiring Reference

The control plate is supplied fully assembled and should not normally require rewiring.

If a connection is removed or you need to service the assembly, use the following information to restore the original wiring.

When working with the included potentiometers, the terminals are identified as follows:

• CCW (lug 1) — counterclockwise lug; on the left when viewed from the bottom

• Wiper (lug 2) — center lug

• CW (lug 3) — clockwise lug; on the right when viewed from the bottom

9V Battery

Positive, red wire → 9V+

Negative, black wire → Output jack Ring

Volume Potentiometer — A25K or B25K

CW (lug 3), purple wire → VOL CW

Wiper (lug 2), white wire → VOL WIPER

CCW (lug 1), black wire → GROUND

Treble Potentiometer — C1M

CW (lug 3), purple wire → TREBLE CW

Wiper (lug 2), green wire → TREBLE WIPER

CCW (lug 1), yellow wire → TREBLE CCW

Bass Potentiometer — A100K

CW (lug 3) → Not connected

Wiper (lug 2), green wire → BASS WIPER

CCW (lug 1), yellow wire → BASS CCW

Output Jack

Tip, white wire → OUTPUT JACK

Ring, black wire → Battery negative

Sleeve, black wire → GROUND

The supplied WAGO Lever-Nut makes it easier to connect an existing battery box or battery connector to the output jack Ring connection.

Battery and Output Jack Operation

The supplied output jack is a TRS jack with Tip, Ring, and Sleeve connections.

• Tip carries the audio signal.

• Ring connects to battery negative.

• Sleeve connects to circuit ground.

Connecting battery negative to Ring is intentional.

A standard instrument cable uses a TS mono plug. When the plug is inserted into the TRS output jack, the plug's sleeve contacts both Ring and Sleeve inside the jack.

This connects battery negative to circuit ground and powers the preamp.

Removing the instrument cable breaks the battery-negative connection and switches the preamp off.

For this reason:

Always unplug the instrument cable when the bass is not being used.

Grounding and Shielding

The MMSR77 screw terminals are large enough to accommodate more than one wire.

The output jack Sleeve ground wire and Volume CCW ground wire may therefore share the same GROUND terminal.

If several ground wires need to be joined, a WAGO Lever-Nut or similar connector may be used to create a common ground connection.

Make sure this common ground is connected to the MMSR77 GROUND terminal.

The metal control plate normally bonds the potentiometer bodies together.

After installation, use a multimeter to verify continuity between:

• the Volume potentiometer body

• the Treble potentiometer body

• the Bass potentiometer body

• the metal control plate

• and circuit ground

If you encounter excessive hum or noise, verify that the bridge ground is connected.

An additional ground wire connecting the potentiometer bodies to circuit ground may be added if necessary.

Shielding the control cavity with conductive paint or copper foil can further reduce noise, although it is not always necessary.

If shielding is used, make sure it is connected to circuit ground and cannot contact the underside of the MMSR77.

Output Protection

The MMSR77 includes the 1kΩ output protection resistor Music Man incorporated into later versions of the StingRay preamp.

This helps protect the increasingly scarce LM4250CN opamp from damage if the instrument output is accidentally shorted.

The protection resistor is part of the normal MMSR77 circuit and requires no modification.

Installing the Controls and Knobs

Each potentiometer includes a washer, locking or shake-proof washer, nut, and rubber O-ring spacer used to center the potentiometer in the control plate hole.

Do not overtighten the potentiometer nuts.

Excessive force can damage the potentiometer.

The included knobs fit 6mm, 18-tooth splined shafts and are push-on.

Use gentle, even pressure when installing them.

When removing a knob, carefully lift upward from both sides rather than applying excessive force to one side of the shaft.

Before Applying Power

Before connecting the battery, inspect the complete installation.

Verify:

1. Pickup signal → PICKUP INPUT

2. Pickup ground/shield → GROUND

3. Bridge ground → GROUND

4. Battery positive → 9V+

5. Battery negative → output jack Ring through the supplied WAGO connector

6. Output jack Sleeve is connected to GROUND.

7. Output jack Tip is connected to OUTPUT JACK.

8. Every conductor is actually captured inside its screw-terminal box clamp.

9. No loose wire strands can contact adjacent terminals.

10. The underside of the MMSR77 cannot touch conductive shielding, potentiometers, output jack hardware, or other metal.

11. The metal control plate and potentiometer bodies have continuity to circuit ground.

12. No wires are pinched or under excessive tension.

Only after completing these checks should the battery be connected.

Complete Wiring Diagram

The diagram below shows a complete MMSR77 Control Plate Kit installation with a single humbucker.

The pickup wire colors shown are representative of the Sterling by Music Man H-1 pickup configuration tested by Boscoe Music.

Pickup wire colors can vary by manufacturer, model, and production run.

Always verify your pickup before making connections.

For additional pickup models, coil identification, magnetic polarity, and series/parallel wiring information, see the Pickup Wiring Reference.

Testing the Installation

Before fully reinstalling the control plate:

1. Connect the battery.

2. Plug in a known-good instrument cable.

3. Connect the bass to an amplifier at a moderate volume.

4. Verify that the Volume control operates throughout its full range.

5. Verify that the Bass control boosts and cuts normally.

6. Verify that the Treble control boosts and cuts normally.

7. Listen for excessive hum, distortion, crackling, or intermittent output.

8. Gently move the wiring and verify that the signal remains stable.

9. Unplug the instrument cable before completing final assembly.

Testing the electronics while they are still accessible makes troubleshooting much easier.

Troubleshooting

No Output

First check the basic power and signal connections.

Verify:

Battery positive → 9V+

Battery negative → output jack Ring

Output jack Sleeve → GROUND

Output jack Tip → OUTPUT JACK

Pickup signal → PICKUP INPUT

Also make sure the instrument cable is fully inserted.

The cable completes the battery circuit, so the MMSR77 will not normally power up without a plug inserted.

Check every screw-terminal connection with a gentle pull.

A conductor inserted underneath the internal box clamp may look correctly installed while making little or no electrical contact.

Intermittent Output

Check the screw terminals first.

Make sure every wire is actually captured inside its internal box clamp and cannot be pulled free.

Also inspect for:

• loose wire strands

• wires under tension

• a loose WAGO connection

• output jack contacts touching nearby hardware

• or the underside of the PCB touching conductive material

Excessive Hum or Noise

Check the bridge ground first.

Use a multimeter to verify continuity between:

• bridge

• metal control plate

• Volume potentiometer body

• Treble potentiometer body

• Bass potentiometer body

• output jack Sleeve

• MMSR77 GROUND

If the cavity uses conductive shielding paint or copper foil, make sure the shielding is also connected to circuit ground.

Make sure the underside of the MMSR77 cannot touch the shielding.

If the hum changes significantly when you touch the strings or bridge, inspect the bridge-ground connection.

Pickup Sounds Much Louder, Thicker, or Darker Than Expected

Check whether the humbucker is wired in series rather than parallel.

The original StingRay used its two pickup coils in parallel.

A series-wired pickup will generally have higher resistance, inductance, and output and will therefore produce a thicker, darker response.

For tested pickup configurations, see the Pickup Wiring Reference.

Bass or Treble Control Does Not Behave Normally

Because the control plate is supplied fully wired and tested, first check the connections at the MMSR77 screw terminals.

Verify that none of the prewired control leads became loose during installation.

If servicing the control plate, compare the wiring to the Control Plate Wiring Reference section above.

Remember:

Bass CW → Not connected

Volume Control Does Not Behave Normally

Check the Volume control connections:

CW → VOL CW

Wiper → VOL WIPER

CCW → GROUND

Also verify that the pickup is connected to PICKUP INPUT and has not accidentally been connected to one of the Volume terminals.

Battery Drains Quickly

Unplug the instrument cable whenever the bass is not being used.

If the battery continues to drain quickly, verify that battery negative is connected to output jack Ring and has not been permanently connected to Sleeve or GROUND.

Also inspect the output jack for bent contacts or accidental shorts.

The Bass Works Before the Control Plate Is Installed but Stops Afterward

This strongly suggests a mechanical short or pinched wire.

Inspect the underside of the MMSR77 for contact with:

• conductive shielding paint

• copper foil

• a potentiometer body

• output jack hardware

• or other grounded metal

Also inspect for wires pinched between the control plate and the body.

Use the supplied self-adhesive insulating pad to protect the underside of the preamp as needed.

Pickup Wire Colors Do Not Match the Manual

Do not rely on wire color alone.

Sterling by Music Man and other manufacturers have used different pickup wire colors and configurations over time.

If your pickup differs from the H-1 configuration shown in this manual, identify the coils with a multimeter and refer to the Pickup Wiring Reference before making changes.

Final Installation

After the electronics have been tested successfully:

• Confirm that all screw-terminal connections are secure.

• Confirm that the WAGO battery connection is secure.

• Make sure the underside of the preamp is insulated from conductive surfaces.

• Arrange the wiring so that it is not pinched or under tension.

• Make sure the control plate sits flat without forcing the preamp or wiring into the cavity.

• Tighten the control-plate mounting screws only enough to secure the plate.

Test the bass once more after final assembly.

Need More Help?

For pickup-specific wiring, coil identification, magnetic polarity, and series/parallel information, see the Pickup Wiring Reference.

If you have any questions about installation, compatibility, or troubleshooting, please contact us!