Boscoe MMSA78+ kit - Music Man Sabre Bass Preamp Replica, Improved

PREAMP WITH CONTROL PLATE SOON AVAILABLE! If you're looking for the preamp already mounted onto a control plate for a StingRay style bass, please message me or stay tuned!

Note: This preamp is a replica of the late 1970s and early 1980s Music Man Sabre preamp. If you have one of the later Sabre basses (the ones with the blade switch) they normally use a StingRay preamp. You can use this preamp with those as it has a very similar voice to the StingRay but also includes the bright switch, or you can use my StingRay preamp replica instead, which can be found at: https://reverb.com/item/78583151

Overview:

This is an improved reproduction of the classic late 1970s Pre-Ernie Ball Music Man Sabre 2-band preamp. This preamp recreates the exact tone of a late 1970s Sabre but is made with modern manufacturing methods and uses screw terminals to easily attach connections without soldering. It differs from the original preamp in that it offers the choice of two different frequency boosts for the bright switch (see + ).

I'm a bass player and computer geek and I'm a huge fan of Leo Fender's late work, so I decided to design this preamp to recreate the vintage late 1970s Sabre sound - but modernize it and make it easier to work with.

Design goals:

• Must reproduce the bass and treble response of late 1970s Music Man Sabres. This includes support for the bright switch which was only present for a few of the early years.
• Must use the original, now discontinued LM4250CN opamp that's key to the distinctive sound and phenomenal battery life. The opamp is installed in a socket so it has never been exposed to the heat of a soldering iron. This also allows one to experiment with alternative opamps should you desire.
• Use screw terminals instead of soldered on wires to make installation easier
• Incorporate modern surface mounted electronics
• Attractive silk screening with clearly labeled terminals
• Incorporate a 1kΩ protection resister between the output jack and the LM4250CN opamp. Music Man attached this in between the output jack and the opamp to protect it from shorts that in rare circumstances could fry it. Other reproductions do NOT include this and it must be soldered on separately.

Bonus features of the MMSA78+:

The original Sabre preamp (and my MMSA78 replica) used a 1.8nF bright capacitor, which in this circuit has a corner frequency of around 19kHz, right at the top of human hearing range. Most owners report barely hearing a difference with it engaged. My MMSA78+ preamp removes the 1.8nF capacitor and offers two choices, configurable by a tiny DIP switch on the preamp itself (use the tiny screwdriver provided to slide the switch):

• 10nF - this has a corner frequency of 3.4kHz and sounds more like what one would expect in a bright switch
• 22nF - has a corner frequency of 1.5kHz and is more of a high-mids presence switch

The MMSA78+ also includes an extra ground terminal to make wiring easier.

This kit includes:

• B25K (volume) linear taper potentiometer
• A100K (bass) audio taper potentiometer with center detent
• C1M (treble) reverse audio taper potentiometer with center detent and a push-pull switch for the bright/presence function
• Quality stereo audio jack, wired to preserve battery life
• 9V battery clip with included Wago connector (so no additional soldering is needed should you have an existing 9V connector)
• Pre-cut and soldered extra-long wiring, which can be easily shortened to your needed length
• Neoprene pad for insulating the back of the preamp (install after connecting wires)
• Mini screwdriver

Installation notes:

This is an unusually designed preamp as Leo Fender designed it to obtain a particular sound. Thus, to recreate the late 1970s sound exactly the preamp needs to be paired with either one or two Music Man Sabre pickups or vintage-spec StingRay bass pickups.

However note that vintage-spec Sabre bass pickups are not readily available. You can either buy used ones sold online at places like eBay or Reverb or buy StingRay vintage-style Alnico humbucking pickups wired in parallel with around 1800Ω resistance. Suggestions that work well are Nordstrand MM4.2, Seymour Duncan SMB-4A, and Aguilar AG-4M. You can use this preamp with just one or multiple pickups.

There are other replica pickups around, and the circuit will still sound good if you use a higher resistance pickup as found in Sterling by Music Man basses, but it won't necessarily have the exact sound.

To use the bright functionality you just pull out on the treble potentiometer and it will engage. Note that the circuit completes itself through the ground connection with the control plate, so if you use a plastic control plate or pickguard you will need to add an additional ground wire to the treble pot casing.

When wiring, see attached image for which lug on the potentiometer is the wiper, CW (clockwise), and CCW (counter clockwise). Do not attach a battery until all components have been attached.

This preamp should fit easily into basses with large control cavities or rear cavities (such as 5 string StingRays, StingRays with double humbuckers, and others). It will be a tighter fit in 4 string StingRays with crescent shaped control cavities, though it should still fit. 16mm potentiometers (like the ones suggested above) are recommended as they're more compact. Due to slight differences in routing between different models you may have more or less room.

There is a manual online at my website.

Preamp dimensions: 50mm x 21mm x 11mm

Final notes:

Unfortunately I do not usually accept returns or refund requests as it's easy to damage the preamp if you're careless or don't know what you're doing. This preamp was designed to be as durable as possible and each one is individually tested before shipment. I want your project to be a success so if you have any issues please let me know and I will do my best to help you and make things right.

This includes only the preamp, potentiometers, battery clip, jack, and wiring. You will need to obtain a pickup (if you don't have one already). Screw terminals on the preamp require a 1.5mm precision flathead screwdriver to tighten. A small one has been included.

Shipping is free via USPS with tracking to the United States. Please contact me with any questions. Thanks!