The Fender Marcus Miller Signature Jazz Bass – Tommy Thompson’s Modifications

Posted by Giacomo on February 10, 2012
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Tommy Thompson covers the modifications he has made to his Fender Marcus Miller Jazz Bass.



The “Marcus Miller Sound” has been very intriguing to me since my freshman year in college. Marcus Miller is the man that possesses the “magical tone.” Tommy ThompsonFrom my introduction to his sound until now, he continues to elevate his sound and talents in recording, arranging, and producing. An attempt to make a jazz bass (TheYumpy) that would duplicate the Marcus Miller Sound was initiated in 1990. The Yumpy was in a preliminary completion state in 2001 after a large number of variations and combinations of bodies, necks, bridges, preamps and pickups. The Yumpy was not in my possession from 2001 thru mid 2005. During the 1998 Winter NAMM Show in Anaheim, CA, Fender (JAPAN) introduced the Fender Marcus Miller Signature Jazz Bass. My first review on harmony-central about the Fender Marcus Miller Signature Jazz Bass was on 03/28/2000. About 11 or 12 reviews followed until the fall of 2005; only two reviews remain.

My order for the Fender Marcus Miller Signature Jazz Bass (MM4) and hard shell case was placed during February 1998 at a local music store. The MM4 arrived eight months later in October 1998. I took The Yumpy to the store with me to compare to the MM4. Two of my bass buddies in the store went to the sound room with me to hear the two instruments. Both of my bass buddies agreed that The Yumpy had better tone and more output than the MM4. The MM4 was played for about two or three weeks, then I left it alone for about three or four months. I decided to play the instrument in January or February of 1999 and the active preamp would not engage. That’s when my journey began. 🙂


A. After opening the control cavity I discovered that the “battery’s ground wire” was soldered to the “common ground” connection. Hence, the battery was fooled to believed that it was in a 24/7 “on-mode.” To solve the first part of the battery problem, I unsoldered the battery’s ground wire from the common ground connection and soldered it to one of the outside legs (opposite the hot wire) on the stereo output jack.

B. The “bare solid wire” that stems from the Fender FMEQ preamp must also be covered or insulated (use heat shrink tubing or electrical tape). If the “bare solid wire” makes contact with the shielding paint (or any other grounding point(s)) the battery will return to the 24/7 “on-mode” and drain.


The pickup cavity shielding plates were missing, Fender FMEQ preamp wires were broken, and the pickups sounded very thin. I installed shielding plates, replaced the Fender FMEQ with Aguilar and Suhr preamps, and replaced the pickups with DiMarzio, Fralin, and Suhr jazz bass pickups. NOTE: In the very end, after solving all of the problems, all of the “Original STOCK parts” were re-installed in the MM4.


Prior to 2001, The Yumpy did not have an active/passive switch. On the MM4, the active/passive switch was factory equipment. I experimented with the active/passive DPDT mini-toggle switch on the MM4 and found what I believe is the difference between bypass and “true-bypass.” When the volume controls were full-up and the DPDT switch was in the active mode, there was bleed over from the pickups output. To me, that indicated that the wiring scheme on the DPDT mini-toggle switch was normal bypass. To me, “True-bypass” does not allow bleed over when the battery is removed from the circuit and the active/passive switch is in the active mode.

THE LOW END: (The REAL story in 2002)

In 1999, a bass buddy of mine agreed to use the MM4 at his gig to see how it would support the band. During his gig he played the MM4 one song and placed it back in its case and continued to use his Fender Geddy Lee. His conclusion was that it lacked “low end.” The PROBLEM was finally located three (3) years later in 2002. “The SOLUTION was hidden in the RESISTANCE of the Volume Potentiometers (pots).” After disconnecting all of the wires on the volume pots I measured the resistance of each pot. I found that the resistance of the neck pot was 206 kohms, and the resistance of the bridge pot was 275 kohms. The difference in resistance was 69,000 ohms (69 kohms). To me, since I like to utilize the pickups individually, that was significant. The solution was to swap the pots. The neck pot resistance became 275 kohms and the bridge pot resistance became 206 kohms. Eventually, other pots were used in order to have a lesser difference in resistance between the neck and bridge volume pots. Pots are readily available for $5 each. WOW!!!


The Yumpy was returned in the fall of 2005 and all of the unfinished modifications were completed. Lessons learned from the MM4 contributed a great deal to levels of understanding that seemed to elude me for 15 years. These modifications to The Yumpy and the MM4 help determine a true evaluation of both jazz basses. The correct combination of components can take a lot longer to find than expected. In the final comparison test, both basses sounded better than when first compared.

ACTIVE/PASSIVE SWITCH – (True Bypass): In the fall of 2005, an active/passive switch with a “true-bypass” wiring scheme was installed on The Yumpy. An active/passive switch is a very useful tool. For a comparison test, it helps provide a clearer picture. In an emergency case, when the battery dies in a preamp, it can be a life saver. This one switch made all the difference in the world. Something I never paid attention to reappeared doing the final comparison test between The Yumpy and the MM4. When the active/passive switches on both basses were placed in the passive mode, the true output of the pickups and preamps were finally realized. Finally, because of the active/passive switch, I could study both instruments in detail.

PICKUPS (output/tone): Using different types of single – coil sized pickups, both basses sounded very similar. The Yumpy had a set of Bartolini 9J#4 jazz bass pickups and the MM4 had a stock set of Fender jazz pickups. The Bartolini 9J#4 pickups were completely quiet when both pickups were used together or individually. The MM4 single-coil jazz pickups were only quiet when both pickups were used simultaneously. The Bartolini 9J#4 pickups possessed more low mids, but the pickups in the MM4 (stock – industry standard) had good mids and were “twice as loud.” That was significant!!! During the previous 8 to 10 years, I never realized the Bartolini pickups were low output. Low output pickups come into play when using ¼” inputs on mixer boards that have microphone preamps of low quality; DI box is a must. Even though the Fender pickups have twice the output of the Bartolini pickups, I tend to favor the Bartolinis.

PREAMP: The preamp in the Yumpy is the Bartolini NTBT 2-band treble (boost/cut) & bass (boost/cut) controls with an adjustable gain pot. After the return of The Yumpy in 2005, a 1.5 kohms-1/8 watt resistor replaced the 2.7 kohms-1/8 watt resistor used in parallel with the gain pot to adjust the output of the preamp. NOTE: In the active mode, with the treble and bass controls set flat (detent), the trim pot on the Bartolini NTBT was adjusted to equal the “passive output” of the Fender jazz bass pickups. The change in resistors improved the bang effect in the Bartolini preamp. The Fender FMEQ preamp has a 2-band treble & bass preamp with boost only controls, and the tone and output are similar to the older Bartolini preamps I have heard.

TOTAL OUTPUT: The preamp on The Yumpy has been adjusted to equal the output of the Fender Japan Marcus Miller Signature Jazz Bass (MM4). In this mode, the MM4 has more output when the preamp controls are full-up. If the gain pot on The Yumpy is set to maximum, then The Yumpy would easily have more output; it’s loud. The volume of the Yumpy has been adjusted to make it more compatible with mixer boards and recording consoles. The advantage the Fender Japan Marcus Miller Signature Jazz Bass had was if the battery connected to the preamp failed its pickups provided more output and support. In a critical situation, the output of the Fender single-coil pickups “might be a vital parameter.” Therefore, from my perspective, the Fender Japan Marcus Miller Signature Jazz Bass was the winner!!!

Personally, I have to look at the Fender Japan Marcus Miller Signature Jazz Bass and the experience gained as a BIG lesson. “I must commend Fender Japan for recognizing the contributions of Marcus Miller and what he has done for the musical industry.” I don’t think many companies would have taken on the task of doing what Fender Japan has done. Fender Japan satisfied many “Millerheads” by re-creating a jazz bass that is truly a “custom-boutique instrument at an affordable price.” Marcus went through several iterations and variations of preamps before he finally achieved the magical tone. After years of tinkering with various bodies and necks, pickups, preamps, and reading numerous articles I have finally gotten to the point where I’m starting to understand the “Marcus Miller Sound.” The Marcus Miller Sound is the sound that pleases Marcus Miller and it is derived from his fingers and soul; the bass is optional.

Tommy Thompson, Ph.D.

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