MMSR77

Thank you for your recent purchase of a Boscoe MMSR77 kit!  This is a replica of the vintage preamp used in late 1970s Music Man StingRay basses. Each preamp kit has been individually tested before shipping and should help recreate the classic StingRay tone in your bass.

While this preamp will work great with many different kinds of pickups and wiring configurations, if you are looking to recreate a vintage StingRay tone it is important that a vintage style Music Man type humbucker is used.  

The preamp was designed to sound best when paired with a humbucker using Alnico V magnets wired in parallel with approximately 1750-1950Ω resistance and approximately 700mH inductance (early StingRays had varied winding counts).

Some examples of third party vintage-style humbuckers:

• Aguilar AG 4M and AG 5M

• Nordstrand MM4.2 and MM5.2

• Seymour Duncan SMB-4A and SMB-5A

When assembling, make sure to complete all connections before attaching the battery.  The preamp may be a tight fit on some 4 string StingRay style basses with crescent control plates.  If so, make sure you have longer wires so you can move things around as needed to fit everything or route out some additional space.

Carefully attach wires to the screw terminals.  Tinning the ends of stranded wire with solder is recommended to ensure a good connection.  Make sure the pins on the bottom of the preamp aren't in contact with conductive paint or metal - cover with electrical tape as needed.

Should you encounter any noise in the circuit, make sure you have the potentiometers grounded and the bridge ground attached.  If you use a vintage humbucker like the Nordstrand MM4.2 note that it is built to the original spec and does not have its pole pieces grounded.  Extra shielding and grounding may be required.

This preamp includes as an extra feature the 1kΩ protection resistor that Music Man incorporated into its later basses.  This protects the LM4250CN opamp, which could become damaged should the guitar lead be shorted even momentarily.

When wiring potentiometers to the preamp, make note of the nomenclature used.

• CCW - the counterclockwise lug, on the left when looking from the bottom

• Wiper - the middle lug

• CW - the clockwise lug, on the right when looking from the bottom

Here is a simple diagram for reference:

When installing the preamp kit, here is how the components ought to be connected:

9V Battery connector

• Positive (red wire) connect to the terminal marked 9V+

• Negative (black wire) connect to the ring connector on the output jack

Volume potentiometer (marked A25K or B25K)

• CW lug (purple wire) connects to the terminal marked VOL CW

• Wiper lug (white wire) connects to the terminal marked VOL WIPER

• CCW lug (black) connects to the terminal marked GROUND

Treble potentiometer (marked C1M)

• CW lug (purple wire) connects to the terminal marked TREBLE CW

• Wiper lug (green wire) connects to the terminal marked TREBLE WIPER

• CCW lug (yellow wire) connects to the terminal marked TREBLE CCW

Bass potentiometer (marked A100K)

• CW lug - not used

• Wiper lug (green wire) connects to the terminal marked BASS WIPER

• CCW lug (yellow wire) connects to the terminal marked BASS CCW

Output jack

• Tip (white wire) connects to the terminal marked OUTPUT JACK

• Ring (black wire) connects to negative (black) wire on the battery connector

• Sleeve (black wire) connects to the terminal marked GROUND

A WAGO LeverNut has been included to make it easier to connect existing battery connectors to the output jack ring.

Note that the screw terminals are more than big enough to accommodate a couple of wires, so it's okay (and maybe ideal) to connect both the output jack sleeve and the volume CCW lug to the same terminal.  If you have more than two wires needing grounded you might want to use a LeverNut or some other wire connector to ensure a good connection.  Just ensure the preamp is grounded to them.

If you're installing the kit into a bass with a metal control plate, the potentiometers will be grounded through the plate to the output jack sleeve.  However if you have a rear control cavity and are mounting the potentiometers through the wood, you might want to solder a ground wire between the potentiometers attached to their back.  You would then run a small wire from the back of the volume potentiometer to the CCW lug.  Shielding the cavity with conductive paint or copper tape is also recommended, but not necessarily required.  

Each potentiometer will include a washer, a locking (shake proof) washer, a nut, and a rubber spacer (used to center the pot inside the control plate hole).  The locking washer and spacer may not be needed for your build.  The small tabs on the bottom of the potentiometers can be removed with pliers should they cause the potentiometers to not sit flush with the control plate or wood.  Do not over-tighten the nuts on the potentiometers or they will break.

The included 6mm (18 tooth) knobs are the push-on kind.  Use gentle pressure when putting them on or prying them off.  They should fit snugly.