MUSICMANBASS.GLOBAL
MUSICMANBASS.GLOBAL 

Formerly MUSICMANBASS.ORG

 

SR4 PUPs AND PREAMPS 

(Pre-EB & EB)


Pre-EB Pickups (1976 - 1984)


1976 up to circa early 1978 (First Version).

Pickup from Sting Ray Bass dated Jan/Feb 1977.

Two separate coils are wired in parallel to cancel hum.

Note that the pole pieces extend below the bottom of the pickup cover and are longer than the latter version Pre-EB pickup (further on). Each pole piece is 1 inch long and 3/8 inch diameter. The resistance of each individual coil is approx 2,400 ohms. As the pickups are wired in parallel, the total output resistance is approx 1,200 ohms.

This resistance is considerably lower than the latter version Pre-EB pickup (introduced circa early 1978) with each individual coil measuring approx 3,900 ohms resulting in a total output resistance of approx 1,950 ohms (in parallel) and fitted with pole pieces measuring a shorter 5/8 inches in length but retaining the same 3/8 inch diameter (see further on).

Note that coil windings varied due to techniques used at the time resulting in slightly different resistance readings between individual Pre-EB pickups.

Pickup cavity routing and Pickup from Sting Ray Bass.
Body date 17 June 1977. Pics courtesy of "calzone".

The main pickup cavity is routed deeper at the bottom to accommodate the extended length of the pole pieces of the two coils.

Throughout the Pre-EB (and EB period), Sting Ray 4 pickups are passive (not active), the coils are wired in parallel and pole pieces are Alnico. The battery powers the pre-amp only.
 

Early 1978 to end of Pre-EB period [1984] (Second Version).

Pickup from a late 1978/79 Bass.

Pole pieces are now shorter (5/8 inch length) and flush with the bottom of the pickup cover. The poles remain at 3/8 inch diameter. Each coil now has a resistance of approx 3,900 ohms. Resistance of the 2 coils in parallel gives an overall resistance of approx 1,950 Ohms.

Underneath view of same pickup.

Top view of the pickup and pickup routing.

As the pole pieces are now shorter, the pickup
cavity has a single routing.

Towards the end of the Pre-EB period (circa 1983), the
pickup routing is re-shaped to the outline ot the 
pickup. It is thought that this may have
coincided with the introduction of
clear pickguards.

A Carey Nordstrand pickup type "MM 4.2"
with alnico pole pieces.

The Nordstrand pickup is designed on the 1978 Pre-EB pickups and will fit all Sting Ray 4 Basses (Pre-EB & EB) from 1976 to present date EXCEPT for the dual pickup Sting Rays introduced in 2005 (with pickup covers similar to the Bongo Bases). Resistance measurements are the same as for the Pre-EB pickup above with the shorter pole pieces.
 

Pre-EB PREAMPS (1976 - 1984)


Intro.

Although the Treble and Bass controls have no centre detent position, the preamps are CUT and BOOST. With respect to the treble control, the cut and boost takes place during normal clockwise/anticlockwise rotation of the control. The flat position is approx. mid way through rotation. On the other hand, the cut position on the bass control appears to be at the extreme anticlockwise position of rotation and begins to boost as the control is advanced clockwise from that point.

The earlier Pre-EB preamps use a 25K audio (log) taper pot for the volume control. Towards the end of the Pre-EB period it changes to a linear taper to make adjustment smoother throughout rotation (see further on). The audio taper tends to bunch the volume adjustment to the upper limit of the pot rotation. A 1Meg reverse audio (log) pot is used for treble control and 100K audio (log) pot is used for the bass control.

All Pre-EB preamps use an "LM4250CN" IC chip. The same chip is also used on all Ernie Ball 2EQ pre-amps to current date. The 3EQ option introduced by Ernie Ball in 1987 uses a "TL062" chip.

1979 pot with code dating on the side.

Pots are code dated on all preamps during the Pre-EB period. For example "1377626". The "137" component identifies the type of pot (a single pot rather than a stacked pot). The next two numbers identify the year ("76" indicates 1976 as the year of manufacture). The remaining two numbers identify the week of the year ("26" indicates the 26th week of 1976 which is June). The code example "1377626" therefore identifies the pot as being manufactured in June 1976. Pot dates do not necessarily identify the date of the preamp. As Music Man purchased pots in large quantities it’s not unusual to find pots that are made one to two years earlier than the pre-amp itself.

1976 to early 1977 (Black Epoxy).

1976 preamp.

From 1976 to early 1977 a red/orange coloured outboard capacitor is located on the treble pot rather than being included on the circuit board itself.

Preamps are sealed in black epoxy. The IC chip is soldered direct to the circuit board. The sequence of lead-out wires from the board is completely different to subsequent Pre-EB preamps boards.

Schematic preamp wiring for 1976 and early 1977 Basses.

1977 to 1978 inclusive (Black Epoxy).

There appears to be three versions of the preamp used during this period.

Type 1.

Pics of type 1.

Type 1 schematic.

Type 2.

Type 2. Preamps are normally attached to the pots, at
each endof the board, with material similar to that
used for thestring mute pads. After time the
material candegrade. In the above picture,
the preamphas been re-attached with a
strip mouse pad.

Type 2 schematic.

Note that the lead-out wires to the bass pot (on right) are now yellow instead of violet and have been reduced from three to two. The bottom lug of this pot is now unsoldered (as opposed to Type 1 above). Note also that the two lead out wires to the volume pot have had their colours reversed as opposed to Type 1. White now goes to the centre lug of the volume pot and black to the bottom lug.

Type 3.

Type 3. Webmasters 1978 preamp.

Type 3 Schematic.
 

Note that the lead-out wires to the bass pot revert back to being violet. This pre-amp appears to be the main one used towards the end of 1978.
 

Sept 1978 (Non Epoxy Preamps Introduced).

1979 preamp. (Pics courtesy of "freedok"). Note the red
and blue coloured Tantalum capacitors. Green and
maroon Tantalumswere often used as well. On
latter preamps, Electrolytic capacitors
become standard.

From Sept 1978 the non-epoxy version of the Type 3 preamp began to replace the previous black epoxy Type 3 version. This extended over several months and existing stock of the black epoxy would still have been used until depleted. It’s not unusual to find the black epoxy version in early 1979 Basses. Putting aside the deletion of the epoxy, the two versions are the same as each other. Both use the same circuit board which is designated “B3”. Also the wire lead-out orientation and lead-out colours remain the same for each. 

The IC chip for the non-epoxy version is now mounted to the board via an IC socket rather than soldered directly to the board itself. However, from 1984 (beginning of the Ernie Ball period) all ICs returned to being soldered directly to the circuit board.

Schematic for non-epoxy preamp wiring from late 1978 to
1984 (end of Pre-EB period). Although the epoxy is now
deleted, note that the colour & sequence of the
lead-out wires is the same as for the Type 3
epoxy preamp used during the
1977-1978 period above.

The same non-epoxy preamp and colour coding is used by Ernie Ball from 1984. Although the circuit board has changed its shape several times since 1990 the 2EQ circuit still remains the same to current date.

Circa late 1979 or early 1980.

At left is the non-switchable jack first used with Pre-EB
preamps.The jack (right), introduced late
1979 (early 1980), disconnects the battery
when the guitarlead is removed.

Initially, all pre-amps remained permanently turned on. Removal of the guitar lead did not disconnect the battery. Current drain was considered to be low enough for the battery to last its normal shelf life whether left connected or not. A newer jack was introduced late 1979 (or 1980) to disconnect the battery. This is the position to current date.

March 1982. Introduction Of Protection Resistor.

1982 schematic showing where protection resistor is placed in circuit. 
Reproduced with permission.

Protection resistor installed by the factory and covered
with a black plastic sleeve.

The IC chip can be damaged if the guitar lead becomes short-circuited. In 1982 the addition of an out-board 1K ohm protection resistor was recommended to protect the chip.

Circa 2nd half of 1982. Electrolytic Capacitors Replace Tantalums.

The "LM4250CN" chip as used in the preamps (left),
Electrolytic capacitor (centre) and a
Tantalum capacitor (right).

Electrolytic (as opposed to Tantalum) capacitors appear on non-epoxied preamps from circa the 2nd half of 1982 onwards. Audiophiles believe that the electrolytic has a mellower pleasing tone.

1982. Linear Taper Replaces Audio (Log) Taper On Volume Control.

The previous 25K audio (log) taper pot for the volume control tended to bunch the volume control adjustment to the upper limit of the pot rotation. The linear taper corrects this by allowing a smoother adjustment throughout the whole pot rotation.

1983 Volume pot with linear ("LIN") taper marked on rear.

1983. All updates of the Preamp board completed.

Front and rear pics of Webmasters N.O.S. 1983 Preamp.
Music Man has covered the protection resistor with
a black plastic sleeve and is ready to be installed.

The Ernie Ball replacement preamp for all Pre-EB &
EB Sting Rays up to 1990 which use the same circuit
board shape. The protection resistor is included
on the board.

Reproduced with permission. A schematic wiring diagram for

the M05400 replacement board directly above.

Note the violet lead-out wire on left hand side as opposed to the normal three yellow lead-outs. However this is the general schematic for all Pre-EB and EB 2 band preamps up to circa 1990. Although lead-out colours may be different, the leadout and hook up wiring sequences are the same.


EB Pickups (From 1984)


OVERVIEW.
 

Pre-EB pickups (above) varied individually due to winding techniques adopted at that time. Ernie Ball automated the windings to make the pickups more consistent.

As with the Pre-EB Sting Ray pickups, Ernie Ball Sting Ray 4 pickups are passive, the coils are wired in parallel and pole pieces are Alnico. The battery powers the pre-amp only.

As with the second version of the Pre-EB pickup from early 1978 onwards (above), pole pieces measure 5/8 inch in length with a diameter of 3/8 inch. Likewise, each coil measures approx 3,900 ohms with a total output of approx 1,950 ohms (in parallel).

Above two pics from a 1989 SR4. Note the Orange and
Blue wires. The coils have no outside tape winding.
Pre-EB pickups are Yellow and Green.

From a 1992 SR4 (courtesy "Oliver"). Wire at right hand
side is now Green. The owner advises this pickup has no
outside tape winding on the coils. The metalic shielding
tape acrossthe pole pieces is an after-market
modification and is not original
from the factory.

Above two pics from a 1994 SR4. Note, for first time, the
inclusion of a winding of Black tape over the coil
windings. It's unknownif this was the
case in 1993.

A more recent SR4 pickup (exact vintage unknown). As
with other pickups the Black lead-out wire is "Ground"
(earth). The White lead-out goes to the pre-amp.

Mid 2003-Current. Rounded Pole Edges.

SR4 Pickup with rounded-edge Alnico pole pieces.
Introduced mid 2003. In all other respects the
pickup remains the same.
(Picture "Davtran").

2005-Current. Dual Pickups.

Introduced 2005 Sting Ray with dual Humbucker pickups.
(Picture "Steve Dude Barr").

Close-up view of the dual Humbuckers.
(Picture "hmagman").

The new dual pickup Sting Ray Basses were introduced at the July 2005 NAMM Show. Pole pieces remain Alnico with rounded edges. However, the pickup covers differ slightly to the single pickup (H) Sting Ray The area on the side which supports the two height adjustment screws is similar in shape to the pickups featured on the Bongo Bass.

As well as two Humbuckers (HH) above, the Sting Ray was also available with one Humbucker plus a Single coil pickup (HS). The HS option is no longer offered. The HH is  offered with 3 band pre-amps only (no 2 band).

 

EB 2EQ PREAMPS (From 1984)

Introduction.

The Ernie Ball 2 Band EQ preamp (to current date) is the same circuit as the Pre-EB non-epoxy preamp as it was at the end of the Pre-EB period in 1984.

Wiring of the preamp board to the pots, pickup and jack remains the same as the Pre-EB non-epoxy preamp. The sequence and colour of lead-outs from the preamp board also remains the same.

The board shape changed from rectangular to crescent moon in circa 1990 but the circuit remains electrically the same to current date.

1984 to circa 1987 (2 band).

A 1985 pre-amp.

A protection resistor has been added as per the 1982 Pre-EB schematic (pictured previously) and is located within the plastic sleeving to the right. Note that, from the beginning of the EB period (1984), the IC socket is now deleted and the chip is soldered directly to the circuit board. From c.1985, preamps were dated with a black marker pen on the rear of the control plate.

Circa 1988 to circa 1990 (2 band).

Pre-amp as found from circa 1988 to circa 1990.

The protection resistor is now relocated on the circuit board. It was from circa 1988 that the preamps were dated with a round sticker located on the rear of one of the control pots. Preamps are still dated this way today.

Circuit wiring for EB preamps from 1984 to 1990 is the same as the
Pre-EB non-epoxy preamps from late 1978 to 1984.

The Ernie Ball replacement preamp for all Pre-EB &
EB Sting Rays up to 1990 which use the same circuit
board shape. The protectionresistor is included
on the board.

Reproduced with permission. A schematic wiring diagram for

the M05400 replacement board directly above.

Note the violet lead-out wire on left hand side as opposed to the normal three yellow lead-outs. However this is the general schematic for all Pre-EB and EB 2 band preamps up to circa 1990. Although lead-out colours may be different, the hook up wiring sequences are the same.

Pots used with preamps.

Up to this stage, pots have had lugs for point to point wiring (above left). From circa 1990, direct mount pots (above centre) have been used in 2 band preamps due to the circuit board design (see below). As the pot values (and tapers) remain the same, the direct mount pots can be modifiedfor use in the earlier preamps by bending and cutting the pins (above right).

Circa 1990-Sept 2009 (2 band).

2 Band preamp with new circuit board design.

From circa 1990, the 2 band pre-amp circuit board changed from rectangular to crescent moon. Note that the lug pots are replaced with direct mount pots that solder to the circuit board with pins. The circuit remains the same as the earlier preamps.

Reproduced with permission. Schematic wiring for 2 band
pre-amps from circa 1990 to Sept 2009.

Sept 2009- Current (2 band).

Above two pics of the newer 2EQ pre-amp introduced
in September 2009.
(Pics courtesy of Mike).

The circuit remains the same and continues to use the LM4250CN chip. Although pot resistance values also remain the same, the previous larger pots are replaced by smaller "Noble" pots.

2016- Current. "Old Smoothie" 40th Anniversary SR4. 

Black epoxy preamp used in the 2016 "Old Smoothie"
40th Anniversary Sting Ray Bass.

"Old Smoothie" is bassed on Sterling Ball's 1976 Pre-EB Sting Ray (B001026) given to him by Leo Fender. The preamp has the same leadout colours and wiring hook up as the as the Type 3 Pre-EB black epoxy preamp mention earlier. Pot values are also the same as other 2EQ preamps.
 

EB 3EQ PREAMPS (From 1987)

Circa 1987 to circa 1990 (3 band) Option.    

Pic of a 1988 3 Band EQ Preamp.

Ernie Ball introduced the optional 3 band pre-amp in 1987 and is an option to date. The same preamp was included in the new SR5 latter in 1987. Note that, although the two outer pots are hook-up wiring lug pots, the two inner pots are soldered to the circuit board by pins attached to the pots. Note also that the preamps are dated with a round sticker on the rear of a control pot from 1988 onwards. Prior to this some were dated with a black marker pen on the rear of the control plate. The 3 band uses a "TL062" chip rather than the "LM4250CN" used with the 2 band preamp.

Reproduced with permission. Schematic wiring for 3 band
preamps from circa 1987 up to circa 1990.

Circa 1990-October 2006 (3 band) Option.

Pic of a 1994 3 Band EQ Preamp.

Just like the 2 Band preamp, the 3 band preamp circuit board also changed from rectangular to crescent moon shape. Note that the two outer lug pots on the previous 3 Band version (above) are now soldered on the board. The circuit still remains the same as do pot resistance values.

Reproduced with permission. Schematic wiring for 3 band pre-amps
from circa 1990 to Oct 2006.

October 2006-Current (3 band) Option.

Pic of an Oct 2006 3 Band EQ Preamp.

The circuit remains the same and continues to use the TL062 chip. Although pot resistance values also remain the same, the previous larger pots are replaced by smaller "Noble" pots.

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